JP6466145B2 - Positive electrode material for non-aqueous secondary battery, method for producing the same, positive electrode for non-aqueous secondary battery using the positive electrode material for non-aqueous secondary battery, and non-aqueous secondary battery using the same - Google Patents

Description

  The present invention relates to a positive electrode material for a non-aqueous secondary battery excellent in high-voltage charging characteristics, a method for producing the same, a positive electrode for a non-aqueous secondary battery using the positive electrode material for a non-aqueous secondary battery, and a non-use using the same. The present invention relates to a water secondary battery.

  In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, secondary batteries with small size, light weight, high capacity and high energy density have been required. It is coming.

Currently, in non-aqueous secondary batteries that can meet this requirement, particularly lithium ion secondary batteries, lithium-containing composite oxides such as lithium cobaltate (LiCoO ₂ ) and lithium nickelate (LiNiO ₂ ) are used as the positive electrode active material, Graphite or the like is used for the negative electrode active material. And with the further development of the application equipment of a non-aqueous secondary battery, further higher capacity and higher energy density of the non-aqueous secondary battery are required.

One technique for increasing the capacity and energy density of a non-aqueous secondary battery is to charge and use a positive electrode active material at a high voltage. In a battery using a positive electrode active material having a composition represented by LiMO ₂ (M represents a transition metal such as Co, Ni, Mn, etc.) called a layered rock salt structure, such as LiCoO ₂ and LiNiO ₂ , a positive electrode is usually used. Since Li is desorbed and inserted only up to about 50 to 60% of the theoretical capacity of the active material, efficient charge / discharge is not performed. Therefore, the discharge capacity and the average discharge voltage can be increased and the energy density can be improved by increasing the charge voltage from the conventional voltage and removing and inserting more lithium. For example, in the case of LiCoO ₂ , a value close to 200 mAh / g can be obtained as the initial discharge capacity by increasing the charging voltage to 4.5 V with respect to lithium.

However, when a LiMO ₂ type positive electrode active material is used at a high voltage of 4.5 V or more, more Li is desorbed, and the sites from which Li is desorbed become atomic vacancy points. Since the pores increase and the lattice strain increases, the crystal structure becomes unstable, causing irreversible structural changes, and the bulk of the positive electrode active material is deteriorated. In addition, when the voltage is 4.5 V or higher, oxidative decomposition of the electrolytic solution is likely to occur. Since this oxidative decomposition reaction is a side reaction and not a Li elimination reaction (charging reaction), it leads to a decrease in effective charging capacity. Furthermore, in recent years, in addition to bulk deterioration of the positive electrode active material and oxidative decomposition of the electrolytic solution, deterioration at the contact surface between the positive electrode active material surface and the electrolytic solution has been pointed out. That is, on the surface of the positive electrode active material charged at a high voltage, MO ₂ from which Li is desorbed from LiMO ₂ releases oxygen and is reduced to MO. At the same time, the electrolyte in contact with the positive electrode active material surface receives oxygen and oxidizes. To do. MO has a crystal structure called a rock salt structure (NaCl type), and since there is no site in which Li can diffuse in this structure, if a MO domain is formed on the surface of the positive electrode active material, resistance that prevents Li desorption Significantly increases and the charge / discharge cycle characteristics deteriorate.

To address the above problem, conventionally, the surface of the ZrO _2, Al ₂ O _3, MgO of the positive electrode active material, and it is the practice to coat a metal oxide such as TiO _2, ZnO, especially ZrO ₂ It is known as a coating material having a high effect of suppressing deterioration of the positive electrode active material (see, for example, Patent Documents 1 and 2).

JP 2003-221234 A JP 2008-311132 A

In general, Zr oxide is poor in solid solubility with a LiMO ₂ type positive electrode active material called a layered rock salt structure. Therefore, when the positive electrode active material is coated with Zr oxide, the surface of the positive electrode active material is mainly composed of Zr and oxygen. It is deposited and deposited as a granular Zr oxide phase. Since this Zr oxide has low Li ion permeability, an excessive amount of Zr oxide increases the resistance of Li desorption / insertion on the surface of the positive electrode active material. In particular, at a charging voltage of 4.5 V or more, most of the Li in the positive electrode active material is desorbed, so that charging is performed in a region where the charge transfer resistance (R _ct ) between the positive electrode and the electrolyte increases. .

That is, the charge transfer resistance is R _ct , the exchange current is i ₀ , the Faraday constant is F, the reaction rate constant is k, the Li activity in the positive electrode active material is a _sol , and the Li activity in the electrolyte is a _liq When the symmetry factor is α, the concentration of Li in the positive electrode active material is x, and the concentration of Li in the electrolyte is C _Li , the following formulas (1) to (4) are established.

Here, in the charging voltage region of 4.5 V or more, most of Li in the positive electrode active material is desorbed, so that the Li activity a _sol in the positive electrode active material represented by the above formula (2) is small. As a result, the charge transfer resistance represented by the above formula (1) increases.

  When an increase in resistance due to the coating of the Zr oxide is added thereto, a voltage drop (= product of current and resistance) due to IR drop increases, and the effective charging voltage decreases. As a result, the charge capacity is reduced and the discharge capacity is also reduced. For this reason, it is desirable that the coating amount of the positive electrode active material with the Zr oxide be as small as possible. However, on the other hand, if the coating amount of the positive electrode active material with the Zr oxide is reduced, it becomes difficult to uniformly coat the entire surface of the positive electrode active material, the effect of suppressing the deterioration of the positive electrode active material is reduced, and charging / discharging of the battery There arises a problem that the cycle characteristics deteriorate. Therefore, in order to effectively draw out the charge / discharge capacity of the battery by high voltage charging and to fully exert the effect of suppressing the deterioration of the positive electrode active material, the surface of the positive electrode active material is made very thin and uniform with the Zr oxide. Although it is necessary to coat, a coated positive electrode material satisfying such requirements has not yet been obtained.

  The present invention has been made in view of such circumstances, and in order to obtain a high capacity and a high energy density, even when used at a high charging voltage of 4.6 V or more, the resistance increase during charging is increased. The present invention provides a non-aqueous secondary battery that has a large effective charge / discharge capacity and excellent charge / discharge cycle characteristics.

