JP6601500B2 - Positive electrode material, method for producing the same, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a positive electrode material for a lithium ion secondary battery, a manufacturing method thereof, and a lithium ion secondary battery including a positive electrode including the positive electrode material.

  In recent years, due to concerns about the prevention of global warming and the depletion of fossil fuels, there are high expectations for electric vehicles that require less energy for driving and power generation systems that use natural energy such as sunlight and wind power. However, these technologies have the following technical problems, which hinders their spread.

  In an electric vehicle, the energy density of the driving battery is low, and the traveling distance by one charge tends to be shorter than that of a normal vehicle. On the other hand, a power generation system using natural energy has a large fluctuation in the amount of power generation, requires a large capacity battery for leveling the output, and tends to be a factor of high cost. In any technique, in order to solve the above-described problems, a secondary battery having a low energy density and a high energy density is required.

  For example, lithium ion secondary batteries have higher energy density than secondary batteries such as nickel metal hydride batteries and lead batteries, and are expected to be applied to batteries for driving electric vehicles and power storage systems. However, in order to meet the demand for batteries for electric vehicles and power storage systems, it is necessary to further increase the energy density of lithium ion secondary batteries. For this purpose, it is necessary to increase the energy density of the positive electrode and the negative electrode of the lithium ion secondary battery.

As a positive electrode material constituting the positive electrode of the lithium ion secondary battery, a material having a layered structure attributed to R-3m and represented by a composition formula LiMO ₂ (a layered structure compound, M is a metal element other than Li) ) Is widely used. In the case where a large amount of Ni is contained as the metal element M, the capacity tends to be improved as the ratio of Ni is higher. Particularly, when the ratio of Ni in the metal element M exceeds 70 atomic%, the capacity exceeds 180 Ah / kg. A reversible capacity can be obtained, and the energy density per weight can be improved. Furthermore, in order to improve the energy density per volume, the electrode density of the positive electrode is important.

In the lithium ion secondary battery described in Patent Document 1, for example, as described in claim 1, the positive electrode mixture layer included in the positive electrode includes a mixture of the first active material and the second active material. . The first active material includes secondary particles P1 having an average particle diameter D1, and the secondary particles P1 are a sintered body of a plurality of primary particles p1, and the crushing strength of the secondary particles P1 is 85 Mpa or more. The second active material includes secondary particles P2 having an average particle diameter D2, where D2 <D1, and the secondary particles P2 are a sintered body of a plurality of primary particles p2. The active material density of the positive electrode mixture layer is 3.65 g / cm ³ or more.

  In the positive electrode active material powder for a lithium ion secondary battery described in Patent Document 2, for example, as described in claim 1, a large number of fine particles of a lithium composite oxide represented by a predetermined general formula are aggregated. The formed first granular powder having an average particle diameter D50 of 3 to 15 μm and a compressive fracture strength of 50 Mpa or more and a second granular powder having a compressive fracture strength of less than 40 Mpa are used as the first granular powder. / The second granular powder contains 50/50 to 90/10 by weight.

JP 2013-65468 A International Publication No. 2005/020354

  Patent Document 1 describes that, for example, claim 3 satisfies 20 μm ≦ D1 ≦ 35 μm, and for example, claim 4 describes that 4 μm ≦ D2 ≦ 8 μm is satisfied. However, since the difference between D1 and D2 is excessive, the life characteristics of the lithium ion secondary battery may be deteriorated. Further, as seen in FIG. 3, since the secondary particles P1 having a large average particle diameter D1 are cracked, it is considered that the crushing strength of the secondary particles P2 is excessive. The cracking of the secondary particles P1 causes an increase in resistance and a decrease in capacity due to the charge / discharge cycle of the lithium ion secondary battery.

In Patent Document 2, the second granular powder having a low compressive fracture strength is broken and refined, so that the refined second granular powder is press-fitted into the gaps of the first granule to achieve high density. It is. As described above, the destruction of the granular powder causes an increase in resistance and a decrease in capacity due to the charge / discharge cycle of the lithium ion secondary battery.
In the positive electrode active material powder described in Patent Document 2, the difference between the average particle diameter D50 of the first granular powder and the average particle diameter D50 of the second granular powder is too small. Therefore, it is difficult to increase the density of the positive electrode mixture layer so as to achieve an active material density of 3.65 g / cm ³ or more without breaking the granular powder.

  The present invention has been made in view of the above problems, and a positive electrode material capable of achieving both high energy density and high cycle characteristics of a lithium ion secondary battery, a manufacturing method thereof, and a positive electrode including the positive electrode material. An object of the present invention is to provide a lithium ion secondary battery provided.

In order to achieve the above object, the positive electrode material of the present invention comprises:
Including first active material particles and second active material particles,
The first active material particles and the second active material particles are Li compounds having a layered structure in which the Ni concentration in the metal element other than Li exceeds 70 atomic%,
The weight W1 of the first active material particles is larger than the weight W2 of the second active material particles,
The average particle diameter D1 of the first active material particles is larger than the average particle diameter D2 of the second active material particles,
The particle strength St1 of the first active material particles is higher than the particle strength St2 of the second active material particles,
The average particle diameter D _ave of the mixture of the first active material particles and the second active material particles satisfies the inequality: 0.88> (D1-D2) / D _ave > 0.50.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode material which can make high energy density and high cycle characteristics of a lithium ion secondary battery compatible can be provided.

1 is a schematic cross-sectional view of a positive electrode material according to an embodiment of the present invention. The flowchart which shows each process of the manufacturing method of the positive electrode material which concerns on embodiment of this invention. 1 is a schematic partial cross-sectional view of a lithium ion secondary battery according to an embodiment of the present invention. The horizontal axis is (D1-D2) / D _ave , and the vertical axis is the resistance increase rate and electrode density. A graph with the horizontal axis representing electrode density and the vertical axis representing resistance increase rate.

  Hereinafter, embodiments of a positive electrode material, a manufacturing method thereof, and a lithium ion secondary battery of the present invention will be described in detail with reference to the drawings.

(Positive electrode material)
FIG. 1 is a schematic cross-sectional view of a positive electrode material 10 according to an embodiment of the present invention.

The positive electrode material 10 of the present embodiment includes first active material particles 11 and second active material particles 12 that are Li compounds having a layered structure in which the Ni concentration in a metal element other than Li exceeds 70 atomic%. The Li compound constituting the first active material particle 11 and the second active material particle 12 can be represented by the following composition formula (1), for example.
_{Li 1 + a Ni b Mn c} Co d M1 e O 2 + α ... (1)

  In the composition formula (1), M1 is a metal element other than Li, Ni, Mn, and Co, and −0.03 ≦ a ≦ 0.11, 0.7 <b <1.0, 0 ≦ c <. 0.3, 0 <d <0.3, 0 ≦ e <0.1, b + c + d + e = 1, and −0.1 <α <0.1 are satisfied. As the metal element M1, various elements such as B, Al, Ti, V, Zr, Nb, Mo, and W can be used. The first active material particles and the second active material particles may be provided with various coatings such as M1 oxides such as Al, Ti, V, Zr, Nb, and Mo, and Li oxides.

A in said composition formula (1) is the stoichiometric ratio of active material 10 (LiMO ₂₎ represented by LiMO ₂ represents the excess or deficiency of Li from (Li: M: O = 1 :: 1 2) Yes. As the amount of Li increases, the valence of the transition metal before charging increases, and the rate of change in the valence of the transition metal during Li desorption is reduced, so that the charge / discharge cycle characteristics are improved. On the other hand, the larger the amount of Li, the lower the charge / discharge capacity of the layered positive electrode active material. Therefore, the range of a is preferably −0.03 or more and 0.11 or less, and more preferably 0.0 or more and 0.06 or less. If a is -0.03 or more, the crystal structure change in a charged state can be suppressed by a small amount of cation mixing. Moreover, if a is 0.11 or less, sufficient charge compensation due to a change in the valence of the transition metal can be secured, and both high capacity and high charge / discharge cycle characteristics can be achieved.

  When Ni, Co, or Mn is used as the transition metal in the composition formula (1), the Li insertion / desorption potential is as high as 3 V or more, and a high charge / discharge capacity can be obtained. In the composition formula (1), b is the Ni content. b is preferably more than 0.7 and less than 1.0. The higher the b, the Ni content, the higher the capacity. C in the composition formula (1) is the content of Mn. c is preferably 0 or more and less than 0.3. The more c, the Mn content, the more stable the crystal structure and the better the charge / discharge cycle characteristics. On the other hand, when the valence of Mn is tetravalent, it does not contribute to charging / discharging, so Mn may not be included. In the composition formula (1), d is the Co content. d is preferably greater than 0 and less than 0.3. As d, which is the Co content, increases, as in the case where c, which is the Mn content, increases, the crystal structure is stabilized and the charge / discharge cycle characteristics are improved.

