WO2012098960A1 - Positive electrode active material and manufacturing method therefor, and secondary battery - Google Patents

Abstract

Provided are a positive electrode active material that can improve cycle characteristics and that contains lithium iron phosphate, and a manufacturing method therefor, as well as a secondary battery comprising a positive electrode containing the positive electrode active material. The positive electrode active material has lithium iron phosphate as a main component, and contains iron phosphide and an oxygen-containing layer formed on the surface of the iron phosphide.

Description

Positive electrode active material, method for producing the same, and secondary battery

The present invention generally relates to a positive electrode active material, a method for manufacturing the same, and a secondary battery, and more specifically, includes a positive electrode active material having an olivine structure, a method for manufacturing the same, and a positive electrode including the positive electrode active material. The present invention relates to a secondary battery.

As a secondary battery having a high energy density, a secondary battery that is charged and discharged by moving lithium ions between a positive electrode and a negative electrode is used.

In such secondary batteries, a lithium transition metal composite oxide such as lithium cobaltate (LiCoO ₂ ) is generally used as a positive electrode active material. In recent years, from the viewpoint of cost, resources, etc., an inexpensive positive electrode material replacing lithium cobalt oxide has been demanded. Accordingly, a lithium-containing phosphate compound having an olivine structure has attracted attention as a positive electrode material.

Among lithium-containing phosphate compounds having an olivine type structure, lithium iron phosphate (LiFePO ₄ ) has characteristics such as excellent chemical stability, low environmental load, and low cost. Therefore, it is a positive electrode material that has been actively studied in recent years. However, lithium iron phosphate has the disadvantages of low electronic conductivity and low ionic conductivity. For this reason, it is essential to take measures such as using lithium iron phosphate by coating it with carbon in order to improve electronic conductivity, and using it by atomizing in order to improve ionic conductivity.

Recently, a positive electrode material including a first phase containing lithium iron phosphate and a second phase having higher electron conductivity and ion conductivity than the first phase has been studied.

For example, Japanese translations of PCT publication No. 2008-518880 (patent document 1) and JP-T 2008-528437 (patent document 2) include a first phase containing lithium iron phosphate and iron phosphide (Fe ₂ P). A positive electrode active material containing a second phase containing, etc. is described.

However, as described in JP 2010-27604 A (Patent Document 3), when the positive electrode active material contains an Fe ₂ P phase as a second phase together with lithium iron phosphate, the Fe ₂ P phase Elutes in the electrolyte and affects the negative electrode side in particular, degrading the high-temperature storage performance (cycle characteristics).

Special table 2008-518880 Special table 2008-528437 JP 2010-27604 A

The inventor has found that when the positive electrode active material contains the Fe ₂ P phase as the second phase together with lithium iron phosphate, the cycle characteristics are deteriorated.

Accordingly, an object of the present invention is to provide a positive electrode active material containing lithium iron phosphate, a method for manufacturing the same, and a secondary battery including a positive electrode containing the positive electrode active material, capable of improving cycle characteristics. It is.

The positive electrode active material according to the present invention is a positive electrode active material mainly composed of lithium iron phosphate, and includes iron phosphide and an oxygen-containing layer formed on the surface of the iron phosphide.

In the positive electrode active material of the present invention, the oxygen-containing layer preferably contains an iron oxide.

A secondary battery according to the present invention includes a positive electrode including the positive electrode active material.

The method for producing a positive electrode active material of the present invention having the above characteristics includes the following steps.

(A) Mixing step of mixing starting materials including lithium-containing material, iron-containing material, and phosphorus-containing material

(B) Drying step of drying the mixture obtained in the mixing step in the air

(C) Firing step of firing the dried product obtained in the drying step

The mixing step includes a step of adding water to the starting material.

In the method for producing a positive electrode active material of the present invention, it is preferable that the mixing step includes a step of adding water having a mass ratio of 1.5 to 3.0 with respect to the total mass of the starting materials.

In the method for producing a positive electrode active material of the present invention, it is preferable that the mixing step includes a step of adding an organic acid to the starting material. In this case, the organic acid is preferably ascorbic acid.

