JP6848181B2 - Positive electrode active material for non-aqueous electrolyte secondary battery and its manufacturing method, and non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery.

In recent years, with the increasing performance and rapid spread of mobile phones and notebook computers, there is an increasing demand for smaller size, lighter weight, and higher capacity secondary batteries used for these. Non-aqueous electrolyte secondary batteries typified by lithium secondary batteries have higher battery voltages and higher energy densities than nickel-cadmium batteries or nickel-hydrogen batteries, and are rapidly becoming widespread in the above fields. In addition, non-aqueous electrolyte secondary batteries are also expected as a power source for driving motors of electric vehicles and hybrid vehicles against the background of recent environmental problems. In particular, a hybrid vehicle requires a high output density as a battery for energy storage, and a non-aqueous electrolyte secondary battery used for this is required to have high discharge characteristics and high cycle stability.

The positive electrode active material of the non-aqueous electrolyte secondary battery includes lithium cobalt oxide (LiCoO _{2 ) having an α-NaFeO 2} structure, lithium nickel oxide (LiNiO ₂ ), and lithium manganate having a spinel-type structure (LiMn ₂ O ₄ ). Lithium transition metal composite oxide powders such as those represented by the above are mainly used. Especially recently, composition formula LitNi1-x-yCoxMyO2 in which cobalt and aluminum are mainly added to lithium nickelate for EV applications requiring high capacity (M in the formula is Mg, Al, Ca, Ti, V, Cr, Mn). , Zr, Nb, Mo and at least one element selected from the group consisting of W), and lithium transition metal composite oxides are attracting attention. The synthesis of these positive electrode active materials was generally _{obtained by mixing lithium compound (Li 2} CO ₃ , LiOH, etc.) powder and transition metal compound (MnO ₂ , NiO, Co ₃ O _4, etc.) powder, drying, and firing. A method of crushing a lithium transition metal oxide into a positive electrode active material has been widely adopted.

There are several issues with the positive electrode active material, one of which is the improvement of cycle characteristics. The cause of the cycle decrease is that the surface of the positive electrode active material is partially decomposed by the reaction with the electrolytic solution during repeated charging and discharging, and the components in the positive electrode active material are dissolved and adhere to the negative electrode and separator surface, and the charge and discharge capacity is increased. It is said that the surface condition of the positive electrode active material has a great influence on the cycle characteristics and discharge characteristics of the battery, such as causing a decrease.

Therefore, in Patent Document 1, in order to improve the cycle characteristics, (wherein, M represents, Co, at least one of Al) composition formula _Li x _Ni y _M z _{O 2} in the lithium transition metal composite oxide represented by , Al, Mg, Sn, Ti, Zn, and Zr, an organic metal compound containing at least one is added, and the mixture is mechanically crushed and then heat-treated at a temperature of 400 ° C. or higher and 700 ° C. or lower. The obtained positive electrode active material has been proposed. In this way, the positive electrode active material obtained by adhering the organometallic compound to the particle surface of the composite oxide by mechanical crushing and then treating it at a high temperature is compound-oxidized by the effect of the additive (organometallic compound). It is stated that the particle surface of the object is stabilized and the cycle characteristics are improved.

_{In Patent Document 2, Ni (OH) 2} , LiOH, and Al (OH) ₃ were blended in order to stabilize the crystal structure of only the particle surface and improve the cycle characteristics, and heat-treated at a temperature of 700 ° C. for 5 hours. Later, aluminum forms a high-concentration layer in an internal region of 0.5 μm or more from the surface of the lithium transition metal composite oxide particles represented by the composition formula LixNiyMzO2 (in the formula, M is at least one of Co and Al). , It is described that the cycle characteristics are improved.

On the other hand, as a problem other than the cycle, when the paste-like composition containing the positive electrode active material (the paste-like composition includes a slurry-like composition and an ink-like composition) is stored for a long period of time, it becomes a gel and collects. It is possible that the coating film cannot be uniformly applied on the electric body.
A non-aqueous electrolyte secondary battery is usually configured by arranging a positive electrode, a negative electrode, and a separator in a battery container and filling the non-aqueous electrolyte solution with an organic solvent. Further, the positive electrode is manufactured by applying a paste-like composition containing a positive electrode active material on a current collector such as aluminum foil and pressure molding, and has a structure in which an electrode material is formed in layers (hereinafter, "" A positive electrode mixture layer ") is formed.

In the above paste-like composition, a conductive agent such as carbon powder having a weight ratio of several to several tens of percent is mixed with the positive electrode active material, and further, VDF (polyfluoride), PTFE (polytetrafluoroethylene) and the like are formed. Manufactured by kneading a paste (binder). After applying this paste-like composition on the current collector foil to a thickness of 20 to 100 μm, the current collector foil to which the paste-like composition is applied is dried and pressed (press molded) to form a positive electrode mixture layer. To form. Here, a conductive agent such as carbon powder is often used as a material having higher electrical conductivity than the positive electrode active material in order to further enhance the electrical conduction between the current collector and the positive electrode active material or between the active materials.

By the way, as the solvent used when preparing the paste-like composition, an aqueous solvent (for example, water) or a water-soluble organic solvent (for example, N-methylpyrrolidone) is adopted (for example, Patent Document 2). ). Therefore, due to the water content of the solvent, lithium ions may be eluted from the particle surface of the lithium transition metal composite oxide, which is the positive electrode active material, into the solvent, and the composition itself may exhibit strong alkalinity. In such an alkaline composition, decomposition of the binder contained in the paste-like composition, aggregation (gelation) of the binder, and aggregation of the positive electrode active material may occur. Further, by working in a place with high humidity, moisture flows in from the outside air, and the paste-like composition tends to gel.

Decomposition or aggregation of such a binder or the like causes an increase in the viscosity of the paste-like composition and a decrease in the adhesive force, and further reduces the dispersibility of the composite oxide powder, which is desired on the current collector. It may be difficult to form a positive electrode mixture layer having a uniform thickness and composition. If the thickness and composition are not uniform, the battery reactivity at the time of charging and discharging deteriorates, and further, it causes an increase in the internal resistance of the battery, which is not preferable.

Therefore, in Patent Document 3, in order to suppress the decomposition and aggregation of the binder and the like, Li _x Ni _{1-y Ay} O ₂ (0.98 ≦ x ≦ 1.06, 0.05 ≦ y ≦ 0. 30 and A are given by at least one of Co and Al), and 5 g is stirred and mixed in 100 g of pure water for 120 minutes and then allowed to stand for 30 seconds to obtain a supernatant having a pH of 12.7 at 25 ° C. The following positive electrode active materials for non-aqueous electrolyte secondary batteries have been proposed.

Further, in Patent Document 4, a solgel step of forming a gel film in which a metal organic compound and a micellar surfactant are dispersed and adhered to the surface of a positive electrode active material, and the gel film obtained in the solgel step are described. It is characterized by having a firing step of decomposing and removing the surfactant by firing to form a porous metal oxide coating layer in which movable pores of lithium ions are formed on the surface of the positive electrode active material. A method for producing a porous metal oxide-coated positive electrode active material has been proposed.

Japanese Unexamined Patent Publication No. 2005-346965 Japanese Patent Application Laid-Open No. 8-138670 Japanese Unexamined Patent Publication No. 2003-31222 Japanese Unexamined Patent Publication No. 2009-200007

However, in the composite oxide particles described in Cited Document 1, Li insertion / detachment is reduced due to the stabilization of the particle surface with a high concentration additive, and further, damage to the particle surface during crushing causes initial damage to the particle surface. The charge / discharge characteristics deteriorate. Further, in the composite oxide particles described in Cited Document 2, since the surface layer portion needs to be added in an excessive amount in order to have a high concentration of the added element, Li insertion / removal is suppressed and the charge / discharge capacity is lowered. .. Since these stabilized surface layers do not form a dense layer, they do not function as a protective layer for Li elution and do not improve gelation.

On the other hand, the positive electrode active material described in Cited Document 3 is described to have improved gelation resistance by controlling the pH, but no specific production method thereof is mentioned. Further, according to the method for producing a positive electrode active material described in Patent Document 4, the porous metal oxide coating layer effectively suppresses deterioration of the positive electrode active material due to reaction with an electrolytic solution or the like to improve cycle characteristics. However, the above-mentioned problems in the paste used for producing the positive electrode mixture layer have not been examined.

That is, with _{regard to the deterioration of the cycle characteristics during charging and discharging, which is a problem with the LiNiO 2} system positive electrode active material, as a conventional method for suppressing the deterioration, the positive electrode activity is performed in order to suppress the reaction with the electrolytic solution during charging and discharging. An oxide coating film thick enough to cover the entire surface of the substance was provided to improve the barrier property of the particle surface, or the particle surface was reacted with different elements to change the structure and stabilize it. .. However, as an adverse effect of forming the oxide coating film, since the oxide coating film reduces Li insertion / discharge during charging / discharging, a phenomenon that the initial charge / discharging capacity deteriorates occurs. Similarly, even if the structure is changed by reacting with a different element on the particle surface, the initial charge / discharge capacity deteriorates.

On the other hand, regarding gelation, which is another problem, as a conventional suppression method, in order to prevent the elution of lithium ions that occurs in contact with water, the entire surface of the positive electrode active material is covered with a dense film to cover the particle surface. It was to protect. However, as an adverse effect of forming a dense film, as in the case of cycle characteristics, the dense film reduces Li insertion / discharge during charging / discharging, resulting in deterioration of the initial charging / discharging capacity. Further, even if the particle surface is reacted with a different element to change the structure, the reaction on the surface is local in the conventional addition method, so that lithium ions are eluted without forming a layer that covers the entire surface densely. It cannot be prevented.

Therefore, the present invention does not impair the initial battery performance such as the charge / discharge characteristics inherent in the composite oxide particles, suppresses gelation of the paste-like composition for a long period of time, and has a secondary battery having high cycle characteristics. It is an object of the present invention to provide a positive electrode active material for a non-aqueous electrolyte secondary battery, and a simple method for producing the same.

In a first aspect of the present invention, the positive active material for a non-aqueous electrolyte secondary battery, and a surface layer portion and the other central portion disposed on the surface, the composition is _{Li t Ni 1-x-y} Co _x M ¹ _y M ² _z O _{2 + α} (In the formula, M ¹ is at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W. M ² is Nb, 1.01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0.03, 0 ≦ α ≦ 0 It is composed of lithium nickel composite oxide particles represented by (1), and M ² further has a coating layer contained in the surface layer portion and covering at least a part of the surface of the lithium nickel composite oxide particles. , The coating layer contains M ² at a higher concentration than the surface layer portion .

Further, M ² may have a concentration gradient such that its concentration decreases in the direction from the particle surface toward the center. Further, ^{at least a part of the M 2} may react with at least a part of Ni and Co in the composite oxide particles to form a product. Further, at least a part of the product is a spinel-type crystal represented by _{the composition formula AB 2} O ₄ (A is at least one metal element of Ni and Co, and B is M ^2). It may consist of phases. Further, the thickness of the surface layer portion may be 10 nm or more and 100 nm or less.

In another aspect of the present invention, the non-aqueous electrolyte positive electrode active material for secondary batteries, and a surface layer portion and the other central portion disposed on the surface, the composition is _{Li t Ni 1-x-y} Co x M ¹ _y M ² _z O _{2 + α} (In the formula, M ¹ is at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W. Yes, M ² is at least one element of Al and Nb, 1.01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0. It is composed of lithium nickel composite oxide particles represented by 03, 0 ≦ α ≦ 0.1), the M ² is contained in the surface layer portion, and at least a part of the ^{M 2 is the composite oxide.} A product is formed by reacting with at least a part of Ni and Co in the particles, and at least a part of the product is composed of composition formula AB ₂ O ₄ (A is at least one of Ni and Co). a metallic element, B is made of a spinel-type crystal phase represented by a M ^2.).
Further, M ² may have a concentration gradient such that its concentration decreases in the direction from the particle surface toward the center. Further, the thickness of the surface layer portion may be 10 nm or more and 100 nm or less. Further, the positive electrode active material further has a coating layer covering at least a part of the surface of the lithium nickel composite oxide particles, and the coating layer ^{may contain M 2} at a higher concentration than the surface layer portion. Further, the coating layer may contain fine particles having an average particle size of 1 nm or more and 20 nm or less. Further, the content of Al or Nb may be in the range of 0.02% by mass or more and 3.0% by mass or less with respect to the entire positive electrode active material. Further, the positive electrode active material may have an a-axis length of 2.8647 Å or more and 2.8655 Å or less and a c-axis length of 14.1801 Å or more and 14.890 Å or less, which are determined by Rietveld analysis of X-ray diffraction. Further, the thickness of the coating layer may be 0.1 nm or more and 20 nm or less. Further, after adding 0.1 g of the positive electrode active material to 50 ml of pure water at 24 ° C., the pH of the slurry stirred for 10 minutes was 11.2 or less, and 9.5 g of the positive electrode active material and vinylidene fluoride (PVDF) as a binder were used. ) 0.5 g, 5.5 g of N-methyl-2-pyrrolidinone (NMP) as a solvent, and 0.2 g of water are added to make a slurry by a self-revolving kneading machine, and then the mixture is stored statically at 24 ° C. for 3 days. Does not have to be gelled.

