Cathode material manufacturing method

Abstract

To provide a method of manufacturing a positive electrode material capable of reducing an amount of a dispersion medium when slurry is generated.SOLUTION: A method of manufacturing a positive electrode material of a solid-state battery 1 includes: a first mixing step of mixing a positive electrode active material PAM and a conductive assistant CA to generate a first powder 21; a second mixing step of mixing a solid electrolyte SE and the conductive assistant CA to generate a second powder 22; and a third mixing step of mixing the first powder 21 and the second powder 22 to generate a third powder.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cathode material. [Background technology]

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable and advanced energy.

[0003] Lithium-ion secondary batteries are widely used as secondary batteries. Lithium-ion secondary batteries use a liquid electrolyte, and have a structure in which a separator is placed between a positive electrode and a negative electrode, and the space between them is filled with a liquid electrolyte (electrolytic solution).

[0004] Since the electrolyte solution of lithium-ion secondary batteries is usually a flammable organic solvent, safety, especially against heat, can be a problem. Therefore, solid-state batteries using a flame-retardant solid electrolyte instead of an organic liquid electrolyte have been proposed.

[0005] A solid secondary battery has an inorganic solid electrolyte, an organic solid electrolyte, or a gel-like solid electrolyte as an electrolyte layer between a positive electrode and a negative electrode. Compared to batteries that use an electrolytic solution, solid batteries using a solid electrolyte can solve the heat problem, have a higher capacity and / or a higher voltage, and also meet the demand for compactness.

[0006] The cathode material for such lithium-ion secondary batteries is prepared by mixing a cathode active material, a conductive additive, and a solid electrolyte, and further mixing a dispersion medium to form a slurry, which is then applied to a current collector and dried (see, for example, Patent Document 1). In this disclosure, the dispersion medium refers to a solvent containing a binder. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-76387 Summary of the Invention [Problem to be solved by the invention]

[0008] Here, it is preferable to use a small amount of dispersion medium in the process of generating the slurry. Reducing the amount of dispersion medium required can reduce manufacturing costs and manufacturing time. As a result of intensive research by the inventors, it was found that in order to reduce the amount of dispersion medium required, it is necessary to combine the positive electrode active material, the conductive additive, and the solid electrolyte to reduce the total surface area of ​​the entire material, and to achieve this, it is necessary to achieve an appropriate particle dispersion configuration at the raw material stage.

[0009] The present invention provides a method for producing a cathode material that can reduce the amount of dispersion medium used when producing a slurry, thereby contributing to improved energy efficiency. [Means for solving the problem]

[0010] The present invention provides A method for producing a cathode material for a solid-state battery, comprising: a first mixing step of mixing a positive electrode active material and a conductive additive to generate a first powder; a second mixing step of mixing the solid electrolyte and the conductive additive to generate a second powder; and a third mixing step of mixing the first powder and the second powder to generate a third powder. [Effects of the Invention]

[0011] According to the present invention, the amount of dispersion medium used in producing a slurry for producing a positive electrode material can be reduced. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a cross-sectional view of the solid-state battery 1. [Figure 2] FIG. 1 is a flow diagram schematically illustrating a method for producing a positive electrode material. [Figure 3]1 is a graph showing the relationship between solid content and HIS area. [Figure 4] 1 is a graph showing the relationship between solid content and viscosity. [Figure 5] FIG. 2 is a schematic diagram showing the state of particles dispersed in a slurry. DETAILED DESCRIPTION OF THE INVENTION

[0013] First, a solid-state battery in which the cathode material of the present invention is used will be described. [Solid battery] 1, the solid-state battery 1 includes a battery body 10, a negative electrode current collector 50, and a positive electrode current collector 60. In this specification, a solid-state battery refers to a battery that is made completely solid.

