JP6428996B2 - Mixed active material for lithium secondary battery, electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Description

  The present invention relates to a mixed active material for a lithium secondary battery, an electrode for a lithium secondary battery containing the mixed active material, and a lithium secondary battery including the electrode.

Currently, non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries, in particular lithium secondary batteries, are widely installed in portable terminals and the like. In these nonaqueous electrolyte secondary batteries, LiCoO ₂ is mainly used as a positive electrode active material. However, the discharge capacity of LiCoO ₂ is about 120 to 130 mAh / g.

Further, a solid solution of LiCoO ₂ and other compounds is known as a positive electrode active material for a lithium secondary battery. Li [Co _1-2x Ni _x Mn _x ] O ₂ (0 <x ≦ 1/2) having a α-NaFeO ₂ type crystal structure and being a solid solution of three components of LiCoO ₂ , LiNiO ₂ and LiMnO ₂ Was announced in 2001. LiNi _1/2 Mn _1/2 O ₂ and LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , which are examples of the solid solution, have a discharge capacity of 150 to 180 mAh / g, and are charged and discharged. Excellent cycle performance.

For the so-called “LiMeO ₂ type” active material as described above, the composition ratio Li / Me of lithium (Li) with respect to the ratio of transition metal (Me) is larger than 1, for example, Li / Me is 1.25 to 1.6. There are known so-called “lithium-rich” active materials (see, for example, Patent Documents 1 and 2). Such a material can be expressed as Li _{1 + α} Me _1-α O ₂ (α> 0). Here, when the composition ratio Li / Me of lithium (Li) with respect to the ratio of the transition metal (Me) is β, β = (1 + α) / (1-α), and thus, for example, Li / Me is 1.5. In this case, α = 0.2.

Patent Documents 1 and 2 describe active materials as described above. Further, in these patent documents, a positive electrode potential range of 4.3 V (vs. Li ^/ Li ⁺ ) and 4.8 V or less (vs. Li ^/ Li ⁺ ) is described as a battery manufacturing method using the active material. In this case, the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less. Or even if it is a case where the charge method which is less than 4.4V (vs.Li/Li <^+> ) is employ | adopted, it describes that the battery which can obtain the discharge capacity of 180 mAh / g or more can be manufactured.

Thus, unlike the so-called “LiMeO ₂ type” positive electrode active material, the so-called “lithium-excess type” positive electrode active material has a relatively high potential exceeding 4.3 V, particularly 4.4 V or more, at least in the first charge. A characteristic is that a high discharge capacity can be obtained by carrying out the process to a potential of.

  Moreover, the invention of the active material for lithium secondary batteries which improved the volume energy density etc. by mixing two types of active materials from which an average particle diameter and a composition differ is known (for example, patent documents 3-6) reference).

  Patent Document 3 states that “a method of manufacturing a battery electrode by applying a slurry for an active material layer on a current collector and drying the slurry, wherein the slurry includes a first active material as a main component. A method for producing a battery electrode, comprising: a first electrode material having a porous structure, a second electrode material having a dense structure mainly composed of a second active material, and a conductive additive and a binder. (Claim 1) is described, and as an object of the present invention, "a battery electrode capable of suppressing a decrease in energy density of the battery even when the electrode layer is thick and suppressing an influence on output performance" Is provided "(paragraph [0008]).

Patent Document 4 discloses a powdery electrode active material for a rechargeable lithium secondary battery, which is composed of a lithium transition metal oxide Li _a M _b O ₂ having a particle size-dependent composition, In which 0.9 <a <1.1, 0.9 <b <1.1, and M is a transition metal selected from Mn, Co, and Ni) The particles have a particle size gradient The composition of M changes depending on the particle size, the component ratio of Co in one particle increases as the particle size increases, and 1 increases as the particle size increases. The component ratio of Mn in the particles decreases, all the bulks of all the particles have a layered crystal structure, large particles and small particles, and the large particles , it has a composition _Li a _M b _{O 2,} [in the _{formula, M = Mn x Ni y (} Co _-X-y) a and, x + y <0.35] the small particles, of a different composition _Li a _M b _{O 2} [in the _{formula, M = Mn x 'Ni y} ' (Co 1-x'- _{y ′} ), at least 10% less cobalt (1-x′-y ′) <0.9 * (1-xy), and at least 5% more manganese (x′-x> 0.05) A powdered electrode active material. The invention of (Claim 1) is described, and as an object of the present invention, "not only a high volumetric energy density and a gravimetric energy density but also an electrode active material that is inexpensive and has high cycle stability and safety" is provided. (Paragraph [0017]).

  Patent Document 5 states that “a first lithium nickel composite oxide having a volume particle distribution of 3.0 μm ≦ D25 ≦ 10.0 μm, 5.0 μm ≦ D50 ≦ 20.0 μm and 10.0 μm ≦ D75 ≦ 25.0 μm; A second lithium nickel composite oxide having a volume particle distribution of 0.01 μm ≦ D25 ≦ 5.0 μm, 1.0 μm ≦ D50 ≦ 10.0 μm and 5.0 μm ≦ D75 ≦ 15.0 μm. The positive electrode active material for a lithium battery is described. (Claim 1) The invention of the present invention is described. As an object of the present invention, "improvement of packing density and thermal stability, and at the same time improving capacity" It is possible to provide a new and improved positive electrode active material, and a positive electrode and a lithium battery employing this positive electrode active material "(paragraph [0007]).

Patent Document 6 states that “Li [Li _1/3 M ¹ _2/3 ] O ₂ (a) (wherein M ¹ is one or more metal elements and has an average valence of 4). And LiM ² O ₂ (b) (wherein M ² is one or more metal elements and the average valence is trivalent), the median diameter differs in the solid solution positive electrode material using the solid solution A solid solution positive electrode material formed by combining a plurality of solid solutions. "(Claim 1) is described. As an object of this invention," a tap density is improved and a capacity density per volume is improved. Providing a cathode material "(paragraph [0008]) is shown.

JP 2010-086690 A WO2012 / 091015 JP 2010-092622 A JP 2011-091050 A JP 2011-216485 A JP 2012-059528 A

The so-called “lithium-rich” active materials described above generally have a higher capacity than the so-called “LiMeO ₂ type” active materials, but are known to be inferior in high rate discharge performance. It has also been found that this high rate discharge performance can be improved by using carbonate as the precursor in the “lithium-rich” active material. However, it has been found that the active material using the carbonate precursor is prone to cracking of the active material during electrode pressing, and it is difficult to increase the density of the electrode. On the other hand, it has been found that an active material using a hydroxide precursor is inferior in high rate discharge performance compared to an active material using a carbonate precursor.
Further, as described above, there is known an invention in which two types of active materials having different average particle diameters and compositions are mixed to form an active material or electrode for a lithium secondary battery. However, high-rate discharge performance and electrode workability are known. It has not been shown to improve.

  The present invention has been made in view of the above problems, and provides a mixed active material for a lithium secondary battery excellent in high-rate discharge performance and electrode processability, an electrode using the mixed active material, and a lithium secondary battery The task is to do.

  The configuration and operational effects of the present invention will be described with the technical idea. However, the action mechanism includes estimation, and the correctness does not limit the present invention. It should be noted that the present invention can be implemented in various other forms without departing from the spirit or main features thereof. For this reason, the following embodiments or experimental examples are merely examples in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

In the present invention, in order to solve the above problems, the following means are adopted.
(1) It has an α-NaFeO ₂ structure, the transition metal (Me) contains Co, Ni and Mn, the molar ratio Li / Me of lithium (Li) to the transition metal is larger than 1, and the average particle diameter D50 is a different two lithium secondary battery mixing active material containing a lithium transition metal composite oxide particles, a large first lithium transition metal composite oxide particle having an average particle diameter D50 is an average particle size D50 The second lithium transition metal composite oxide particles having a small average particle diameter D50 of 5 μm or more have an average particle diameter D50 of 5 μm or less, a difference between them of at least 2 μm, and a large average particle diameter D50. One lithium transition metal composite oxide particle has a pore diameter in the range of 30 to 40 nm where the differential pore volume obtained by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method shows the maximum value. And a peak differential pore volume is 0.8mm 3 / (g ^· nm) or more, the average particle size D50 of smaller second lithium transition metal composite oxide particles, the nitrogen gas adsorption method from an adsorption isotherm using The differential pore volume obtained by the BJH method has a maximum pore diameter in the range of 50 to 70 nm, and the peak differential pore volume is 0.5 mm ³ / (g · nm) or less. Mixed active material for secondary batteries.
( 2 ) The electrode for lithium secondary batteries containing the mixed active material for lithium secondary batteries of said (1 ) .
( 3 ) The lithium secondary battery provided with the electrode for lithium secondary batteries of said ( 2 ).

According to the present invention, a mixed active material for a lithium secondary battery excellent in high-rate discharge performance and electrode processability, containing two types of lithium transition metal composite oxide particles having different average particle diameters D50 , and the mixed active material The used electrode and lithium secondary battery can be provided.