The positive electrode material for a non-aqueous secondary battery of the present invention is a positive electrode material for a non-aqueous secondary battery comprising lithium-containing composite oxide particles, and the lithium-containing composite oxide particles are formed from an outermost surface and the outermost surface. Including a surface layer portion in a depth range of at least 2 nm, and a bulk portion inside from the surface layer portion, wherein the bulk portion is represented by the following general composition formula (1),
LiMO ₂ (1)
In the general composition formula (1), M represents one element selected from Co, Ni and Mn , or a plurality of element groups including at least one selected from Co, Ni and Mn, and the element group The total number of elements of Co, Ni, and Mn contained in is 50 mol% or more, a granular Zr oxide is disposed on the outermost surface, and the average particle size of the Zr oxide is 30 nm or less, When the outermost surface region where the Zr oxide is disposed is defined as a deposited portion, and the outermost surface region where the Zr oxide is not disposed is defined as a non-deposited portion, the area of the non-deposited portion is equal to that of the outermost surface. 50% or more and 97% or less with respect to the total area, the surface layer portion of the non-deposited portion includes M and Zr, and with respect to the total number of atoms of M included in the surface layer portion in the non-deposited portion , Z contained in the surface layer portion of the non-deposited portion Ratio of the total number of atoms, characterized in that it is 3 atomic% or more and 40 or less atomic%.

The method for producing a positive electrode material for a non-aqueous secondary battery according to the present invention is a first method in which a lithium-containing composite oxide particle, zirconium alkoxide, and dipropylene glycol are dispersed in an organic solvent to prepare a dispersion. A step of adding a base and water to the dispersion to form a gel film on the surface of the lithium-containing composite oxide particles; and the lithium-containing composite oxide particles having the gel film formed thereon. A solid content obtained by filtering the dispersion, and a third step of firing the solid, and the dipropylene glycol contained in the dispersion prepared in the first step When the number of moles is A and the number of moles of the zirconium alkoxide contained in the dispersion is B, the molar ratio A / B is 0.3 or more and 1.0 or less,
The lithium-containing composite oxide particles are represented by the following general composition formula (1):
LiMO ₂ (1)
In the general composition formula (1), M, Co, one element selected from Ni and Mn, or, Co, a plurality of element group including at least one selected from Ni and Mn was table, the element The total number of elements of Co, Ni and Mn contained in the group is 50 mol% or more .

  Moreover, the positive electrode for nonaqueous secondary batteries of this invention is characterized by including the said positive electrode material for nonaqueous secondary batteries of this invention as a positive electrode active material.

  The nonaqueous secondary battery of the present invention is a nonaqueous secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the positive electrode is the positive electrode for a nonaqueous secondary battery of the present invention. It is characterized by that.

  According to the present invention, it is possible to provide a non-aqueous secondary battery having a high capacity and excellent charge / discharge cycle characteristics even under a high voltage.

FIG. 1 is a schematic cross-sectional view showing an example of a surface portion of lithium-containing composite oxide particles constituting the positive electrode material for a non-aqueous secondary battery of the present invention. FIG. 2 is a view showing an SEM image of the positive electrode active material of Example 1 at a magnification of 100 k. FIG. 3 is a view showing an SEM image of the positive electrode active material of Example 1 at a magnification of 300 k. 4 is a diagram showing a cross-sectional STEM image of the positive electrode active material of Example 1. FIG.

(Positive electrode material for non-aqueous secondary battery of the present invention)
The positive electrode material for a non-aqueous secondary battery of the present invention comprises lithium-containing composite oxide particles, and the lithium-containing composite oxide particles have an outermost surface and a surface layer portion in a range of a depth of at least 2 nm from the outermost surface. And a bulk portion located inside from the surface layer portion.

The bulk part is represented by the following general composition formula (1), and in the following general composition formula (1), M is a single transition metal element or transition metal element containing at least one selected from Co, Ni, and Mn. Represents a group.
LiMO ₂ (1)

  Further, granular Zr oxide is disposed on the outermost surface, the average particle diameter of the Zr oxide is 30 nm or less, and the region of the outermost surface on which the Zr oxide is disposed is a deposition part. If the region of the outermost surface where the Zr oxide is not disposed is defined as a non-deposited portion, the area of the non-deposited portion is 50% or more and 97% or less with respect to the total area of the outermost surface.

  Further, the surface layer portion of the non-deposited portion includes M and Zr, and is included in the surface layer portion of the non-deposited portion with respect to the total number of M atoms included in the surface layer portion in the non-deposited portion. The ratio of the total number of atoms of Zr is 3 atom% or more and 40 atom% or less.

  The positive electrode material for a non-aqueous secondary battery according to the present invention suppresses an increase in resistance during charging and obtains a large effective charge / discharge capacity even when used at a high charging voltage of 4.6 V or more based on lithium. And has a stable crystal structure and excellent charge / discharge cycle characteristics under high voltage.

<Bulk part of lithium-containing composite oxide particles>
The bulk part of the lithium-containing composite oxide particles constituting the positive electrode material for a non-aqueous secondary battery of the present invention usually has a layered rock salt structure. As the lithium-containing composite oxide, for example, it can be used _{LiCoO 2, LiNiO 2, LiNi 0.33} Co 0.33 Mn 0.33 O 2 , etc. suitably.

  In the general composition formula (1), when M contains Co, the capacity of the positive electrode material for a non-aqueous secondary battery of the present invention is improved, and also when M contains Ni, the positive electrode for a non-aqueous secondary battery of the present invention When the capacity of the material is improved and M contains Mn, the thermal stability of the positive electrode material for a non-aqueous secondary battery of the present invention is improved. Further, when M contains a small amount of at least one element such as Mg, Zn, Cu, Cr, Fe, Ni, Ti, Mo, V, Al, B, Ge, Nb, and W, the above lithium-containing composite oxidation The crystal structure of the bulk part of the product particles can be further stabilized.

  When the total number of elements of M is 100 mol%, the total number of elements of Co, Ni and Mn contained in M is preferably 50 mol% or more, more preferably 70 mol or more, still more preferably 90% or more, and M is Co, Ni. And it may be a case containing only Mn.

  From the viewpoint of increasing the density of the positive electrode mixture layer in order to increase the capacity of the positive electrode, the average particle size of the lithium-containing composite oxide particles including the bulk part is preferably 0.05 to 30 μm, and preferably 0.1 to 15 μm. More preferred. The average particle diameter means D50 which is the value of the particle diameter at a volume-based integrated fraction of 50%. As a method for measuring the particle diameter, for example, a laser diffraction / scattering method or the like can be used.