[0014] The negative electrode current collector 50 and the positive electrode current collector 60 are conductive plate-like members that sandwich the battery body 10 from both sides. The negative electrode current collector 50 has a function of collecting current from the negative electrode layer 30, and the positive electrode current collector 60 has a function of collecting current from the positive electrode layer 20. The battery body 10 includes a positive electrode layer 20 that functions as a positive electrode, a negative electrode layer 30 that functions as a negative electrode, and a conductive solid electrolyte layer 40 located between the positive electrode layer 20 and the negative electrode layer 30. The positive electrode layer 20 is produced by applying a slurry containing a positive electrode active material (positive electrode material), a conductive additive, and a solid electrolyte to the positive electrode current collector 60 and drying the slurry.

[0015] [Cathode material manufacturing method] Hereinafter, one embodiment of the method for producing a cathode material of the present invention will be described with reference to FIG. The method for producing the cathode material includes the following steps. 1. A first mixing step in which the positive electrode active material PAM and the conductive additive CA are mixed to generate the first powder 21 2. A second mixing step of mixing the solid electrolyte SE and the conductive additive CA to generate the second powder 22 3. A third mixing step in which the first powder 21 and the second powder 22 are mixed to produce a third powder 23 4. Slurry generation step of mixing the third powder 23 with a dispersion medium 5. Slurry application step of applying the slurry onto the current collector

[0016] The method for producing the cathode material of this embodiment is different from the conventional method in which the cathode active material PAM, the solid electrolyte SE, and the conductive additive CA are mixed at once. The method is characterized in that the cathode active material PAM and the conductive additive CA are mixed separately, and the solid electrolyte SE and the conductive additive CA are mixed together, and then these mixtures are further mixed. If the cathode active material PAM is too coated with the insulating solid electrolyte SE, an electron conduction path cannot be formed. However, by previously compounding the conductive additive CA on the surfaces of the cathode active material PAM and the solid electrolyte SE, the electrons and lithium ions (Li + ) conduction path can be achieved. Furthermore, if the compounding is insufficient, the surface area of ​​the particles is large, so a large amount of dispersion medium is required to make a slurry, but by compounding sufficiently, the amount of dispersion medium can be reduced.

[0017] To ensure the proper function of the positive electrode active material PAM, if the positive electrode active material PAM is coated with a coating material, it must be crushed without damaging the coating material. To ensure the proper function of the solid electrolyte SE, which tends to aggregate, it is necessary to take measures to prevent re-aggregation during crushing. Furthermore, to ensure the proper function of the conductive additive CA, it must be crushed to a length that allows the conductive additive CA to function as an electronic conduction path after drying.

[0018] Therefore, in this embodiment, the positive electrode active material PAM and the conductive additive CA are dry-mixed in the first mixing step, and the solid electrolyte SE and the conductive additive CA are dry-mixed in the second mixing step. The particles that have undergone the first and second mixing steps are composited, with the positive electrode active material PAM and the solid electrolyte SE as mother particles and the conductive additive CA as child particles. "Compositing" refers to the formation of composite particles by crushing and dispersing aggregates of each material using a shear stress above a certain level, resulting in the Van der Waals forces acting between the larger mother particles and the smaller child particles due to the difference in particle size. Hereinafter, particles mixed through the first and second mixing steps may be referred to as composite particles.

[0019] To separate the mixing steps, if the amount of conductive additive CA required is 1, for example, half of the conductive additive CA is mixed with the positive electrode active material PAM in the first mixing step, and half of the conductive additive CA is mixed with the solid electrolyte SE in the second mixing step. Separating the mixing steps allows for a dispersion process suited to each material, as mentioned above. In other words, if all materials are mixed under the same conditions, the material functionality cannot be guaranteed. However, by separating the mixing steps into the first and second mixing steps and mixing the solid electrolyte SE and positive electrode active material PAM under optimal conditions, a dispersion process suited to each material is possible.

[0020] By mixing the appropriately dispersed composite particles, the structure of the composite particles that are finally produced can be controlled. This reduces the amount of dispersion medium and shortens the time required for the slurry production step. Note that the dry method means that mixing is performed without using a dispersion medium. Each step will be described in detail below.