In a second aspect of the present invention, and a surface layer portion and the other central portion disposed on the surface, the composition is _{^{Li t Ni 1-x-y}} Co x M 1 y M 2 z O 2 + α ( wherein , M ¹ is at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, and M ² is among Al and Nb. At least one element, 1.01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0.03, 0 ≦ α ≦ 0.1. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is composed of lithium nickel composite oxide particles represented by (shown) and is contained in the surface layer portion of ^{M 2, is at least one of Al and Nb.} A monomer or oligomer of a metal alkoxide containing seeds and an organic solvent are mixed to obtain a mixed solution, and then a chelating agent is added to the mixed solution to obtain a coating solution. The coating liquid is mixed or sprayed to form a coating layer precursor having a film thickness of 3 nm or more and 100 nm or less on the surface of the lithium nickel composite oxide particles, and 350 composite oxide particles on which the coating layer precursor is formed are formed. Includes heat treatment in an oxygen atmosphere of ° C. or higher and 700 ° C. or lower.

The coating liquid is obtained by mixing a metal alkoxide monomer or an oligomer thereof containing at least one of Al and Nb with an organic solvent to obtain a mixed liquid, then adding a chelating agent to the mixed liquid, and then adding water. The coating liquid can be obtained by dispersing fine particles having an average particle size D50 of 1 nm or more and 20 nm or less. The coating layer precursor is discontinuously formed in a porous and island shape on the surface of the base material, and the covering area measured by cross-sectional observation with a transmission electron microscope is 80% or more and 95% or less of the surface area of the base material. It may be. In the heat treatment, the value obtained by [mixture amount (g) / furnace volume (L)] × oxygen gas introduction amount (L / min) of the composite oxide particles forming the coating layer precursor is 33 g / min or more and 1333 g / min. It may be performed in a controlled atmosphere within the range of minutes or less. Further, the surface layer portion is composed of LitNi _1-xy Co _x MyO ₂ (in the formula, M is from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W. A mother composed of lithium nickel composite oxide particles which are at least one selected element and are represented by 1.01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15). After forming the coating layer precursor containing at least one of Al and Nb on the surface of the material, it may be formed by reacting the coating layer precursor with the particle interface of the base material by heat treatment. Further, the positive electrode active material may have a discharge capacity of 3.0 V-4.3 V and a rate of 0.5 C within ± 3% of the initial discharge capacity of the base material. Further, the positive electrode active material is charged at a charging potential of 4.1 V, measured by the AC impedance method, and the interfacial resistance value (Ω) calculated from the obtained Nyquist plot is relative to the interfacial resistance value of the base material. It may be in the range of 2 times or less.

In the third aspect of the present invention, the non-aqueous electrolyte secondary battery includes a positive electrode containing the positive electrode active material for the non-aqueous electrolyte secondary battery described above.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a surface layer portion containing at least one of Al and Nb in excess on the surface of a lithium nickel composite oxide, and is contained in conventional lithium nickel composite oxide particles. The initial battery performance is maintained at the same level, and gelation of the paste-like composition is suppressed. In addition, since it is not easily affected by the humidity of the outside air, gelation of the paste-like composition is suppressed even if the work is not performed in a place where the humidity is reduced, such as in a dry room, when the secondary battery is manufactured. The handleability inside is improved. Further, since the secondary battery using the positive electrode active material for the non-aqueous electrolyte secondary battery has high cycle characteristics, the battery life is extended and the practicality is also improved.

It is a schematic diagram which shows an example of the positive electrode active material which concerns on embodiment. It is a schematic diagram which shows an example of the manufacturing method of the positive electrode active material which concerns on this embodiment. It is a flowchart which shows an example of the manufacturing method of the positive electrode active material which concerns on embodiment. It is a flowchart which shows an example of the manufacturing method of the positive electrode active material which concerns on embodiment. It is the schematic sectional drawing of the coin-type battery used for the battery evaluation. It is a photograph which observed the positive electrode active material obtained in Example 3 by SEM and TEM. It is a photograph which observed the positive electrode active material obtained in Example 7 by SEM and TEM. It is a photograph which observed the positive electrode active material obtained in Comparative Example 1 by SEM and TEM.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Further, in the drawings, in order to make each configuration easy to understand, a part is emphasized or a part is simplified, and the actual structure or shape, scale, etc. may be different. Hereinafter, this embodiment will be described.

1. 1. Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery and Its Manufacturing Method FIG. 1 shows an example of positive electrode active material 1 for non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “positive electrode active material”) according to the present embodiment. It is a schematic diagram which shows. As shown in FIG. 1 (A), the positive electrode active material 1 is composed of lithium nickel composite oxide particles 2 (hereinafter, also simply referred to as “composite oxide particles 2”), and the composite oxide particles 2 are the surfaces thereof. It has a surface layer portion 3 including the above, and a central portion 4 other than the above. As will be described later, the surface layer portion 3 is formed by modifying at least a part of the surface of conventionally known composite oxide particles, and contains at least one element of Al and Nb. The surface layer 3 is
It is possible to block the invasion of water into the composite oxide particles 2, and it is possible to suppress the gelation of the positive electrode active material 1 and to maintain the discharge capacity and improve the cycle characteristics at the same time.

Further, as shown in FIGS. 1B and 1C, the composite oxide particles 2 may have a coating layer 5 that covers at least a part of the surface of the composite oxide particles 2. The coating layer 5 contains Al or Nb at a higher concentration than that of the surface layer portion 3. The coating layer 5 contains, for example, fine particles having an average particle size of 1 nm or more and 20 nm. As a result, it is possible to block the invasion of water into the composite oxide particles 2 without inhibiting the insertion / detachment of Li ions during charging / discharging. Further, as shown in FIG. 1B, the coating layer 5 may be formed on a part of the surface of the composite oxide particles 2. Further, as shown in FIG. 1C, the composite oxide particles 2 may be uniformly formed on the entire surface.

The composition of the composite oxide particles 2 is Li _t Ni _1-xy Co _x M ¹ _y M ² _z O _{2 + α} (M ¹ in the formula is Mg, Al, Ca, Ti, V, Cr, At least one element selected from the group consisting of Mn, Zr, Nb, Mo and W, M ² is at least one element of Nb and Al, 1.01 ≦ t ≦ 1.20. , 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0.03, 0 ≦ α ≦ 0.1). The metal element having the above composition can be measured by ICP emission spectroscopic analysis. Oxygen is an element constituting a layered compound, and its composition is determined by the composition of the metal element, but it includes fluctuations within the above composition due to the occurrence of oxygen deficiency or excess that can usually occur.

In the composition of the composite oxide particles 2, the lower limit of t indicating the composition ratio of Li is 1.01 or more, preferably 1.02 or more. Li content in the composite oxide particles 2 are excessively detected than stoichiometric composition of the layered compound except for ^{_{M 2 (Li t Ni 1-}} x-y Co x M 1 y O 2 + α). The upper limit of t is 1.20 or less, preferably 1.08 or less. In the composition of the composite oxide particles 2, the value of x indicating the composition ratio of Co is 0 ≦ x ≦ 0.22, and the viewpoint of increasing the capacity and improving the cycle characteristics in the secondary battery using the positive electrode active material 1 Therefore, it is preferably 0.05 ≦ x ≦ 0.20.

In the composition of the composite oxide particles 2, M ¹ is at least one element selected from the group consisting of Mg, Al, Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W. From the viewpoint of thermal stability of the positive electrode active material, it is preferable to contain at least Al, and ^{the value of y indicating the composition ratio of M 1} is 0 ≦ y ≦ 0.15, preferably 0.01 ≦ y ≦ 0. 10, more preferably 0.02 ≦ y ≦ 0.06. y, as will be described later, shows the same value as the composition ratio of the additive metal M ¹ in the preform 6 which is a raw material of the positive electrode active material 1.

In the composition of the composite oxide particles 2, M ² is at least one element of Nb and Al, and ^{z indicating the composition ratio of M 2} is more than 0 and 0.03 or less, preferably 0.0001. ≦ z ≦ 0.025. M ² is included in the surface layer portion 3. ^{At least a part of M 2} contained in the surface layer portion 3 may react with at least a part of Li, Ni, and Co in the composite oxide particles 2 to form a product. Further, M ² may be contained in the coating layer 5. ^{At least a part of M 2} contained in the coating layer 5 may react with at least a part of Ni and Co in the composite oxide particles 2 to form a product. M ² is an element derived from Nb and Al contained in the coating layer precursor 7 described later.

The lower limit of the contents of Nb and Al with respect to the entire positive electrode active material 1 is preferably 0.02% by mass or more, and more preferably 0.05% by mass or more. The upper limit of the contents of Nb and Al is preferably 3.0% by mass or less, more preferably 2.0% by mass or less, and further preferably 1.5% by mass or less. As a result, not only the contact with water can be suppressed, but also the reaction between the electrolytic solution and the particle surface during charging / discharging is suppressed, so that the capacity retention rate is lowered and the interface resistance value is suppressed by the AC impedance method. , The effect on the battery characteristics is also exhibited. When the amount of Al and Nb contained in the positive electrode active material 1 is less than 0.02% by mass, the thickness (area) of the surface layer portion 3 becomes small, the surface layer portion 3 is formed non-uniformly, and the water resistance and the battery The characteristics may not improve. On the other hand, when the amount of Al and Nb contained in the positive electrode active material 1 exceeds 3.0% by mass, the coating layer precursor 7 must be formed very thick in the manufacturing process of the positive electrode active material 1, as will be described later. In addition, since it takes a long time to prepare, there are problems such as a decrease in productivity and a decrease in adhesion of the coating layer. The contents of Nb and Al can be measured by ICP emission spectroscopic analysis.

2 (A) to 2 (C) are schematic views showing an example of a method for producing the positive electrode active material 1. FIG. 2A shows lithium nickel composite oxide particles serving as a base material 6 for the positive electrode active material. Preform 6, in the composition is _{Li t Ni 1-x-y} Co x M 1 y O 2 ( wherein, ^{M 1} is, Mg, Al, Ca, Ti , V, Cr, Mn, Zr, Nb, Mo and It is represented by at least one element selected from the group consisting of W, 1.01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15), and the amount of Li is stoichiometry. It is contained in excess of the composition.

In the composition of the base material 6, the amount of Li is 1.01 ≦ t ≦ 1.20, preferably 1.02 ≦ t ≦ 1.08. When the amount of Li in the base material 6 is insufficient, for example, when the amount of Li in the composition formula of the base material is t ≦ 1.00, a part of Li in the base material 6 is a coating layer precursor described later. The battery characteristics of the positive electrode active material 1 may deteriorate due to the reaction with the body 7. In order to avoid this, the amount of Li in the base material 6 is set to be excessive in advance so that the battery characteristics do not deteriorate even if the Li compound phase is formed. However, when the amount of Li is too large, for example, when t> 1.20, the elution and volatilization of lithium become active during the heat treatment, and it becomes difficult to control the heat treatment conditions.