Furthermore, in the method for producing a positive electrode active material of the present invention, it is preferable that the lithium-containing raw material contains at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium acetate.

Furthermore, in the method for producing a positive electrode active material of the present invention, it is preferable that the iron-containing raw material contains iron oxalate.

In the method for producing a positive electrode active material of the present invention, it is preferable that the phosphorus-containing raw material contains at least one of diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

Since the positive electrode active material of the present invention is provided with an oxygen-containing layer formed on the surface of iron phosphide, it is possible to suppress elution of iron into the electrolytic solution, thereby improving cycle characteristics.

It is a figure which shows the coin-type nonaqueous electrolyte secondary battery as one embodiment of this invention, and the coin-type nonaqueous electrolyte secondary battery produced by the Example and comparative example of this invention. It is a figure which shows the X-ray-diffraction measurement result of the lithium iron phosphate synthesize | combined by the Example and comparative example of this invention. It is a scanning transmission electron micrograph of the lithium iron phosphate synthesize | combined in Example 1 of this invention. It is a scanning transmission electron micrograph of the lithium iron phosphate synthesize | combined in Example 2 of this invention. It is a scanning transmission electron micrograph of lithium iron phosphate synthesized in Comparative Example 1 of the present invention.

One embodiment of the positive electrode active material of the present invention is a lithium-containing phosphate compound having an olivine structure, and lithium iron phosphate represented by LiFePO ₄ , iron phosphide represented by Fe ₂ P, and phosphation And an oxygen-containing layer formed on the surface of iron. The iron phosphide is preferably coated with an oxygen-containing layer. The oxygen-containing layer preferably contains an iron oxide.

The positive electrode active material of the present invention can improve rate characteristics by including iron phosphide having higher electron conductivity than lithium iron phosphate, and an oxygen-containing layer formed on the surface of iron phosphide. Since the elution of iron into the electrolytic solution can be suppressed by providing, cycle characteristics can be improved. The content of iron phosphide in the positive electrode active material is preferably at most about 10% by mass or less. The content of iron phosphide in the positive electrode active material is more preferably about 5% by mass or less. When iron phosphide is contained excessively, the positive electrode capacity decreases.

One embodiment of the secondary battery of the present invention includes a positive electrode including the positive electrode active material.

One embodiment of the method for producing a positive electrode active material of the present invention is a method for producing a positive electrode active material containing lithium iron phosphate represented by LiFePO ₄ as a lithium-containing phosphate compound having an olivine structure. If the positive electrode active material of the present invention has an olivine structure, a part of Fe may be substituted with Al, Ti, V, Cr, Mn, Co, Ni, Zr, Nb, or the like. A part of P may be replaced with B, Si, or the like.

In one embodiment of the method for producing a positive electrode active material of the present invention, first, a lithium-containing raw material, an iron-containing raw material, and a phosphorus-containing raw material are mixed as a starting material for the positive electrode active material (mixing step).

As the lithium-containing raw material, lithium hydroxide, lithium carbonate, lithium acetate or the like can be used.

As the iron-containing raw material, iron oxalate (FeC ₂ O ₄ ), iron oxide (Fe ₂ O ₃ ), iron phosphate (Fe ₃ (PO ₄ ) ₂ ), metallic iron (Fe), and the like can be used.

As the phosphorus-containing raw material, diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), or the like can be used.

As a raw material serving both as a lithium-containing raw material and a phosphorus-containing raw material, lithium phosphate (Li ₃ PO ₄ ), lithium metaphosphate (LiPO ₃ ), lithium dihydrogen phosphate (LiH ₂ PO ₄ ), and the like can be used.

In the above mixing process, water is added to the starting material. Preferably, water is added to the starting material so that the ratio of the mass of water added to the starting material (water injection ratio) is 1.5 or more and 3.0 or less with respect to the total mass of the starting material.

Thus, since the mixing step is performed by adding water as a solvent to the starting material, safety can be improved compared to the case where an organic solvent is used as the solvent.