[0021] [First mixing step] In the first mixing step, the positive electrode active material PAM and the conductive additive CA are mixed in a dry state to produce the first powder 21.

[0022] The positive electrode active material PAM may be an oxide containing lithium and cobalt as constituent metal elements, or an oxide containing at least one other metal element as a constituent metal element in addition to lithium and cobalt. Examples of metal elements other than lithium and cobalt include Ni, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce, and these may be contained alone or in combination of two or more.

[0023] Examples of the positive electrode active material PAM include LiCoO2. Another example is lithium nickel cobalt manganese oxide (NCM) represented by the following general formula (1). NCM is preferred because it has a high energy density per volume and excellent thermal stability. LiNi a Co b Mn c O2(1) (where 0 < a < 1, 0 < b < 1, 0 < c < 1, and a + b + c = 1.)

[0024] In addition, examples of the positive electrode active material PAM include lithium nickel cobalt aluminum-based oxide (NCA) represented by the following general formula (2). Li t Ni 1-x-y Co x Al y O2(2) (where 0.95 ≤ t ≤ 1.15, 0 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.2, and x + y < 0.5.)

[0025] It is preferable that the surface of the positive electrode active material PAM is previously coated with an oxide-based solid electrolyte. By coating the surface of the positive electrode active material PAM with an oxide-based solid electrolyte, the interfacial resistance between the positive electrode active material PAM and the sulfide-based solid electrolyte in contact with it can be reduced, and the ionic conductivity can be improved.

[0026] Note that the coating with the oxide-based solid electrolyte is preferably in a film form without grain boundaries and covers all of the surface of the positive electrode active material. Thereby, the grain boundary resistance of the particles after coating can be reduced. Such a film-like coating layer without grain boundaries is formed, for example, by spray coating.

[0027] Examples of the oxide-based solid electrolyte include LiNbO3 in the case of a lithium ion battery. In addition, NASICON-type oxides, garnet-type oxides, perovskite-type oxides, etc. can be mentioned. Examples of the NASICON-type oxide include oxides containing Li, Al, Ti, P, and O (for example, Li 1.5 Al<​​​​Examples of perovskite oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3).

[0028] The conductive additive CA is carbon, and examples thereof include acetylene black, carbon nanotubes, graphene, and graphite particles.

[0029] In the first mixing step, the positive electrode active material PAM and the conductive additive CA are dispersed and coated with the conductive additive CA. To achieve this, the positive electrode active material PAM and the conductive additive CA are gently loosened and coated with each other. Specifically, the stirring speed is set to a peripheral speed of 40 m / s to 80 m / s, and the stirring time is set to 30 to 60 minutes. The temperature during stirring is preferably 150°C or lower.

[0030] [Second mixing step] In the second mixing step, the solid electrolyte SE and the conductive additive CA are mixed in a dry state to produce the second powder 22.

[0031] Examples of the solid electrolyte SE include sulfide-based solid electrolytes. Sulfide-based solid electrolyte materials typically contain a metal element (M) that becomes ions to conduct, and sulfur (S). Examples of M include Li, Na, K, Mg, and Ca, with Li being preferred. In particular, sulfide-based solid electrolyte materials preferably contain Li, A (wherein A is at least one element selected from the group consisting of P, Si, Ge, Al, and B), and S. Furthermore, A is preferably P (phosphorus). Furthermore, sulfide-based solid electrolyte materials may contain halogens such as Cl, Br, and I. This is because the inclusion of halogens improves ionic conductivity. Furthermore, sulfide-based solid electrolyte materials may contain O.

[0032] Examples of sulfide-based solid electrolyte materials having Li ion conductivity include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z m S n (where m and n are positive numbers. Z is Ge, Zn, or Ga.), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is any of P, Si, Ge, B, Al, Ga, and In.) The above description of "Li2S-P2S5" means a sulfide-based solid electrolyte material obtained using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0033] The conductive additive CA is the same as the conductive additive CA described in the first mixing step, and therefore a description thereof will be omitted here.