M1 in the composition formula (1) can be various elements such as B, Al, Ti, V, Zr, Nb, Mo, and W, and e is the content of these elements. e can be 0 or more and less than 0.1. In the composition formula (1), the electrochemical activity of the positive electrode material 10 can be ensured by containing one or more elements selected from the group consisting of Ni, Co, and Mn as metal elements. Further, by substituting these transition metal sites with various elements such as B, Al, Ti, V, Zr, Nb, Mo, and W as elements of M1, the stability of the crystal structure and the layered positive electrode active material Electrochemical characteristics (cycle characteristics, etc.) can be improved.
The first active material particles and the second active material particles may have the same composition or different compositions.

  The first active material particles 11 and the second active material particles 12 constituting the positive electrode material 10 include M1, which is a metal element other than Li, Ni, Mn, and Co, such as Al, Ti, V, Zr, Nb, and Mo. Various coatings such as oxide or Li oxide may be provided. Since the first active material particles 11 and the second active material particles 12 have such a coating, the contact between the first active material particles 11 and the second active material particles 12 and the electrolytic solution is suppressed, and the lithium ion secondary It is possible to suppress an increase in resistance and a decrease in capacity accompanying the charge / discharge cycle of the battery.

  The weight W1 of the powder of the first active material particles 11 included in the positive electrode material 10 is larger than the weight W2 of the powder of the second active material particles 12 included in the positive electrode material 10. That is, the weight ratio W1 / W2 between the weight W1 of the powder of the first active material particles 11 and the weight W2 of the powder of the second active material particles 12 included in the positive electrode material 10 is greater than 1. More specifically, the weight ratio W1 / W2 can be selected between 70/30 and 95/5, for example. If it is the range of this weight ratio, the 2nd active material particle 12 with a small particle size will enter into the clearance gap between the 1st active material particles 11 with a large particle size, and it will become easy to raise a density.

  By the way, the first active material particles 11 and the second active material particles 12 included in the positive electrode material 10 are preferably secondary particles in which a plurality of primary particles are bonded (more practically aggregated). Here, the primary particle is a particle having no grain boundary, and is a fine particle constituting a secondary particle by aggregation or bonding of a plurality of particles.

  The average particle diameter D1 of the first active material particles 11 is larger than the average particle diameter D2 of the second active material particles 12. The average particle diameter D1 of the first active material particles 11 is preferably 6 μm or more from the viewpoint of increasing the density of the positive electrode mixture layer. Further, even when the lithium ion secondary battery charges and discharges at a high rate, the average particle diameter D1 of the first active material particles 11 is used in order to use the portion near the center of the first active material particles 11 as a reaction field. Is preferably less than 20 μm, and preferably 15 μm or less. From these viewpoints, a more preferable range of the average particle diameter D1 of the first active material particles 11 is, for example, 8 μm or more and 13 μm or less.

  Further, (D1-D2) is preferably more than 2 and less than 15. When (D1-D2) is 2 or less, the particle size difference between the first active material particles 11 and the second active material particles 12 is small, and it is difficult to achieve high density. On the other hand, when (D1-D2) is 15 or more, the difference in particle size between the first active material particles 11 and the second active material particles 12 is too large, and the first necessary for filling the gap between the first active material particles 11 The amount of the two active material particles 12 becomes very large. In general, the smaller the particle size, the lower the bulk density. Therefore, if the amount of the small particle size is too large, the density is difficult to increase even if the gap is filled. A preferred range of (D1-D2) is 3 or more and 12 or less.

  The average particle diameters D1 and D2 of the first active material particles 11 and the second active material particles 12 can be measured by, for example, a particle size distribution measuring apparatus using a laser diffraction / scattering method. The average particle diameters D1 and D2 of the first active material particles 11 and the second active material particles 12 are particle diameters at which the volume-based integrated distribution is 50%.

  The particle strength St1 of the first active material particles 11 is higher than the particle strength St2 of the second active material particles 12. The particle strength St1 of the first active material particles 11 and the particle strength St2 of the second active material particles 12 are both preferably 40 MPa or more from the viewpoint of suppressing particle cracking due to stress during electrode fabrication. Furthermore, the particle strength St1 of the first active material particles 11 is preferably 60 MPa or more. By doing so, even when strong pressure is applied in the molding process described later, the particle strength of the first active material particles having a high ratio is high, so that the particles are less likely to be cracked, and charging / discharging of the lithium ion secondary battery It is possible to suppress an increase in resistance and a decrease in capacity due to the cycle.

The particle strength St1 of the first active material particles 11 and the particle strength St2 of the second active material particles 12 can be obtained, for example, by a compression test. The compression test can be performed using, for example, a micro compression tester MCT-W201 manufactured by Shimadzu Corporation. The particle strength St [MPa] per secondary particle obtained by a compression test using a micro compression tester is expressed by the following formula (2) using the test force P [N] and the particle size d [mm]. Can be represented by
St = 2.8P / πd ² (2)

  As is clear from the equation (2), the particle strength St depends on the particle size d. Therefore, the particle strength St1 of the first active material particle 11 and the particle strength St2 of the second active material particle 12 are measured by selecting five particles within ± 20% of the average particle diameters D1 and D2, respectively. The average value of the obtained particle strength St can be obtained.

Further, the particle strength St1 of the first active material particles 11 and the particle strength St2 of the second active material particles 12 can be obtained by measuring Vickers hardness as another method. Vickers hardness can be measured using, for example, a micro Vickers hardness measurement tester HM-210A manufactured by Mitutoyo Corporation. The particle strength St [kgf / mm ² ] measured by the micro Vickers hardness tester is expressed by the following formula (3) using the load F [kgf] and the diagonal length L [mm] of the indentation. Can do.
St = 1.854 F / L ² (3)

The average particle diameter D _ave of the mixed powder of the first active material particles 11 and the second active material particles 12 contained in the positive electrode material 10 satisfies the following inequality (4), and more preferably, the following inequality (5 ) Is satisfied. That is, the difference (D1-D2) between the average particle diameter D1 of the first active material particles 11 and the average particle diameter D2 of the second active material particles 12 is the powder of the first active material particles 11 and the second active material particles. The average particle diameter D _ave of the mixed powder obtained by mixing 12 powders is within a certain range.
0.88> (D1-D2) / D _ave > 0.50 (4)
0.75> (D1-D2) / D _ave > 0.55 (5)

The average particle diameter D _ave of the mixed powder of the powder of the first active material particles 11 and the second active material particles 12 is a particle diameter (10% particles with a volume-based integrated distribution of 10% from the viewpoint of easy handling. The diameter) is desirably 1 μm or more, and the 90% particle diameter is desirably 20 μm or less. The average particle diameter D _ave can be measured by, for example, a particle size distribution measuring apparatus using a laser diffraction / scattering method, or can be calculated by image analysis of a cross section of the positive electrode.

The specific surface area of the mixed powder of the powders of the first active material particles 11 and the second active material particles 12 contained in the positive electrode material 10 is 2.0 m ² / g or less from the viewpoint of suppressing a side reaction of the electrolytic solution. Desirably, 1.0 m ² / g or less is further desirable. On the other hand, from the viewpoint of securing the charge / discharge reaction field and reducing the resistance, the specific surface area of the mixed powder is preferably 0.1 m ² / g or more.

  Hereinafter, the operation and effect of the positive electrode material 10 of the present embodiment will be described.

  As a method for improving the density of the positive electrode mixture layer that is a part of the positive electrode of the lithium ion secondary battery, there are a method for increasing the ratio of the positive electrode material in the positive electrode mixture layer and a method for controlling the particle size distribution of the positive electrode material. It is common. However, when the ratio of the positive electrode material contained in the positive electrode mixture layer is increased, the ratio of the conductive agent and the binder is decreased, the conductivity is decreased and the binding property is decreased, and the positive electrode resistance is increased. Become.

  In addition, when the particle size distribution of the positive electrode material is simply controlled, if the positive electrode mixture layer is pressed at a high pressure during the production of the positive electrode, a large particle having a relatively large particle size is loaded and the large particle is likely to break. Become. When the large-diameter particles break, the surface newly appearing due to the cracking of the particles comes into contact with the electrolytic solution, and promotes the decomposition of the electrolytic solution. Furthermore, a decomposition product of the electrolyte is deposited on the surface newly appearing due to the cracking of the particles. Such a decomposition of the electrolytic solution and a coating on the particle surface due to the deposition of decomposition products cause an increase in resistance and a decrease in capacity due to a charge / discharge cycle of the lithium ion secondary battery.

Here, as described above, the positive electrode material 10 of the present embodiment includes the first active material particle 11 and the second active material, which are Li compounds having a layered structure in which the Ni concentration in the metal element other than Li exceeds 70 atomic%. It is a positive electrode material for a lithium ion secondary battery including a mixed powder of particles 12. The weight W1 of the powder of the first active material particles 11 contained in the positive electrode material 10 is larger than the weight W2 of the powder of the second active material particles 12. The average particle diameter D1 of the first active material particles 11 is larger than the average particle diameter D2 of the second active material particles 12. Further, the particle strength St1 of the first active material particles 11 is higher than the particle strength St2 of the second active material particles 12. Furthermore, the average particle diameter D _ave of the mixed powder of the first active material particles 11 and the second active material particles 12 satisfies the inequality (4) or (5).