<Outermost surface of lithium-containing composite oxide particles>
A granular Zr oxide is arranged on the outermost surface of the lithium-containing composite oxide particles constituting the positive electrode material for a non-aqueous secondary battery of the present invention. It is considered that the decomposition reaction of the electrolytic solution under a high voltage occurs based on reaction active points such as lattice defects existing on the surface of the positive electrode active material. Since this defect portion is in a state of being large in energy, when the Zr oxide is deposited on the surface of the positive electrode active material, it is preferentially deposited on the active point. Since this active site is covered with an inactive Zr oxide, the reaction activity is lowered, and the decomposition of the electrolytic solution under a high voltage can be suppressed.

  Here, when the region of the outermost surface where the Zr oxide is arranged is a deposition part, and the region of the outermost surface where the Zr oxide is not arranged is a non-deposition part, the non-deposition part becomes small, Since the deposited portion where the Zr oxide having low Li ion permeability is arranged increases and the resistance during charging and discharging increases, the area of the non-deposited portion is 50% of the total area of the outermost surface. The area of the non-deposited portion is 97% or less with respect to the total area of the outermost surface in order to ensure the effect of suppressing the electrolyte decomposition reaction during high voltage charging by the deposited portion. There is a need.

  The ratio of the area of the non-deposited portion to the total area of the outermost surface can be detected by observing the lithium-containing composite oxide particles using, for example, SEM (Scanning Electron Microscope) or TEM (Transmission Electron Microscope).

  The average particle size of the Zr oxide needs to be 30 nm or less. When the average particle diameter of the Zr oxide exceeds 30 nm, when the Zr oxide segregates on the surface of the lithium-containing composite oxide particles, Li is taken away from the bulk part, and Li is contained in the Zr oxide. Since the immobilized and immobilized Li does not participate in charging / discharging, the amount of Li that can be used for charging / discharging decreases and the capacity decreases. The lower limit value of the average particle diameter of the Zr oxide is not particularly limited, but is usually about 5 nm due to the production legal limit.

  The average particle diameter of the Zr oxide is calculated as an arithmetic average value of the major axis diameters of 100 Zr oxide particles observed by SEM or TEM.

As described above, since Li immobilized in the Zr oxide does not participate in charge / discharge, the Zr oxide preferably does not contain Li. The Zr oxide is usually represented by a composition formula of ZrO ₂ .

<Surface layer portion of lithium-containing composite oxide particle>
The surface layer portion of the non-deposited portion of the lithium-containing composite oxide particles constituting the positive electrode material for a non-aqueous secondary battery of the present invention has a depth of at least 2 nm from the outermost surface of the lithium-containing composite oxide particles. It is a part. The surface layer portion of the non-deposited portion includes M and Zr, and the Zr included in the surface layer portion of the non-deposited portion with respect to the total number of M atoms included in the surface layer portion of the non-deposited portion. The ratio of the total number of atoms needs to be 3 atomic% or more and 40 atomic% or less. The surface layer portion of the non-deposited portion is an interdiffusion layer of Zr element and the element of the bulk portion, and this portion becomes a Li ion transmission layer. Moreover, the surface layer portion of the non-deposited portion has an effect of suppressing the formation of the MO domain on the surface of the positive electrode active material during high voltage charging because it contains Zr. During high voltage charging, most of Li is desorbed from LiMO ₂ to become V _L MO ₂ (V _L represents a vacancy of Li), and as shown in the following chemical formula (1), M cation is 4 Oxidized to valence. On the surface of the positive electrode active material in such a state, the M cation easily moves to V _L , and a surface degradation reaction that generates MO occurs. As shown in the following chemical formula (2), the elementary process of this deterioration reaction is the reduction of M cation from tetravalent to divalent and transfer to V _L , release of O ²⁻ anion, and electrolyte molecule (E). It is thought that it consists of oxidation. That, V _L M ⁴⁺ O ^2- ₂ is at the same time becomes M ²⁺ O ^2- to release the O ^2- with receive 2 electrons, becomes E ⁺² and E is releasing 2 electrons O ^2- To form E ²⁺ O ^2- . This reaction occurs because M is a transition metal such as Co, Ni, Mn and the like that can be divalent, and E that emits electrons and receives O ²⁻ is V on the surface of the positive electrode active material. This is because direct contact with the _L MO _2. On the other hand, the Zr cation is stable in tetravalence, hardly changes in valence, and hardly releases O ²⁻ . In general, a metal oxide has a structure in which a plurality of oxygen anions are coordinated to a metal cation (six-coordinate in a layered rock salt structure), so that M and Zr share oxygen in the surface layer portion of the non-deposited portion. it is conceivable that. It is considered that Zr, which hardly changes its valence and hardly releases oxygen, coexists with M in the surface layer portion, so that the elementary process of the deterioration reaction does not easily occur, and as a result, the deterioration reaction as a whole does not easily occur. When the ratio of the total number of Zr atoms contained in the surface layer part of the non-deposited part is less than 3 atomic%, the effect of suppressing the deterioration reaction is lowered, and when the ratio of the total number of Zr atoms exceeds 40 atomic%, Li Ion permeability decreases.

_{^{Charging: Li + M 3+ O 2- 2}} → Li + + e - + V L M 4+ O 2- 2 (1)
^{_{Deterioration: V L M 4+ O 2- 2}} + E → M 2+ O 2+ E 2+ O 2- (2)

  The composition of the surface layer portion of the deposited portion and the non-deposited portion can be, for example, STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Analysis) or AES (Auger electron spectroscopy).

  Next, the surface part of the lithium-containing composite oxide particles constituting the positive electrode material for a non-aqueous secondary battery of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of a surface portion of lithium-containing composite oxide particles constituting the positive electrode material for a non-aqueous secondary battery of the present invention. Although FIG. 1 is a cross-sectional view, the cross-sectional portion is not hatched except for a part for easy understanding of the drawing.

  In FIG. 1, the lithium-containing composite oxide particle is composed of an outermost surface 1, a surface layer portion 2 in a depth range of 2 nm from the outermost surface 1, and a bulk portion 3 inside the surface layer portion 2. Yes. Further, on the outermost surface 1, granular Zr oxide 4 having an average particle diameter of 30 nm or less is disposed. The region of the outermost surface 1 where the Zr oxide 4 is disposed is defined as a deposition portion A, and the Zr oxide 4 is disposed. Assuming that the region of the outermost surface 1 that is not formed is the non-deposited portion B, the area of the non-deposited portion B is set to 50% or more and 97% or less with respect to the total area of the outermost surface 1.