In the composition of the base material 6, the value of x is preferably 0.05 ≦ x ≦ 0.20 from the viewpoint of increasing the capacity and improving the cycle characteristics of the secondary battery using the positive electrode active material 1. In the composition of the base material 6, ^{M 1} is, ^{M 1} is, Mg, Al, Ca, Ti , V, Cr, Mn, Zr, Nb, at least one kind of element selected from the group consisting of Mo and W From the viewpoint of thermal stability of the positive electrode active material, it is preferable to contain at least Al. The value of y is preferably 0.01 ≦ y ≦ 0.10, more preferably 0.02 ≦ y ≦ 0.06. Incidentally, the composition definitive M ¹ of the composite oxide particles 2 described above, M ¹ in the composition of the base material 6 denote the same elements.

FIG. 2B shows a base material 6 having a coating layer precursor 7 containing at least one of Al and Nb on its surface. By heat-treating the base material 6 having the coating layer precursor 7, the positive electrode active material 1 as shown in FIG. 2C can be obtained. In the positive electrode active material 1, the Li component in the base material 6 and the component contained in the coating layer precursor 7 react from around 400 ° C. (for example, 350 ° C. or higher) to once form a Li compound phase, and then the temperature is higher. It is considered that the surface layer portion 4 is formed by being exposed to the surface layer portion 4. For example, when the coating layer precursor 7 is heated to 600 ° C., the formation of fine particles having an average particle size of 20 nm or less can be confirmed on the surface of the positive electrode active material 1 by SEM or STEM observation. The surface of one particle of the positive electrode active material is finely organized by the reaction with the coating layer precursor 7, and the surface becomes uneven. As a result, the specific surface area of the positive electrode active material 1 increases 1.2 times or more and 1.8 times or less as compared with the surface area of the base material 6 before coating. When the specific surface area increases, the contact with the electrolytic solution during evaluation by the battery cell increases, and Li insertion and removal during charging and discharging can be activated, and the discharge capacity is maintained at the same level as before the coating treatment. can do. Furthermore, as will be described later, since it has a reaction phase with the Ni or Co component in the parent phase as part of the reaction, it is modified not only to battery characteristics such as cycle characteristics but also to a stable surface state with high water resistance. To. The average particle size indicates the number average, and was measured by directly observing the particle cross section with a transmission electron microscope (TEM) or a spherical aberration-corrected scanning transmission electron microscope (Cs-TEM).

As a result, the surface layer portion 3 has a concentration gradient such that the concentrations of at least one of Al and Nb are lowered in the radial direction from the particle surface toward the center.

Further, as described above, the coating layer 5 may be provided on the surface of the composite oxide particles 2. The coating layer 5 is a layer derived from the coating layer precursor 7, which does not diffuse into the composite oxide particles 2 even after the heat treatment and remains on the surface thereof. The thickness of the coating layer 5 is, for example, 0.1 nm or more and 150 nm or less, preferably 0.5 nm or more and 80 nm or less. When the coating layer 5 has a thin-film form without the formation of fine particles, the thickness of this form is preferably 0.1 nm or more and 20 nm or less.

The distribution (concentration) of Al or Nb in the surface layer portion 3 is important, and the concentration of Al or Nb on the outermost surface of the positive electrode active material 1 is not too high, and the composite oxide particles 2 should be hung from the outermost surface to the inside. Even if the concentration of Al or Nb is too low, the above-mentioned effect cannot be achieved. When the concentration of Al or Nb on the outermost surface of the composite oxide particles 2 is too high, the coating layer precursor 7 is not sufficiently diffused by the reaction with the surface (particle interface) of the base material 6, and the obtained positive electrode active material is not sufficiently diffused. It is shown that the oxide containing Al or Nb having high resistance is present only on the surface of 1. Therefore, when this positive electrode active material is used in a secondary battery, the interfacial resistance is maintained high and the initial discharge capacity is not improved. Further, when the concentration of Al or Nb on the outermost surface is too high, it indicates that the concentration of Al or Nb on the surface layer portion 3 is low because the heat diffusion has not progressed.

For example, the distribution (concentration) of Al or Nb in the surface layer portion 3 can be confirmed by observing the manufacturing process of the positive electrode active material 1. In the manufacturing process of the positive electrode active material 1, the film thickness of the coating layer precursor 7 (coating layer 5 after heat treatment) is observed to decrease or disappear after the heat treatment by observing the cross section TEM. This can be confirmed indirectly. Further, in the manufacturing process, by TEM-EDS surface analysis, the high concentration portion of Al or Nb of the coating layer precursor 7 (coating layer 5 after heat treatment) is observed to decrease due to the reaction after the heat treatment. Can be confirmed indirectly.

When the film thickness of the coating layer precursor 7 is several nm, even if the state after the reaction is observed by cross-sectional TEM observation or TEM-EDS surface analysis, the surface layer portion 4 is formed due to the problem of sensitivity. May not be able to figure out. In this case, the presence of Al and Nb in the surface layer portion 3 can be confirmed by observing the detailed reaction in the surface layer portion 3 by TEM-EELS. The surface layer portion refers to a portion where Al or Nb has a concentration gradient such that the concentration of Al or Nb decreases in the direction from the particle surface toward the center, and the thickness of the surface layer portion is, for example, 10 nm or more and 100 nm or less. be able to.

As will be described later, the coating layer precursor 7 hydrolyzes the base material 6 with a coating liquid containing a metal alkoxide containing at least one element composed of Al and Nb (see, for example, FIG. 3) or the metal alkoxide. It is formed by immersing it in a coating liquid containing fine particles of hydroxide (for example, see FIG. 4) or spraying it on the surface of the base metal 6.

The thickness (layer thickness) of the coating layer precursor 7 is preferably 3 nm or more and 100 nm or less, whereby a surface layer can be formed after the heat treatment. If the thickness of the coating layer precursor 7 is increased too much, the amount of thermal decomposition during heat treatment may decrease, organic residues may be generated in the surface layer portion 3, and the cycle characteristics may not be improved. In addition, since the heat treatment temperature and the holding time of the reached temperature are increased, there is a great disadvantage in terms of cost.

The positive electrode active material 1 of the present embodiment is different from the conventional positive electrode active material (which does not form the surface layer portion 3) having a coating layer containing at least one element composed of Al and Nb on the surface thereof. The part 3 itself does not prevent the insertion and desorption of Li ions during charging and discharging. Therefore, unlike the conventional positive electrode active material having a coating layer, it is not necessary to make the coating layer precursor 7 extremely thin to 3 nm or less. This makes it possible to simplify the process of thinning and homogenizing the coating layer, which is technically difficult. Further, since the thickness of the coating layer precursor 7 can be increased, the voids in the coating layer precursor 7 and the uncoated portion on the particle surface are reduced, and the obtained coating layer precursor 7 is further improved in uniformity. Become. In this case, the film thickness of the coating layer precursor 7 is preferably 20 nm or more and 50 nm or less, and the surface layer portion 3 generated by the heat treatment can be uniformly formed on the particle surface.

The coating layer precursor 7 may be formed discontinuously on the surface of the composite oxide particles 2, may be porous, or may have high uniformity. In any case, the surface layer may be formed by a reaction by heat treatment. It suffices if the part 3 can be formed. However, it is more preferable that the coating area of the coating layer precursor 7 measured by observing the cross section of the transmission electron microscope is 80% or more, 80% or more and 95% or less with respect to the entire surface area of the base material 6. .. When the covering area is within the above range, a uniform reaction with the surface of the base material 6 can be expected, and the surface layer portion 3 can be formed evenly on the entire surface.

In the positive electrode active material in which a conventionally known oxide film is formed on the surface thereof, the oxide film itself has poor conductivity, and in order to avoid an increase in interfacial resistance, the oxide film itself is thinned or in the oxide film. It was necessary to impart conductivity to the film. In this case, the optimum film thickness of the oxide film is required to be about 3 nm, and even if it is thick, it is required to be 10 nm or less. It takes time and effort to coat the coating with a thin coating so that there are no film defects, and the heat treatment temperature is about 300 ° C to suppress the reaction with the core material (base material) as much as possible in order to avoid a decrease in capacity. However, the temperature is limited to 400 ° C. or lower at the highest.

In the present embodiment, the upper limit of the film thickness of the coating layer precursor 7 formed in the manufacturing process is 100 nm or less, and a thick film larger than the conventional one is allowed. This is because the coating layer precursor 7 diffuses into the particles due to the effect of the high temperature heat treatment, and the thickness of the finally formed coating layer 5 is significantly reduced. There is no decrease in discharge capacity. By having the surface layer portion 4 in the positive electrode active material 1 of the present embodiment, the improvement of water resistance that suppresses gelation, which has been a problem of the positive electrode active material having a coating layer (product film), and after the surface layer is generated. The reduction of the initial discharge capacity and the improvement of deterioration during repeated charging and discharging are achieved. In the present embodiment, it is important to perform high temperature treatment after forming the coating layer precursor 7, and as a result of forming the surface layer portion 3 by the reaction between the base material 6 and the coating layer, gelation during long-term storage, which is the main purpose, is performed. The initial discharge capacity before and after the formation of the surface layer portion 3 can be maintained without change, and stable cycle characteristics can be obtained while suppressing an increase in interfacial resistance even when charging and discharging are repeated.

As will be described later, the formation of the surface layer portion 3 can be confirmed from the particle cross section by using, for example, an electron image by TEM or a surface analysis by TEM-EDS. For example, a coating liquid (containing Nb) described later is thickly coated on the surface of the lithium nickel composite oxide particles (base material 6), and an Nb precursor layer (coating layer precursor 7) having a thickness of 30 nm is applied to the surface of the base material 6. After the formation, heat treatment was performed by changing the temperature conditions, and when this heat treatment process was observed or surface-analyzed, at 300 ° C., the thickness from the particle interface (composite oxide particle surface) mainly containing high concentration Nb. A coating layer 5 having a diameter of about 30 nm is detected. Further, when the temperature is changed from 600 ° C. to 700 ° C., the observed coating layer 5 is reduced, and it can be confirmed by surface analysis that a high concentration of Nb is dispersed. From this, it can be understood that the coating layer 5 containing a high concentration of Nb is significantly reduced and the surface layer portion 3 is formed. When the Nb precursor layer (coating layer precursor 7) is heat-treated, even if it is heated to 600 ° C. or higher, the Nb layer (coating layer 5) having a high concentration locally on the surface is not completely diffused. May be unevenly distributed. Even when the Nb layer (coating layer 5) remains, the water resistance is improved by forming the coating layer 5 by the heat treatment, and the discharge capacity can be recovered by the formation of the surface layer portion 3.

On the other hand, the effect of the Al coating layer (for example, improvement of interfacial resistance and recovery of discharge capacity) tends to be more remarkable as compared with the Nb coating layer. For example, when the heat treatment is performed at 300 ° C., Al may be diffused inside the particles and the coating layer 5 may be reduced. At this time, by observing the surface of the positive electrode active material 1 by SEM, a fine structure which is an Al reaction product is observed on the surface of the positive electrode active material 1. The difference in diffusion behavior from these Nb coating layers is largely due to the difference in the diffusion rate of each element, and it can be said that Al is more effective on the low temperature side because the diffusion is considerably faster than that of Nb. Due to the diffusion of Al, the Al concentration decreases from the surface of the positive electrode active material 1, the interfacial resistance decreases, and the discharge capacity recovers to the same level as uncoated.

As described above, the coating layer precursor 7 is transformed into the surface layer portion 3 by the heat treatment. During the heat treatment, a compound is generated by the reaction of excess Li, Ni, Co, etc. derived from the lithium composite oxide particles (base material 6) with the components derived from the coating layer precursor 7, and the coating layer precursor 7 / coating layer 5 is formed. Morphological change occurs. For example, in the lithium composite oxide particles (base material 6), Li is added slightly in excess of the stoichiometric composition so that Li is not lost during firing, so that the excess Li content and components derived from the coating layer precursor 7 are added. Reactions with ( ^{including M 2} ) may occur. Further, when a local Li-deficient portion is generated on the surface of one particle of the positive electrode active material, a compound is generated by the reaction between the ^{exposed Ni or Co and the component (including M 2) derived from the coating layer precursor 7.} Sometimes. In particular, since Ni-Al compounds with Ni and Co and Co-Al compounds are likely to be produced at a relatively low temperature side, such compounds are generated inside a part of the surface layer portion 3 or the coating layer 5. Such a compound has, for example, a spinel-type crystal phase represented by _{the composition formula AB 2} O ₄ (A is at least one metal element of Ni and Co, and B is M ^2). Including. Examples of the spinel-type crystal phase include a phase in which NiAl ₂ O ₄ and CoAl ₂ O ₄ are formed.