[0034] In the second mixing step, the solid electrolyte SE and the conductive additive CA are dispersed and the conductive additive CA is coated on the solid electrolyte SE. To achieve this, the positive electrode active material PAM and the conductive additive CA are thoroughly loosened and coated. Specifically, the stirring speed is set to a peripheral speed of 40 m / s to 80 m / s, and the stirring time is set to 30 to 60 minutes. The temperature during stirring is preferably 100°C or lower.

[0035] [Third mixing step] In the third mixing step, the first powder 21 (composite particles of the positive electrode active material PAM and the conductive additive CA) obtained in the first mixing step and the second powder 22 (a mixture of the solid electrolyte SE and the conductive additive CA) obtained in the second mixing step are dry mixed to produce the third powder 23.

[0036] The third mixing step is intended to loosen and coat the first powder 21 and the second powder 22 in a short time. Specifically, the stirring speed is set to a peripheral speed of 0 m / s to 10 m / s, and the stirring time is set to 10 to 30 minutes. The temperature during stirring is preferably 100°C or lower.

[0037] Comparing the third mixing step with the first and second mixing steps, the stirring speed in the third mixing step is preferably slower than that in the first and second mixing steps.

[0038] [Slurry generation step] In the slurry producing step, the third powder 23 (composite particles of the positive electrode active material PAM, the solid electrolyte SE, and the conductive additive CA) is mixed with a dispersion medium.

[0039] The dispersion medium is not particularly limited, and examples thereof include organic solvents such as N-methyl-2-pyrrolidone (NMP), toluene, butyl butyrate, and alcohol, as well as water, etc. Butyl butyrate is preferred.

[0040] The dispersion medium also contains a binder, such as styrene butadiene rubber, polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyethylene oxide (PEO), polypropylene oxide (PPO), and polyethylene oxide-propylene oxide copolymer (PEO-PPO).

[0041] [Slurry application step] The slurry application step can be carried out by a known method, such as roller coating using an applicator roll or the like, screen coating, blade coating, spin coating, or bar coating.

[0042] In the cathode material for the solid-state battery of the present invention, the cathode layer may be formed on at least one side of the current collector, or may be formed on both sides. This can be appropriately selected depending on the type and structure of the target solid-state battery. After the slurry is applied to the current collector, steps such as drying and rolling may be performed.

[0043] Furthermore, in the manufacturing process of cathode materials, it is desirable to be able to easily evaluate the cathode material. Therefore, it is preferable to mix a dispersion medium after each process and evaluate the stability of the particles. That is, after the first mixing step, a predetermined amount of the first powder is mixed with the dispersion medium before the third mixing step, and quality evaluation is performed. After the second mixing step, a predetermined amount of the second powder is mixed with the dispersion medium before the third mixing step, and quality evaluation is performed. After the third mixing step, a predetermined amount of the third powder is mixed with the dispersion medium before the slurry generation step, and quality evaluation is performed. The predetermined amount is a small amount relative to the total amount generated, but is sufficient for quality evaluation. For example, the quality evaluation may be performed by determining whether at least one of an evaluation based on the relationship between the solid content of the slurry and the hysteresis area (hereinafter referred to as the HIS area) and an evaluation based on the relationship between the solid content of the slurry and the viscosity, as described below, satisfies predetermined requirements. The predetermined requirements are pass criteria and can be set appropriately. Note that the quality evaluation method is not limited to this, and other methods may also be used. By evaluating the stability of the composite particles at each step, quality for each process can be ensured.

[0044] [Example of reducing the amount of dispersion medium] Fig. 3 is a graph showing the relationship between the solid content and the HIS area of ​​a slurry in which a dispersion medium is mixed with composite particles compounded by mixing in the first mixing step, and Fig. 4 is a graph showing the relationship between the solid content and the viscosity of the slurry. Note that the viscosity of a slurry changes depending on the shear rate, and therefore in this disclosure, viscosity refers to the viscosity at a shear rate of around 30 [1 / s].