  Thereby, when forming the positive mix layer of the positive electrode of a lithium ion secondary battery using the positive electrode material 10, the crack of the 1st active material particle 11 can be suppressed and a positive mix layer can be densified. And high cycle characteristics of the lithium ion secondary battery can be obtained.

  More specifically, the positive electrode material 10 of the present embodiment satisfies the inequality (4) or (5), so that the first active material particles 11 having a large particle size and the second active material particles 12 having a small particle size are used. A sufficient particle size difference can be ensured. Therefore, it is easy to increase the density of the positive electrode mixture layer containing the mixed powder of these particles by pressing. Furthermore, since the first active material particles 11 having a large particle size have a higher particle strength than the second active material particles 12 having a small particle size, the positive electrode material mixture layer containing the positive electrode material 10 is pressed during the production of the positive electrode. Then, the first active material particles 11 having a large particle size are pushed and crushed, and the second active material particles 12 having a small particle strength are easily cracked, and the first active material having a large particle size Cracks of the particles 11 are suppressed.

  Therefore, when the positive electrode mixture layer including the positive electrode material 10 is pressed during the production of the positive electrode, the ratio of the surface newly appearing due to the cracking of the first active material particles 11 or the second active material particles 12 is smaller than the conventional one. . Thereby, the decomposition of the electrolytic solution and the formation of a film due to the deposition of the decomposition product on the first active material particles 11 or the second active material particles 12 are suppressed, and the resistance increase accompanying the charge / discharge cycle of the lithium ion secondary battery Capacity reduction is suppressed. Therefore, according to the positive electrode material 10 of the present embodiment, it is possible to achieve both high energy density and high cycle characteristics of the lithium ion secondary battery.

On the other hand, the difference (D1-D2) between the average particle diameter D1 of the powder of the first active material particles 11 and the average particle diameter D2 of the powder of the second active material particles 12, and the average particle diameter D _ave of these mixed powders, Even when the ratio (D1-D2) / D _ave is 0.88 or more, that is, 0.88 ≦ (D1-D2) / D _ave , the positive electrode mixture layer can be densified. However, the specific surface area of the mixed powder of the powder of the first active material particles 11 and the powder of the second active material particles 12 becomes excessive, the decomposition of the electrolytic solution is promoted, and the resistance accompanying the charge / discharge cycle of the lithium ion secondary battery There is a risk of increase or capacity decrease.

Further, the difference (D1-D2) between the average particle diameter D1 of the powder of the first active material particles 11 and the average particle diameter D2 of the powder of the second active material particles 12, and the average particle diameter D _ave of these mixed powders, When the ratio of (D1-D2) / D _ave is 0.5 or less, that is, (D1-D2) / D _ave ≦ 0.50, the particle size of the first active material particles 11 and the second active material particles 12 The difference becomes too small, and it is difficult to increase the density of the positive electrode mixture layer, which may reduce the energy density of the lithium ion secondary battery.

(Method for producing positive electrode material)
Hereinafter, an embodiment of a method for producing a positive electrode material of the present invention will be described with reference to FIG. FIG. 2 is a flowchart showing each step of the method for producing the positive electrode material of the present embodiment.

  The positive electrode material manufacturing method of the present embodiment includes, for example, a pulverizing and mixing step S1, a granulating step S2, a firing step S3, and a powder mixing step S4.

  In the pulverization and mixing step S1, a raw material containing a metal element other than Li and a lithium raw material containing 80% by mass or more of lithium carbonate are pulverized and mixed to obtain a mixture. As raw materials containing metal elements other than Li, carbonates, hydroxides, oxyhydroxides, acetates, citrates, oxides, etc., from compounds composed of metal elements and C, H, O, N It can be selected appropriately. Carbonates and hydroxides are particularly desirable from the viewpoint of ease of pulverization and the amount of gas released after thermal decomposition.

  In the pulverization and mixing step S1, various methods such as a ball mill, a jet mill, and a rod mill can be used. Both a wet method of pulverizing in a liquid such as water and a dry method not using a liquid can be used. From the viewpoint of preparing a pulverized mixed powder having a small particle size, a wet method is desirable. That is, in the pulverization and mixing step S1, the mixture can be made into a slurry by a wet method.

  In the granulation step S2, a plurality of particles constituting the mixture are combined (more practically aggregated), the first active material particle precursor having a relatively large average particle size, and the relatively small average particle size. The second active material particle precursor is granulated individually. In the granulation step S2, for example, it is preferable to granulate a second active material particle precursor having an average particle size of 1 μm or more. Here, when the average particle size is less than 1 μm, there is a high possibility that non-granulated primary particles that are not aggregated with other primary particles are present, and the binder is used in the mixture adjustment step when producing the positive electrode described later. Is required in large quantities, and the positive electrode mixture layer is peeled off from the positive electrode current collector in the molding process. The first active material particle precursor and the second active material particle precursor are secondary particles formed by aggregating or bonding a plurality of primary particles.

  In the granulation step S2, a spray drying method is employed in which the mixture of the slurry in the pulverization and mixing step S1 is sprayed from a nozzle and dried to granulate the first active material particle precursor and the second active material particle precursor. be able to. As the spraying method, various methods such as a two-fluid nozzle, a four-fluid nozzle, and a disk type can be adopted. By adopting a spray drying method and adjusting or controlling the spray pressure, slurry spray amount, and drying temperature, the average particle diameter and particle strength of the first active material particles 11 and the second active material particles 12 contained in the positive electrode material 10 are controlled. Alternatively, the porosity can be controlled.

  For example, the average particle diameters of the first active material particles 11 and the second active material particles 12 can be changed depending on the slurry spray pressure, the slurry spray amount, the slurry concentration and the slurry viscosity, or by appropriately combining these conditions. . Specifically, the average particle size can be increased by increasing the slurry spray pressure, increasing the slurry spray amount, increasing the slurry concentration, and increasing the slurry viscosity.

  Further, the particle strength of the first active material particles 11 and the second active material particles can be changed by adjusting the viscosity of the slurry, for example. Specifically, the porosity of the first active material particles 11 and the second active material particles 12 can be increased or decreased by adjusting the viscosity of the slurry. Increasing the viscosity of the slurry decreases the porosity. Here, the first active material particles 11 and the second active material particles 12 tend to increase in particle strength as the porosity decreases. Therefore, by increasing the slurry viscosity, the porosity is reduced, and as a result, the particle strength can be increased.

  In the firing step S3, the first active material particle precursor and the second active material particle precursor are fired at 650 ° C. or more and 900 ° C. or less, respectively. Get powder. The firing temperature of the first active material particle precursor and the second active material particle precursor may be 850 ° C. or less.

  The firing step S3 can be performed by various methods such as a batch method and a continuous method. The firing step S3 is preferably performed in an oxidizing atmosphere, and particularly preferably performed in an oxygen atmosphere. From the viewpoint of discharging the raw material containing the metal element and the gas generated from the lithium raw material and supplying sufficient oxygen to the pulverized mixed powder, it is preferable to flow the gas during the firing step S3.

  The appropriate firing temperature in the firing step S3 varies depending on the composition and density of the pulverized mixed powder. Therefore, the firing temperature can be appropriately set in consideration of the composition of the pulverized mixed powder, powder physical properties, and the like. Specifically, as described above, the firing temperature can be in the range of 650 ° C. or higher and 900 ° C. or lower. A more preferable range of the firing temperature is 740 ° C. or more and less than 860 ° C. As the firing temperature increases, the particle strength tends to increase.

When the firing temperature is lower than the appropriate temperature, the reaction between the lithium raw material and the metal element becomes insufficient, and the amount of Li in the first active material particles 11 and the second active material particles 12 is decreased, and cation mixing is increased. Occur. Also, if the firing temperature is higher than the proper sintering temperature, decomposition of the first active material particles 11 and the second active material particles 12 occurs, Li 2 _O is produced and the moisture of the Li 2 _O is in the air To produce lithium hydroxide. In this case, the amount of lithium hydroxide increases, which is not preferable. Further, in this case, the grain growth proceeds and there is a possibility that the high-capacity positive electrode material 10 cannot be obtained.

  In the powder mixing step S4, the weight W1 of the powder of the first active material particles 11 is larger than the weight W2 of the powder of the second active material particles 12, and the inequality (4) or (5) is satisfied. The mixing ratio of the powder of the first active material particles 11 and the powder of the second active material particles 12 is set. By the above, cracking of the first active material particles 11 can be suppressed, the positive electrode mixture layer can be densified, and both high energy density and high cycle characteristics of the lithium ion secondary battery can be achieved. The positive electrode material 10 described above can be manufactured.

  Moreover, in the manufacturing method of the positive electrode material of the present embodiment, lithium carbonate can be used as the lithium raw material in order to suppress the residual lithium hydroxide. When the ratio of Ni in a metal element other than Li is 70 atomic% or less, it is common to use lithium carbonate as a lithium raw material. However, when the ratio of Ni in the metal element other than Li is greater than 70 atomic%, the firing temperature is 650 ° C. or higher and 900 ° C. or lower, which is lower than the general firing temperature, which is close to the melting point of lithium carbonate, 723 ° C. It becomes temperature. Therefore, a reaction for generating a positive electrode active material occurs before diffusion of lithium due to melting of lithium carbonate, which may result in non-uniform crystals.