However, when the heat treatment temperature exceeds 700 ° C., not only the base materials 6 start sintering but also Li volatilization may occur. Therefore, it is preferable that the heat treatment temperature is at least 700 ° C. or lower.

Further, the reaction state between the coating layer precursor 7 and the surface of the base material 6 can be confirmed by XRD measurement and a change in the lattice constant by Rietvelt analysis. For example, a coating material of Nb—O is coated on the surface of lithium nickel composite oxide particles with a thick coating of 30 nm, and the heat treatment temperature is changed to perform a Lattice constant analysis on a crystal phase derived from the _{LiNi 0.85} Co _0.15 O _{2 phase.} Then, an increase in the a-axis length and the c-axis length of the lattice constant is confirmed from around 300 ° C. This increase in the lattice constant indicates the spread of the lattice, and it can be confirmed that the Nb atom, which is a constituent element of the coating layer, is replaced with the 3a site of nickel ions. In this phenomenon, it is confirmed that the a-axis length and the c-axis length increase as the heat treatment temperature is increased. For example, the positive electrode active material 1 has an a-axis length of 2.8647 or more and 2.8655 or less and a c-axis length of 14.1801 or more and 14.890 or less, which is determined by Rietveld analysis of X-ray diffraction. The upper limit of the c-axis length is preferably 14.3 or less, more preferably 14.2 or less.

Conventional lithium-nickel composite oxide particles have low resistance to water and are easily eluted as lithium ions from the surface. _{For example, when 0.1 g of Li 1.03} Ni _0.85 Co _0.12 Al _0.03 O ₂ powder containing an excess of Li having no surface layer is added to 50 ml of pure water at 24 ° C., it is instantaneous. A large amount of lithium begins to elute, the aqueous solution shifts to the alkaline side, and the pH reaches around 13. On the other hand, in the positive electrode active material 1 of the present embodiment, the elution of lithium is reduced due to the effect of the modified surface layer, and the pH in the aqueous solution becomes 11.2 or less. By maintaining the pH at 11.2 or less, the paste composition after kneading used for producing the positive electrode material has a reduced alkali elution, and as a result, the long-term storage stability of the paste composition is improved and gelation is eliminated.

The positive electrode active material 1 contains, for example, 9.5 g of the positive electrode active material, 0.5 g of vinylidene fluoride (PVDF), 5.5 g of N-methyl-2-pyrrolidinone (NMP), and 0. Even if 2 g is added and kneaded to form a slurry, and the slurry is stored at 24 ° C. for 3 days without gelation, no gelation is observed, and a fluid slurry can be maintained. By suppressing gelation, variations in charge / discharge characteristics due to non-uniformity when applied to the positive electrode current collector are suppressed, and problems such as a decrease in the density of the coating film due to deterioration of the fluidity of the paste also occur. Decrease.

The positive electrode active material 1 can be selected according to the characteristics required for the target positive electrode active material. For example, the average particle size of the positive electrode active material 1 is preferably 3 μm or more and 25 μm or less, more preferably 3 μm or more and 15 μm or less, from the viewpoint of high battery capacity and high filling property. Here, the average particle size indicates a median diameter (D50) and is measured by a particle size distribution measuring device based on a laser diffraction / scattering method.

The positive electrode active material 1 not only has excellent long-term storage stability of the kneaded paste composition, but also the change in initial discharge capacity after surface layer formation is controlled to ± 3%, and long-term cycle characteristics can be improved. Therefore, for example, when used for the positive electrode of a 2032 type coin battery, an initial discharge capacity of 185 mAh / g or more, and 190 mAh / g or more under more optimum conditions can be stably obtained. Further, a battery cell was prepared using a voltage range of 3.0V-4.3V, a rate of 0.5C, a carbon negative electrode, and LiClO ₄ / EC-DEC for the electrolytic solution, and the discharge capacity after performing a cycle test for 100 cycles. The retention rate is a decrease of 10% or less with respect to the initial capacity, and has good cycle characteristics.

The method for producing the positive electrode active material 1 will be described with reference to FIGS. 3 to 4. However, the following description is an example and does not limit the manufacturing method. As shown in FIG. 3, in the method for producing the positive electrode active material 1 of the present embodiment, a metal alkoxide monomer or an oligomer thereof containing at least one of Al and Nb is mixed with an organic solvent to obtain a mixed solution. After that, a chelating agent is added to the mixed solution to obtain a coating liquid (step S1), and the coating liquid is mixed or sprayed with the lithium nickel composite oxide particles to obtain the lithium nickel composite oxide particles. The coating layer precursor 7 is formed on the surface of the coating layer precursor 7 (step S2), and the composite oxide particles on which the coating layer precursor 7 is formed are heat-treated in an oxygen atmosphere of 400 ° C. or higher and 700 ° C. or lower (step S3). ,including.

Further, as shown in FIG. 4, the coating liquid is prepared by mixing a metal alkoxide monomer or an oligomer thereof containing at least one of Al and Nb with an organic solvent to obtain a mixed liquid, and then using the mixed liquid. It can also be obtained by adding a chelating agent and then adding water (step S1'). The details of each step will be described below.

First, a coating liquid for forming the coating layer precursor 7 is prepared (step 1). The coating liquid is obtained by mixing a monomer or oligomer composed of a metal alkoxide containing at least one of Al and Nb with an organic solvent such as alcohol, and then adding a chelating agent.

As the metal alkoxide containing at least one of Al and Nb, conventionally known metal alkoxides can be used, and for example, metal alkoxides of each monomer composed of -ethoxide, -methoxide, -isopropoxide, and -butoxide can be used. it can. Further, since the metal element contained in the metal alkoxide is contained as it is in the coating layer to form an oxide, it is preferable that the metal element contains a hydroxide that easily forms an oxide. As the metal alkoxide, any of a metal alkoxide containing Al, a metal alkoxide containing Nb, or a metal alkoxide containing Al and Nb can be used. Specifically, for example, a monomer composed of aluminum triethoxyde, aluminum triisopropoxide, aluminum tributoxide, and nioboxide can be used. Further, even an oligomer can be used as long as it can be dissolved in the alcohol solvent to be used.

As the solvent, for example, alcohol can be used, and specifically, one or more lower alcohols selected from ethanol, 2-propanol, and 1-butanol can be used. It is not preferable to volatilize and dry it by using it in a higher alcohol having 5 or more carbon atoms or a hydrocarbon solvent because it causes problems of harmfulness and offensive odor. Among the lower alcohols, ethanol and / or 2-propanol are preferable from the viewpoint of solubility and cost of organometallic compounds and additives. Further, it is preferable to use a dehydrated lower alcohol. Dehydration suppresses the hydrolysis reaction when mixed with the metal alkoxide. Further, the fine particles can be formed by a hydrolysis reaction with water added after the addition of the chelating agent.

The solvent is used as a solution when mixed with the metal alkoxide, and the concentration of the metal alkoxide is preferably 60% by mass or less, more preferably 0.1 to 40% by mass, and further preferably 0.1 to 20% by mass. To mix. If the concentration of the metal alkoxide exceeds 60% by mass, the reaction with the chelating agent tends to be non-uniform, and white turbidity may occur when a solvent diluting to a concentration suitable for the dispersion is added. Although the coating liquid can be prepared even if it is less than 0.1% by mass, the amount of alcohol used will increase.

Next, a chelating agent is added to a solution in which the metal alkoxide and the solvent are mixed. The metal alkoxide has a high hydrolysis rate and easily forms a hydroxide due to the humidity in the outside air. Therefore, in order to control the hydrolysis reaction rate, it is necessary to modify (chelate) a part of the functional groups (alkoxy groups) in the alkoxide metal compound with a chelating agent.

Chelation of the alkoxide metal compound facilitates the control of the hydrolysis reaction. As a result, a part of the functional group of the metal alkoxide can be partially hydrolyzed into an oligomer, and the hydrolyzing group (hydroxyl group) improves the adsorptivity to the particle surface. As the chelating agent, at least one selected from aminocarboxylic acid, a salt thereof, and diketones is preferably used, and acetylacetone is more preferable among them. As other chelating agents, known ethyl acetoacetate, nitrilotriacetic acid, methylglycine diacetic acid, dicarboxymethyl glutamic acid, L-aspartic acid and the like, or salts thereof can be substituted, but acetylacetone having excellent thermal decomposability can be used. Especially preferable. For example, out of the three functional groups of aluminum triisopropoxide, the hydrolysis rate is slowed down by adding the same number of moles of acetylacetone as the amount for exchanging one functional group to modify it, and water is used. Resistance to is greatly improved.

In addition, during chelation, if all the alkoxy groups are modified, not only will they not dissolve in the lower alcohol, but they will not be adsorbed or chemically reacted on the surface of the composite oxide particles, resulting in insufficient formation of the coating layer. Therefore, it is important to partially modify the functional group. Therefore, by modifying one of the aluminum isopropoxides having three alkoxy groups as described above, it is possible to improve the stability to the outside air and maintain the adsorptivity to the particles. ..

In order to carry out a sufficient modification reaction during chelation, for example, an alkoxide monomer is dissolved in a lower alcohol such as 2-propanol to prepare a solution having a concentration of 60% by mass or less, and a chelating agent such as acetylacetone is contained therein. Is gradually added and then heated at 20 to 70 ° C. for 0.5 to 4 hours to obtain a chelated solution of the alkoxide monomer. By such an operation, the modification reaction is promoted and the stability to water is increased. The liquid thus obtained is further diluted with alcohol to complete the coating liquid.

Further, when the chelated solution is partially hydrolyzed to obtain a dispersion liquid, a slight cloudiness may occur for a moment after dropping water, but the liquid immediately returns to a transparent liquid. Further, by holding and stabilizing at 20 to 80 ° C. for 0.5 to 25 hours, cloudiness and formation of a precipitate can be suppressed even if a large amount of solvent is added for dilution thereafter. For example, 1 It is possible to obtain a dispersion having a shelf life that does not change even if it is left for a month. This phenomenon is probably due to partial hydrolysis in the presence of organic matter, resulting in an apparently transparent liquid.

Here, the transparency of the liquid is the degree to which visible particles floating in the liquid can be confirmed. If there are coarse particles, they show cloudiness due to light scattering, and if they are fine particles (nanoparticles), light is transmitted. The liquid gains transparency to do so. Nanoparticles are particles with a central particle size of 100 nm or less. The central particle size (for example, D50) is the particle size when the number or mass of particles larger than a certain particle size occupies 50% of the total number or mass of particles in the particle size distribution of nanoparticles. The particle size is measured by the dynamic light scattering method / laser Doppler method.

Further, as shown in FIG. 4, after adding the chelating agent, water can be further added to partially hydrolyze the metal alkoxide to generate fine particles in the coating liquid (step S1'). Since both steps S1 and S1'can undergo the same steps until water is added and hydrolyzed, the description of the same conditions as described above is omitted.

The fine particles formed in the coating liquid by partial hydrolysis of the metal alkoxide preferably have a flat or scaly shape. The fine particles in the coating liquid have a flat or scaly shape, and when the fine particles are deposited on the particle surface of the composite oxide, a dense coating layer is formed on at least a part of the particle surface of the composite oxide. The precursor 7 is formed, while fine gaps are formed between the fine particles at least a part of the surface of the base material 6. By densely forming such fine particles as the coating layer precursor 7, the reaction can easily proceed at a low temperature and in a short time even in the heat treatment step for obtaining the surface layer portion 3, and it becomes possible to form a high-quality uniform layer. .. As a result, not only is it possible to secure sufficient contact between the positive electrode active material 1 and the electrolyte while suppressing the water absorption of the positive electrode active material 1, but also the surface layer moves lithium ions during charging and discharging of the secondary battery. Since it does not interfere, the decrease in initial discharge capacity due to the increase in surface resistance can be reduced.