  The surface layer portion 2 includes a surface layer portion 2a corresponding to the deposited portion A and a surface layer portion 2b corresponding to the non-deposited portion B. The surface layer portion 2b includes M and Zr, and is included in the surface layer portion 2b. The ratio of the total number of Zr atoms contained in the surface layer portion 2b to the total number of M atoms is set to 3 atom% or more and 40 atom% or less.

(Method for producing positive electrode material for non-aqueous secondary battery of the present invention)
The method for producing the positive electrode material for a non-aqueous secondary battery of the present invention is not particularly limited as long as the positive electrode material for the non-aqueous secondary battery of the present invention can be produced, and a vapor phase method, a solid phase method, a solution method, etc. are applied. However, a solution method may be applied in order to reliably form a deposited portion in which the Zr oxide is disposed on the surface of the lithium-containing composite oxide particle and a non-deposited portion in which the Zr oxide is not disposed. Among the above-described solution methods, a sol-gel method using a liquid phase synthesis reaction is particularly preferable.

  In the sol-gel method, a metal alkoxide or a metal salt is used as a reaction precursor, a hydrolysis reaction is caused in a solution to change to a sol in which a metal oxide is dispersed, and a polycondensation reaction is further promoted to change to a gel. The method of drying.

  That is, a Zr alkoxide, which is a reaction precursor, and lithium-containing composite oxide particles are previously dispersed in a solution to prepare a dispersion, and an acidic or basic catalyst and water are added to the dispersion to perform hydrolysis reaction and dehydration. When polycondensation is caused, a gel film made of a polymer of Zr oxide is formed on the surface of the lithium-containing composite oxide particles. Thereafter, the solid content obtained by filtering the dispersion is dried and further baked, so that the Zr oxide particles are deposited and deposited on a part of the outermost surface of the lithium-containing composite oxide particles to form a deposited portion. In addition, a surface layer portion having a depth of several nm in which Zr and the constituent element (M) of the lithium-containing composite oxide coexist is formed in the vicinity of the outermost surface of the lithium-containing composite oxide particles on which no Zr oxide particles are deposited. Is done. Zr can hardly be dissolved in the bulk portion of the lithium-containing composite oxide, but can be dissolved at a certain concentration in the vicinity of the outermost surface of the lithium-containing composite oxide particles.

  At this time, the gel film before firing needs to be as thin and uniform as possible. When the gel film is thick, many Zr oxides are deposited on the surface of the lithium-containing composite oxide particles, and the permeation resistance of Li ions increases. In addition, when the gel film is unevenly formed and there are a part where a lot of gel film is formed and a part where a gel film is little formed, the Zr oxide deposited in the part where the gel film is much formed Lithium-containing composite oxide at the time of high-voltage charging is reduced in the amount of Zr in the surface layer portion of the lithium-containing composite oxide particles in the portion where the particles are increased, the lithium ion permeation resistance is increased, and the gel film is less formed The effect of suppressing the structural change at the active material / electrolyte interface of the particles is reduced.

As a result of thorough examination of the above situation, it has been found that the following production method is preferable as the production method of the positive electrode material for a non-aqueous secondary battery of the present invention. That is, the method for producing a positive electrode material for a non-aqueous secondary battery according to the present invention is obtained by dispersing lithium-containing composite oxide particles, zirconium alkoxide (Zr alkoxide), and dipropylene glycol (DPG) in an organic solvent. A first step of preparing a liquid; a second step of adding a base and water to the dispersion to form a gel film on the surface of the lithium-containing composite oxide particles; and the above-described step of forming the gel film. And a third step of drying the solid content obtained by filtering the dispersion containing the lithium-containing composite oxide particles and firing the solid content. Further, assuming that the number of moles of the DPG contained in the dispersion prepared in the first step is A and the number of moles of the Zr alkoxide contained in the dispersion is B, the mole ratio A / B is 0.00. 3 or more and 1.0 or less. Furthermore, the lithium-containing composite oxide particles are represented by the following general composition formula (1), and in the following general composition formula (1), M is a single transition containing at least one selected from Co, Ni and Mn. Represents a metal element or a group of transition metal elements.
LiMO ₂ (1)

  The above DPG is considered to have an action of substituting the alkoxide of the reaction precursor (Zr alkoxide) to slow the hydrolysis reaction and equalize the progress of the reaction. Furthermore, by adjusting the molar ratio A / B (DPG / Zr) to 0.3 or more and 1.0 or less, a very thin gel film having a thickness of several nanometers can be obtained depending on the location of the lithium-containing composite oxide particles. It is thought that it forms uniformly. For this reason, according to the method for producing a positive electrode material for a non-aqueous secondary battery of the present invention, a gel film made of a polymer of Zr oxide can be thinly and uniformly formed on the surface of the lithium-containing composite oxide particles. it can.

  In the above hydrolysis reaction, from the idea that DPG replaces the alkoxide of the reaction precursor (Zr alkoxide), it is usual to use a DPG having the number of moles corresponding to the number of moles of the alkoxide of the reaction precursor (Zr alkoxide). It is. That is, since Zr is tetravalent, the use molar ratio of DPG (DPG / Zr) is usually 4. However, in the production method of the present invention, the molar ratio A / B (DPG / Zr) is set to 0.3 to 1.0, which is smaller than usual, so that the surface of the lithium-containing composite oxide particles has a Zr oxide. It has been found that a gel film made of a polymer can be formed thinly and uniformly. Details of the formation mechanism are unknown, but when the hydrolyzed reaction precursor is in the range of the above molar ratio A / B (DPG / Zr), a stable multimer consisting of several molecules is specifically formed. It is thought that it is. By firing the lithium-containing composite oxide particles on which the gel film is formed, the positive electrode material for a non-aqueous secondary battery of the present invention can be formed.

  Here, when the molar ratio A / B (DPG / Zr) is less than 0.3, the effect of equalizing the progress of the reaction is not sufficient, and the surface of the lithium-containing composite oxide particles has a coarse Zr oxide. When a non-uniform gel film made of a polymer is formed and the molar ratio A / B (DPG / Zr) exceeds 1.0, the reaction proceeds too slowly, leaving an unreacted residue and uniform. A gel film cannot be formed.