  Therefore, conventionally, lithium hydroxide having a lower melting point has been generally used in order to obtain a uniform active material by utilizing diffusion of lithium by melting. On the other hand, the first active material particles and the second active material particles included in the positive electrode material 10 of the present embodiment are prepared in advance by using a lithium raw material containing 80% by mass or more of lithium carbonate and a raw material containing a metal element other than Li. It can be produced by grinding and mixing. Thereby, the mixed state of metal elements other than Li and Li becomes uniform even in a region of 1 μm or less, and as a result, a uniform positive electrode material 10 can be obtained.

(Lithium ion secondary battery)
Hereinafter, an embodiment of the lithium ion secondary battery of the present invention will be described with reference to FIG. FIG. 3 is a partial cross-sectional view showing a schematic configuration of the secondary battery 100 according to the embodiment of the present invention. Although the details will be described later, the secondary battery 100 of the present embodiment is characterized by including the positive electrode 111 including the positive electrode material 10 described above.

  The secondary battery 100 of the present embodiment is, for example, a cylindrical lithium ion secondary battery, and has a bottomed cylindrical battery can 101 that contains a non-aqueous electrolyte, and a winding that is accommodated in the battery can 101. An electrode group 110 and a disk-shaped battery lid 102 that seals the upper opening of the battery can 101 are provided. The battery can 101 and the battery lid 102 are made of, for example, a metal material such as aluminum, and the battery lid 102 is fixed to the battery can 101 by caulking or the like via a sealing material 106 made of an insulating resin material. The battery cans 101 are sealed by the battery lid 102 and are electrically insulated from each other. Note that the shape of the secondary battery 100 is not limited to a cylindrical shape, and other arbitrary shapes such as a flat shape, a square shape, a coin shape, a button shape, and a laminate sheet shape can be adopted.

  The wound electrode group 110 is manufactured by winding a long strip-like positive electrode 111 and a negative electrode 112 facing each other with a long strip-like separator 113 around a winding center axis. In the wound electrode group 110, the positive electrode current collector 111 a is electrically connected to the battery lid 102 via the positive electrode lead piece 103, and the negative electrode current collector 112 a is electrically connected to the bottom of the battery can 101 via the negative electrode lead piece 104. Connected. An insulating plate 105 is disposed between the wound electrode group 110 and the battery lid 102 and between the wound electrode group 110 and the bottom of the battery can 101 to prevent a short circuit. The positive electrode lead piece 103 and the negative electrode lead piece 104 are members for current extraction made of the same material as the positive electrode current collector 111a and the negative electrode current collector 112a, respectively, and the positive electrode current collector 111a and the negative electrode current collector, respectively. 112a is joined by spot welding or ultrasonic pressure welding.

  The positive electrode 111 of this embodiment includes a positive electrode current collector 111a and a positive electrode mixture layer 111b formed on the surface of the positive electrode current collector 111a. As the positive electrode current collector 111a, for example, a metal foil such as aluminum or an aluminum alloy, an expanded metal, a punching metal, or the like can be used. The metal foil can have a thickness of, for example, about 8 μm to 30 μm. The positive electrode mixture layer 111b contains the positive electrode material 10 shown in FIG. The positive electrode mixture layer 111b may include a conductive material, a binder, and the like.

  The negative electrode 112 includes a negative electrode current collector 112a and a negative electrode mixture layer 112b formed on the surface of the negative electrode current collector 112a. As the negative electrode current collector 112a, metal foil such as copper or copper alloy, nickel or nickel alloy, expanded metal, punching metal, or the like can be used. The metal foil can have a thickness of, for example, about 5 μm or more and 20 μm or less. The negative electrode mixture layer 112b contains a negative electrode active material used in a general lithium ion secondary battery. The negative electrode mixture layer 112b may include a conductive material, a binder, and the like.

  The negative electrode 112 preferably has a low discharge potential.

  As the negative electrode active material, for example, one or more of a carbon material, a metal material, a metal oxide material, and the like can be used. As the carbon material, graphites such as natural graphite and artificial graphite, carbides such as coke and pitch, amorphous carbon, carbon fiber, and the like can be used. Further, as the metal material, lithium, silicon, tin, aluminum, indium, gallium, magnesium and alloys thereof, and as the metal oxide material, a metal oxide containing tin, silicon, lithium, titanium, or the like is used. it can.

The material of the separator 113 may be a material that has an insulating property capable of preventing a short circuit across the positive electrode 111 and the negative electrode 112 and an ionic conductivity through which lithium ions (Li ⁺ ) pass and does not dissolve in the electrolytic solution. There is no particular limitation. For example, a polyolefin resin such as polyethylene, polypropylene, or a polyethylene-polypropylene copolymer, a microporous film such as a polyamide resin or an aramid resin, a nonwoven fabric, or the like can be used as the separator 113.

  The positive electrode 111 and the negative electrode 112 can be manufactured through, for example, a mixture preparation step, a mixture coating step, and a molding step. In the mixture preparation step, for example, the positive electrode material 10 or the negative electrode active material is stirred and mixed with a solution containing a conductive material and a binder, for example, using a stirring means such as a planetary mixer, a disper mixer, and a rotation / revolution mixer. Homogenize to prepare a mixture slurry.

  As the conductive material, a conductive material used in a general lithium ion secondary battery can be used. Specifically, for example, carbon particles such as graphite powder, acetylene black, furnace black, thermal black, and channel black, carbon fibers, and the like can be used as the conductive material. As the conductive material, for example, an amount of about 1% by mass to about 10% by mass with respect to the total mass of the mixture can be used.

  As the binder, a binder used in a general lithium ion secondary battery can be used. Specifically, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber, carboxymethylcellulose, polyacrylonitrile, modified polyacrylonitrile, and the like can be used as the binder. For example, the binder can be used in an amount of about 1% by mass to about 10% by mass with respect to the total mass of the mixture, more preferably about 5% by mass with respect to the total mass of the mixture.

  As the solvent of the solution, N-methylpyrrolidone, water, N, N-dimethylformamide, N, N-dimethylacetamide, methanol, ethanol, propanol, isopropanol, ethylene glycol, diethylene glycol, glycerin depending on the type of binder. , Dimethyl sulfoxide, tetrahydrofuran and the like.

  In the mixture coating process, first, the mixture slurry containing the positive electrode material 10 prepared in the mixture preparation process and the mixture slurry containing the negative electrode active material are applied to, for example, a bar coater, a doctor blade, a roll transfer machine, or the like. By the means, it apply | coats on the surface of the positive electrode collector 111a and the negative electrode collector 112a, respectively. Next, the positive electrode current collector 111a and the negative electrode current collector 112a coated with the mixture slurry are each heat-treated to volatilize or evaporate the solvent of the solution contained in the mixture slurry, thereby removing the positive electrode current collector. A positive electrode mixture layer 111b and a negative electrode mixture layer 112b are formed on the surfaces of 111a and the negative electrode current collector 112a, respectively.

  In the molding step, first, the positive electrode mixture layer 111b formed on the surface of the positive electrode current collector 111a and the negative electrode mixture layer 112b formed on the surface of the negative electrode current collector 112a are subjected to, for example, a roll press or the like. Using pressure means, each is press-molded by hot press. Thereby, the filling property of the mixture is improved, the thickness of the positive electrode mixture layer 111b is, for example, about 15 μm or more and 300 μm or less, and the thickness of the negative electrode mixture layer 112b is, for example, about 10 μm or more and 150 μm or less. Can be.

  Here, in the secondary battery 100 of the present embodiment, the positive electrode mixture layer 111b includes the positive electrode material 10 described above. Therefore, when the positive electrode mixture layer 111b of the positive electrode 111 of the secondary battery 100 is formed using the positive electrode material 10, the cracking of the first active material particles 11 is suppressed as described above, and the positive electrode mixture layer 111b is increased. Densification can be achieved. Therefore, it is possible to achieve both high energy density and high cycle characteristics in the secondary battery 100. Note that a value obtained by dividing the difference between the weight of the positive electrode 111 and the weight of the positive electrode current collector 111 a by the volume of the positive electrode mixture layer 111 b can be defined as the electrode density of the positive electrode 111.

  Thereafter, the positive electrode current collector 111a and the positive electrode material mixture layer 111b, and the negative electrode current collector material 112a and the negative electrode material mixture layer 112b are each cut into long strips, whereby the positive electrode 111 and the negative electrode 112 can be manufactured. . The positive electrode 111 and the negative electrode 112 manufactured as described above are wound around the winding central axis in a state of being opposed to each other with the separator 113 interposed therebetween, so that a wound electrode group 110 is formed.

  In the wound electrode group 110, the negative electrode current collector 112a is connected to the bottom of the battery can 101 via the negative electrode lead piece 104, and the positive electrode current collector 111a is connected to the battery lid 102 via the positive electrode lead piece 103 for insulation. A short circuit with the battery can 101 and the battery lid 102 is prevented by the plate 105 and the like, and the battery can 101 is accommodated. Thereafter, the secondary battery 100 can be manufactured by injecting a non-aqueous electrolyte into the battery can 101, fixing the battery lid 102 to the battery can 101 through the sealing material 106, and sealing the battery can 101. .