The fine particles in the coating liquid preferably have an aspect ratio of 0.3 or more and 0.8 or less, and more preferably 0.4 or more and 0.8 or less. The aspect ratio is obtained by dividing the minimum diameter of the particles by the maximum diameter, and indicates the degree of deformation of the fine particles in the coating liquid from a true sphere. The smaller the value, the larger the degree of deformation. That is, by setting the aspect ratio of the fine particles within the above range, it is possible to increase the density of the coating layer, further suppress the water absorption of the positive electrode active material 1, and secure the contact between the positive electrode active material and the electrolyte. it can.

The fine particles in the coating liquid are precursors of oxide fine particles forming the coating layer 5 of the positive electrode active material 1, and greatly affect the shape of the oxide fine particles. Further, the shape of the fine particles in the coating liquid is maintained even in the oxide fine particles forming the coating layer 5. The fine particles in the coating liquid have an average particle size D50 of 100 nm or less, preferably 1 nm or more and 12 nm or less, more preferably 3 nm or more and 10 nm or less, and further preferably 5 nm or more and 10 nm or less. As a result, when the average particle size is in the above range, the coating layer can be formed thinly and uniformly. Further, the oxide fine particles forming the coating layer 5 also have the same shape, and sufficient contact between the positive electrode active material 1 and the electrolyte can be ensured. As a commercially available product, there is a liquid in which an organometallic compound having an alkoxide group is hydrolyzed and fine particles are dispersed, but many of them contain coarse particles, and even if this is used as a coating liquid, the present embodiment It is difficult to obtain the surface layer portion 3 and the coating layer 5 of the positive electrode active material 1.

By adding the chelating agent, it is possible to control the hydrolyzability of the organometallic alkoxide having a high hydrolysis rate, and it is possible to maintain high adsorptivity to the composite oxide particles. On the other hand, when the chelating agent is not added, the reaction with the water in the outside air or the water added for hydrolysis becomes remarkable, and all the alkoxides are immediately hydroxideed to cause precipitation due to coarse graining. Since Nb alkoxide is rapidly hydrolyzed and difficult to chelate, it lacks storage stability after partial hydrolysis. Therefore, it is preferable to use the metal alkoxide as a coating raw material without hydrolysis. On the other hand, Al has a high chelating effect, and when a small amount of chelating agent is added, the functional group of the alkoxide is replaced by the chelate ring, and the responsiveness to water is lowered. As a result, the partially chelated functional group is partially hydrolyzed, so that it can be easily adsorbed on the surface of the base material 6 while maintaining the fine particles without sedimentation. Therefore, the chelated Al alkoxide can be used as it is as a metal alkoxide, or can be used in the form of partially hydrolyzed fine particles.

In addition to the alcohol content used during hydrolysis, the solvent also includes those used to dilute the coating liquid. The concentration of the coating liquid or the dispersion liquid itself is high, and if it is deposited on the surface of the base metal 6 in this state, it becomes locally thick and causes extreme non-uniformity. In order to facilitate obtaining a thin and uniform coating layer, a diluent is further added to reduce the concentration. Moisture can be used as the diluent, but the drying at the time of coating is slow, and the base material 6 may be deteriorated. In order to avoid this, it is possible to improve the drying rate by adding a lower alcohol. Most preferably, all the diluents are alcohols, but at least when water is used as the diluent, it is necessary to prepare a mixed solution containing 30% or more of alcohol in the whole solution. As the lower alcohol used here, ethanol or 2-propanol is preferable in consideration of an offensive odor during drying.

In the partial hydrolysis reaction, it is preferable to add 5 to 50% by mass, preferably 10 to 30% by mass of water with respect to 100% by mass of the metal alkoxide, and after adding water, further heating is performed. Terminate the partial hydrolysis reaction. When the water content exceeds 50% by mass, hydrolysis proceeds too rapidly and gelation is likely to occur, and when it is 5% by mass or less, the amount of hydrolysis is small.

The dispersion liquid needs to be diluted to reduce the concentration in order to homogenize the precursor fine particles deposited on the surface of the base material 6 particles. Since the partially hydrolyzed chelate solution has a high concentration, it is diluted with alcohol or a mixed solvent of water and alcohol to prepare a coating solution so as not to form a non-uniform film during spray coating. The minimum amount of coating liquid to be mixed with the base material 6 is such that the dispersion liquid is adsorbed and permeated over the entire surface of the base material 6, and a sufficient amount of precursor fine particles to be deposited on the particle surface is required. It is preferable to dilute the total amount of fine particles adhered to the base material 6 and the coating layer precursor 7 so as to be in the range of 0.02% by mass or more and 3.0% by mass or less by ICP analysis. .. Even if the amount of the dispersion liquid is large, the drying time is only long, and there is no problem in the powder characteristics of the obtained positive electrode active material, but the determination may be made in consideration of the efficiency at the time of drying. If it is less than 0.02% by mass, it may not be possible to form a sufficient amount of fine particles in the coating layer. On the other hand, if it exceeds 3.0% by mass, the coating layer becomes too thick when the amount to be adsorbed on the entire surface of the composite oxide particles is mixed, and peeling may occur during drying.

Further, the amount of Al or Nb contained in the coating liquid is adjusted to be in the range of 0.02 to 3.0% by mass by ICP analysis. If the amount added is small, it may not be possible to deposit the coating layer required for surface layer formation.

Next, as shown in FIGS. 3 and 4, a coating layer precursor 7 is formed on the surface of the base material 6 (step S2). The coating method may be any method in which the coating liquid is uniformly deposited (coated) on the surface of the base metal 6. For example, a method in which the precursor fine particles are simultaneously deposited and dried on the surface of the core material particles by spraying like a rolling flow device is more preferable. It is also possible to mix the coating liquid and the base material 6 using a kneading mixer of the rotation / revolution type, and then volatilize only the solvent for the coating treatment.

In the method of coating using a rolling flow device, it is possible to spray the particles in a fluid state without damaging the surface of the base material 6. The characteristic of the coating by the rolling fluid device is that it can be deposited uniformly and thinly. In the rolling flow device, for example, the base material 6 accumulated in the inner bottom of the device is agitated by a rotor to loosen the originally generated agglomeration, and the base material 6 is made to flow in the form of single particles by the heated air introduced from the inner bottom of the device. It is a mechanism. The coating layer can be uniformly deposited on the surface of the base material 6 by spraying the coating liquid with a two-fluid nozzle or the like during this flow and drying the coating liquid while advancing hydrolysis with the introduced air.

The kneading mixer can perform uniform mixing by applying an appropriate shearing force to the mixture by rotating and revolving, and can be performed in a short time. The mixing time is preferably 1 to 5 minutes. Mixing for a short time with a kneading mixer is also effective in suppressing damage to the particle surface. On the other hand, if a device such as a bead mill, a ball mill, a rod mill, a homogenizer, or the like in which a large force is directly applied to the base material 6, the particles themselves are crushed or the surface of the particles is greatly distorted, resulting in battery characteristics. May decrease.

The mixture after the treatment with the kneading mixer is first dried by evaporating the solvent in the coating liquid. In the process of this drying, the coating liquid is hydrolyzed and adsorbed and bonded to the surface of the core material particles, and deposition is performed. At this time, since a large amount of the liquid still remains in the drying of the mixture obtained by the kneading mixer, if the solvent is rapidly volatilized at once, the agglomeration between the particles tends to proceed at the same time as the drying. In order to suppress this, it is preferable to evaporate the solvent slowly so as not to cause adhesion between the particles. It is also effective to repeat mixing in parallel with drying. Since the evaporation rate strongly depends on the temperature, it is effective to gradually expose it to a high temperature from room temperature.
When the rolling flow device is used, the process from mixing to drying can be performed, so that the process can be immediately shifted to the heat treatment in the next step after being taken out from the device.

On the other hand, in the conventional wet coating method in which the core material particles are immersed in an alcohol solvent and the metal alkoxide and water are dropped while stirring, there is a problem that the added water elutes lithium ions from the base material 6. In addition, it takes a long time to form a film due to the bonding of hydroxyl groups in the metal alkoxide, and the film formation time of several hours and the subsequent drying time not only cause deterioration of battery characteristics, but also increase productivity. There was also an issue in terms of cost due to the decline.

In the above-mentioned mixing and drying steps, the moisture contained in the solvent does not cause elution of lithium ions in the positive electrode active material. The reason for this is unknown, but the liberated chelating agent contained in the coating liquid acts on the lithium on the electrode surface of the positive electrode active material during the mixing and drying process, so that the positive electrode active material itself is also chelated and becomes water. On the other hand, it is presumed that it is stable.

The drying temperature after forming the coating layer precursor is preferably 50 to 150 ° C., more preferably in vacuum. On the other hand, if the drying temperature exceeds 200 ° C., the base material 6 tends to deteriorate. The drying time may be such that the solvent does not evaporate and adhesion between the particles does not occur, and is preferably 1 to 24 hours. If it is less than 1 hour, drying may be insufficient, and if it exceeds 24 hours, productivity will decrease.

Next, the base material 6 on which the coating layer precursor 7 is formed is heat-treated in an oxygen atmosphere of 400 ° C. or higher and 700 ° C. or lower to cause a reaction between the coating layer precursor 7 and the surface of the base material 6 (step S3). .. The coating layer precursor 7 formed on the surface of the base material 6 is firmly bonded to the particle surface in a temperature range of 250 ° C. or higher and 300 ° C. or lower, and most of the organic substances existing in the layer are removed. The film quality is improved by forming a film (coating layer 5) made of an oxide. As a result, the coating layer 5 formed on the surface of the base material 6 becomes more dense and strong, the water resistance is improved, and the effect of suppressing gelation is further improved. At this stage, no significant reaction occurred between the base material 6 and the coating layer 5. On the other hand, since the coating layer obtained at this stage is in the form of an oxide, the interface resistance tends to be significantly deteriorated and the initial discharge capacity tends to decrease.

In the conventional production method, the heat treatment is completed in the above temperature range (for example, 250 ° C. or higher and 300 ° C. or lower), and the film is evaluated as having a high gelling effect. In order to alleviate the decrease in discharge capacity at this time, it was necessary to make the coating layer as thin as possible to about 3 nm so as not to prevent Li from being inserted and removed during charging and discharging. By increasing the thinness and uniformity, the balance between the initial charge capacity and the water resistance is maintained, and in order to suppress defects in the film (generation of voids due to decomposition of organic substances) caused by the thinness, a dilute solution is used over time. It took time and effort to process it.

In the production method of the present embodiment, heat treatment is further performed at a high temperature range of 350 ° C. or higher and 700 ° C. or lower, preferably 400 ° C. or higher and 700 ° C. or lower. Therefore, the coating layer reacts at the particle interface, and the coating layer becomes a surface layer to suppress gelation while avoiding a decrease in discharge capacity.

Further, in a known technique, the organic matter in the coating layer is left to remain by performing the low temperature treatment, and the deterioration of the interfacial resistance is suppressed. However, when it is used as a positive electrode active material that requires high output for automobiles, a part of the remaining organic matter reacts with the electrolytic solution and dissolves, which may affect the cycle characteristics.

The residue of the organic substance contained in the coating layer is analyzed as carbon. In the present invention, not only the residual organic substance is decomposed by the treatment at high temperature, but also the heat treatment is performed in an oxygen-rich atmosphere, so that carbon is used. The residue as is significantly reduced. This carbon content is determined not only by the amount of oxygen but also by the conditions at the time of heat treatment, and can be achieved by controlling the amount of the mixture to be charged into the furnace used for heat treatment, the heat treatment temperature, and the rate of temperature rise.

As a condition for heat-treating the mixture, the value obtained by the following formula (1) is preferably 33 (g / min) or more and 1333 (g / min) or less, more preferably 60 (g / min) or more and 400 (. g / min) Within the following range.
[Mixture amount (g) / furnace volume (L)] x oxygen gas introduction amount (L / min) ... (1)
If the treatment temperature is 300 ° C. or lower, the effect can be sufficiently obtained even if the oxygen gas flow rate is suppressed, but when the treatment is performed at a high temperature, _{the positive electrode active material of the LiNiO 2} system causes Li scattering and oxygen deficiency. It is necessary to flow a large amount of oxygen gas in order to avoid the above.