[0045] The solid lines (with compounding treatment) in Figures 3 and 4 are examples, and represent slurries prepared by mixing composite particles that have undergone the first mixing step described above with a dispersion medium. The dashed lines (without compounding treatment) in Figures 3 and 4 are comparative examples, and represent slurries prepared by mixing the same amounts of positive electrode active material PAM and conductive additive CA as the composite particles that have undergone the first mixing step shown by the solid lines with a dispersion medium without compounding them (without undergoing the first mixing step).

[0046] The solid content is the proportion of solid material in the slurry (solid material + liquid material). The HIS area (hysteresis area) is the open area of ​​the hysteresis curve (the area surrounded by the hysteresis curve) obtained from a graph showing the relationship between shear rate (x-axis) and shear stress (y-axis). The HIS area (hysteresis area) indicates the dispersion state of the solid material, and a small HIS area indicates that each material is dispersed properly. Viscosity is the degree of stickiness of a substance. The solvent in the dispersion medium is an unnecessary material that evaporates and evaporates after the slurry is applied.

[0047] As shown in Figures 3 and 4, the slurry containing the composite particles of the example has a smaller HIS area and a lower viscosity. From a different perspective, Table 1 shows a comparison of the solid content when the HIS area is 2 kPa / s and when the viscosity reaches 2700 [mPa / s] @ 30 [1 / s].

[0048] [Table 1]

[0049] As can be seen from Table 1, the composite particles of the examples tended to have a higher solid content of about 5% when the HIS area reached 2 kPa / s and the viscosity reached 2700 mPa / s @ 30 1 / s compared to the comparative examples. This indicates that the composite particles require less dispersion medium.

[0050] FIG. 5 is a schematic diagram showing the state of particles dispersed in a slurry in a dispersion medium. In the case without composite treatment (comparative example), the positive electrode active material PAM, the solid electrolyte SE, and the conductive additive CA are dispersed in a dispersion medium without any composite treatment. In the case with composite treatment (example), composite particles that have been subjected to the composite treatment through the first to third mixing steps described above are dispersed in a dispersion medium.

[0051] In the slurry without composite treatment, the total surface area of ​​each particle is large, so the amount of dispersion medium is also large. On the other hand, the composite particles with composite treatment have a large amount of lithium ions (Li + The solid electrolyte SE, which acts as a conductive path for electron conduction (e - The conductive additive CA, which acts as a path for the cathode active material PAM, is also properly dispersed. This reduces the total surface area of ​​each composite particle, so less dispersion medium is required. Furthermore, the contact area between the cathode active material PAM and the solid electrolyte SE is increased, reducing reaction resistance.

[0052] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0053] This specification describes at least the following items. Note that the components in parentheses correspond to those in the above-described embodiment, but are not limited to these.

[0054] (1) A method for producing a cathode material for a solid-state battery (solid-state battery 1), a first mixing step of mixing a positive electrode active material (positive electrode active material PAM) and a conductive additive (conductive additive CA) to generate a first powder (first powder 21); a second mixing step of mixing a solid electrolyte (solid electrolyte SE) and a conductive additive to generate a second powder (second powder 22); a third mixing step of mixing the first powder and the second powder to produce a third powder (third powder 23).

[0055] According to (1), by mixing the positive electrode active material and the conductive additive in the first mixing step, the positive electrode active material and the conductive additive can be dispersed while the conductive additive is wrapped around the positive electrode active material (composite formation). Furthermore, by mixing the solid electrolyte and the conductive additive in the second mixing step, the solid electrolyte and the conductive additive can be dispersed while the conductive additive is wrapped around the solid electrolyte (composite formation). Then, by mixing the first powder and the second powder produced in each step in the third mixing step, the conductive additive can be properly dispersed while ensuring contact between the positive electrode active material and the solid electrolyte. This significantly reduces the time required for mixing with the dispersion medium when preparing a slurry. Furthermore, since the surface area of ​​the third powder can be reduced, the contact area with the dispersion medium when preparing a slurry can be reduced, thereby reducing the amount of dispersion medium required.