  The content of the lithium-containing composite oxide particles contained in the dispersion prepared in the first step is not particularly limited as long as a uniform dispersion is formed, and is usually 10 to 75% by mass. Although it is good, it is determined by the amount of the dispersion and the content of the Zr alkoxide.

  Although it does not restrict | limit especially as said Zr alkoxide, From a viewpoint of forming the gel film which consists of a polymer of Zr oxide on the surface of lithium containing complex oxide particle thinly and uniformly, Zr alkoxide which has a C3 or more alkyl group is mentioned. Is preferred. Examples of the Zr alkoxide having an alkyl group having 3 or more carbon atoms include tetrapropoxyzirconium, tetraethoxyzirconium, tetratertiary butoxyzirconium, tetra-1-butoxyzirconium, and the like. These Zr alkoxides may be used alone or in combination of two or more.

  The content of the Zr alkoxide contained in the dispersion prepared in the first step is such that a gel film made of a polymer of Zr oxide is thinly and uniformly formed on the surface of the lithium-containing composite oxide particles. 0.2-10 mass% is preferable and 1-3 mass% is more preferable.

  The organic solvent is not particularly limited as long as it can disperse the lithium-containing composite oxide particles and the Zr alkoxide, but a hydrophobic organic solvent is preferable in the step of initially dispersing the Zr alkoxide. Specifically, for example, aliphatic hydrocarbons such as pentane, cyclopentane, hexane, cyclohexane, heptane, isoheptane, octane, isooctane, nonane, decane; aromatic hydrocarbons such as benzene, toluene, xylene; dichloromethane, Chlorinated solvents such as chloroform; alcohols such as propanol, butanol and pentanol; ketones having a total carbon number of 6 or more such as methyl isobutyl ketone. These organic solvents may be used individually by 1 type, and may use 2 or more types together.

  The dipropylene glycol (DPG) may be diluted with another solvent before being added to the dispersion prepared in the first step. Specific examples of such a solvent include alcohols having 1 to 3 carbon atoms such as methanol, ethanol and 2-propanol. From the viewpoint of boiling point and compatibility with nonpolar solvents, 2-propanol Is more preferable. These solvents may be used alone or in combination of two or more.

  Although it does not restrict | limit especially as said base, Ammonia, sodium hydroxide, a hydroxylamine, a pyridine etc. are mentioned, Ammonia is preferable from a viewpoint of safety | security or ease of handling. These bases may be used individually by 1 type, and may be used in combination of 2 or more type.

  The amount of the base added is not particularly limited, but in order to make the hydrolysis easier to proceed and to gradually deposit the Zr-containing material to make the coating more uniform, the base is added to 1 mol of the Zr alkoxide. It is preferable to set it as 0.01-1 mol.

  The filtration / drying method is not particularly limited. Specifically, the dispersion obtained in the second step may be filtered by a conventional method to remove the solvent from the dispersion, and then the obtained solid content may be dried.

  The drying conditions are not particularly limited, but may be dried at a pressure of about 1.0 kPa to 0.1 MPa and a pressure of about 10 to 200 ° C., preferably about 30 to 120 ° C., in order to avoid rapid evaporation of the solvent. That's fine.

  The firing atmosphere may be a gas atmosphere containing oxygen such as in the air. The firing temperature is not particularly limited, but may be about 200 to 1000 ° C., preferably about 400 to 600 ° C., at a pressure of about 1.0 kPa to 0.1 MPa. Although the firing time is not limited, it may usually be about 10 minutes to 48 hours.

(Positive electrode for non-aqueous secondary battery of the invention)
Next, the positive electrode for nonaqueous secondary batteries of this invention is demonstrated. The positive electrode for a non-aqueous secondary battery of the present invention is characterized by containing the positive electrode material for a non-aqueous secondary battery of the present invention as a positive electrode active material. The positive electrode for a non-aqueous secondary battery of the present invention includes the positive electrode material for a non-aqueous secondary battery of the present invention as a positive electrode active material, and thus has a high capacity and excellent charge / discharge cycle characteristics even under a high voltage.

  The positive electrode for a non-aqueous secondary battery of the present invention has, for example, a positive electrode mixture layer containing the positive electrode material for a non-aqueous secondary battery of the present invention, a binder, a conductive additive, etc. on one or both sides of a current collector. A structure can be used.

  As a conductive support agent used for the said positive mix layer, what is chemically stable should just be in a battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metal powder such as powder; Carbon dioxide; Zinc oxide; Conductive whisker made of potassium titanate and the like; Conductive metal oxide such as titanium oxide; Organic conductive material such as polyphenylene derivative; One species may be used alone, or two or more species may be used in combination. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable.

  As the binder used for the positive electrode mixture layer, any of a thermoplastic resin and a thermosetting resin can be used as long as it is chemically stable in the battery. For example, polyvinylidene fluoride (PVDF), polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), styrene-butadiene rubber (SBR), tetrafluoroethylene-hexafluoroethylene Copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), and the like can be used.

  As the current collector used for the positive electrode, the same one as used for the positive electrode of a conventionally known non-aqueous secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

  The positive electrode is, for example, a positive electrode mixture in which the positive electrode material for a nonaqueous secondary battery (positive electrode active material), a binder, and a conductive additive of the present invention are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). After preparing the containing paste or slurry, applying this to one or both sides of the current collector and drying it, it can be produced through a process of calendering if necessary. The manufacturing method of a positive electrode is not necessarily restricted to the said method, It can also manufacture with another manufacturing method.

  As the composition of the positive electrode mixture layer, for example, the amount of the positive electrode active material is preferably 65 to 98% by mass, the amount of the binder is preferably 1 to 15% by mass, and the amount of the conductive auxiliary agent is It is preferable that it is 1-20 mass%.

(Nonaqueous secondary battery of the present invention)
Next, the nonaqueous secondary battery of the present invention will be described. The nonaqueous secondary battery of the present invention includes the positive electrode for a nonaqueous secondary battery of the present invention, a negative electrode, a nonaqueous electrolyte, and a separator. Since the nonaqueous secondary battery of the present invention includes the positive electrode for a nonaqueous secondary battery of the present invention, it has a high capacity and excellent charge / discharge cycle characteristics even under a high voltage.

  Hereinafter, components other than the positive electrode of the nonaqueous secondary battery of the present invention will be described.