By controlling the heat treatment conditions within the above range, it is possible to prevent Li from scattering and oxygen deficiency in the positive electrode active material. Within the range of this numerical value, the same effect can be obtained by arbitrarily changing the ratio of the furnace volume, the processing amount of the mixture, and the oxygen gas flow rate.

For example, a mixture of 500 to 2000 g filled in an alumina container is put into a heat treatment furnace having a volume of 30 L, and pure oxygen gas is introduced at 3 to 20 L / min (gas pressure 0.1 MPa) at 3 ° C./min. The temperature is raised from 20 ° C./min, preferably 5 ° C./min to 10 ° C./min, and maintained at 400 to 700 ° C. for 0.5 to 5 hours, preferably 500 ° C. to 600 ° C. for 0.5 to 2 hours. As a result, the high-performance positive electrode active material according to the present invention can be obtained.

The heat treatment temperature is in the range of 350 ° C. or higher and 700 ° C. or lower. Since the present embodiment does not aim to form an oxide layer on the surface of the composite oxide particles 2 and provide a protective layer that repels water, it is not a heat treatment at a low temperature as in the conventional case, but 350 ° C. or higher. This mainly causes a reaction between the interface between the base material 6 and the coating layer precursor 7 to form a surface layer from the Li compound layer. Further, since the present invention starts with a coating layer composed of deposits of fine particles, it is not exposed to a high temperature (800 ° C. to 900 ° C.) as in the case of producing a core material. When exposed to a higher temperature side, oxygen and Li are likely to be deficient from the surface of the base metal 6, and the surface may deteriorate. Another factor is that the coated particles adhere to each other due to the firing reaction and form aggregates. Therefore, it is necessary to process at 700 ° C. or lower so that the battery characteristics do not deteriorate. In the present embodiment, since the coating layer precursor 7 made of amorphous material is used as a starting point, the reaction with the base material 6 is easy, and the treatment at a relatively low temperature side is possible. As a result, the damage to the base material 6 as described above can be treated as little as possible.
The reason why the oxide layer can be formed on the surface of the base material 6 by such a relatively easy step and the surface layer can be formed from the relatively low temperature side via the Li compound layer is because there is an excess of Li in the base material 6. This is one of the factors that promote the reaction, and the excess lithium is probably _{precipitated on the surface of the core material particles in the state of LiOH · nH 2} O, and the oxide fine particles are laminated on it to facilitate the reaction. I believe.

On the other hand, the removal of unnecessary components such as an organic solvent remaining in the coating layer 5 can be further reduced by high-temperature treatment. If the heat treatment temperature is less than 250 ° C., an unnecessary organic solvent remains in the coating layer, and gas generation becomes a problem when charging / discharging after the battery cell. Most of the organic matter is thermally decomposed above 300 ° C., but a very small amount of residue is present. This causes long-term cycle deterioration, and it is important to reduce it.

When the temperature dependence of the initial discharge capacity is investigated, it is formed as an oxide layer because organic substances are removed from the coating layer when the heat treatment temperature reaches 300 ° C. Therefore, when the interfacial resistance is 1 when uncoated, the number of coated products increases more than twice, and as a result, the initial discharge capacity tends to decrease. Further, the thicker the oxide layer, the stronger the tendency, and when the thickness of the coating layer is 10 nm or more, the interfacial resistance exceeds 2 to 3 times. When the temperature rises to 300 ° C. or higher, the reaction between the base material 6 and the coating layer precursor 7 starts, and when the temperature rises further, the constituent elements of the coating layer precursor 7 and the base material 6 are mutually diffused, and the temperature as a surface layer on the particle surface. It is generated as it rises. In parallel with this, the interfacial resistance is gradually improved, and the initial discharge capacity tends to recover. At this time, the interfacial resistance is 2 times or less, preferably 1.5 times or less.

The formation of the surface layer 3 can be confirmed from the particle cross section by using an electron image by TEM or a surface analysis by TEM-EDS, for example. For example, when the coating layer precursor 7 of Nb—O is coated on the surface of the lithium nickel composite oxide particles (base material 6) so as to have a thickness of 30 nm and observed or surface-analyzed at different heat treatment temperatures, the positive electrode activity is activated at 300 ° C. A state in which a coating film (coating layer 5) is formed on the surface of the substance 1 is observed, and in surface analysis, it is detected as a coating layer 5 having a thickness of 30 nm from the particle interface mainly containing a high concentration of Nb. Further, the coating layer 5 is reduced by the time the temperature reaches 700 ° C. Further, at 700 ° C., the observed coating film (coating layer 5) disappears locally, and it can be confirmed by surface analysis that the high concentration of Nb is dispersed and the coating layer is significantly reduced. When heat-treated at 300 ° C., an increase in interfacial resistance and a decrease in discharge capacity are observed in the secondary battery using the obtained positive electrode active material. Such a decrease in discharge capacity is caused by a heat treatment temperature of 600 ° C. The interfacial resistance and discharge capacity recover when the temperature reaches about 700 ° C. On the other hand, at 800 ° C., the coating layer is further reduced, so that the surface effect is weakened, and not only the initial charge / discharge capacity but also the water resistance and the effect of improving the cycle characteristics are gradually reduced. From the above observation results, it is inferred that the coating film of 30 nm on the surface of the positive electrode active material is the cause of the deterioration of these battery characteristics. Further, in the present embodiment, the battery characteristics are improved by appropriately diffusing the coating film, which was the resistance layer, into the composite oxide particles 2 by heat treatment at 350 ° C. or higher, and the surface layer portion 3 and the coating layer 5 are formed. It can be said that this is one of the causes.

The formation state of the surface layer portion 3 also differs depending on the difference in the constituent elements. For example, when Al—O is used as the coating layer 5, the surface layer portion 3 is generated from the time of heat treatment near 300 ° C., and the coating layer precursor 7 / coating layer 5 gradually disappears. From this, when Al—O is used as the coating layer 5, the optimum heat treatment is 600 ° C. to 700 ° C., which is a lower temperature. This is because the diffusion rate of Al is faster than that of Nb, and the valence and ionic radius of the coating material are related. Further, when the heat treatment temperature exceeds 700 ° C., not only the base material 6 itself starts to be sintered, but also the surface layer portion 3 is almost eliminated by the progress of diffusion. As a result, the above-mentioned effect of the surface layer portion 3 is diminished, and not only the initial charge / discharge capacity but also the water resistance and the effect of improving the cycle characteristics are reduced. Therefore, the above-mentioned remarkable effect cannot be obtained unless the constituent elements (at least one of Al and Nb) derived from the coating layer precursor 7 remain in the surface layer portion 3 at a constant concentration.

The heat treatment time is preferably 0.2 hours or more and 5 hours or less, more preferably 0.5 hours or more and 5 hours or less, and 0.5 hours or more and 2 hours or less after the temperature is raised to a predetermined temperature. Is even more preferable. This makes it possible to sufficiently adhere to the surface of the composite oxide particles and remove unnecessary organic solvents. If the heat treatment time is less than 0.5 hours, the organic solvent may remain. Further, if it exceeds 5 hours at a high temperature, oxygen deficiency from the base material 6 is likely to occur, so that the initial discharge capacity may decrease. A pure oxygen atmosphere is selected as the atmosphere during the heat treatment, and it is preferable that the surface of the composite oxide particles is not reduced.

The production method of the present embodiment can be applied to almost all positive electrode active materials, and in addition to the above-mentioned lithium nickel composite oxide particles as a base material used as a raw material, for example, lithium cobalt composite oxide. , Lithium nickel cobalt manganese composite oxide, lithium manganese composite oxide and the like can be used. In addition, the particle size distribution of the obtained positive electrode active material is maintained almost the same before and after coating. Therefore, the average particle size of the composite oxide particles before coating may be the same as that of the positive electrode active material to be finally obtained, preferably 3 μm or more and 25 μm or less, and 5 μm or more and 20 μm or less. More preferred. Here, the average particle size is the median diameter (d50), and can be measured by a particle size distribution measuring device based on a laser diffraction / scattering method. It is particularly preferable to use a muffle furnace or a tube furnace as the electric furnace for heat treatment, and by constantly circulating gas while the furnace is filled with pure oxygen, oxygen deficiency due to decomposition of organic substances etc. does not occur during heat treatment. Instead, the surface layer of the base material 6 can be brought into a sound oxidized state.

2. Non-Aqueous Electrolyte Secondary Battery An example of the non-aqueous electrolyte secondary battery of the present embodiment will be described in detail below for each component. The non-aqueous electrolyte secondary battery is composed of components such as a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, like a general lithium ion secondary battery, and is characterized in that the positive electrode active material of the present invention described above is used as the positive electrode. Is to be. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery according to the present embodiment includes the following embodiments and various modifications and improvements based on the knowledge of those skilled in the art. Can be carried out at. Further, the non-aqueous electrolyte secondary battery according to the present embodiment is not particularly limited in its use.

(Positive electrode)
The positive electrode mixture forming the positive electrode and each material constituting the positive electrode mixture will be described. The powdered positive electrode active material of the present invention is mixed with a conductive material and a binder, and if necessary, activated carbon, a solvent for viscosity adjustment, etc. is added, and the mixture is kneaded to form a positive electrode mixture paste ( A paste-like composition) is prepared. The mixing ratio of each in the positive electrode mixture is also an important factor in determining the performance of the lithium secondary battery.

When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the content of the positive electrode active material is 60 to 95% by mass and that of the conductive material, as in the case of the positive electrode of a general lithium secondary battery. It is desirable that the content is 1 to 20% by mass and the content of the binder is 1 to 20% by mass.

The obtained positive electrode mixture paste (paste-like composition) is applied to the surface of a current collector made of aluminum foil, for example, and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-shaped positive electrode can be produced. The sheet-shaped positive electrode can be cut into an appropriate size according to the target battery and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the above-exemplified one, and other methods may be used.

In producing the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, and Ketjen black can be used as the conductive agent. Examples of the binder (binding agent) include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as ethylene propylene diene rubber, polypropylene, and polyethylene, styrene butadiene, and cellulose-based resins. , Polyacrylic acid and the like can be used.

If necessary, the positive electrode active material, the conductive material, and the activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone, dimethylformamide, N, N-dimethylacetamide, N, N-dimethylsulfoxide, hexamethylphosphoamide and the like can be used. .. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(Negative electrode)
For the negative electrode, metallic lithium, lithium alloy, etc., or a negative electrode mixture that is made into a paste by mixing a binder with a negative electrode active material that can occlude and desorb lithium ions and adding an appropriate solvent, is made of copper, etc. A metal foil collector is coated on the surface, dried, and compressed to increase the electrode density as needed.
Examples of the negative electrode active material include calcined organic compounds such as natural graphite, artificial graphite, and phenolic resin, powdered carbon substances such as coke, and oxides such as lithium-titanium oxide (Li ₄ Ti ₅ O ₁₂ ). Materials can be used. In this case, as the negative electrode binder, a fluororesin such as polyvinylidene fluoride can be used as in the positive electrode, and as a solvent for dispersing these active substances and the binder, N-methyl-2-pyrrolidone or the like can be used. An organic solvent can be used.

(Separator)
A separator is sandwiched between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode to retain the electrolyte, and a thin film such as polyethylene or polypropylene, which has a large number of minute holes, can be used.

(Non-aqueous electrolyte)
The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran and 2-. One selected from ether compounds such as methyl tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in combination of two or more. be able to.
As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _2, etc., and a composite salt thereof can be used.
Further, the non-aqueous electrolyte solution may contain a radical catching agent, a surfactant, a flame retardant and the like.

(Battery shape and configuration)
The shape of the lithium secondary battery according to the present invention, which is composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte solution described above, can be various, such as a cylindrical type and a laminated type.
Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolytic solution. The positive electrode current collector and the positive electrode terminal that communicates with the outside, and the negative electrode current collector and the negative electrode terminal that communicates with the outside are connected by using a current collector reed or the like. The battery can be completed by sealing the above configuration in a battery case (container).