In the above mixing step, the dispersibility of the starting material can be improved by adding water having a mass ratio of 1.5 to 3.0 to the starting material with respect to the total mass of the starting material. Thereby, the synthesis reaction of lithium iron phosphate can be promoted. As a result, it is considered that generation of trivalent iron that adversely affects battery characteristics can be suppressed. Therefore, even if the mixture is dried in the air in the subsequent drying step, a positive electrode active material that exhibits good battery characteristics and a particularly high charge / discharge capacity can be obtained. In addition, when water having a mass ratio of more than 3.0 with respect to the total mass of the starting material is added to the starting material, the ratio of the solvent to the starting material increases, so that handling of the mixture is deteriorated and productivity is lowered. As a result, the manufacturing cost increases.

In the above mixing step, it is preferable to add an organic acid to the starting material. Preferably, the organic acid is ascorbic acid. Thereby, a conductive component (carbon) can be provided in lithium iron phosphate. If sucrose is added to the starting material for the purpose of imparting a conductive component to lithium iron phosphate, an oxygen-containing layer is not formed on the surface of iron phosphide.

Next, the mixture of starting materials obtained in the mixing step is dried in the air (drying step).

In this drying step, since the mixture can be dried in the air, the manufacturing cost can be reduced as compared with the case where the mixture is dried in an inert atmosphere or in a vacuum.

In addition, as described above, water is added to the starting material as a solvent, and the mixing step is performed. In addition, the mixture is dried in the air, so that iron in the starting material is oxidized and phosphorylated. It is considered that an oxygen-containing layer is formed on the iron surface. For this reason, it is considered that the oxygen-containing layer contains an iron oxide.

And the dried material obtained at the drying process is baked (baking process). The calcination temperature is a temperature at which lithium iron phosphate having an olivine structure represented by crystalline LiFePO ₄ is obtained. Specifically, it is preferably 550 ° C. to 1000 ° C. The heating temperature and the heating time can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery.

The mixing method and mixing conditions in the mixing step, the drying method and drying conditions in the drying step, and the baking method and baking conditions in the baking step take into account the required characteristics, productivity, etc. of the secondary battery. It can be set arbitrarily. For example, as a method for producing the positive electrode active material of the present invention, a slurry obtained by adding water as a solvent and mixing and dispersing a lithium-containing raw material, an iron-containing raw material, and a phosphorus-containing raw material is spray-dried in the atmosphere. After that, it is preferably fired in an inert gas atmosphere such as a nitrogen gas atmosphere.

Next, an example of a method for producing a nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention will be described in detail below.

First, a positive electrode is formed. For example, a positive electrode active material is mixed with a conductive agent and a binder, water is added to form a positive electrode slurry, the positive electrode slurry is applied on an electrode current collector by an arbitrary coating method, and dried to obtain a positive electrode. Form.

Next, a negative electrode is formed. For example, a negative electrode active material is mixed with a conductive agent and a binder, an organic solvent or water is added to form a negative electrode slurry, and this negative electrode slurry is coated on the electrode current collector by an arbitrary coating method and dried. To form a negative electrode.

In the present invention, the negative electrode active material is not particularly limited, and lithium titanium composite oxide (for example, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure) can be used. Even when a lithium-titanium composite oxide having a high reference potential is used as the negative electrode active material, the effects of the present invention described above can be obtained.

In the present invention, the binder is not particularly limited, and various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, and carboxymethylcellulose can be used.

Further, the organic solvent is not particularly limited, and examples thereof include basic solvents such as dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, acetonitrile, tetrahydrofuran, Nonaqueous solvents such as nitrobenzene and acetone, and protic solvents such as methanol and ethanol can be used. Moreover, the kind of organic solvent, the compounding ratio of the organic compound and the organic solvent, the kind of additive and the amount of the additive, and the like can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery.