Examples of non-aqueous electrolytes injected into the battery can 101 include Li salts such as LiPF ₆ and LiBF ₄ and cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). ), Those dissolved in a chain carbonate such as diethyl carbonate (DEC) can be used.

  The secondary battery 100 having the above configuration uses the battery lid 102 as the positive electrode external terminal and the bottom of the battery can 101 as the negative electrode external terminal, and accumulates the power supplied from the outside in the wound electrode group 110 and the wound electrode. The power stored in the group 110 can be supplied to an external device or the like. Thus, the secondary battery 100 of this embodiment can be used for a battery module, for example.

  Further, the secondary battery 100 of the present embodiment includes, for example, a hybrid railway that travels with an engine and a motor, an electric vehicle that travels with a motor using a battery as an energy source, a hybrid vehicle, a plug-in hybrid vehicle that can charge a battery from the outside, The present invention can be applied to a power source of various vehicles such as a fuel cell vehicle that extracts electric power from a chemical reaction between hydrogen and oxygen. In addition to the examples shown above, the vehicle can be widely applied to forklifts, premises transport vehicles such as factories, electric wheelchairs, various satellites, rockets, submarines, and the like, as long as the vehicle has a battery (battery). It is not applicable.

  In addition, a battery module using one or more secondary batteries 100 including the positive electrode 111 including the positive electrode material 10 can generate natural energy such as solar cells that convert solar light energy into electric power or wind power that is generated by wind power. It can be applied to a power storage power source of a used power generation system (power storage system). In addition, although the power generation system using a solar cell or a wind power generator was illustrated as a power generation system, it is not limited to this, It can apply widely also to the power generation system using another power generation device.

  The embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

[Example]
Hereinafter, the positive electrode material, the manufacturing method thereof, and the lithium ion secondary battery of the present invention will be described in detail using Examples 1 to 8 and Comparative Examples 1 to 3.

Example 1
First, the positive electrode material of Example 1 was manufactured based on the manufacturing method described in the above embodiment. Specifically, in the pulverization and mixing step, lithium carbonate, nickel hydroxide, cobalt hydroxide, and manganese carbonate are mixed in a molar ratio of Li: Ni: Co: Mn = 1.04: 0.80: 0.10: 0.10. Weighed so that the ratio was equal, added pure water, and pulverized and mixed using a planetary ball mill. Next, a granulation step employing a spray drying method is performed, and the resulting pulverized mixed powder slurry is spray dried with a two-particle nozzle to agglomerate primary particles of the above materials. A first active material particle precursor was prepared.

  Similarly, in the pulverization and mixing step, lithium carbonate, nickel hydroxide, cobalt hydroxide, and manganese carbonate are mixed at a molar ratio of Li: Ni: Co: Mn = 1.04: 0.80: 0.15: 0.05. Weighed so that pure water was added, and pulverized and mixed using a planetary ball mill. Next, a granulation step employing a spray drying method is performed, and the resulting pulverized mixed powder slurry is spray dried with a two-particle nozzle to agglomerate primary particles of the above materials. A second active material particle precursor was prepared.

  In this example, the viscosity, concentration, spray pressure, spray amount, drying temperature, etc. of each slurry are adjusted, and the average particle diameter and particle strength of the first active material particles and the second active material particles contained in the positive electrode material are adjusted. I tried to control it. In addition, the viscosity of the slurry was adjusted to control the porosity of the first active material particles and the second active material particles, and thus the particle strength. More specifically, the viscosity of the slurry was adjusted between 5 mPa · S and 30 mPa · S at a spindle rotation speed of 100 rpm. The slurry concentration was in the range of 10% to 70%, and the spraying pressure of the slurry was controlled to 0.05 MPa to 0.5 MPa. The amount of slurry sprayed was in the range of 0.5 kg / h to 20 kg / h, and the drying temperature was controlled to 190 ° C. to 230 ° C.

  Next, as the firing step, the first active material particle precursor obtained in the granulation step is heat-treated at 600 ° C. for 12 hours in an oxygen atmosphere, and then fired at 800 ° C. for 10 hours to obtain the first active material particle precursor. A powder of material particles was obtained. Similarly, as the firing step, the second active material particle precursor obtained in the granulation step is heat-treated at 600 ° C. for 12 hours in an oxygen atmosphere, and then fired at 750 ° C. for 10 hours to obtain the second active material particles. A powder of material particles was obtained.

The Li, Ni, Co, and Mn compositions of the obtained first active material particles and second active material particles were measured by ICP-AES. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _{0. It was 15} Mn _0.05 O ₂ . Moreover, the average particle diameter of the powder of the 1st active material particle and the powder of the 2nd active material particle was measured with the laser diffraction / scattering type particle size distribution measuring apparatus, respectively. The average particle diameter D1 of the first active material particles was about 11 μm, and the average particle diameter D2 of the second active material particles was about 5 μm. Further, the particle strength of the first active material particles and the second active material particles was measured with a micro compression tester. The particle strength St1 of the first active material particles was about 88 MPa, and the particle strength St2 of the second active material particles was about 59 MPa. Further, the specific surface area of the powder of the first active material particles and the specific surface area of the powder of the second active material particles were measured by a measuring apparatus using a gas adsorption method. The specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (see Tables 1 and 2). .

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 80/20 to obtain a positive electrode material of Example 1 which was a mixed powder. And the average particle diameter _Dave of the obtained positive electrode material of Example 1 was measured with the laser diffraction / scattering type particle size distribution measuring apparatus. The average particle diameter D _ave of the positive electrode material of Example 1 was 9.8 μm (see Table 3).

The difference (D1-D2) between the average particle diameter D1 of the powder of the first active material particles and the average particle diameter D2 of the powder of the second active material particles, and the average particle of the positive electrode material of Example 1 which is a mixed powder thereof the ratio of the diameter _{D ave (D1-D2) /} D ave was 0.612 (see Table 3).

  Next, using the produced positive electrode material of Example 1, a positive electrode for a lithium ion secondary battery was produced through the mixture preparation step, the mixture coating step, and the molding step described in the above embodiment. Specifically, in the mixture preparation step, the positive electrode material of Example 1, the carbon-based conductive material, and the binder previously dissolved in N-methyl-2-pyrrolidone (NMP) were each 90: Mixing at a weight ratio of 6: 4.

Then, in the mixture application step, the uniformly mixed mixture slurry was applied on a positive electrode current collector of an aluminum foil having a thickness of 20 μm so as to have an application amount of 10 mg / cm ² . Thereafter, the mixture slurry uniformly applied on the positive electrode current collector is heat-treated at 120 ° C., and the solvent of the solution contained in the mixture slurry is removed by evaporation or evaporation. A mixture layer was formed. Thereafter, in the forming step, the positive electrode mixture layer was pressure-formed by hot pressing to produce a positive electrode. When the electrode density of the produced positive electrode, that is, the density of the positive electrode mixture layer was measured, it was 3.5 g / cm ³ (see Table 3).

  Next, graphite was used as the negative electrode active material, and a negative electrode for a lithium ion secondary battery was produced through the mixture preparation step, the mixture coating step, and the molding step described in the above embodiment. Specifically, in the mixture preparation step, graphite and a binder previously dissolved in NMP were mixed at a weight ratio of 98: 2.

In the mixture application step, the uniformly mixed mixture slurry was applied on a negative electrode current collector of a copper foil having a thickness of 10 μm so as to have an application amount of 6.5 mg / cm ² . Thereafter, the mixture slurry uniformly coated on the negative electrode current collector is heat-treated at 100 ° C., and the solvent of the solution contained in the mixture slurry is removed by volatilization or evaporation. A mixture layer was formed. Thereafter, in the forming step, the negative electrode mixture layer was pressure-formed by hot pressing to produce a negative electrode.

Next, the lithium ion secondary battery of Example 1 was manufactured using the produced positive electrode and negative electrode. Specifically, the positive electrode is punched into a circular shape with a diameter of 15 mm, the negative electrode is punched into a circular shape with a diameter of 16 mm, and a 30 μm-thick PP (polypropylene) porous separator having an ion conductivity and insulating properties is interposed between the positive electrode and the negative electrode. Opposing in water electrolyte. As the non-aqueous electrolyte (electrolyte), organic solvent ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3: 7, and lithium hexafluorophosphate (LiPF ₆ ) was added at 1 mol / L. What was dissolved was used.

  Next, after charging the manufactured secondary battery with a constant current / constant potential charge with a positive electrode material weight standard of 40 A / kg and an upper limit potential of 4.3 V in a 25 ° C. environment, a positive electrode material weight standard of 40 A / kg is fixed. The initial capacity was measured by discharging the current to a lower limit potential of 2.7 V and measuring the discharge capacity. The initial capacity of the secondary battery of Example 1 was 191 Ah / kg (see Table 3).