[Negative electrode]
For the negative electrode, for example, a negative electrode active material, a binder, and a negative electrode mixture layer containing a conductive auxiliary agent as necessary are provided on one or both sides of the current collector, and the negative electrode active material is used alone. Thus, a negative electrode or a negative electrode active material that is laminated as a negative electrode layer on a current collector can be used.

The negative electrode active material is not particularly limited as long as it is a negative electrode active material used in conventionally known non-aqueous secondary batteries, that is, a material capable of occluding and releasing lithium ions. For example, carbon-based materials that can occlude and release lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. One kind or a mixture of two or more kinds is used as the negative electrode active material. In addition, elements such as silicon (Si), tin (Sn), germanium (Ge), bismuth (Bi), antimony (Sb), indium (In) and alloys thereof, lithium such as lithium-containing nitride or lithium-containing oxide A compound that can be charged and discharged at a low voltage close to that of a metal, or a lithium metal or a lithium / aluminum alloy can also be used as the negative electrode active material. Among them, the negative electrode active material is preferably a material represented by SiO _x containing silicon and oxygen as constituent elements, or a composite of SiO _x and a carbon material (SiO _x -C composite). These SiO _x -based materials have a high capacity, and a high-capacity battery can be provided by combining the SiO _x -based material with the same high-capacity positive electrode material for a non-aqueous secondary battery of the present invention. Furthermore, the combined use of the SiO _x -C composite and a graphitic carbon material excellent in load characteristics and charge / discharge cycle characteristics is more preferable.

The SiO _x may contain a microcrystalline or amorphous phase of Si. In this case, the atomic ratio of Si and O is a ratio including Si microcrystalline or amorphous phase Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is only necessary that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5. For example, in the case of a structure in which Si is dispersed in an amorphous SiO ₂ matrix and the molar ratio of SiO ₂ to Si is 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but the presence of fine Si can be confirmed by TEM observation. .

  Examples of the binder used in the negative electrode mixture layer include polysaccharides such as starch, polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, and diacetyl cellulose, and modified products thereof; polyvinyl chloride. , Polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide and other thermoplastic resins and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene -Polymers having rubber-like elasticity such as butadiene rubber (SBR), butadiene rubber, polybutadiene, fluoro rubber, polyethylene oxide, and their modified products; May be used alone or two or more al.

  A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black (trade name), acetylene black, etc. Etc.), carbon fiber, metal powder (powder made of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative and the like can be used alone or in combination. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

  As the current collector used for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used. Usually, a copper foil is used. In the negative electrode current collector, when the thickness of the whole negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit of the thickness is 5 μm in order to ensure mechanical strength. It is desirable to be.

  The negative electrode is, for example, a negative electrode mixture-containing paste in which the above-described negative electrode active material and binder, and further, if necessary, a conductive additive dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water, A slurry is prepared, applied to one or both sides of a current collector, dried, and then subjected to a calendaring process as necessary. The manufacturing method of a negative electrode is not necessarily restricted to the said manufacturing method, It can also manufacture with another manufacturing method.

  In the negative electrode mixture layer, it is preferable that the amount of the negative electrode active material is 80 to 99% by mass and the amount of the binder is 1 to 20% by mass. In addition, when a conductive material is separately used as a conductive auxiliary agent, these conductive materials in the negative electrode mixture layer should be used in such a range that the amount of the negative electrode active material and the amount of the binder satisfy the above preferable values. Is preferred. The thickness of the negative electrode mixture layer can be, for example, 10 to 100 μm.

[Non-aqueous electrolyte]
As the non-aqueous electrolyte, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (SO ₂ F) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is fluoroalkyl Represents a group. And the like can be used.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane, Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Sulfites such as glycol sulfite; and the like. These may be used in combination of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

[Separator]
The separator preferably has a property of blocking its pores (that is, a shutdown function) at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower). A separator used in a normal non-aqueous secondary battery or the like, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be. Furthermore, a separator using a heat-resistant resin such as polyamideimide or polyimide, or a separator provided with heat resistance by forming a porous layer using inorganic particles on the surface of the microporous film may be used.

[Battery form]
Examples of the form of the nonaqueous secondary battery of the present invention include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can, an aluminum can, or the like as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The non-aqueous secondary battery of this invention can be used for the same use as the various uses to which the conventionally known lithium ion secondary battery is applied, for example.

[Battery voltage]
The nonaqueous secondary battery of the present invention can be used with the upper limit of the charging voltage of the positive electrode being 4.6 V or more on the basis of lithium, and the charging voltage of the battery comprising the positive electrode of the present invention and the conventional negative electrode can be increased. Even if the upper limit is set to a high voltage of 4.5 V or more, the charge / discharge cycle characteristics can be maintained satisfactorily.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Covering of positive electrode active material>
A 2-propanol solution in which 1% by mass of dipropylene glycol (DPG) was dissolved in 5.2 g of 1-propanol solution in which 0.65% by mass of tetrapropoxyzirconium (TPZ) as a reaction precursor (Zr alkoxide) was dissolved. 68 g was mixed and stirred, and 10 g of LiNi _0.33 Co _0.33 Mn _0.33 O ₂ powder (hereinafter abbreviated as NCM, average particle size: 10 μm) was added as lithium-containing composite oxide particles, and the dispersion was stirred. Prepared. Here, the molar ratio A / B (DPG / Zr) between the mole number A of DPG contained in the dispersion and the mole number B of TPZ contained in the dispersion was 0.5. The amount of TPZ charged is 0.13 mass in terms of the mass ratio (hereinafter, this is defined as the coating amount) with respect to the total mass of the lithium-containing composite oxide particles when the coating composition to be formed is assumed to be ZrO ₂ . %.

  Next, ammonia water was added as hydrolysis water and base (catalyst) to cause hydrolysis reaction and condensation polymerization reaction to form a gel film on the surface of the lithium-containing composite oxide particles. The amount of ammonia added was doubled in molar ratio to TPZ. The dispersion was suction filtered to remove the solvent, and then vacuum dried at 80 ° C. Thereafter, the dried product was baked in the atmosphere at 500 ° C. for 2 hours to obtain a coated positive electrode active material (a positive electrode material for a non-aqueous secondary battery of the present invention). Further, the collected filtrate was concentrated to confirm that there was no residue, that is, TPZ was completely hydrolyzed and polycondensed.

<Surface observation and composition analysis of positive electrode active material>
The surface morphology of the positive electrode active material subjected to the coating treatment was observed with an SEM. The acceleration voltage of SEM was 1.5 kV. FIG. 2 shows an SEM image of the positive electrode active material at a magnification of 100 k, and FIG. 3 shows an SEM image of the positive electrode active material at a magnification of 300 k.