(A) a typical differential pore volume curve relating to the first lithium transition metal composite oxide particles having a large average particle diameter D50 , and (b) second lithium transition metal composite oxide particles having a small average particle diameter D50. Figure showing a typical differential pore volume curve Schematic showing a power storage device constructed by assembling a plurality of lithium secondary batteries according to the present invention

The composition of the lithium transition metal composite oxide contained in the active material for a lithium secondary battery according to the present invention includes a transition metal element Me containing Co, Ni and Mn, and Li from the point that a high discharge capacity can be obtained. The molar ratio Li / Me of the lithium (Li) to the transition metal (Me) is larger than 1, typically, Li _{1 + α} Me _1-α O ₂ (α> 0), which can be expressed as a so-called “ “Lithium-rich” type.

In the present invention, the molar ratio Li / Me of Li to the transition metal element Me represented by (1 + α) / (1-α) in the composition formula Li _{1 + α} Me _1-α O ₂ is 1.2 (α = 0.0. 09) and smaller than 1.6 (α = 0.23), a lithium secondary battery having a large discharge capacity and excellent high-rate discharge performance can be obtained. It is preferable that (1 + α) / (1−α) <1.6. When the Li / Me ratio is 1.2 or less, the discharge capacity decreases, and the peak differential pore volume of the second lithium transition metal composite oxide particles exceeds 0.5 mm ³ / (g · nm) When the Li / Me ratio is 1.6 or more, the peak differential pore volume of the first lithium transition metal composite oxide particle is less than 0.8 mm ³ / (g · nm), and the high rate Discharge performance deteriorates.
Among these, from the viewpoint that a lithium secondary battery having a particularly large discharge capacity and excellent high rate discharge performance can be obtained, the first lithium transition metal composite oxide particles are 1.25 ≦ (1 + α) / ( 1−α) ≦ 1.5 is more preferable, and 1.25 ≦ (1 + α) / (1−α) ≦ 1.4 is particularly preferable. The second lithium transition metal composite oxide particles are more preferably 1.3 ≦ (1 + α) / (1-α) ≦ 1.55, and 1.35 ≦ (1 + α) / (1-α ) ≦ 1.5 is particularly preferable.
Furthermore, the first lithium transition metal composite oxide particles and the second lithium transition metal composite oxide particles from the viewpoint that a lithium secondary battery having a particularly large discharge capacity and excellent high rate discharge performance can be obtained. Is more preferably 1.25 ≦ (1 + α) / (1-α) ≦ 1.55, and particularly preferably 1.25 ≦ (1 + α) / (1-α) ≦ 1.5.

  In the present invention, the molar ratio Co / Me of Co to the transition metal element Me is 0.05 to 0.00 in that a lithium secondary battery having a large discharge capacity and excellent high rate discharge performance can be obtained. 40 is preferable, and 0.10 to 0.30 is more preferable.

Further, in order to obtain a lithium secondary battery having a large discharge capacity and excellent high-rate discharge performance and cycle characteristics, the molar ratio of Mn to transition metal element Me, Mn / Me, is preferably larger than 0.5. In the LiMeO ₂ type lithium transition metal composite oxide, when the molar ratio Mn / Me is larger than 0.5, spinel transition occurs when charging, and it does not have a structure attributed to the α-NaFeO ₂ structure. While there was a problem as an active material for a lithium secondary battery, the lithium-excess type lithium transition metal composite oxide had α-NaFeO ₂ even when charged with a molar ratio Mn / Me larger than 0.5. Since the structure can be maintained, the configuration in which the molar ratio Mn / Me is larger than 0.5 characterizes the positive electrode active material made of a so-called lithium-excess type lithium transition metal composite oxide. The molar ratio Mn / Me is preferably more than 0.5 to 0.8, more preferably more than 0.5 to 0.75.

The lithium transition metal composite oxide according to the present invention typically has a general formula of Li _{1 + α} (Co _a Ni _b Mn _c ) _1-α O ₂ , where α> 0, a + b + c = 1, a> 0, b > 0, c> 0, which is essentially a composite oxide composed of Li, Co, Ni, and Mn. In order to improve the discharge capacity, it is preferable that Na be included at 1000 ppm or more. . As for content of Na, 2000-10000 ppm is more preferable.

  In order to contain Na, a sodium precursor such as sodium hydroxide or sodium carbonate is used as a neutralizing agent in the step of preparing a hydroxide precursor or carbonate precursor described later, and Na remains in the washing step. Alternatively, a method of adding a sodium compound such as sodium carbonate in the subsequent firing step can be employed.

  In addition, a small amount of other metals such as alkali metals other than Na, alkaline earth metals such as Mg and Ca, transition metals typified by 3d transition metals such as Fe and Zn, and the like are included as long as the effects of the present invention are not impaired. It does not exclude doing.

The lithium transition metal composite oxide according to the present invention has an α-NaFeO ₂ structure. The lithium transition metal composite oxide after synthesis (before charging and discharging) is attributed to the space group P3 ₁ 12 or R3-m. Among these, those belonging to the space group P3 ₁ 12 are superlattice peaks (Li [Li _1/3 Mn _2/3 ] O ₂ near 2θ = 21 ° on the X-ray diffraction diagram using the CuKα tube. The peak observed in the monoclinic type) is confirmed. However, when charging is performed once and Li in the crystal is desorbed, the symmetry of the crystal changes, whereby the superlattice peak disappears and the lithium transition metal composite oxide belongs to the space group R3-m. Will come to be. Here, P3 ₁ 12 is a crystal structure model in which the atomic positions of the 3a, 3b, and 6c sites in R3-m are subdivided, and when ordering is recognized in the atomic arrangement in R3-m, the P3 ₁ 12 model Is adopted. Note that “R3-m” should be represented by adding a bar “-” on “3” of “R3m”.

The lithium transition metal composite oxide according to the present invention has a half-width of the diffraction peak attributed to the (003) plane of 0.18 ° when the space group R3-m is used as a crystal structure model based on the X-ray diffraction pattern. It is preferable to be in the range of ~ 0.22 °. By doing so, it is possible to increase the discharge capacity of the positive electrode active material and improve the high rate discharge performance. A diffraction peak of 2θ = 18.6 ° ± 1 ° that appears when using a CuKα tube is indexed to the (003) plane in the Miller index hkl in the space groups P3 ₁ 12 and R3-m.

Moreover, it is preferable that a lithium transition metal complex oxide does not change a structure during overcharge. This can be confirmed by being observed as a single phase belonging to the space group R3-m on the X-ray diffraction diagram when electrochemically oxidized to a potential of 5.0 V (vs. Li ^/ Li ⁺ ). Thereby, the lithium secondary battery excellent in charge / discharge cycle performance can be obtained.

Further, the lithium transition metal composite oxide has an oxygen positional parameter obtained from a crystal structure analysis by the Rietveld method based on the X-ray diffraction pattern, which is 0.262 or less at the end of the discharge of 2 V (vs. Li ^/ Li ⁺ ). It is preferable that it is 0.267 or more at the end of charge of 4.3 V (vs. Li ^/ Li ⁺ ) after the charge conversion. Thereby, a lithium secondary battery excellent in high rate discharge performance can be obtained. Note that the oxygen positional parameter is Me (transition metal) spatial coordinates (0, 0, 0) for the α-NaFeO ₂ type crystal structure of the lithium transition metal composite oxide belonging to the space group R3-m, This is the value of z when the spatial coordinates of Li (lithium) are defined as (0, 0, 1/2) and the spatial coordinates of O (oxygen) are defined as (0, 0, z). In other words, the oxygen position parameter is a relative index indicating how far the O (oxygen) position is from the Me (transition metal) position (see Patent Document 2).

The positive electrode active material according to the present invention contains two types of lithium transition metal composite oxide particles having different average particle diameters D50 in order to improve high rate discharge performance and electrode workability (press workability). The lithium transition metal composite oxide particles having a large average particle diameter D50 are prepared from a carbonate precursor, and the lithium transition metal composite oxide particles having a small average particle diameter D50 are prepared from a hydroxide precursor.
The lithium transition metal composite oxide particles having a large particle diameter produced from the carbonate precursor have an average particle diameter D50, which is a particle diameter at which the cumulative volume in the particle size distribution of the secondary particles is 50%, is 5 μm or more. Is more preferable, it is more preferable that it is 8 micrometers or more, and it is especially preferable that it is 8-18 micrometers. Moreover, in order to improve electrode workability (press workability), the lithium transition metal composite oxide particles having a small particle diameter produced from the hydroxide precursor have an average particle diameter D50 of 5 μm or less. Is preferable , and it is more preferable that it is 1-5 micrometers. When the average particle diameter D50 of the two types of lithium transition metal composite oxide particles to be mixed is close, the press workability deteriorates.

In the present invention, in order to obtain a positive electrode active material for a lithium secondary battery excellent in high rate discharge performance and electrode workability (press workability), the first lithium transition metal composite oxide particles having a large average particle diameter D50 are: , The differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method has a maximum pore diameter of 30 to 40 nm, and the peak differential pore volume is 0.8 mm ³ / (g · nm) or more, and the second lithium transition metal composite oxide particles having a small average particle diameter D50 are fine particles having a maximum differential pore volume determined by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method. When the pore diameter is in the range of 50 to 70 nm, the peak differential pore volume is 0.5 mm ³ / (g · nm) or less, and both are mixed to obtain an active material.
The large mixing ratio of the first lithium transition metal composite oxide particles and the average particle size D50 of smaller second lithium transition metal composite oxide particle having an average particle diameter D50 is a weight ratio, 70: 30-95 : 5, more preferably 80:20 to 90:10.