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. Each evaluation in the examples of the present invention was carried out by the following method.
(Evaluation methods)
1. 1. Physical properties of coating liquid and positive electrode active material (1) Measurement of particle size of precursor fine particles and positive electrode active material in coating liquid (dispersion liquid):
The particle size (D50) of the fine particles was measured using a particle size distribution meter (Nanotrack Wave, manufactured by Nikkiso Co., Ltd.). The particle size (D50) of the lithium nickel composite oxide powder and the positive electrode active substance was measured using a particle size distribution meter (Microtrac MT3300, manufactured by Nikkiso Co., Ltd.).
(2) Measurement of thickness and coating area of coating layer precursor A cross-section of the base material having the coating layer precursor is cross-sectioned with a cross-section polisher (CP) and cross-sectioned with a transmission electron microscope (TEM: HF-2200 manufactured by HITACHI). The coating layer thickness was directly obtained from the image observed from the side. Regarding the covering area, the area was calculated by image processing from the image observed by TEM. The covering area was measured in five visual fields at different observation locations. The morphology of the precursor fine particles in the dispersion liquid and the fine particles in the coating layer was also observed by TEM, and the length / width (aspect ratio) was calculated directly from the image.
(3) Observation of particle surface structure The particle surface surface of the heat-treated positive electrode active material was observed from the particle surface side with a scanning electron microscope (SEM: JSM-7001F manufactured by JEOL Ltd.). The particle size in the microstructure was directly determined from the cross-sectional side by TEM or Cs-TEM.
(4) Reaction of coating layer and measurement of diffusion state of constituent elements Using a sample whose cross section has been processed, surface or point analysis is performed from the cross section side by TEM-EDS (VANTAGE manufactured by NORAN) to confirm the coating layer and to confirm the composite oxide. The state of diffusion inside the particles was investigated.
Further, a simple identification of wide area measurement was performed by an X-ray diffractometer (XRD: X'PertPRO manufactured by PANalytical), and a crystal phase derived from _{LiNi 0.85} Co _0.15 O _{2 phase was obtained.} Furthermore, based on the wide area measurement results, the zero shift value and half-value range parameter obtained when the Si standard sample (NIST640c) measured at the same time was measured under the same conditions and the Crystal analysis was performed are used as an apparatus. Rietvelt analysis of the crystal phase confirmed by simple identification was performed by the method of determining the parameters and refining them.
(5) Composition of positive electrode active material The composition was determined by ICP analysis.
(6) Water resistance evaluation of the positive electrode active material The water resistance was evaluated by adding 1 g of the positive electrode active material to 50 ml of pure water at 24 ° C., stirring the mixture, and measuring the pH after 10 minutes.
(7) Evaluation of gelation In the evaluation of gelation, 9.5 g of the active material to be positive, 0.5 g of vinylidene fluoride (PVDF) as a binder, 5.5 g of N-methyl-2-pyrrolidinone (NMP) as a solvent, and water. After 0.2 g was made into a slurry by a self-conversion kneading machine, it was statically stored at 24 ° C. for 3 days, and the gelation state was confirmed by visual observation.

2. Battery manufacturing and evaluation of battery characteristics (battery manufacturing)
A 2032 type coin battery BA (hereinafter referred to as a coin type battery) shown in FIG. 5 was used for the evaluation of the positive electrode active material. As shown in FIG. 5, the coin-type battery BA is composed of a case CA and an electrode EL housed in the case CA. The case CA has a positive electrode can PC that is hollow and has one end opened, and a negative electrode can NC that is arranged in the opening of the positive electrode can PEL. When the negative electrode can NC is arranged in the opening of the positive electrode can PC, , The space for accommodating the electrode EL is formed between the negative electrode can NC and the positive electrode can PC.

The electrode EL is composed of a positive electrode PE, a separator SE, and a negative electrode NE, and is laminated so as to be arranged in this order. The positive electrode PE contacts the inner surface of the positive electrode can PC, and the negative electrode NE contacts the inner surface of the negative electrode can NC. It is housed in the case CA. The case CA is provided with a gasket GA, and the relative movement is fixed by the gasket GA so as to maintain a non-contact state between the positive electrode can PC and the negative electrode can NC. Further, the gasket GA also has a function of sealing the gap between the positive electrode can PC and the negative electrode can NC to airtightly and liquidally shut off the inside and the outside of the case CA.

The coin-type battery 1 was manufactured as follows.
First, 52.5 mg of the positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. , Positive electrode 3a was prepared. The prepared positive electrode 3a was dried in a vacuum dryer at 120 ° C. for 12 hours. Using the positive electrode 3a, the negative electrode 3b, the separator 3c, and the electrolytic solution, the above-mentioned coin-type battery 1 was produced in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C. For the negative electrode 3b, a graphite powder having an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and a negative electrode sheet coated with polyvinylidene fluoride on a copper foil were used. A polyethylene porous membrane having a film thickness of 25 μm was used for the separator 3c. As the electrolytic solution, an equal amount mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) using _{1M LiClO 4 as a supporting electrolyte (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.}

(Evaluation of battery characteristics)
The initial discharge capacity, positive electrode resistance, and cycle characteristics indicating the performance of the manufactured coin-type battery 1 were evaluated as follows.
The initial discharge capacity was as follows: after the coin-type battery 1 was manufactured, it was left for about 24 hours, charged at 0.05 C to a cutoff voltage of 4.3 V, paused for 1 hour, and then discharged to a cutoff voltage of 3.0 V. The capacity at that time was taken as the initial discharge capacity.

The positive electrode resistance (interfacial resistance) was evaluated by the AC impedance method. That is, the coin-type battery 1 was charged with a charging potential of 4.1 V and measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) to obtain a Nyquist plot. Since this Nyquist plot is expressed as the sum of the solution resistance, the negative electrode resistance and its capacitance, and the positive electrode resistance and its capacitance, the fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and the positive electrode resistance is performed. The value (Ω) of was calculated. The calculated resistance value was expressed by the following equation with 1 before coating (uncoated product).
Interface resistance = [Interfacial resistance value of heat-treated product / Interface resistance value of uncoated product]

In the cycle characteristic evaluation, after the coin-type battery 1 is manufactured, it is left for about 24 hours, charged at 0.5 C to a cutoff voltage of 4.3 V, paused for 1 hour, and then discharged to a cutoff voltage of 3.0 V. This was repeated 100 times as one cycle. As an evaluation method at this time, the capacity retention rate is obtained, and it is expressed by the following equation with the discharge capacity obtained in the first cycle as 100%.
Capacity retention rate (%) = [Discharge capacity in 100th cycle / Discharge capacity in 1st cycle] x 100

(Example 1)
(Making the base material)
The following lithium nickel composite oxide powder obtained by a known technique was used as a base material. That is, nickel oxide powder containing Ni as a main component and containing Co and Al and lithium hydroxide are mixed and fired, and lithium represented by _{Li 1.02} Ni _0.82 Co _0.15 Al _0.03 O _2. A nickel composite oxide powder was obtained. The average particle size D50 of this lithium nickel composite oxide powder was 11.3 μm, and the specific surface area was 0.27 m ² / g.

(Preparation of Nb-O coating liquid)
To 20 ml of 2-propanol in advance, 1.59 g of pentaniobium ethoxide (manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred to prepare a solution (A). A solution (B) was prepared by adding 1.00 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) to 5 ml of 2-propanol in a separate container and stirring. The solution (B) was put into the solution (A), and the solution (C) was prepared after stirring and mixing. The solution (C) was placed in a tightly closed container and left at 24 ° C. for 1 hour with stirring to prepare a solution (D).
Further, 100 ml of 2-propanol for dilution was added to the solution (D) to obtain a coating solution containing niobium.
(Formation of coating layer)
^{600 g of the base material was stirred for 30 minutes at an outlet temperature of 30 ° C. and an air volume of 0.3 m 3} / hour using a rolling fluid device (manufactured by Paulek Co., Ltd., MP-01) to measure the total amount of the coating liquid. By spraying, a base material having a coating layer precursor on the surface was obtained. The thickness of the obtained coating layer precursor is shown in Table 1 (heat treatment).
600 g of the mixture is heated to 400 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to have a surface layer and a coating layer. A positive electrode active material was obtained. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Example 2)
(Preparation of Nb-O coating liquid)
A coating liquid (E) containing organic niobium obtained under the same conditions as in Example 1 was obtained.
(Formation of coating layer)
600 g of the base material prepared in Example 1 was separately sprayed under the same conditions as in Example 4 to obtain a coating layer. 600 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hours for positive electrode activity having a surface layer. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Example 3)
(Preparation of Nb-O coating liquid)
To 100 ml of 2-propanol in advance, 7.95 g of pentaniobium ethoxide (manufactured by Wako Pure Chemical Industries, Ltd.) was added and stirred to prepare a solution (A). A solution (B) was prepared by adding 5.00 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) to 30 ml of 2-propanol in a separate container and stirring. The solution (B) was put into the solution (A), and the solution (C) was prepared after stirring and mixing. The solution (C) was placed in a tightly closed container and left at 24 ° C. for 1 hour with stirring to prepare a solution (D). Further, 500 ml of 2-propanol for dilution was added to the solution (D) to obtain a coating liquid (E) containing organic niobium.
(Formation of coating layer precursor)
Separate 600 g of the base metal prepared in Example 1 and use a rolling fluid device (manufactured by Paulek Co., Ltd., MP-01) at an outlet temperature of 30 ° C. and an air flow rate of 0.3 m ³ / hour while stirring 2.5. The entire amount of the coating liquid (E) was sprayed over an hour to obtain a coating layer precursor. 600 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hours for positive electrode activity having a surface layer. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2. Further, FIG. 6A shows the surface structure obtained by SEM observation from the particle surface side of the positive electrode active material. FIG. 6B shows the grain shape of the fine particles observed in the microstructure by TEM observation from the particle cross-sectional side of the positive electrode active material. From TEM observation, fine particles having an average particle size of 10 nm or more and 20 nm were observed in the coating layer.

(Example 4)
(Preparation of Al—O dispersion)
1.20 g of trialuminum isopropoxide (manufactured by Wako Pure Chemical Industries, Ltd.) was added to 20 ml of 2-propanol in advance and stirred to prepare a solution (A). 0.50 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) was added to 5 ml of 2-propanol in a separate container and stirred to prepare a solution (B). The solution (B) was put into the solution (A), and the solution (C) was prepared after stirring and mixing. The solution (C) was placed in a tightly closed container, heated at 50 ° C. for 0.5 hours with stirring, cooled and returned to room temperature to prepare a solution (D). A mixed solution of 5 ml of 2-propanol and 0.40 g of pure water was added to the solution (D), kept at 24 ° C. for 3 hours with stirring, and then returned to room temperature to prepare a transparent yellow dispersion (F). Further, 100 ml of 2-propanol for dilution was added to the solution (F) to obtain a coating liquid (E) containing hydrolyzed organoaluminum. The particle size of the coating liquid (E) was measured and found to be D50 = 11 nm.
(Formation of coating layer)
Separate 600 g of the base material prepared in Example 1 and apply it for 30 minutes while stirring at an outlet temperature of 30 ° C. and an air flow rate of 0.3 m3 / hour using a rolling fluid device (manufactured by Paulek Co., Ltd., MP-01). The entire amount of the coating liquid (E) was sprayed to obtain a coating layer. 600 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hours for positive electrode activity having a surface layer. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Example 5)
(Preparation of Al—O coating liquid)
1.20 g of trialuminum isopropoxide (manufactured by High Purity Chemicals) was added to 20 ml of 2-propanol in advance, dissolved and stirred to prepare a solution (A). 0.50 g of acetylacetone (manufactured by Kanto Chemical Co., Ltd.) was added to 5 ml of 2-propanol in a separate container and stirred to prepare a solution (B). The solution (B) was put into the solution (A), and the solution (C) was prepared after stirring and mixing. The solution (C) was placed in a tightly closed container and left at 24 ° C. for 1 hour with stirring to prepare a solution (D). Further, 100 ml of 2-propanol for dilution was added to the solution (F) to obtain a coating liquid (E) containing organoaluminum.
(Formation of coating layer)
Separate 600 g of the base metal prepared in Example 1 and use a rolling fluid device (manufactured by Paulek Co., Ltd., MP-01) at an outlet temperature of 30 ° C. and an air flow rate of 0.3 m3 / hour for 0.5 hours while stirring. A coating layer was obtained by spraying the entire amount of the coating liquid (E).
600 g of this mixture was heated to 400 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hours for positive electrode activity having a surface layer. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.
(Example 6)
(Preparation of Al—O coating liquid)
A coating liquid (E) containing organoaluminum obtained under the same conditions as in Example 5 was obtained.
(Formation of coating layer)
600 g of the base material prepared in Example 1 was separately sprayed under the same conditions as in Example 6 to obtain a coating layer. 600 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hours for positive electrode activity having a surface layer. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Example 7)
(Preparation of Al—O coating liquid)
To 100 ml of 2-propanol in advance, 6.00 g of trialuminum isopropoxide (manufactured by High Purity Chemicals) was added and dissolved and stirred to prepare a solution (A). 2.50 g of acetylacetone (manufactured by Kanto Chemical Co., Inc.) was added to 30 ml of 2-propanol in a separate container and stirred to prepare a solution (B). The solution (B) was put into the solution (A), and the solution (C) was prepared after stirring and mixing. The solution (C) was placed in a tightly closed container and left at 24 ° C. for 1 hour with stirring to prepare a solution (D). Further, 500 ml of 2-propanol for dilution was added to the solution (F) to obtain a coating liquid (E) containing organoaluminum.
(Formation of coating layer)
Separate 600 g of the base metal prepared in Example 1 and use a rolling fluid device (manufactured by Paulek Co., Ltd., MP-01) to take 6 hours while stirring at ^{an outlet temperature of 30 ° C. and an air volume of 0.3 m 3 / hour.} The entire amount of the coating liquid (E) was sprayed to obtain a coating layer. 600 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hours for positive electrode activity having a surface layer. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2. Further, FIG. 7A shows the surface structure obtained by SEM observation from the particle surface side of the positive electrode active material. FIG. 7B shows the grain shape of the fine particles observed in the microstructure by TEM observation from the particle cross-sectional side of the positive electrode active material. By TEM observation, fine particles having an average particle size of 1 nm or more and 2 nm or less were observed in the coating layer.