  Next, the composition in the vicinity of the surface of the coated positive electrode active material was analyzed by the STEM-EDX method. Specifically, the positive electrode active material was embedded in a resin and then polished to expose a cross section, and this was thinned to a thickness of 30 nm using an FIB (Focused Ion Beam) apparatus to obtain an analysis sample. A spherical aberration correction STEM apparatus was used for the above analysis, and the acceleration voltage was 200 kV.

  According to the above composition analysis, the portion shown as the granular bright portion in FIG. 2 and FIG. 3 is the deposited portion where the Zr oxide is deposited, and the portion shown as the dark portion other than the granular bright portion is the Zr oxide. It was found that the deposit was a non-deposited portion. Based on FIG. 2, the major axis diameter of 100 Zr oxides was measured, and the average particle diameter was calculated as the arithmetic average value, which was 16 nm. Further, based on FIG. 3, the ratio of the area of the non-deposited portion to the total area of the surface of the positive electrode active material was calculated to be 84%.

  FIG. 4 shows a cross-sectional STEM image near the surface of the positive electrode active material. From FIG. 4, a portion where the granular Zr oxide is deposited (deposited portion), a portion where it is not deposited (non-deposited portion), and a bulk portion are observed. Composition analysis of the surface layer portion at a depth of 2 nm from the outermost surface of the positive electrode active material was performed by the STEM-EDX method. Specifically, the composition analysis is performed by arbitrarily selecting five surface layer portions of the non-deposited portion, and the total number of atoms of M (Co, Ni and Mn) contained in the surface portion of the non-deposited portion is described above. When the ratio (Zr / M ratio) of the total number of Zr atoms contained in the surface layer part of the non-deposited part was measured and the arithmetic average value thereof was calculated, it was 16 atomic%.

<Preparation of positive electrode>
90 parts by mass of the coated positive electrode active material, 5 parts by mass of acetylene black (average particle size: 50 nm) as a conductive auxiliary agent, and 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder are mixed to mix the positive electrode. A positive electrode mixture-containing paste was prepared by dispersing the positive electrode mixture in N-methyl-2-pyrrolidone (NMP).

  Next, the positive electrode mixture-containing paste is applied to one side of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, dried to form a positive electrode mixture layer, pressed, and dried at 120 ° C. A sheet material was obtained. The thickness of the positive electrode mixture layer after pressing was 20 μm. This positive electrode sheet material was punched out into an area of 20 mm × 20 mm to obtain a positive electrode.

<Battery assembly>
The battery was assembled in an argon glove box. Lithium metal was used for the negative electrode, and a porous polypropylene film was used for the separator. An aluminum laminate film was used for the battery outer package. The laminate in which the positive electrode and the negative electrode were opposed to each other through the separator was loaded into the outer package, and the outer periphery of the outer package was welded and sealed, leaving a part. Next, 200 μL of an electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was injected into the outer package in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. After the injection, the outer package was completely welded and sealed to obtain a non-aqueous secondary battery.

(Example 2)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the coating amount of the positive electrode active material was changed to 0.03% by mass. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Example 3)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the coating amount of the positive electrode active material was changed to 0.3% by mass. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

Example 4
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the molar ratio A / B (DPG / Zr) was set to 0.3 in the coating treatment of the positive electrode active material. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Example 5)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the molar ratio A / B (DPG / Zr) was set to 1.0 in the coating treatment of the positive electrode active material. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Example 6)
A non-aqueous secondary battery in the same manner as in Example 1 except that LiCoO ₂ powder (hereinafter abbreviated as LCO; average particle size: 7 μm) was used as the lithium-containing composite oxide particles in the coating treatment of the positive electrode active material. Was made. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Example 7)
The same procedure as in Example 1 was performed except that LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder (hereinafter abbreviated as NCA; average particle size: 14 μm) was used as the lithium-containing composite oxide particles in the coating treatment of the positive electrode active material. Thus, a non-aqueous secondary battery was produced. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Comparative Example 1)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the coating amount of the positive electrode active material was changed to 0.4% by mass. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Comparative Example 2)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the coating amount of the positive electrode active material was changed to 0.02% by mass. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Comparative Example 3)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that in the coating treatment of the positive electrode active material, the coating amount was 0.3 mass% and the firing temperature was 600 ° C. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Comparative Example 4)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the molar ratio A / B (DPG / Zr) was set to 0.1 in the coating treatment of the positive electrode active material. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Comparative Example 5)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the molar ratio A / B (DPG / Zr) was 1.2 in the coating treatment of the positive electrode active material. Further, in the same manner as in Example 1, the average particle diameter of the granular Zr oxide particles, the area ratio of the non-deposited part, and the Zr / M ratio of the surface layer part of the non-deposited part were calculated.

(Comparative Example 6)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that NCM powder not subjected to coating treatment was used as the positive electrode active material.

(Comparative Example 7)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that LCO powder not subjected to coating treatment was used as the positive electrode active material.

(Comparative Example 8)
A nonaqueous secondary battery was produced in the same manner as in Example 1 except that NCA powder not subjected to coating treatment was used as the positive electrode active material.

  Table 1 shows the types of lithium-containing composite oxides used in the positive electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 8, and the molar ratio A / B (DPG / Zr) among the production conditions of the positive electrode active materials. , Coating amount and firing temperature.

<Evaluation of charge / discharge characteristics>
(1) Initial charge / discharge characteristics The produced non-aqueous secondary battery is constant at 0.05 C (the LiMO ₂ theoretical capacity of about 280 mAh / g is 1 C) at 25 ° C. until the battery voltage reaches 4.6 V. After charging with current and reaching 4.6V, it was charged with a constant voltage of 4.6V until the charging current became less than 0.005C. Thereafter, the battery was discharged at a constant current of 0.05 C until the battery voltage reached 2.5V. This series of operations was performed for one cycle.

(2) Charging / discharging cycle characteristics The battery after measuring the initial charging / discharging characteristics was charged at a constant current of 1C until the battery voltage reached 4.6V at 25 ° C, and after reaching 4.6V, 4. The battery was charged at a constant voltage of 6V until the charging current became less than 0.1C. Thereafter, the battery was discharged at a constant current of 1 C until the battery voltage reached 2.5V. This series of operations was defined as one cycle, and charging / discharging was repeated up to 100 cycles. The discharge capacity at the first cycle in the charge / discharge was defined as 1C discharge capacity. Further, (the discharge amount at the 100th cycle / the discharge capacity at the first cycle) × 100 (%) was defined as the cycle capacity retention rate.