The first lithium transition metal composite oxide particles having a large average particle diameter D50 and a large peak differential pore volume can be produced from a carbonate precursor. In the present invention, in order to improve the high rate discharge performance, the peak differential pore volume of the first lithium transition metal composite oxide particles is set to 0.8 mm ³ / (g · nm) or more. It is preferable to set it as 0.8-1.7mm < ³ > / (g * nm).
The second lithium transition metal composite oxide particles having a small average particle diameter D50 and a small peak differential pore volume can be prepared from a hydroxide precursor. In the present invention, in order to improve electrode workability (press workability), the peak differential pore volume of the second lithium transition metal composite oxide particles is 0.5 mm ³ / (g · nm) or less. It is preferable to set it as 0.5-0.3mm < ³ > / (g * nm).
As shown in the examples, the peak differential pore volume can be adjusted to the above range by adjusting the composition of the lithium transition metal composite oxide, the firing temperature of the active material, and the like.

The BET specific surface area of the positive electrode active material according to the present invention is preferably 1 m ² / g or more as the first active material in order to obtain a lithium secondary battery excellent in initial efficiency and high rate discharge performance, and ² to 5 m. more preferably ² / g, preferably at least 0.5 m ² / g as the second active material, 1 to 4 m ² / g is more preferable.
Further, the tap density is preferably 1.25 g / cc or more and more preferably 1.7 g / cc or more for both active materials in order to obtain a lithium secondary battery having excellent high rate discharge performance.

Next, a method for producing the active material for a lithium secondary battery of the present invention will be described.
The active material for a lithium secondary battery of the present invention basically includes a raw material containing a metal element (Li, Mn, Co, Ni) constituting the active material according to the composition of the active material (oxide). It can be obtained by adjusting and baking this. However, with respect to the amount of the Li raw material, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li raw material during firing.
In producing an oxide having a desired composition, a so-called “solid phase method” in which salts of Li, Co, Ni, and Mn are mixed and fired, or Co, Ni, and Mn were previously present in one particle. A “coprecipitation method” is known in which a coprecipitation precursor is prepared, and a Li salt is mixed and fired therein. In the synthesis process by the “solid phase method”, especially Mn is difficult to uniformly dissolve in Co and Ni, so it is difficult to obtain a sample in which each element is uniformly distributed in one particle. In literatures and the like, many attempts have been made to dissolve Mn in a part of Ni or Co (LiNi _1-x Mn _x O ₂ etc.) by solid phase method, but the “coprecipitation method” is selected. It is easier to obtain a homogeneous phase at the atomic level. Therefore, the “coprecipitation method” is employed in the examples described later.

When preparing a coprecipitation precursor, Mn is easily oxidized among Co, Ni and Mn, and it is not easy to prepare a coprecipitation precursor in which Co, Ni and Mn are uniformly distributed in a divalent state. Uniform mixing at the atomic level of Co, Ni and Mn tends to be insufficient. In particular, in the composition range of the present invention, since the Mn ratio is higher than the Co and Ni ratios, it is particularly important to remove dissolved oxygen in the aqueous solution. Examples of the method for removing dissolved oxygen include a method of bubbling a gas not containing oxygen. The gas not containing oxygen is not limited, but nitrogen gas, argon gas, carbon dioxide (CO ₂ ), or the like can be used. Among these, when producing a coprecipitated carbonate precursor, it is preferable to employ carbon dioxide as a gas not containing oxygen because an environment in which carbonate is more easily generated is provided.

  Although the pH in the step of producing a precursor by co-precipitation of a compound containing Co, Ni and Mn in a solution is not limited, an attempt is made to produce the co-precipitation precursor as a co-precipitation hydroxide precursor. When it does, it can be set to 10-14, and when it is going to produce the said coprecipitation precursor as a coprecipitation carbonate precursor, it can be set to 7.5-11. In order to increase the tap density, it is preferable to control the pH. About a coprecipitation carbonate precursor, tap density can be made into 1.25 g / cc or more by making pH into 9.4 or less, and a high rate discharge performance can be improved. Furthermore, since the particle growth rate can be accelerated by adjusting the pH to 8.0 or less, the stirring continuation time after the raw material aqueous solution dropping is completed can be shortened.

  The coprecipitation precursor is preferably a compound in which Mn, Ni, and Co are uniformly mixed. In addition, a precursor having a larger bulk density can be produced by using a crystallization reaction using a complexing agent. At that time, a higher density active material can be obtained by mixing and firing with a Li source, so that the energy density per electrode area can be improved.

  The raw material of the coprecipitation precursor is manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc. as the Mn compound, and nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate as the Ni compound. As examples of the Co compound, cobalt sulfate, cobalt nitrate, cobalt acetate, and the like can be given as examples.

  In the present invention, a reaction crystallization method is employed in which a raw material aqueous solution of the coprecipitation precursor is continuously supplied dropwise to a reaction tank that maintains alkalinity to obtain a coprecipitation precursor. Here, lithium compounds, sodium compounds, potassium compounds and the like can be used as the neutralizing agent, but when the coprecipitation precursor is prepared as a coprecipitation hydroxide precursor, sodium hydroxide, hydroxide It is preferable to use a mixture of sodium and lithium hydroxide, or sodium hydroxide and potassium hydroxide, and when preparing the coprecipitation precursor as a coprecipitation carbonate precursor, sodium carbonate, sodium carbonate It is preferable to use lithium carbonate or a mixture of sodium carbonate and potassium carbonate. Na / Li, which is a molar ratio of sodium carbonate (sodium hydroxide) and lithium carbonate (lithium hydroxide), or sodium carbonate (sodium hydroxide) and potassium carbonate (potassium hydroxide) in order to leave Na 1000 ppm or more It is preferable that Na / K which is the molar ratio is 1/1 [M] or more. By setting Na / Li or Na / K to 1/1 [M] or more, it is possible to reduce the possibility that Na will be excessively removed in the subsequent washing step and become less than 1000 ppm.

  The dropping speed of the raw material aqueous solution greatly affects the uniformity of element distribution in one particle of the coprecipitation precursor to be generated. In particular, Mn is difficult to form a uniform element distribution with Co and Ni, so care must be taken. The preferred dropping rate is influenced by the reaction vessel size, stirring conditions, pH, reaction temperature, etc., but is preferably 30 ml / min or less. In order to improve the discharge capacity, the dropping rate is more preferably 10 ml / min or less, and most preferably 5 ml / min or less.

  In addition, when a complexing agent is present in the reaction tank and a certain convection condition is applied, the particle rotation and revolution in the stirring tank are promoted by continuing the stirring after the dropwise addition of the raw material aqueous solution. In this process, the particles grow concentrically in stages while colliding with each other. That is, the coprecipitation precursor undergoes a reaction in two stages: a metal complex formation reaction when the raw material aqueous solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex is retained in the reaction tank. It is formed. Therefore, a coprecipitation precursor having a target particle size can be obtained by appropriately selecting a time for continuing stirring after the dropping of the raw material aqueous solution.

  The preferable stirring duration after completion of dropping of the raw material aqueous solution is influenced by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but 0.5 h or more is required to grow the particles as uniform spherical particles. Preferably, 1 h or more is more preferable. Further, in order to reduce the possibility that the output performance in the low SOC region of the battery is not sufficient due to the particle size becoming too large, 30 h or less is preferable, 25 h or less is more preferable, and 20 h or less is most preferable.

  Moreover, the preferable stirring continuation time for making 50% particle diameter (D50) of lithium transition metal complex oxide produced from a coprecipitation hydroxide precursor into 1-8 micrometers, the lithium transition metal produced from a coprecipitation carbonate precursor A preferable stirring duration time for setting the 50% particle diameter (D50) of the composite oxide to 5 to 18 μm varies depending on the pH to be controlled. For example, for the coprecipitated hydroxide precursor, when the pH is controlled to 10 to 12, the stirring duration is preferably 1 to 10 h, and when the pH is controlled to 12 to 14, the stirring duration is 3 ~ 20h is preferred. For the coprecipitated carbonate precursor, when the pH is controlled to 7.5 to 8.2, the stirring duration is preferably 1 to 20 h, and when the pH is controlled to 8.3 to 9.4. The stirring duration is preferably 3 to 24 hours.

  When coprecipitation precursor particles are prepared using sodium compounds such as sodium hydroxide and sodium carbonate as neutralizing agents, sodium ions adhering to the particles are washed away in the subsequent washing step. In the present invention, it is preferable to wash and remove under conditions such that Na remains at 1000 ppm or more. For example, when the produced coprecipitation precursor is taken out by suction filtration, a condition such that the number of washings with 200 ml of ion-exchanged water is 5 times can be employed.