Next, as shown in FIG. 1, the positive electrode 14 obtained above is immersed in an electrolyte, and after impregnating the positive electrode 14 with the electrolyte, on the positive current collector at the bottom center of the case 11 that also serves as the positive electrode terminal. The positive electrode 14 is placed. Thereafter, the separator 16 impregnated with the electrolyte is laminated on the positive electrode 14, the negative electrode 15 and the current collector plate 17 are sequentially laminated, and the electrolyte is injected into the internal space. Then, a metal spring member 18 is placed on the current collector plate 17, and a gasket 13 is arranged on the periphery, and a sealing plate 12 that also serves as a negative electrode terminal is fixed to the case 11 with a caulking machine or the like to seal the exterior. By doing so, the coin-type non-aqueous electrolyte secondary battery 1 is manufactured.

The electrolyte is interposed between the positive electrode 14 and the negative electrode 15 which is a counter electrode, and transports charge carriers between the two electrodes. As such an electrolyte, one having an ionic conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at room temperature can be used. For example, an electrolytic solution in which an electrolyte salt is dissolved in an organic solvent can be used. Examples of the electrolyte salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, Li (C ₂ F ₅ SO ₂ ) ₃ C, or the like can be used.

As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc. are used. be able to.

Moreover, you may use a solid electrolyte for electrolyte. Examples of the polymer compound used in the solid electrolyte include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-monofluoroethylene copolymer, and fluoride. Vinylidene fluoride polymers such as vinylidene-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and acrylonitrile-methyl methacrylate copolymer Polymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-ethyl methacrylate copolymer, acrylonitrile-ethyl acrylate copolymer, acrylonitrile-methacrylic acid copolymer, acrylonitrile- Examples include acrylonitrile polymers such as crylic acid copolymer and acrylonitrile-vinyl acetate copolymer, as well as polyethylene oxide, ethylene oxide-propylene oxide copolymer, and polymers of these acrylates and methacrylates. be able to. Moreover, you may use what made these polymer compounds contain electrolyte solution and made it gelatinous as electrolyte. Alternatively, only a polymer compound containing an electrolyte salt may be used as an electrolyte as it is. Incidentally, as an _{electrolyte, Li 2 S-P 2 S} 5 _{based, Li 2 S-B 2 S} 3 type, sulfide or glass represented by Li ₂ S-SiS ₂ system, such as oxides having a NASICON-type structure An inorganic solid electrolyte may be used.

In the above embodiment, the coin-type secondary battery has been described. However, it is needless to say that the battery shape is not particularly limited, and can be applied to a cylindrical type, a square type, a sheet type, and the like. Also, the exterior method is not particularly limited, and a metal case, mold resin, aluminum laminate film, or the like may be used.

Next, specific examples of the present invention will be described. In addition, the Example shown below is an example and this invention is not limited to the following Example.

As described in Examples 1 and 2 and Comparative Example 1 below, lithium iron phosphate represented by LiFePO ₄ having an olivine structure was synthesized, and a coin-type non-aqueous electrolyte secondary battery using the same was manufactured.

(Example 1)

The above lithium iron phosphate was synthesized by the following method.

Lithium hydroxide monohydrate (LiOH.H ₂ O) as a lithium (Li) -containing raw material, iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O), phosphorus (P) as an iron (Fe) -containing raw material Diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) was prepared as a containing raw material. These raw materials were weighed so that the molar ratio was Li: Fe: P = 1: 1: 1 and the mass after firing was 100 g. Further, ascorbic acid is added to the starting material so that 3% by mass of carbon remains with respect to the mass after firing, and water added to the starting material with respect to the total mass of the starting material weighed in a 1 liter container. Pure water was added to the starting material so that the mass ratio was 1.5, and wet mixing was performed for 25 hours to prepare a slurry. The obtained slurry was spray-dried in the air atmosphere to obtain a dry powder. The obtained dry powder was fired at 700 ° C. for 10 hours in a nitrogen gas atmosphere, thereby synthesizing the above lithium iron phosphate.