  Moreover, the measurement of the resistance change accompanying the charging / discharging cycle of the secondary battery of Example 1 was performed in the following procedure. First, the secondary battery was charged and discharged at a positive electrode material weight standard of 40 A / kg, and then the direct current resistance at 300 A / kg and 10 s was measured. Thereafter, in a constant temperature bath at 50 ° C., the secondary battery was charged at a constant current / constant potential of 200 Ah / kg and discharged at a constant current of 600 Ah / kg for 100 cycles. Thereafter, the DC resistance of the secondary battery is measured again in an environment of 25 ° C., the change in resistance of the secondary battery accompanying the charge / discharge cycle is calculated, and the resistance increase rate after 100 cycles of the secondary battery, that is, (after 100 cycles) DC resistance) / (DC resistance after one cycle). The resistance increase rate of the secondary battery of Example 1 was 115% (see Table 3).

(Example 2)
The pulverization and mixing step, the granulation step, and the granulation step are the same as in Example 1 except that the amount of slurry sprayed in the granulation step of the first active material particles is increased and the slurry concentration in the granulation step of the second active material particles is lowered. A firing step was performed to obtain a powder of the first active material particles and a powder of the second active material particles. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. Mn _0.05 O ₂ . The average particle diameter D1 of the powder of the first active material particles was about 15 μm, and the average particle diameter D2 of the powder of the second active material particles was about 3.8 μm. Further, the particle strength St1 of the first active material particles was about 82 MPa, and the particle strength St2 of the second active material particles was about 65 MPa. Further, the specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 80/20 to obtain a positive electrode material of Example 2. The average particle diameter D _ave of the positive electrode material of Example 2 was 12.8 μm, and the ratio (D1-D2) / D _ave was 0.878 (see Table 3).

Thereafter, in the same manner as in Example 1, a positive electrode using the positive electrode material of Example 2 was produced and the electrode density was measured. As a result, it was 3.6 g / cm ³ . Moreover, the secondary battery of Example 2 was produced using the produced positive electrode and negative electrode similarly to Example 1, and the resistance change accompanying an initial capacity and a charging / discharging cycle was measured. The initial capacity of the secondary battery of Example 2 was 193 Ah / kg, and the resistance increase rate was 130% (see Table 3).

(Example 3)
The pulverization and mixing step, the granulation step, and the granulation step are the same as in Example 1 except that the amount of slurry sprayed in the granulation step of the first active material particles is reduced and the slurry concentration in the granulation step of the second active material particles is reduced. A firing step was performed to obtain a powder of the first active material particles and a powder of the second active material particles. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. Mn _0.05 O ₂ . The average particle diameter D1 of the first active material particles was about 6.3 μm, and the average particle diameter D2 of the second active material particles was about 3.4 μm. Further, the particle strength St1 of the first active material particles was about 108 MPa, and the particle strength St2 of the second active material particles was about 70 MPa. Further, the specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 80/20 to obtain a positive electrode material of Example 3. The average particle diameter D _ave of the positive electrode material of Example 3 was 5.7 μm, and the ratio (D1-D2) / D _ave was 0.507 (see Table 3).

Thereafter, in the same manner as in Example 1, a positive electrode using the positive electrode material of Example 3 was produced and the electrode density was measured. As a result, it was 3.4 g / cm ³ . Moreover, the secondary battery of Example 3 was produced using the produced positive electrode and negative electrode similarly to Example 1, and the resistance change accompanying an initial capacity and a charging / discharging cycle was measured. The initial capacity of the secondary battery of Example 3 was 186 Ah / kg, and the resistance increase rate was 124% (see Table 3).

(Example 4)
In the pulverizing and mixing step, the raw material manganese carbonate of the first active material particles is aluminum hydroxide, the molar ratio is Li: Ni: Co: Al = 1.04: 0.80: 0.15: 0.05, and the firing step In Example 1, except that the firing temperature was changed from 850 ° C. to 750 ° C., the pulverization and mixing step, the granulation step, and the firing step were performed in the same manner as in Example 1, and the first active material particle powder and the second active material particle A powder was obtained. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.15 Al _0.05 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. Mn _0.05 O ₂ (see Tables 1 and 2).

The average particle diameter D1 of the first active material particles was about 10 μm, and the average particle diameter D2 of the second active material particles was about 5.0 μm. Further, the particle strength St1 of the first active material particles was about 75 MPa, and the particle strength St2 of the second active material particles was about 59 MPa. The specific surface area of the powder of the first active material particles was 0.7 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 80/20 to obtain a positive electrode material of Example 4. The average particle diameter D _ave of the positive electrode material of Example 4 was 9.0 μm, and the ratio (D1-D2) / D _ave was 0.556 (see Table 3).

Thereafter, as in Example 1, a positive electrode using the positive electrode material of Example 4 was prepared and the electrode density was measured. As a result, it was 3.4 g / cm ³ . Moreover, the secondary battery of Example 4 was produced using the produced positive electrode and negative electrode similarly to Example 1, and the resistance change accompanying an initial capacity and a charging / discharging cycle was measured. The initial capacity of the secondary battery of Example 4 was 180 Ah / kg, and the resistance increase rate was 108% (see Table 3).

(Example 5)
In the pulverization and mixing step, titanium oxide is added as a raw material of the first active material particles, and the molar ratio is Li: Ni: Co: Mn: Ti = 1.04: 0.80: 0.10: 0.08: 0.02. Except for the above, the pulverization and mixing step, the granulation step and the firing step were carried out in the same manner as in Example 2 to obtain a powder of the first active material particles and a powder of the second active material particles. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.08 Ti _0.02 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80. Co _0.15 Mn _0.05 O ₂ (see Tables 1 and 2).

The average particle diameter D1 of the first active material particles was about 9.6 μm, and the average particle diameter D2 of the second active material particles was about 3.8 μm. The particle strength St1 of the first active material particles was about 93 MPa, and the particle strength St2 of the second active material particles was about 65 MPa. The specific surface area of the powder of the first active material particles was 0.4 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 80/20 to obtain a positive electrode material of Example 5. The average particle diameter D _ave of the positive electrode material of Example 5 was 8.4 μm, and the ratio (D1-D2) / D _ave was 0.687 (see Table 3).

Thereafter, in the same manner as in Example 1, when a positive electrode using the positive electrode material of Example 5 was produced and the electrode density was measured, it was 3.6 g / cm ³ . Moreover, the secondary battery of Example 5 was produced using the produced positive electrode and negative electrode similarly to Example 1, and the resistance change accompanying an initial capacity and a charging / discharging cycle was measured. The initial capacity of the secondary battery of Example 5 was 195 Ah / kg, and the resistance increase rate was 105% (see Table 3).

(Example 6)
Compared to Example 1, the weight ratio W1 / W2 between the weight W1 of the powder of the first active material particles and the weight W2 of the powder of the second active material particles was changed.
First, the pulverization and mixing step, the granulation step, and the firing step were performed in the same manner as in Example 1 to obtain a powder of the first active material particles and a powder of the second active material particles. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. Mn _0.05 O ₂ . The average particle diameter D1 of the first active material particles was about 11 μm, and the average particle diameter D2 of the second active material particles was about 5.0 μm. Further, the particle strength St1 of the first active material particles was about 88 MPa, and the particle strength St2 of the second active material particles was about 59 MPa. Further, the specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 95/5 to obtain a positive electrode material of Example 6. The average particle diameter D _ave of the positive electrode material of Example 6 was 10.7 μm, and the ratio (D1-D2) / D _ave was 0.561 (see Table 3).

Thereafter, in the same manner as in Example 1, a positive electrode using the positive electrode material of Example 6 was produced and the electrode density was measured. As a result, it was 3.4 g / cm ³ . Moreover, the secondary battery of Example 6 was produced using the produced positive electrode and negative electrode similarly to Example 1, and the resistance change accompanying an initial capacity and a charging / discharging cycle was measured. The initial capacity of the secondary battery of Example 6 was 185 Ah / kg, and the resistance increase rate was 112% (see Table 3).

(Example 7)
Compared to Example 1, the weight ratio W1 / W2 between the weight W1 of the powder of the first active material particles and the weight W2 of the powder of the second active material particles was changed.
First, the pulverization and mixing step, the granulation step, and the firing step were performed in the same manner as in Example 1 to obtain a powder of the first active material particles and a powder of the second active material particles. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. Mn _0.05 O ₂ . The average particle diameter D1 of the first active material particles was about 11 μm, and the average particle diameter D2 of the second active material particles was about 5.0 μm. Further, the particle strength St1 of the first active material particles was about 88 MPa, and the particle strength St2 of the second active material particles was about 59 MPa. Further, the specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 70/30 to obtain a positive electrode material of Example 7. The average particle diameter D _ave of the positive electrode material of Example 7 was 9.2 μm, and the ratio (D1-D2) / D _ave was 0.652 (see Table 3).

Thereafter, in the same manner as in Example 1, when a positive electrode using the positive electrode material of Example 7 was produced and the electrode density was measured, it was 3.5 g / cm ³ . Moreover, the secondary battery of Example 7 was produced using the produced positive electrode and negative electrode similarly to Example 1, and the resistance change accompanying an initial capacity and a charging / discharging cycle was measured. The initial capacity of the secondary battery of Example 7 was 193 Ah / kg, and the resistance increase rate was 118% (see Table 3).