(Example 8)
(Preparation of Al—O coating liquid)
A coating liquid (E) containing organoaluminum obtained under the same conditions as in Example 7 was obtained.
(Formation of coating layer)
600 g of the base material prepared in Example 1 was separately sprayed under the same conditions as in Example 7 to obtain a coating layer. 600 g of this mixture was heated to 700 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hours for positive electrode activity having a surface layer. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 1)
The positive electrode active material was evaluated without coating 600 g of the base material produced in Example 1. The results are summarized in Tables 1 and 2. Further, FIG. 8A shows the surface structure obtained by SEM observation from the particle surface side of the positive electrode active material. FIG. 8B shows the grain shape of the fine particles observed in the microstructure by TEM observation from the particle cross-sectional side of the positive electrode active material. No coating layer was observed by TEM observation.

(Comparative Example 2)
Without coating 600 g of the base metal prepared in Example 1, a muffle furnace having a volume of 30 L was used, and the temperature was raised to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min to activate the positive electrode. Obtained the substance. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 3)
(Preparation of Ti-O coating liquid)
1.66 g of titanium butoxide (manufactured by Kanto Chemical Co., Inc.) was added to 50 ml of 2-propanol in advance and stirred in a tightly closed container to prepare a coating liquid (A).
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture was heated to 300 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 4)
(Preparation of Ti-O coating liquid)
A coating liquid (A) containing organic titanium obtained under the same conditions as in Comparative Example 3 was obtained.
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture is heated to 400 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace with a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 5)
(Preparation of Ti-O coating liquid)
A coating liquid (A) containing organic titanium obtained under the same conditions as in Comparative Example 3 was obtained.
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 6)
(Preparation of Nb-O coating liquid)
1.59 g of pentaniobium ethoxide (manufactured by Kanto Chemical Co., Inc.) was added to 50 ml of 2-propanol in advance and stirred in a tightly closed container to prepare a coating liquid (A).
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture was heated to 300 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 7)
(Preparation of Nb-O coating liquid)
A coating liquid (A) containing organic niobium obtained under the same conditions as in Comparative Example 5 was obtained.
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 8)
(Preparation of Al—O coating liquid)
1.20 g of trialuminum isopropoxide (manufactured by Kanto Chemical Co., Inc.) was added to 50 ml of 2-propanol in advance and stirred in a tightly closed container to prepare a coating liquid (A).
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture was heated to 300 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 9)
(Preparation of Al—O coating liquid)
A coating liquid (A) containing organoaluminum obtained under the same conditions as in Comparative Example 7 was obtained.
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture was heated to 600 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

(Comparative Example 10)
(Preparation of Al—O coating liquid)
A coating liquid (A) containing organoaluminum obtained under the same conditions as in Comparative Example 7 was obtained.
(Formation of coating layer)
20 g of the base material prepared in Example 1 was separately added to the coating liquid (A) and stirred for 6 hours to obtain a coating layer. 20 g of this mixture was heated to 800 ° C. at 3 ° C./min while introducing pure oxygen gas at 10 L / min using a muffle furnace having a volume of 30 L, and then held for 0.5 hour to obtain a positive electrode active material. It was. The evaluation results of the positive electrode active material are summarized in Tables 1 and 2.

1 ... Positive electrode active material 2 ... Lithium-nickel composite oxide particles 3 ... Surface layer 4 ... Central 5 ... Coating layer 6 ... Base material 7 ... Coating layer precursor CBA ... Coin-type battery CA ... ... Case PC ... Positive electrode NC ... Negative electrode GA ... Gasket PE ... Positive electrode NE ... Negative electrode SE ... Separator

Claims (22)

And a surface layer portion and the other central portion disposed on the surface, in the composition is ^{_{Li t Ni 1-x-y}} Co x M 1 y M 2 z O 2 + α ( wherein, ^{M 1} is, Mg, Al, At least one element selected from the group consisting of Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, M ² is Nb, 1.01 ≦ t ≦ 1.20, It is composed of lithium nickel composite oxide particles represented by 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0.03, 0 ≦ α ≦ 0.1). ² is contained in the surface layer portion,
It further has a coating layer that covers at least a part of the surface of the lithium nickel composite oxide particles, and the coating layer contains the M ² at a higher concentration than the surface layer portion.
A positive electrode active material for a non-aqueous electrolyte secondary battery. The M ² The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the particle has a concentration gradient such that the concentration thereof decreases in the direction from the surface of the particles toward the center. The M ² The non-aqueous electrolyte secondary battery according to claim 1, wherein at least a part of the above reacts with at least a part of Ni and Co in the lithium nickel composite oxide particles to form a product. For positive electrode active material. At least a part of the product is composed of composition formula AB. ₂ O ₄ (A is at least one metal element of Ni and Co, and B is M. ² Is. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, which comprises a spinel-type crystal phase represented by). The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the thickness of the surface layer portion is 10 nm or more and 100 nm or less. And a surface layer portion and the other central portion disposed on the surface, in the composition is ^{_{Li t Ni 1-x-y}} Co x M 1 y M 2 z O 2 + α ( wherein, ^{M 1} is, Mg, Al, 1. At least one element selected from the group consisting of Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, and M ² is at least one element among Al and Nb. 01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0.03, 0 ≦ α ≦ 0.1) It is composed of oxide particles, and the M ² is contained in the surface layer portion.
At ^{least a part of the M 2} reacts with at least a part of Ni and Co in the composite oxide particles to form a product.
At least a part of the product is a spinel-type crystal phase represented by _{the composition formula AB 2} O ₄ (A is at least one metal element of Ni and Co, and B is M ^2). Consists of
A positive electrode active material for a non-aqueous electrolyte secondary battery. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6 , wherein the M ² has a concentration gradient such that the concentration thereof decreases in the direction from the particle surface toward the center. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 6 or 7 , wherein the thickness of the surface layer portion is 10 nm or more and 100 nm or less. The positive electrode active material further has a coating layer covering at least a part of the surface of the lithium nickel composite oxide particles, and the coating layer contains the M ² at a higher concentration than the surface layer portion. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of 6 to 8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5 and 9, wherein the coating layer contains fine particles having an average particle diameter of 1 nm or more and 20 nm or less. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, 9 and 10, wherein the thickness of the coating layer is 0.1 nm or more and 20 nm or less. The item according to any one of claims 1 to 11 , wherein the content of Al or Nb is in the range of 0.02% by mass or more and 3.0% by mass or less with respect to the entire positive electrode active material. The above-mentioned positive electrode active material for a non-aqueous electrolyte secondary battery. The positive active material is characterized in that a shaft length which is determined by Rietveld analysis of X-ray diffraction is less 2.8655Å more 2.8647Å, c-axis length is less than 14.890Å more 14.1801Å The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 12. After adding 0.1 g of the positive electrode active material to 50 ml of pure water at 24 ° C., the pH of the slurry stirred for 10 minutes was 11.2 or less, and 9.5 g of the positive electrode active material and vinylidene fluoride (PVDF) as a binder were used. ) 0.5 g, 5.5 g of N-methyl-2-pyrrolidinone (NMP) as a solvent, and 0.2 g of water were added to make a slurry by a self-revolving kneading machine, and then the mixture was stored statically at 24 ° C. for 3 days. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 13, wherein the electrode does not gel. And a surface layer portion and the other central portion disposed on the surface, in the composition is ^{_{Li t Ni 1-x-y}} Co x M 1 y M 2 z O 2 + α ( wherein, ^{M 1} is, Mg, Al, At least one element selected from the group consisting of Ca, Ti, V, Cr, Mn, Zr, Nb, Mo and W, M ² is at least one element of Al and Nb, and 1 Lithium nickel represented by 0.01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15, 0 <z ≦ 0.03, 0 ≦ α ≦ 0.1) ^{The M 2} is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which is composed of composite oxide particles and is contained in the surface layer portion.
A metal alkoxide monomer or oligomer containing at least one of Al and Nb is mixed with an organic solvent to obtain a mixed solution, and then a chelating agent is added to the mixed solution to obtain a coating solution.
The coating liquid is mixed or sprayed with the lithium nickel composite oxide particles to form a coating layer precursor having a film thickness of 3 nm or more and 100 nm or less on the surface of the lithium nickel composite oxide particles.
The composite oxide particles forming the coating layer precursor are heat-treated in an oxygen atmosphere of 350 ° C. or higher and 700 ° C. or lower.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises. The coating liquid is obtained by mixing a metal alkoxide monomer or an oligomer thereof containing at least one of Al and Nb with an organic solvent to obtain a mixed liquid, and then adding a chelating agent to the mixed liquid. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 15 , wherein the coating liquid is obtained by adding water and is formed by dispersing fine particles having an average particle size D50 of 1 nm or more and 20 nm or less. Method of manufacturing active material. The coating layer precursor is discontinuously formed in a porous and island shape on the surface of the base material, and the coating area measured by cross-sectional observation of a transmission electron microscope is 80% or more of the surface area of the base material 95. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 15 or 16 , wherein the content is 0% or less. In the heat treatment, the value obtained by [mixture amount (g) / furnace volume (L)] × oxygen gas introduction amount (L / min) of the composite oxide particles forming the coating layer precursor is 33 g / min or more. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 15 to 17 , wherein the operation is carried out in a controlled atmosphere within a range of 1333 g / min or less. The surface layer portion, composition _{Li t Ni 1-x-y} Co x M y O 2 ( where, M is, Mg, Al, Ca, Ti , V, Cr, Mn, Zr, Nb, from Mo and W Lithium-nickel composite oxide particles which are at least one element selected from the above group and are represented by 1.01 ≦ t ≦ 1.20, 0 ≦ x ≦ 0.22, 0 ≦ y ≦ 0.15). on the surface of the base material made of, after forming the coating layer precursor claim 15, characterized in that it is formed by reacting a particle interface of the base material and the coating layer precursor by heat treatment The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of 18. The positive electrode active material is characterized in that the discharge capacity at a voltage range of 3.0V-4.3V and a rate of 0.5C is within ± 3% of the initial discharge capacity of the base material. Item 19. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to Item 19. The positive electrode active material is charged at a charging potential of 4.1 V, measured by the AC impedance method, and the interfacial resistance value (Ω) calculated from the obtained Nyquist plot is 2 with respect to the interfacial resistance value of the base material. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 19 or 20 , wherein the range is not more than double. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 14.

Images