The coprecipitation precursor is preferably dried at 80 ° C. to less than 100 ° C. in an air atmosphere under normal pressure. By drying at 100 ° C. or higher, more water can be removed in a short time, but by drying at 80 ° C. for a long time, an active material having more excellent electrode characteristics can be obtained. The reason for this is not always clear, but the inventors have inferred the carbonate precursor as follows. That is, since the carbonate precursor is a porous body having a specific surface area of 50 to 100 m ² / g, it has a structure that easily adsorbs moisture. Therefore, by drying at a low temperature, a state in which a certain amount of adsorbed water remains in the pores in the state of the precursor is removed from the pores in the firing step of mixing with the Li salt and firing. It is inferred that molten Li can enter the pores so as to replace the adsorbed water, and thereby, an active material having a more uniform composition can be obtained as compared with the case of drying at 100 ° C. doing. In addition, although the carbonate precursor obtained by drying at 100 ° C. exhibits a black brown color, the carbonate precursor obtained by drying at 80 ° C. exhibits a skin color, so depending on the color of the precursor Can be distinguished.

Therefore, in order to quantitatively evaluate the difference in the precursors found above, the hues of the respective precursors are measured, and standard colors for paints (JPMA Standard Paint Colors) issued by the Japan Paint Manufacturers Association in accordance with JIS Z 8721. ) Compared with the 2011 F version. For measuring the hue, a color reader CR10 manufactured by Konica Minolta Co., Ltd. was used. According to this measuring method, the value of dL * representing lightness is larger in white and smaller in black. Further, the value of da * representing the hue is larger when red is stronger and smaller when green is stronger (red is weaker). Further, the value of db * representing the hue becomes larger when yellow is strong, and becomes smaller when blue is strong (yellow is weak).
The hue of the 100 ° C. dried product (Comparative Example) is in the range reaching the standard color F05-40D in the red direction compared to the standard color F05-20B, and in the white direction compared to the standard color FN-10. It was found to be within the range leading to the standard color FN-25. Among these, it was recognized that the color difference from the hue exhibited by the standard color F05-20B was the smallest.
On the other hand, the hue of the 80 ° C. dried product (Example) is in the range reaching the standard color F19-70F in the white direction as compared with the standard color F19-50F, and is black compared with the standard color F09-80D. It was found that it was in the range reaching the standard color F09-60H in the direction. Especially, it was recognized that the color difference with the hue which standard color F19-50F exhibits is the smallest.
From the above knowledge, the hue of the carbonate precursor is preferably positive in all of dL, da and db as compared with the standard color F05-20B, dL is +5 or more, da is +2 or more, and db is It can be said that +5 or more is more preferable.

  The active material for a lithium secondary battery of the present invention can be suitably produced by mixing the hydroxide precursor or carbonate precursor and the Li compound and then performing a heat treatment. As a Li compound, it can manufacture suitably by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, etc. However, with respect to the amount of the Li compound, it is preferable to add an excess of about 1 to 5% in view of the disappearance of a part of the Li compound during firing.

  In the present invention, in order to make the content of Na in the lithium transition metal composite oxide 1000 ppm or more, even if Na contained in the hydroxide precursor or carbonate precursor is 1000 ppm or less, the firing step The amount of Na contained in the active material can be set to 1000 ppm or more by mixing the Na compound together with the Li compound and the hydroxide precursor or carbonate precursor. As the Na compound, sodium carbonate is preferable.

The firing temperature affects the reversible capacity of the active material.
When the firing temperature is too high, the obtained active material collapses with an oxygen releasing reaction, and in addition to the hexagonal crystal of the main phase, the monoclinic Li [Li _1/3 Mn _2/3 ] O ₂ type is obtained. The defined phase tends to be observed as a phase separation rather than as a solid solution phase. If too many such phase separations are contained, it is not preferable because it leads to a reduction in the reversible capacity of the active material. In such materials, impurity peaks are observed around 35 ° and 45 ° on the X-ray diffraction pattern. Therefore, the firing temperature is preferably less than the temperature at which the oxygen release reaction of the active material affects. The oxygen release temperature of the active material is approximately 1000 ° C. or higher in the composition range according to the present invention. However, there is a slight difference in the oxygen release temperature depending on the composition of the active material. It is preferable to keep it. In particular, it is confirmed that the oxygen release temperature of the precursor shifts to the lower temperature side as the amount of Co contained in the sample increases. As a method for confirming the oxygen release temperature of the active material, a mixture of a coprecipitation precursor and a lithium compound may be subjected to thermogravimetric analysis (DTA-TG measurement) in order to simulate the firing reaction process. In this method, the platinum used in the sample chamber of the measuring instrument may be corroded by the Li component volatilized, and the instrument may be damaged. Therefore, a composition in which crystallization is advanced to some extent by adopting a firing temperature of about 500 ° C. in advance. Goods should be subjected to thermogravimetric analysis.

On the other hand, if the firing temperature is too low, crystallization does not proceed sufficiently and the electrode characteristics tend to deteriorate. In the present invention, when coprecipitated hydroxide is used as a precursor, the firing temperature is preferably at least 700 ° C. or higher. When coprecipitated carbonate is used as a precursor, the firing temperature is preferably at least 800 ° C. or higher. In particular, when the precursor is a coprecipitated carbonate, the optimum firing temperature tends to be lower as the amount of Co contained in the precursor is larger. Thus, by sufficiently crystallizing the crystallites constituting the primary particles, the resistance of the crystal grain boundary can be reduced and smooth lithium ion transport can be promoted.
The present inventors analyzed the half width of the diffraction peak of the active material of the present invention in detail, and in the case where the precursor is a coprecipitated hydroxide, in the sample synthesized at a temperature of less than 650 ° C. Strain remains in the lattice and can be remarkably removed by synthesizing at a temperature of 650 ° C. or higher, and when the precursor is a coprecipitated carbonate, the firing temperature is 750. In the sample synthesized at a temperature of less than 0 ° C., strain remained in the lattice, and it was confirmed that the strain could be remarkably removed by synthesis at a temperature of 750 ° C. or higher. The crystallite size was increased in proportion to the increase in the synthesis temperature. Therefore, even in the composition of the active material of the present invention, a favorable discharge capacity can be obtained by aiming at a particle having almost no lattice distortion in the system and having a sufficiently grown crystallite size. Specifically, it is preferable to employ a synthesis temperature (firing temperature) and a Li / Me ratio composition in which the strain amount affecting the lattice constant is 2% or less and the crystallite size is grown to 50 nm or more. all right. Although changes due to expansion and contraction are observed by charging and discharging by molding these as electrodes, it is preferable as an effect that the crystallite size is maintained at 30 nm or more in the charging and discharging process.

As described above, the calcination temperature is related to the oxygen release temperature of the active material, but crystallization is caused by large growth of primary particles at 900 ° C. or higher without reaching the calcination temperature at which oxygen is released from the active material. The phenomenon is seen. This can be confirmed by observing the fired active material with a scanning electron microscope (SEM). The active material synthesized through a synthesis temperature exceeding 900 ° C. has primary particles grown to 0.5 μm or more, and is in a disadvantageous state for Li ⁺ movement in the active material during the charge / discharge reaction, and has a high rate discharge performance. Decreases. The size of the primary particles is preferably less than 0.5 μm, and more preferably 0.3 μm or less.

As shown in the examples, the peak differential pore volume is affected by the calcination temperature, and the peak differential pore volume decreases as the calcination temperature increases. In order to set it to 8 mm < ³ > / (g * nm) or more, it is preferable that a calcination temperature is lower than 950 degreeC. In addition, since the peak differential pore volume increases as the firing temperature decreases, the firing temperature is set to 750 in order to keep the peak differential pore volume of the hydroxide precursor to 0.5 mm ³ / (g · nm) or less. It is preferable to be higher than ° C.
In the present invention, a lithium transition metal composite oxide having a Li / Me molar ratio (1 + α) / (1-α) of 1.2 <(1 + α) / (1-α) <1.6 is used as a positive electrode active material. In this case, the firing temperature is preferably 800 to 900 ° C. for the carbonate precursor, and preferably 800 to 950 ° C. for the hydroxide precursor.

In order for the positive electrode active material according to the present invention to have a high discharge capacity, the transition metal element constituting the lithium transition metal composite oxide is present in a portion other than the transition metal site of the layered rock salt type crystal structure. It is preferable that the ratio is small. This is because, in the precursor to be subjected to the firing step, the transition metal elements such as Co, Ni, and Mn in the precursor core particles are sufficiently uniformly distributed, and appropriate for promoting the crystallization of the active material sample. This can be achieved by selecting the conditions for the firing process. If the distribution of the transition metal in the precursor core particles subjected to the firing step is not uniform, a sufficient discharge capacity cannot be obtained. Although the reason for this is not necessarily clear, when the distribution of the transition metal in the precursor core particles to be subjected to the firing step is not uniform, the resulting lithium transition metal composite oxide has a layered rock salt type crystal structure other than the transition metal site. The present inventors speculate that this is due to the occurrence of so-called cation mixing, in which a part of the transition metal element is present at the lithium site. The same inference can be applied to the crystallization process in the firing step. If the crystallization of the active material sample is insufficient, cation mixing in the layered rock salt type crystal structure is likely to occur. When the distribution uniformity of the transition metal element is high, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane when the X-ray diffraction measurement result belongs to the space group R3-m is large. Tend. In the present invention, the intensity ratio I ₍₀₀₃₎ / I ₍₁₀₄₎ of diffraction peaks of the (003) plane and the (104) plane measured by X-ray diffraction measurement is 1.0 or more at the end of discharge and 1.75 at the end of charge. The above is preferable. If the precursor synthesis conditions and procedure are inadequate, the peak intensity ratio will be smaller and often less than 1.