(Example 8)
Zirconium oxide is added as a raw material for the second active material particles in the pulverization and mixing step, and the molar ratio is Li: Ni: Co: Mn: Zr = 1.04: 0.80: 0.15: 0.04: 0.01 Except that, the pulverization and mixing step, the granulation step and the firing step were carried out in the same manner as in Example 1 to obtain the powder of the first active material particles and the powder of the second active material particles. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. It was Mn _0.04 Zr _0.01 O ₂ (see Tables 1 and 2).

The average particle diameter D1 of the first active material particles was about 11 μm, and the average particle diameter D2 of the second active material particles was about 4.0 μm. The particle strength St1 of the first active material particles was about 88 MPa, and the particle strength St2 of the second active material particles was about 66 MPa. The specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 1.2 m ² / g (Tables 1 and 2). reference).

Next, a powder mixing step is performed, and the powder of the first active material particles and the powder of the second active material particles are divided into the weight W1 of the first active material particles and the weight W2 of the second active material particles. The weight ratio W1 / W2 was mixed at a ratio of 80/20 to obtain a positive electrode material of Example 8. The average particle diameter D _ave of the positive electrode material of Example 8 was 9.6 μm, and the ratio (D1-D2) / D _ave was 0.729 (see Table 3).

Thereafter, in the same manner as in Example 1, when a positive electrode using the positive electrode material of Example 8 was produced and the electrode density was measured, it was 3.5 g / cm ³ . Moreover, the secondary battery of Example 8 was produced using the produced positive electrode and negative electrode similarly to Example 1, and the resistance change accompanying an initial capacity and a charging / discharging cycle was measured. The initial capacity of the secondary battery of Example 8 was 190 Ah / kg, and the resistance increase rate was 106% (see Table 3).

(Comparative Example 1)
Sulfate is used as a metal raw material for the first active material particles, and weighed so that the molar ratio is Ni: Co: Mn = 0.8: 0.1: 0.1, and pure water is added to the powder. An aqueous solution was prepared. The aqueous solution was dropped into an aqueous sodium hydroxide solution, and the precipitate was filtered and dried to obtain a transition metal composite hydroxide. The obtained transition metal composite hydroxide was baked at 500 ° C., so that the transition metal composite oxide was Li: Ni: Co: Mn = 1.06: 0.8: 0.1: 0.1. Lithium hydroxide was mixed and heat-treated at 600 ° C. for 12 hours in an oxygen atmosphere. Then, it baked over 10 hours at 740 degreeC, and synthesize | combined the 1st active material particle. The second active material particles were synthesized in the same manner as in Example 1.

The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. Mn was _0.05 . The average particle diameter D1 of the first active material particles was about 7.0 μm, and the average particle diameter D2 of the second active material particles was about 5.0 μm. The particle strength St1 of the first active material particles was about 90 MPa, and the particle strength St2 of the second active material particles was about 59 MPa. Further, the specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, the first active material particle powder and the second active material particle powder have a weight ratio W1 / W2 between the weight W1 of the first active material particle powder and the weight W2 of the second active material particle powder. The positive electrode material of Comparative Example 1 was obtained by mixing at a ratio of 80/20. The average particle diameter D _ave of the positive electrode material of Comparative Example 1 was 6.6 μm, and the ratio (D1-D2) / D _ave was 0.303.

Thereafter, in the same manner as in Example 1, a positive electrode using the positive electrode material of Comparative Example 1 was prepared and the electrode density was measured. As a result, it was 3.2 g / cm ³ . Further, similarly to Example 1, a secondary battery of Comparative Example 1 was produced using the produced positive electrode and negative electrode, and an initial capacity and a resistance change accompanying a charge / discharge cycle were measured. The initial capacity of the secondary battery of Comparative Example 1 was 190 Ah / kg, and the resistance increase rate was 128% (see Table 3).

(Comparative Example 2)
Except for increasing the slurry concentration and the spray amount in the granulation step of the first active material particles, the pulverization and mixing step, the granulation step and the firing step were carried out in the same manner as in Example 1, and the powder of the first active material particles and A powder of second active material particles was obtained. The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.10 Mn _0.10 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.15. Mn _0.05 O ₂ . The average particle diameter D1 of the first active material particles was about 20 μm, and the average particle diameter D2 of the second active material particles was about 5.0 μm. Further, the particle strength St1 of the first active material particles was about 71 MPa, and the particle strength St2 of the second active material particles was about 59 MPa. Further, the specific surface area of the powder of the first active material particles was 0.3 m ² / g, and the specific surface area of the powder of the second active material particles was 0.9 m ² / g (Tables 1 and 2). reference).

Next, the first active material particle powder and the second active material particle powder have a weight ratio W1 / W2 between the weight W1 of the first active material particle powder and the weight W2 of the second active material particle powder. The positive electrode material of Comparative Example 2 was obtained by mixing at a ratio of 80/20. The average particle diameter D _ave of the positive electrode material of Comparative Example 2 was 17.0 μm, and the ratio (D1-D2) / D _ave was 0.882 (see Table 3).

Thereafter, in the same manner as in Example 1, a positive electrode using the positive electrode material of Comparative Example 2 was produced and the electrode density was measured. As a result, it was 3.7 g / cm ³ . Further, similarly to Example 1, a secondary battery of Comparative Example 2 was produced using the produced positive electrode and negative electrode, and an initial capacity and a resistance change associated with a charge / discharge cycle were measured. The initial capacity of the secondary battery of Comparative Example 2 was 191 Ah / kg, and the resistance increase rate was 147% (see Table 3).

(Comparative Example 3)
In the pulverization and mixing step, the material of the second active material particle precursor of Example 1 is used as the material of the first active material particle precursor, and in the granulation step, the first active material particle precursor is included than in Example 1. The spraying pressure and the spray amount of the slurry were increased, and in the firing step, the firing temperature was made higher than that in Example 1 to obtain the first active material particles. Further, in the pulverization and mixing step, the material of the first active material particle precursor of Example 1 is used as the material of the second active material particle precursor, and in the granulation step, the second active material particle precursor is more than that of Example 1. The second active material particles were obtained by reducing the spray pressure and the spray amount of the slurry containing, and lowering the firing temperature in comparison with Example 1 in the firing step.

The composition of the first active material particles is Li _1.01 Ni _0.80 Co _0.15 Mn _0.05 O ₂ , and the composition of the second active material particles is Li _1.01 Ni _0.80 Co _0.10. It was Mn _0.10 O _2. The average particle diameter D1 of the first active material particles was about 11 μm, and the average particle diameter D2 of the second active material particles was about 7.0 μm. Further, the particle strength St1 of the first active material particles was about 68 MPa, and the particle strength St2 of the second active material particles was about 60 MPa. The specific surface area of the powder of the first active material particles was 1.0 m ² / g, and the specific surface area of the powder of the second active material particles was 0.4 m ² / g (Tables 1 and 2). reference).

Next, the first active material particle powder and the second active material particle powder have a weight ratio W1 / W2 between the weight W1 of the first active material particle powder and the weight W2 of the second active material particle powder. The positive electrode material of Comparative Example 2 was obtained by mixing at a ratio of 80/20. The average particle diameter D _ave of the positive electrode material of Comparative Example 3 was 10.2 μm, and the ratio (D1-D2) / D _ave was 0.392.

Thereafter, in the same manner as in Example 1, a positive electrode using the positive electrode material of Comparative Example 3 was produced and the electrode density was measured. As a result, it was 3.1 g / cm ³ . Further, similarly to Example 1, a secondary battery of Comparative Example 3 was produced using the produced positive electrode and negative electrode, and an initial capacity and a resistance change accompanying a charge / discharge cycle were measured. The secondary battery of Comparative Example 3 had an initial capacity of 190 Ah / kg and a resistance increase rate of 166% (see Table 3).

  Table 1 below shows the composition, average particle diameter D1, particle strength St1, and specific surface area of the first active material particles of Examples 1 to 8 and Comparative Examples 1 to 3 described above.

  Table 2 below shows the composition, average particle diameter D2, particle strength St2, and specific surface area of the second active material particles of Examples 1 to 8 and Comparative Examples 1 to 3.

Table 3 below shows the weight ratio W1 / W2 of the powders of the first active material particles and the second active material particles of the positive electrode materials of Examples 1 to 8 and Comparative Examples 1 to 3, and the positive electrode material. The average particle diameter D _ave and the ratio (D1-D2) / D _ave are shown. Furthermore, in Table 3, the electrode density of the positive electrode mixture layer of the positive electrode containing the positive electrode material of Examples 1 to 8 and Comparative Example 1 to Comparative Example 3 is compared with those of Examples 1 to 8 and Comparative Example 1. The initial capacity | capacitance and resistance increase rate of a secondary battery provided with the positive electrode of Example 3 are shown.