  The results are shown in Table 2. Table 2 also shows the average particle diameter of the aforementioned Zr oxide particles, the area ratio of the non-deposited portion, and the Zr / M ratio of the surface layer portion of the non-deposited portion.

  From Table 2, in the nonaqueous secondary batteries of Examples 1 to 7 using the positive electrode material for a nonaqueous secondary battery of the present invention, the 1C discharge capacity was 170 mAh / g or more, and the cycle capacity maintenance rate was 70% or more. It can be seen that it has a high capacity and excellent charge / discharge cycle characteristics even under a high voltage. In particular, Example 6 using LCO as the lithium-containing composite oxide serving as the bulk part and Example 7 using NCA as the lithium-containing composite oxide serving as the bulk part had a 1C discharge capacity of 188 mAh / g or more, It can be seen that the cycle capacity retention rate is 70% or more, the capacity is extremely high, and the charge / discharge cycle characteristics are excellent even under a high voltage.

  On the other hand, Comparative Example 1 in which the average particle size of the Zr oxide exceeded 30 nm and the area ratio of the non-deposited portion was less than 50%, the area ratio of the non-deposited portion exceeded 97%, and the Zr of the surface layer portion of the non-deposited portion Comparative Example 2 in which the / M ratio was less than 3 atomic%, Comparative Example 3 in which the average particle diameter of the Zr oxide exceeded 30 nm, and the Zr / M ratio in the surface layer part of the non-deposited part exceeded 40 atomic%, Zr oxidation Comparative Example 4 in which the average particle size of the product exceeded 30 nm and the Zr / M ratio of the surface layer portion of the non-deposited portion was less than 3 atomic%, the average particle size of the Zr oxide exceeded 30 nm, and the surface layer portion of the non-deposited portion In Comparative Example 5 in which the Zr / M ratio was less than 3 atomic%, and Comparative Example 6 using a positive electrode active material that was not coated, the 1C discharge capacity and the cycle capacity maintenance rate were higher than those in Examples 1-7. Both are inferior.

  In Comparative Examples 7 and 8 using a positive electrode active material that was not coated, Examples 1 and 7 were used as positive electrode active materials coated with the same lithium-containing composite oxide, although the 1C discharge capacity was high. It can be seen that the cycle capacity retention rate is significantly inferior to that of the previous one.

  The non-aqueous secondary battery using the positive electrode material for a non-aqueous secondary battery of the present invention can suppress deterioration in charge / discharge cycle characteristics even when charged at a very high voltage of 4.6 V or higher. Capacity and charge / discharge cycle characteristics are good. The non-aqueous secondary battery of the present invention makes use of such characteristics to provide electronic devices (especially portable electronic devices such as mobile phones and notebook personal computers), power supply systems, vehicles (electric cars, electric bicycles, etc.). It can be preferably used for power supply applications of various devices such as.

DESCRIPTION OF SYMBOLS 1 Outermost surface 2 Surface layer part 3 Bulk part 4 Zr oxide A Deposition part B Non-deposition part

Claims (7)

A positive electrode material for a non-aqueous secondary battery comprising lithium-containing composite oxide particles,
The lithium-containing composite oxide particles include an outermost surface, a surface layer portion in a range of a depth of at least 2 nm from the outermost surface, and a bulk portion located inside the surface layer portion,
The bulk part is represented by the following general composition formula (1):
LiMO ₂ (1)
In the general composition formula (1), M is
One element selected from Co, Ni and Mn , or
A plurality of element groups including at least one selected from Co, Ni and Mn ;
The total number of elements of Co, Ni and Mn contained in the element group is 50 mol% or more,
A granular Zr oxide is disposed on the outermost surface,
The average particle size of the Zr oxide is 30 nm or less,
When the outermost surface region where the Zr oxide is disposed is defined as a deposited portion, and the outermost surface region where the Zr oxide is not disposed is defined as a non-deposited portion, the area of the non-deposited portion is equal to that of the outermost surface. 50% or more and 97% or less with respect to the total area,
The surface layer portion of the non-deposited portion includes M and Zr,
The ratio of the total number of atoms of Zr contained in the surface layer part of the non-deposited part to the total number of atoms of M contained in the surface part in the non-deposited part is 3 atomic% or more and 40 atomic% or less. A positive electrode material for a non-aqueous secondary battery.   The positive electrode material for a non-aqueous secondary battery according to claim 1, wherein the lithium-containing composite oxide constituting the bulk part has a layered rock salt structure.   The positive electrode material for a non-aqueous secondary battery according to claim 1, wherein the Zr oxide does not contain Li. It is a manufacturing method of the positive electrode material for nonaqueous secondary batteries given in any 1 paragraph of Claims 1-3,
A first step of preparing a dispersion by dispersing lithium-containing composite oxide particles, zirconium alkoxide, and dipropylene glycol in an organic solvent;
A second step of adding a base and water to the dispersion to form a gel film on the surface of the lithium-containing composite oxide particles;
A third step of drying the solid content obtained by filtering the dispersion containing the lithium-containing composite oxide particles that formed the gel film, and firing the solid content;
When the mole number of the dipropylene glycol contained in the dispersion prepared in the first step is A and the mole number of the zirconium alkoxide contained in the dispersion is B, the molar ratio A / B is 0.00. 3 or more and 1.0 or less,
The lithium-containing composite oxide particles are represented by the following general composition formula (1):
LiMO ₂ (1)
In the general composition formula (1), M is
One element selected from Co, Ni and Mn , or
Co, a plurality of element group including at least one selected from Ni and Mn was table,
The total number of elements of Co, Ni, and Mn contained in the element group is 50 mol% or more, and the method for producing a positive electrode material for a non-aqueous secondary battery.   The method for producing a positive electrode material for a non-aqueous secondary battery according to claim 4, wherein the base is ammonia.   A positive electrode for a non-aqueous secondary battery comprising the positive electrode material for a non-aqueous secondary battery according to claim 1 as a positive electrode active material. A non-aqueous secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The said positive electrode is a positive electrode for nonaqueous secondary batteries of Claim 6, The nonaqueous secondary battery characterized by the above-mentioned.