[0056] (2) A method for producing a cathode material according to (1), a method for producing a cathode material, wherein after the first mixing step, the first powder and a dispersion medium are mixed and a quality evaluation is performed, and if predetermined requirements are satisfied, the third mixing step is performed.

[0057] According to (2), the quality of the first powder produced in the first mixing step can be ensured.

[0058] (3) A method for producing a cathode material according to (1) or (2), a method for producing a cathode material, wherein after the second mixing step, the second powder and a dispersion medium are mixed and a quality evaluation is performed, and if predetermined requirements are satisfied, the third mixing step is performed.

[0059] According to (3), the quality of the second powder produced in the second mixing step can be ensured.

[0060] (4) A method for producing a cathode material according to (2) or (3), The quality evaluation determines whether or not at least one of an evaluation based on a relationship between a solid content rate of the slurry and an HIS area and an evaluation based on a relationship between a solid content rate of the slurry and a viscosity of the slurry satisfies the predetermined requirements.

[0061] According to (4), the dispersion state of particles contained in the powder can be appropriately determined.

[0062] (5) A method for producing a cathode material according to any one of (1) to (4), the positive electrode active material is nickel-cobalt-manganese oxide, the conductive additive is carbon, The method for producing a cathode material, wherein the solid electrolyte is a sulfide-based solid electrolyte.

[0063] (6) A method for producing a cathode material according to any one of (1) to (5), The method for producing a positive electrode material further comprises a step of mixing the third powder with a dispersion medium to produce a slurry.

[0064] According to (6), a slurry can be produced with a small amount of dispersion medium.

[0065] (7) A method for producing a cathode material according to (6), a method for producing a cathode material, wherein after the third mixing step, the third powder and a dispersion medium are mixed and a quality evaluation is performed, and if predetermined requirements are satisfied, the slurry producing step is performed.

[0066] According to (7), the quality of the third powder produced in the third mixing step can be guaranteed.

[0067] (8) A method for producing a cathode material according to (6) or (7), The method for producing a positive electrode material, wherein the dispersion medium is butyl butyrate. [Explanation of symbols]

[0068] 1 solid state battery 21 1st powder 22 Second powder 23 Third powder CA Conductive Aid PAM positive electrode active material SE solid electrolyte

Claims

1. A method for producing a cathode material for a solid-state battery, comprising: a first mixing step of mixing a positive electrode active material and a conductive additive to generate a first powder; a second mixing step of mixing the solid electrolyte and the conductive additive to generate a second powder; a third mixing step of mixing the first powder and the second powder to generate a third powder.

2. The method for producing a cathode material according to claim 1, After the first mixing step, the first powder and a dispersion medium are mixed and a quality evaluation is performed, and if predetermined requirements are satisfied, the third mixing step is performed.

3. The method for producing a cathode material according to claim 1 or 2, After the second mixing step, the second powder and a dispersion medium are mixed and a quality evaluation is performed, and if predetermined requirements are satisfied, the third mixing step is performed.

4. The method for producing a cathode material according to claim 2 or 3, The method for manufacturing a cathode material includes determining whether or not at least one of an evaluation based on a relationship between a solid content rate of the slurry and an HIS area and an evaluation based on a relationship between a solid content rate of the slurry and a viscosity of the slurry satisfies the predetermined requirements.

5. A method for producing a cathode material according to any one of claims 1 to 4, the positive electrode active material is nickel-cobalt-manganese oxide, the conductive additive is carbon, The method for producing a cathode material, wherein the solid electrolyte is a sulfide-based solid electrolyte.

6. A method for producing a cathode material according to any one of claims 1 to 5, The method for producing a positive electrode material further comprises a slurry production step of mixing the third powder with a dispersion medium.

7. The method for producing a cathode material according to claim 6, After the third mixing step, the third powder and a dispersion medium are mixed and a quality evaluation is performed, and if predetermined requirements are satisfied, the slurry producing step is performed.

8. The method for producing a cathode material according to claim 6 or 7, The method for producing a positive electrode material, wherein the dispersion medium is butyl butyrate.

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