In FIG. 4, the horizontal axis represents the ratio (D1−D2) / D _ave relating to the average particle diameter of the positive electrode material, and the vertical axis represents the resistance increase rate [%] of the secondary battery and the electrode density [g / cm ³ ] of the positive electrode. It is a graph to do. In FIG. 4, black circles (●) indicate the relationship between (D1−D2) / D _{ave of} Example 1 to Example 8 and the resistance increase rate [%] of the secondary battery, and white circles (◯) _These show the relationship between (D1-D2) / _{Dave of} Comparative Example 1 to Comparative Example 3 and the resistance increase rate [%] of the secondary battery. Black square points (♦) indicate the relationship between (D1-D2) / D _{ave of} Example 1 to Example 8 and the electrode density [g / cm ³ ] of the positive electrode, and white square points (◇) _These show the relationship between (D1-D2) / D _{ave of} Comparative Examples 1 to 3 and the electrode density [g / cm ³ ] of the positive electrode.

FIG. 5 is a graph in which the horizontal axis represents the electrode density [g / cm ³ ] of the positive electrode, and the vertical axis represents the resistance increase rate [%] of the secondary battery. In FIG. 5, black circle points (●) indicate the relationship between the electrode density [g / cm ³ ] of the positive electrodes of Example 1 to Example 8 and the resistance increase rate [%] of the secondary battery. ) Shows the relationship between the electrode density [g / cm ³ ] of the positive electrodes of Comparative Examples 1 to ³ and the resistance increase rate [%] of the secondary battery.

In the positive electrode materials of Examples 1 to 8, the difference between the average particle diameter D1 of the first active material particle powder and the average particle diameter D2 of the second active material particle powder (D1-D2) The ratio (D1-D2) / D _ave of the average particle diameter D _ave of the mixed powder of the material particle powder and the second active material particle powder is smaller than 0.88 and larger than 0.50. In other words, the inequality: 0.88> (D1-D2) / D _ave > 0.50 is satisfied. In the positive electrode materials of Examples 1 to 8, the particle strength St1 of the first active material particles is higher than the particle strength St2 of the second active material particles, that is, the inequality: St1> St2 is satisfied.

As a result, in the secondary batteries of Example 1 to Example 8, the electrode density of the positive electrode was 3.4 g / cm ³ or more and 3.6 g / cm ³ or less, and the electrode density of Comparative Example 1 was 3.2 g / m ^2. And the electrode density of Comparative Example 3 is higher than 3.1 g / m ² . Furthermore, the secondary batteries of Examples 1 to 8 have an initial discharge capacity as high as 180 Ah / kg or more and 195 Ah / kg or less, and the resistance increase rate after 100 cycles is 130% or less, and the increase in resistance is suppressed. Thus, both high capacity and resistance increase suppression are compatible.

On the other hand, in Comparative Example 1, the difference (D1-D2) between the average particle diameter D1 of the first active material particles and the average particle diameter D2 of the second active material particles is too small, and (D1-D2) / D _ave is 0. .303, which is below 0.50. Therefore, the electrode density of the positive electrode of the secondary battery of Comparative Example 1, in a 3.2 g / cm ³ below 3.4 g / cm ^3, the electrode density of the positive electrode of the secondary battery of Example 8 from Example 1 It became low compared with.

In Comparative Example 2, the difference (D1-D2) between the average particle diameter D1 of the first active material particles and the average particle diameter D2 of the second active material particles is excessive, and (D1-D2) / D _ave is 0.882. It exceeds 0.88. Therefore, the electrode density of the positive electrode of the secondary battery of Comparative Example 2 is a high value of 3.7 g / cm ³ . However, the average particle diameter D1 of the first active material particles of the positive electrode material becomes excessive, and the rate of increase in resistance associated with the charge / discharge cycle of the secondary battery exceeds 130% to 147%. The resistance increase rate was higher than that of the secondary battery.

In Comparative Example 3, the particle strength St1 of the first active material particles of the positive electrode material is higher than the particle strength St2 of the second active material particles, but the electrode density of the positive electrode of the secondary battery is as small as 3.1 g / cm ³ . Further, in Comparative Example 3, since the first active material particles were cracked during the production of the positive electrode, the rate of increase in resistance accompanying the charge / discharge cycle of the secondary battery greatly exceeded 130% and reached 166%. The resistance increase rate was higher than that of the secondary battery of Example 8.

DESCRIPTION OF SYMBOLS 10 Positive electrode material 11 1st active material particle 12 2nd active material particle 100 Secondary battery 111 Positive electrode S1 Crushing mixing process S2 Granulation process S3 Firing process S4 Powder mixing process

Claims (11)

Including first active material particles and second active material particles,
The first active material particles and the second active material particles are Li compounds having a layered structure in which the Ni concentration in the metal element other than Li exceeds 70 atomic%,
The weight W1 of the first active material particles is larger than the weight W2 of the second active material particles,
The average particle diameter D1 of the first active material particles is larger than the average particle diameter D2 of the second active material particles,
The first active material particles have a particle strength St1 of 60 MPa or more, the second active material particles have a particle strength St2 of 40 MPa or more, and the first active material particles have a particle strength St1 of the second active material particles. Higher than the particle strength St2 of the substance particles,
The average particle diameter _{D ave} of the mixture of the first active material particles and the second active material particles, the inequality: 0.88> meets _{(D1-D2) / D ave} > 0.50,
The Li compound, composition _formula is represented by _{Li 1 + a Ni b Mn c} Co d M1 e O 2 + α,
In the composition formula, M1 is a metal element other than Li, Ni, Mn, and Co, and −0.03 ≦ a ≦ 0.11, 0.7 <b <1.0, 0 ≦ c <0.3. , 0 <d <0.3,0 ≦ e <0.1, b + c + d + e = 1, -0.1 <α < cathode material characterized in Succoth meet 0.1. 2. The positive electrode material according to claim 1, wherein W1 / W2, which is a ratio of the weight W1 of the first active material particles to the weight W2 of the second active material particles, is 70/30 or more and 95/5 or less. . 3. The positive electrode material according to claim 1, wherein an average particle diameter D < b > 1 of the first active material particles is 6 μm or more and less than 20 μm. Exceeds the difference (D1-D2) is 2 and the average particle diameter D1 of the first active material particles and the average particle size D2 of the second active material particles, according to claim 1 to claim, characterized in that less than 15 The positive electrode material according to any one of 3 . The specific surface area of the first active material particles and the second active material particles, 0.1 m ² / g or more, any one of claims 1 to 4, characterized in that it is 2.0 m ² / g or less The positive electrode material according to one item. 6. The positive electrode material according to claim 1, wherein the composition of the first active material particles and the composition of the second active material particles are different from each other. A pulverizing and mixing step in which a raw material containing a metal element other than Li and a lithium raw material containing 80% by mass or more of lithium carbonate are pulverized and mixed to obtain a mixture;
Aggregating a plurality of primary particles constituting the mixture and granulating a first active material particle precursor having a relatively large average particle diameter and a second active material particle precursor having a relatively small average particle diameter. Each granulation process,
The first active material particle precursor and the second active material particle precursor are fired at 650 ° C. or more and 900 ° C. or less, respectively, so that the Ni concentration in the metal element other than Li exceeds 70 atomic%. Li compound, which is represented by a composition formula: Li _{1 + a} Ni _b Mn _c Co _d M1 _e O _{2 + α} , where M1 is a metal element other than Li, Ni, Mn, and Co; 03 ≦ a ≦ 0.11, 0.7 <b <1.0, 0 ≦ c <0.3, 0 <d <0.3, 0 ≦ e <0.1, b + c + d + e = 1, −0.1 A firing step of obtaining first active material particles and second active material particles that are Li compounds satisfying <α <0.1 ;
A powder mixing step of mixing the first active material particles and the second active material particles,
The weight W1 of the first active material particles is larger than the weight W2 of the second active material particles, and the average particle diameter D1 of the first active material particles is larger than the average particle diameter D2 of the second active material particles. The particle strength St1 of the first active material particles is 60 Mpa or more, the particle strength St2 of the second active material particles is 40 MPa or more, and the particle strength St1 of the first active material particles is 2 active material particles greater than the particle strength St2 of further average particle size _{D ave} of the mixture of the first active material particles and the second active material particles, the inequality: 0.88> (D1-D2) / D _{In the} powder mixing step, W1 / W2, which is a ratio of the weight W1 of the first active material particles to the weight W2 of the second active material particles, is 70/30 or more and 95/5 so as to satisfy _ave > 0.50. Within the following range, the first active material Method for producing a cathode material and setting the mixing ratio of the particle second active material particles.   The method for producing a positive electrode material according to claim 7, wherein in the granulation step, the second active material particle precursor having an average particle diameter of 1 μm or more is granulated. In the pulverization and mixing step, a slurry in which the concentration and / or viscosity of the mixture is adjusted,
In the granulation step, the first active material particle precursor and the second active material particle precursor are granulated by adjusting the pressure and / or spray amount and spraying the slurry from a nozzle and drying the slurry. The manufacturing method of the positive electrode material of Claim 7 or Claim 8 characterized by these.   A lithium ion secondary battery comprising a positive electrode comprising the positive electrode material according to any one of claims 1 to 6. The lithium ion secondary battery according to claim 10, wherein an electrode density of the positive electrode is 3.4 g / cm ³ or more.

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