The negative electrode material is not limited, and any negative electrode material that can occlude and release lithium ions may be selected. For example, titanium-based materials such as lithium titanate having a spinel crystal structure represented by Li [Li _1/3 Ti _5/3 ] O ₄ , alloy-based materials such as Si, Sb, and Sn-based lithium metal, lithium alloys (Lithium metal-containing alloys such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloys), lithium composite oxide (lithium-titanium), silicon oxide In addition, an alloy capable of inserting and extracting lithium, a carbon material (for example, graphite, hard carbon, low-temperature fired carbon, amorphous carbon, etc.) can be used.

  It is desirable that the positive electrode active material powder and the negative electrode material powder have an average particle size of 100 μm or less. In particular, the positive electrode active material powder is desirably 10 μm or less for the purpose of improving the high output characteristics of the non-aqueous electrolyte battery. In order to obtain the powder in a predetermined shape, a pulverizer or a classifier is used. For example, a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill or a sieve is used. At the time of pulverization, wet pulverization in the presence of water or an organic solvent such as hexane may be used. There is no particular limitation on the classification method, and a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

  The positive electrode active material and the negative electrode material, which are the main components of the positive electrode and the negative electrode, have been described in detail above. In addition to the main components, the positive electrode and the negative electrode include a conductive agent, a binder, a thickener, and a filler. Etc. may be contained as other constituents.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Conductive materials such as ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, and conductive ceramic material can be included as one kind or a mixture thereof. .

  Among these, as the conductive agent, acetylene black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 50% by weight, and particularly preferably 0.5% by weight to 30% by weight with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black by pulverizing into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene. Polymers having rubber elasticity such as rubber (SBR) and fluororubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight, based on the total weight of the positive electrode or the negative electrode.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefin polymers such as polypropylene and polyethylene, amorphous silica, alumina, zeolite, glass, carbon and the like are used. The addition amount of the filler is preferably 30% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the main constituents (positive electrode active material in the positive electrode, negative electrode material in the negative electrode) and other materials into a mixture and mixing with an organic solvent such as N-methylpyrrolidone or toluene or water. After that, the obtained mixed solution is applied on a current collector such as an aluminum foil or a copper foil, or is pressed and heat-treated at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. Is done. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. It is not limited.

  The nonaqueous electrolyte used for the lithium secondary battery according to the present invention is not limited, and those generally proposed for use in lithium batteries and the like can be used. Nonaqueous solvents used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; chain esters such as methyl formate, methyl acetate and methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy Ethers such as ethane, 1,4-dibutoxyethane and methyldiglyme; Nitriles such as acetonitrile and benzonitrile; Dioxolane or derivatives thereof; Ethylene sulfide, sulfolane, sultone or derivatives thereof Examples thereof include a conductor alone or a mixture of two or more thereof, but are not limited thereto.

Examples of the electrolyte salt used for the nonaqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr. , KClO ₄ , KSCN, and other inorganic ion salts containing one of lithium (Li), sodium (Na), or potassium (K), LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , ( CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C _{4 H 9) 4 NI, (} C 2 H 5) 4 N-mal ate, include _{(C 2 H 5) 4 N} -benzoate, (C 2 H 5) 4 N-pht h alate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts such as lithium dodecylbenzenesulfonate These ionic compounds can be used alone or in admixture of two or more.

Furthermore, by mixing and using LiPF ₆ or LiBF ₄ and a lithium salt having a perfluoroalkyl group such as LiN (C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further reduced. The low temperature characteristics can be further improved, and self-discharge can be suppressed, which is more desirable.

  Moreover, you may use normal temperature molten salt and an ionic liquid as a nonaqueous electrolyte.

  The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / l to 5 mol / l, more preferably 0.5 mol / l to 2 in order to reliably obtain a non-aqueous electrolyte battery having high battery characteristics. .5 mol / l.

  As the separator, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the material constituting the separator for a nonaqueous electrolyte battery include polyolefin resins typified by polyethylene and polypropylene, polyester resins typified by polyethylene terephthalate and polybutylene terephthalate, polyvinylidene fluoride, and vinylidene fluoride-hexa. Fluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, fluorine Vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene - hexafluoropropylene copolymer, vinylidene fluoride - ethylene - can be mentioned tetrafluoroethylene copolymer.

  The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

  The separator may be a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride, and an electrolyte. Use of the non-aqueous electrolyte in the gel state as described above is preferable in that it has an effect of preventing leakage.

  Furthermore, it is desirable that the separator be used in combination with the above-described porous film, non-woven fabric, or the like and a polymer gel because the liquid retention of the electrolyte is improved. That is, by forming a film in which the surface of the polyethylene microporous membrane and the microporous wall are coated with a solvophilic polymer having a thickness of several μm or less, and holding the electrolyte in the micropores of the film, Gels.

  Examples of the solvophilic polymer include polyvinylidene fluoride, an acrylate monomer having an ethylene oxide group or an ester group, an epoxy monomer, a polymer having a monomer having an isocyanate group, and the like crosslinked. The monomer can be subjected to a crosslinking reaction using a radical initiator in combination with heating or ultraviolet rays (UV), or using an actinic ray such as an electron beam (EB).

  The configuration of the lithium secondary battery of the present invention is not particularly limited, and examples thereof include a cylindrical battery having a positive electrode, a negative electrode, and a roll separator, a square battery, and a flat battery. When the lithium secondary battery of the present invention is used as a power source for an automobile such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV), a battery module (set) having a plurality of lithium secondary batteries is used. Battery).

  The lithium secondary battery of the present invention may constitute a power storage device such as an assembled battery or a battery pack. As shown in FIG. 2, the assembled battery 101 is configured by assembling a plurality of lithium secondary batteries 100. The battery pack 102 may include a plurality of assembled batteries 101.

Both the conventional positive electrode active material and the active material of the present invention can be charged / discharged when the positive electrode potential reaches around 4.5 V (vs. Li ^/ Li ⁺ ). However, depending on the type of nonaqueous electrolyte used, if the positive electrode potential during charging is too high, the nonaqueous electrolyte may be oxidized and decomposed, resulting in a decrease in battery performance. Therefore, in use, a lithium secondary battery capable of obtaining a sufficient discharge capacity even when a charging method is adopted in which the maximum potential of the positive electrode during charging is 4.3 V (vs. Li ^/ Li ⁺ ) or less. May be required. When the active material of the present invention is used, for example, 4.4 V (vs. Li ^/ Li) such that the maximum potential of the positive electrode during charging is lower than 4.5 V (vs. Li ^/ Li ⁺ ) during use. ⁺ ) Or less and 4.3 V (vs. Li ^/ Li ⁺ ) or less, even if a charging method is adopted, it is possible to take out a discharge electric quantity exceeding the capacity of the conventional positive electrode active material of about 200 mAh / g or more. Is possible.
By adopting the synthesis conditions and synthesis procedures described in the present specification, a high-performance positive electrode active material as described above can be obtained.

(Example 1)
[Production of first lithium transition metal composite oxide particles]
Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00 g) and manganese sulfate pentahydrate (65.27 g) were weighed, and all of these were dissolved in 200 ml of ion-exchanged water, and Co: Ni: Mn A 2.0 M aqueous sulfate solution having a molar ratio of 12.5: 20.0: 67.5 was prepared. On the other hand, 750 ml of ion exchange water was poured into a ₂ L reaction tank, and CO ₂ gas was bubbled for 30 minutes to dissolve CO _{2 in the} ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred at a rate of 3 ml / min while stirring the inside of the reaction vessel at a rotational speed of 700 rpm using a paddle blade equipped with a stirring motor. It was dripped. Here, during the period from the start to the end of the dropping, an aqueous solution containing 2.0 M sodium carbonate and 0.4 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 7.9 (± 0.05 ) Was controlled. After completion of the dropwise addition, stirring in the reaction vessel was continued for 20 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.

  Next, using a suction filtration device, the coprecipitated carbonate particles generated in the reaction vessel are separated, and further, washing is performed 5 times when 200 ml is washed once with ion-exchanged water. Sodium ions adhering to the particles were washed and removed under the conditions, and dried for 20 hours at 80 ° C. under normal pressure in an air atmosphere using an electric furnace. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated carbonate precursor was produced.

Add 0.970 g of lithium carbonate to 2.278 g of the coprecipitated carbonate precursor and mix well using a smoked automatic mortar, and the molar ratio of Li: (Co, Ni, Mn) is 130: 100 A powder was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), heated in air at atmospheric pressure and normal temperature to 900 ° C. over 10 hours, Firing was performed at 900 ° C. for 4 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. Thus, lithium transition metal composite oxide Li _1.13 Co _0.11 Ni _0.17 Mn _0.59 containing 2100 ppm of Na, which is the first lithium transition metal composite oxide particle having a large average particle diameter D50. Particles made of O ₂ were prepared.

[Production of second lithium transition metal composite oxide particles]
Cobalt sulfate heptahydrate (14.08 g), nickel sulfate hexahydrate (21.00 g) and manganese sulfate pentahydrate (65.27 g) were weighed, and all of these were dissolved in 200 ml of ion-exchanged water, and Co: Ni: Mn A 2.0 M aqueous sulfate solution having a molar ratio of 12.5: 20.0: 67.5 was prepared. On the other hand, 750 ml of ion exchange water was poured into a 2 L reaction tank, and Ar gas was bubbled for 30 minutes to remove dissolved oxygen in the ion exchange water. The temperature of the reaction vessel was set to 50 ° C. (± 2 ° C.), and the aqueous sulfate solution was stirred at a rate of 3 ml / min while stirring the inside of the reaction vessel at a rotational speed of 700 rpm using a paddle blade equipped with a stirring motor. It was dripped. Here, during the period from the start to the end of the dropping, an aqueous solution containing 2.0 M sodium hydroxide and 1.0 M ammonia is appropriately dropped, so that the pH in the reaction tank is always 11.5 (± 0. 05). After completion of the dropping, stirring in the reaction vessel was continued for 3 hours. After the stirring was stopped, the mixture was allowed to stand for 12 hours or more.

  Next, using a suction filtration device, the coprecipitated hydroxide particles produced in the reaction vessel are separated, and further, washing is performed 5 times when the washing with 200 ml is performed once using ion-exchanged water. Sodium ions adhering to the particles were washed and removed under the conditions, and dried for 20 hours at 80 ° C. under normal pressure in an air atmosphere using an electric furnace. Then, in order to arrange | equalize a particle size, it grind | pulverized for several minutes with the smoked automatic mortar. In this way, a coprecipitated hydroxide precursor was produced.

To 1.729 g of the coprecipitated hydroxide precursor, 1.160 g of lithium hydroxide monohydrate is added and mixed well using a smoked automatic mortar. The molar ratio of Li: (Co, Ni, Mn) is 140. : A mixed powder of 100 was prepared. Using a pellet molding machine, molding was performed at a pressure of 6 MPa to obtain pellets having a diameter of 25 mm. The amount of the mixed powder subjected to pellet molding was determined by conversion so that the mass of the assumed final product was 2 g. One pellet was placed on an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace (model number: AMF20), heated in air at atmospheric pressure and normal temperature to 900 ° C. over 10 hours, Firing was performed at 900 ° C. for 4 hours. The box-type electric furnace has internal dimensions of 10 cm in length, 20 cm in width, and 30 cm in depth, and heating wires are inserted at intervals of 20 cm in the width direction. After firing, the heater was turned off and allowed to cool naturally with the alumina boat placed in the furnace. As a result, the temperature of the furnace decreases to about 200 ° C. after 5 hours, but the subsequent temperature decrease rate is somewhat moderate. After the passage of day and night, it was confirmed that the furnace temperature was 100 ° C. or lower, and then the pellets were taken out and pulverized for several minutes in a smoked automatic mortar in order to make the particle diameter uniform. Thus, lithium transition metal composite oxide Li _1.17 Co _0.10 Ni _0.17 Mn _0.56 containing 1000 ppm of Na, which is the second lithium transition metal composite oxide particle having a small average particle diameter D50. O ₂ was produced.

The first lithium transition metal composite oxide particles and the second lithium transition metal composite oxide particles obtained as described above were mixed at a mass ratio of 8: 2, and the mixed active material according to Example 1 Was made.
It was confirmed by X-ray diffraction measurement that this lithium transition metal composite oxide had an α-NaFeO ₂ structure.

(Example 2)
In the production process of the first lithium transition metal composite oxide particles, Example 2 was performed in the same manner as in Example 1 except that the stirring continuation time in the reaction vessel after completion of dropping of the raw material aqueous solution was changed from 20 h to 5 h. Such a mixed active material was produced.

Example 3
In the production process of the first lithium transition metal composite oxide particles, Example 3 was performed in the same manner as in Example 1 except that the stirring continuation time in the reaction tank after the dropping of the raw material aqueous solution was changed from 20 h to 3 h. Such a mixed active material was produced.

(Example 4)
In the step of preparing the first lithium transition metal composite oxide particles, 1.022 g of lithium carbonate is added to 2.228 g of the prepared coprecipitated carbonate precursor, and the lithium transition metal composite oxide Li _1.17 Co _{0. A} mixed active material according to Example 4 was produced in the same manner as in Example 2 except that particles made of ₁₀ Ni _0.17 Mn _0.56 O ₂ were produced.

(Example 5)
In the step of preparing the first lithium transition metal composite oxide particles, 0.996 g of lithium carbonate is added to 2.253 g of the prepared coprecipitated carbonate precursor, and the lithium transition metal composite oxide Li _1.15 Co _{0. A} mixed active material according to Example 5 was produced in the same manner as in Example 2 except that particles made of ₁₁ Ni _0.17 Mn _0.57 O ₂ were produced.

(Example 6)
In the step of preparing the first lithium transition metal composite oxide particles, 0.943 g of lithium carbonate is added to 2.304 g of the prepared coprecipitated carbonate precursor, and the lithium transition metal composite oxide Li _1.11 Co _{0. A} mixed active material according to Example 6 was produced in the same manner as in Example 2 except that particles made of ₁₁ Ni _0.18 Mn _0.60 O ₂ were produced.

(Example 7)
In the step of preparing the second lithium transition metal composite oxide particles, 1.131 g of lithium hydroxide monohydrate was added to 1.749 g of the prepared coprecipitated hydroxide precursor, and the lithium transition metal composite oxide Li ₁ was added. _A mixed active material according to Example 7 was prepared in the same manner as in Example 2, except that particles made of _.15 Co _0.11 Ni _0.17 Mn _0.57 O ₂ were prepared.

(Example 8)
In the production process of the second lithium transition metal composite oxide particles, 1.102 g of lithium hydroxide monohydrate is added to 1.768 g of the prepared coprecipitated hydroxide precursor, and the lithium transition metal composite oxide Li ₁ is added. _{.13 A} mixed active material according to Example 8 was prepared in the same manner as in Example 2, except that particles made of Co _0.11 Ni _0.17 Mn _0.59 O ₂ were prepared.

Example 9
In the step of preparing the first lithium transition metal composite oxide particles, 1.047 g of lithium carbonate is added to 2.204 g of the prepared coprecipitated carbonate precursor, and the lithium transition metal composite oxide Li _1.18 Co _{0. 10} Ni _0.17 Mn _0.55 O ₂ was produced, the firing temperature was changed from 900 ° C. to 850 ° C., and the second lithium transition metal composite oxide particles were produced in the production process. 1.174 g of lithium hydroxide monohydrate is added to 1.720 g of the coprecipitated hydroxide precursor, and the lithium transition metal composite oxide Li _1.18 Co _0.10 Ni _0.17 Mn _0.55 O ₂ is added. A mixed active material according to Example 9 was prepared in the same manner as in Example 2 except that the resulting particles were prepared.

(Example 10)
In the step of preparing the first lithium transition metal composite oxide particles, 1.071 g of lithium carbonate is added to 2.180 g of the prepared coprecipitated carbonate precursor, and the lithium transition metal composite oxide Li _1.20 Co _{0. 10} Ni _0.16 Mn _0.54 O ₂ particles were produced, the firing temperature was changed from 900 ° C. to 800 ° C., and produced in the production process of the second lithium transition metal composite oxide particles. Lithium transition metal complex oxide Li _1.20 Co _0.10 Ni _0.16 Mn _0.54 O ₂ is added to 1.292 g of the coprecipitated hydroxide precursor, and 1.216 g of lithium hydroxide monohydrate. A mixed active material according to Example 10 was produced in the same manner as Example 2 except that the particles to be produced were produced.

(Example 11)
In the step of preparing the first lithium transition metal composite oxide particles, 1.095 g of lithium carbonate is added to 2.157 g of the prepared coprecipitated carbonate precursor, and the lithium transition metal composite oxide Li _1.21 Co _{0. 10} Ni _0.16 Mn _0.53 O ₂ particles were produced, the firing temperature was changed from 900 ° C. to 800 ° C., and produced in the production process of the second lithium transition metal composite oxide particles. Lithium transition metal composite oxide Li _1.21 Co _0.10 Ni _0.16 Mn _0.53 O ₂ is added to 1.474 g of the coprecipitated hydroxide precursor. A mixed active material according to Example 11 was produced in the same manner as in Example 2 except that the particles to be produced were produced.

(Example 12)
In the step of preparing the second lithium transition metal composite oxide particles, 1.071 g of lithium hydroxide monohydrate is added to 1.788 g of the prepared coprecipitated hydroxide precursor, and the lithium transition metal composite oxide Li ₁ is added. _.11 Co _0.11 Ni _0.18 Mn _0.60 O ₂ was produced, and the firing temperature was changed from 900 ° C. to 950 ° C. Such a mixed active material was produced.

(Example 13)
A mixed active material according to Example 13 was produced in the same manner as in Example 8, except that the firing temperature was changed from 900 ° C. to 925 ° C. in the production process of the second lithium transition metal composite oxide particles.

(Example 14)
A mixed active material according to Example 14 was produced in the same manner as in Example 7, except that the firing temperature was changed from 900 ° C. to 925 ° C. in the production process of the second lithium transition metal composite oxide particles.

(Example 15)
In the production process of the first lithium transition metal composite oxide particles, the stirring continuation time in the reaction vessel after completion of dropping of the raw material aqueous solution was changed from 20 h to 1 h, and the production of the second lithium transition metal composite oxide particles A mixed active material according to Example 15 was prepared in the same manner as in Example 1, except that the stirring continuation time in the reaction vessel after completion of dropping of the raw material aqueous solution was changed from 3 h to 2 h.

(Example 16)
In the production process of the first lithium transition metal composite oxide particles, the stirring continuation time in the reaction vessel after completion of dropping of the raw material aqueous solution was changed from 20 h to 1 h, and the production of the second lithium transition metal composite oxide particles A mixed active material according to Example 16 was produced in the same manner as in Example 1, except that the stirring continuation time in the reaction vessel after completion of dropping of the raw material aqueous solution was changed from 3 h to 1 h.

(Comparative Example 1)
In the production process of the first lithium transition metal composite oxide particles, the same procedure as in Example 1 was performed except that the stirring duration in the reaction vessel after completion of dropping of the raw material aqueous solution was changed from 20 h to 1 h. Such a mixed active material was produced.

(Comparative Example 2)
An active material according to Comparative Example 2 was produced in the same manner as in Example 2, except that only the first lithium transition metal composite oxide particles were used without mixing the second lithium transition metal composite oxide particles.

(Comparative Example 3)
The mixing according to Comparative Example 3 was performed in the same manner as in Example 2 except that the first lithium transition metal composite oxide particles prepared in Comparative Example 1 were mixed instead of the second lithium transition metal composite oxide particles. An active material was prepared.

(Comparative Example 4)
An active material according to Comparative Example 4 was produced in the same manner as in Example 1 except that only the second lithium transition metal composite oxide particles were used without mixing the first lithium transition metal composite oxide particles.

(Comparative Example 5)
The lithium transition metal produced in the same manner as in Example 1 except that in the production process of the second lithium transition metal composite oxide particles, the stirring duration in the reaction vessel after the dropping of the raw material aqueous solution was changed from 3h to 4h. The composite oxide particles were used as the first lithium transition metal composite oxide particles, and this was mixed with the second lithium transition metal composite oxide particles in the same manner as in Example 1 according to Comparative Example 5. A mixed active material was prepared.

(Comparative Example 6)
A mixed active material according to Comparative Example 6 was produced in the same manner as in Example 2 except that the firing temperature was changed from 900 ° C. to 950 ° C. in the production process of the first lithium transition metal composite oxide particles.

(Comparative Example 7)
A mixed active material according to Comparative Example 7 was produced in the same manner as in Example 2 except that the firing temperature was changed from 900 ° C. to 750 ° C. in the production process of the second lithium transition metal composite oxide particles.

(Comparative Example 8)
In the step of preparing the first lithium transition metal composite oxide particles, 1.118 g of lithium carbonate is added to 2.134 g of the prepared coprecipitated carbonate precursor, and the lithium transition metal composite oxide Li _1.23 Co _{0. The} mixed active material according to Comparative Example 8 was prepared in the same manner as in Example 2 except that particles made of ₁₀ Ni _0.15 Mn _0.52 O ₂ were prepared and the firing temperature was changed from 900 ° C. to 800 ° C. Produced.

(Comparative Example 9)
In the step of preparing the second lithium transition metal composite oxide particles, 1.040 g of lithium hydroxide monohydrate is added to 1.809 g of the prepared coprecipitated hydroxide precursor, and the lithium transition metal composite oxide Li ₁ is added. _A mixed active material according to Comparative Example 9 was prepared in the same manner as in Example 2 _{except that} particles made of _0.09 Co _0.11 Ni _0.19 Mn _0.61 O ₂ were prepared.

<Production and evaluation of lithium secondary battery>
Using each of the active materials of Examples 1 to 16 and Comparative Examples 1 to 9, lithium secondary batteries (model cells) were produced by the following procedure, and battery characteristics were evaluated.

  The positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 90: 5: 5. This mixture was kneaded and dispersed by adding N-methylpyrrolidone as a dispersion medium to prepare a coating solution having a solid content concentration of 43% by mass. In addition, about PVdF, it converted into solid mass by using the liquid by which solid content was melt | dissolved and dispersed. The coating solution is applied to an aluminum foil current collector with a thickness of 20 μm, NMP is removed by drying on a hot plate at 120 ° C., and the porosity of the positive electrode mixture layer is reduced to 35% by passing through a roll press several times. It was adjusted. In this way, a positive electrode plate having an active area of 50 mm × 30 mm was produced.

  Lithium metal was used for the counter electrode (negative electrode) in order to observe the single behavior of the positive electrode. This lithium metal was adhered to a nickel foil current collector. However, preparation was performed such that the capacity of the nonaqueous electrolyte secondary battery was sufficiently positive electrode regulated.

As the electrolytic solution, a solution obtained by dissolving LiPF ₆ in a mixed solvent having a volume ratio of EC / EMC / DMC of 6: 7: 7 so that its concentration becomes 1 mol / l was used. As the separator, a microporous membrane made of polyethylene was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) was used for the outer package. The electrode was accommodated in this exterior body so that the open ends of the positive electrode terminal, the negative electrode terminal, and the reference electrode terminal were exposed to the outside. After injecting 0.5 ml of the electrolytic solution, the fusion allowance in which the inner surfaces of the metal resin composite film face each other was hermetically sealed.

  The initial charge / discharge process of 2 cycles was implemented at 25 degreeC with respect to the nonaqueous electrolyte secondary battery produced as mentioned above. The charging was constant current constant voltage charging with a current of 0.1 CmA and a voltage of 4.6V. The charge termination condition was the time when the current value attenuated to 0.02 CmA. The discharge was a constant current discharge with a current of 0.1 CmA and a final voltage of 2.0 V. In all cycles, a 10 minute rest period was set after charging and discharging. Thus, the nonaqueous electrolyte secondary battery which concerns on an Example and a comparative example was completed.

  The completed nonaqueous electrolyte secondary battery was charged and discharged for 3 cycles. All voltage control was performed on the positive electrode potential. The conditions for this charge / discharge cycle are the same as the conditions for the initial charge / discharge step, except that the charge voltage is 4.3V. In all cycles, a 30 minute rest period was set after charging and after discharging. Next, a high rate discharge test was performed. The charging conditions of the high rate discharge test are the same as the conditions of the initial charge / discharge process, and the discharge conditions are the same as the conditions of the initial charge / discharge process except that the discharge current is changed to 1 CmA. The discharge capacity obtained at this time was defined as “1C capacity (mAh)”.

<Measurement of average particle diameter D50 and peak differential volume of lithium transition metal composite oxide particles in active material>
About the average particle diameter D50 and peak differential pore volume of the lithium transition metal composite oxide particles in the active materials of Examples 1 to 16 and Comparative Examples 1 to 9, the active material in the test battery (positive electrode plate) was collected. It was done by doing. The electrode disassembled in the discharged state was taken out, and the electrolyte solution adhering to the electrode was thoroughly washed using DMC. Thereafter, the mixture on the aluminum foil current collector (substrate) is collected, and this mixture is baked at 600 ° C. for 4 hours using the above-mentioned small electric furnace, thereby being carbon as a conductive agent and a binder. The PVdF binder was removed to obtain only the mixed active material. Thereafter, classification, mean particle diameter D50 of two different active material (mean large first lithium transition metal composite oxide particles and small average particle size D50 second lithium transition metal composite oxide particles having a particle diameter D50 ). Comparative Examples 2 and 4 were not mixed active materials.

  The particle size distribution of the first lithium transition metal composite oxide particles and the second lithium transition metal composite oxide particles separated as described above was measured according to the following conditions and procedures. Microtrac (model number: MT3000) manufactured by Nikkiso Co., Ltd. was used as the measuring device. The measurement apparatus includes an optical bench, a sample supply unit, and a computer equipped with control software. A wet cell having a laser light transmission window is installed on the optical bench. The measurement principle is a method in which a wet cell in which a dispersion liquid in which a sample to be measured is dispersed in a dispersion solvent circulates is irradiated with laser light, and the scattered light distribution from the measurement sample is converted into a particle size distribution. The dispersion is stored in a sample supply unit and circulated and supplied to a wet cell by a pump. The sample supply unit is always subjected to ultrasonic vibration. In this measurement, water was used as a dispersion solvent. Moreover, Microtrac DHS for Win98 (MT3000) was used for the measurement control software. For the “substance information” to be set and input to the measuring apparatus, 1.33 is set as the “refractive index” of the solvent, “TRANSPARENT” is selected as the “transparency”, and “non-spherical” is selected as the “spherical particle”. Was selected. Prior to sample measurement, perform “Set Zero” operation. The “Set zero” operation is an operation to subtract the influence of disturbance elements other than the scattered light from the particles (glass, dirt on the glass wall, glass irregularities, etc.) on subsequent measurements. A background operation is performed in a state where only certain water is added and only water as a dispersion solvent is circulating in the wet cell, and the background data is stored in the computer. Next, perform the “Sample LD (Sample Loading)” operation. The Sample LD operation is an operation for optimizing the sample concentration in the dispersion that is circulated and supplied to the wet cell during measurement, and manually reaches the optimum amount of the sample to be measured in the sample supply unit according to the instructions of the measurement control software. It is an operation to throw up. Subsequently, the measurement operation is performed by pressing the “Measure” button. The measurement operation is repeated twice, and the measurement result is output from the computer as the average value. The measurement results are as a particle size distribution histogram and values of D10, D50, and D90 (D10, D50, and D90 are particle sizes at which the cumulative volume in the particle size distribution of the secondary particles is 10%, 50%, and 90%, respectively) To be acquired.

For the active materials of Examples 1 to 16 and Comparative Examples 1 to 9, the measured average particle diameter D50 of the first lithium transition metal composite oxide particles and the second lithium transition metal composite oxide particles is expressed as “ particle The diameter (μm) ”is shown in Table 1.
As a result of the measurement, the first lithium transition metal composite oxide particles of Examples 1 to 16 and Comparative Examples 1 to 3 and 5 to 9 (Comparative Example 5 is from a hydroxide precursor) have an average particle diameter. D50 is 5 to 18 μm, and the second lithium transition metal composite oxide particles of Examples 1 to 16, Comparative Examples 1 and 3 to 9 (Comparative Example 3 is from a carbonate precursor) have an average particle diameter D50 was 2 to 5 μm.

  For the measurement of the peak differential pore volume, “autosorb iQ” manufactured by Quantachrome and control / analysis software “ASiQwin” were used. 1.00 g of a sample to be measured (first lithium transition metal composite oxide particles or second lithium transition metal composite oxide particles separated as described above) is placed in a measurement sample tube, and at 120 ° C. Water in the measurement sample was sufficiently removed by vacuum drying for 12 hours. Next, the adsorption side and desorption side isotherms were measured by a nitrogen gas adsorption method using liquid nitrogen within a relative pressure P / P0 (P0 = about 770 mmHg) range of 0 to 1. And pore distribution was evaluated by calculating by BJH method using the desorption side isotherm, and the peak differential pore volume was obtained.

Table 1 shows measured peak differential pore volume values of the first lithium transition metal composite oxide particles and the second lithium transition metal composite oxide particles for the active materials of Examples 1 to 16 and Comparative Examples 1 to 9. It is shown in 1. FIG. 1 shows a differential pore volume curve of the first lithium transition metal composite oxide particles and the second lithium transition metal composite oxide particles.
As a result of the measurement, the first lithium transition metal composite oxide particles of Examples 1 to 16 and Comparative Examples 1 to 3, 7 and 9 have a pore diameter of 30 to 40 nm in which the differential pore volume shows the maximum value. And the peak differential pore volume is 0.8 to 1.7 mm ³ / (g · nm), and the second lithium transition metal composite oxide particles of Examples 1 to 16 and Comparative Examples 1, 4 to 6, and 8 The pore differential diameter was in the range of 50 to 70 nm, and the peak differential pore volume was 0.3 to 0.5 mm ³ / (g · nm). The first lithium transition metal composite oxide particles of Comparative Example 5 (from the hydroxide precursor) had a pore diameter in the range of 50 to 70 nm and a peak differential pore volume of 0.3 mm ³ / (g · nm). The first lithium transition metal composite oxide particles of Comparative Example 6 and Comparative Example 8 (from the carbonate precursor) have a pore diameter in the range of 30 to 40 nm where the differential pore volume shows the maximum value. The peak differential pore volumes were 0.6 mm ³ / (g · nm) and 0.7 mm ³ / (g · nm), respectively. The second lithium transition metal composite oxide particle of Comparative Example 3 (from the carbonate precursor) has a peak differential pore volume of 1 in a pore diameter range of 30 to 40 nm where the differential pore volume shows a maximum value. 4 mm ³ / (g · nm), and the second lithium transition metal composite oxide particles of Comparative Example 7 and Comparative Example 9 (from the hydroxide precursor) have a pore diameter in the range of 50 to 70 nm. The peak differential pore volume was 0.7 mm ³ / (g · nm).

<Press workability test>
After the electrode (positive electrode plate) obtained by disassembling by the above method is washed with DMC and sufficiently dried, a 20 kN flat plate press (RIKEN hydraulic pump TYPE P-1B, press stand CDM-20M) is applied to form aluminum. The mixture peeling from the foil (current collector) was checked. When the electrode plate was bent after applying a press pressure of ² t / cm ² , the mixture was not peeled off, and the peeled plate was crossed. As a result, the mixture using the active materials of Examples 1 to 16 and Comparative Examples 4 to 6, 8, and 9 did not peel from the current collector. The mixture using the active materials of Comparative Examples 1 to 3 was peeled from the current collector.

About the active material which concerns on Examples 1-16 and Comparative Examples 1-9, average particle diameter D50 (particle diameter) , the measurement result of a peak differential pore volume, the test result of the lithium secondary battery using said active material, respectively Is shown in Table 1.

From Table 1, the differential pore volume obtained by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method has a maximum pore diameter in the range of 30 to 40 nm and the peak differential pore volume is 0.8 mm ³ / The differential pore volume obtained by the BJH method from the first lithium transition metal composite oxide particles having a large average particle diameter D50 of (g · nm) or more and the adsorption isotherm using the nitrogen gas adsorption method is the maximum value. A second lithium transition metal composite oxide particle having a small average particle diameter D50 having a peak differential pore size in the range of 50 to 70 nm and a peak differential pore volume of 0.5 mm ³ / (g · nm) or less; By using a positive electrode active material for a lithium secondary battery, the 1C capacity becomes 180 mAh / g or more and high-rate discharge performance is improved, and there is no peeling of the mixture from the current collector by a press workability test. Improved (See Examples 1 to 16).

On the other hand, even if the peak differential pore volume satisfies the requirements of the present invention, if the average particle diameter D50 of the first and second lithium transition metal composite oxide particles is the same, the 1C capacity is 180 mAh / g or more. Although the high rate discharge performance is excellent, the mixture is peeled from the current collector by the press workability test, and the press workability is poor (see Comparative Example 1).
When the Li / Me ratio is larger than 1.2 and smaller than 1.6, and only the first lithium transition metal composite oxide particles, the peak differential pores of the second lithium transition metal composite oxide particles When the volume exceeds 0.5 mm ³ / (g · nm), high-rate discharge performance is excellent, but press workability is poor (see Comparative Examples 2, 3, and 7). When the Li / Me ratio is 1.2 or less, the press workability is improved even when the peak differential pore volume of the second lithium transition metal composite oxide particles exceeds 0.5 mm ³ / (g · nm). However, the high rate discharge performance decreases (see Comparative Example 9).
In the case of only the second lithium transition metal composite oxide particles, the firing temperature is too high or the Li / Me ratio is too large, and the peak differential pore volume of the first lithium transition metal composite oxide particles is 0. When it is less than 0.8 mm ³ / (g · nm), the press workability is excellent, but the high rate discharge performance is poor (see Comparative Examples 4 to 6 and 8).

As described above, in the present invention, the peak differential pore volume is 30 to 40 nm in which the differential pore volume obtained by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method shows the maximum value, and the peak differential pore volume is Differential lithium determined by BJH method from first lithium transition metal composite oxide particles having a large average particle diameter D50 of 0.8 mm ³ / (g · nm) or more and an adsorption isotherm using a nitrogen gas adsorption method Second lithium transition metal composite oxide having a small average particle diameter D50 having a maximum pore size in the range of 50 to 70 nm and a peak differential pore volume of 0.5 mm ³ / (g · nm) or less By mixing the particles to obtain a positive electrode active material for a lithium secondary battery, the high rate discharge performance and electrode processability are remarkably improved.

  The lithium secondary battery using the positive electrode active material excellent in high rate discharge performance and electrode processability of the present invention is particularly useful as a lithium secondary battery for hybrid vehicles and electric vehicles.

Claims (3)

has alpha-NaFeO ₂ structure, the transition metal (Me) is Co, includes Ni and Mn, the molar ratio Li / Me is greater than 1 lithium (Li) to the transition metal, the average particle diameter D50 is different 2 The first lithium transition metal composite oxide particles having a large average particle diameter D50 , which are mixed active materials for lithium secondary batteries containing different types of lithium transition metal composite oxide particles, have an average particle diameter D50 of 5 μm or more. The second lithium transition metal composite oxide particles having a small average particle diameter D50 have an average particle diameter D50 of 5 μm or less, a difference between the two is at least 2 μm, and the first lithium having a large average particle diameter D50 The transition metal composite oxide particles have a pore diameter in the range of 30 to 40 nm where the differential pore volume obtained by the BJH method from the adsorption isotherm using the nitrogen gas adsorption method shows the maximum value, Differential pore volume is not less 0.8mm 3 / (g ^· nm) or more, a small second lithium transition metal composite oxide particles of said average particle diameter D50 of, BJH from an adsorption isotherm using a nitrogen gas adsorption method Lithium secondary characterized in that the differential pore volume obtained by the method has a maximum pore diameter in the range of 50 to 70 nm and the peak differential pore volume is 0.5 mm ³ / (g · nm) or less. Mixed active material for batteries. The electrode for lithium secondary batteries containing the mixed active material for lithium secondary batteries of Claim 1 . A lithium secondary battery comprising the electrode for a lithium secondary battery according to claim 2 .

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