The obtained lithium iron phosphate was subjected to element mapping analysis by X-ray diffraction (XRD) measurement and energy dispersive X-ray spectroscopy (EDX: Energy Dispersive X-ray Spectroscopy). Moreover, the structure | tissue of the obtained lithium iron phosphate was observed with the scanning transmission electron microscope.

Using the obtained lithium iron phosphate as a positive electrode active material, a coin-type non-aqueous electrolyte secondary battery as shown in FIG. 1 was produced.

As shown in FIG. 1, a coin-type nonaqueous electrolyte secondary battery 1 includes a case 11 that also serves as a positive electrode terminal, a sealing plate 12 that also serves as a negative electrode terminal, and a gasket 13 that insulates the case 11 and the sealing plate 12. The positive electrode 14, the negative electrode 15, the separator 16 interposed between the positive electrode 14 and the negative electrode 15, the current collector plate 17 disposed on the negative electrode 15, and between the current collector plate 17 and the sealing plate 12. It is comprised from the arrange | positioned spring member 18, and the inside of case 11 is filled with electrolyte solution.

Specifically, the positive electrode mixture was prepared by mixing lithium iron phosphate, acetylene black, and polyvinylidene fluoride prepared above in a mass ratio of 88: 6: 6. This positive electrode mixture was dispersed in a solvent (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry. The positive electrode slurry was applied on the surface of an aluminum foil having a thickness of 20 μm at a coating amount of 10 mg / cm ² , dried at a temperature of 140 ° C., and then pressed at a pressure of 1 ton / cm ² to obtain a positive electrode sheet. Produced. The positive electrode 14 was produced by punching this positive electrode sheet into a disk having a diameter of 12 mm. As the negative electrode 15 as a counter electrode, a disk made of a metal lithium foil having a diameter of 15.5 mm was used. A current collector plate 17 was bonded to the negative electrode 15. As the separator 16, a disk-like polyethylene porous film having a diameter of 16 mm was used. As the electrolytic solution, an organic electrolytic solution in which 1 mol of lithium hexafluorophosphate (LiPF ₆ ) was dissolved per liter of the solvent in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 was used. In this way, a coin-type non-aqueous electrolyte secondary battery 1 having a diameter of 20 mm and a thickness of 3.2 mm was produced.

The charge / discharge characteristics were evaluated using the coin-type non-aqueous electrolyte secondary battery 1 produced as described above. In a constant temperature bath at 25 ° C., the battery was charged and discharged three times with a current value of 0.15 mA and a voltage range of 2.0 to 4.2 V. Thereafter, charging and discharging were performed once at each current value of 0.15 mA, 0.75 mA, 2.25 mA, and 3.75 mA in the same voltage range as described above.

(Example 2)

Lithium iron phosphate was synthesized in the same manner as in Example 1 except that ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) was used as the P-containing raw material. About the obtained lithium iron phosphate, the element mapping analysis by XRD measurement and EDX was performed. Moreover, the structure | tissue of the obtained lithium iron phosphate was observed with the scanning transmission electron microscope.

Using the obtained lithium iron phosphate as a positive electrode active material, a coin-type non-aqueous electrolyte secondary battery 1 was produced in the same manner as in Example 1. Using the produced coin-type non-aqueous electrolyte secondary battery 1, the charge / discharge characteristics of the battery were evaluated in the same manner as in Example 1.

(Comparative example 1)

リ チ ウ ム Lithium iron phosphate was synthesized in the same manner as in Example 1 except that ascorbic acid was not added to the starting material. About the obtained lithium iron phosphate, the element mapping analysis by XRD measurement and EDX was performed. Moreover, the structure | tissue of the obtained lithium iron phosphate was observed with the scanning transmission electron microscope.

Using the obtained lithium iron phosphate as a positive electrode active material, a coin-type non-aqueous electrolyte secondary battery 1 was produced in the same manner as in Example 1. Using the produced coin-type non-aqueous electrolyte secondary battery 1, the charge / discharge characteristics of the battery were evaluated in the same manner as in Example 1.

FIG. 2 shows the XRD measurement results for the lithium iron phosphate obtained in Examples 1 and 2 and Comparative Example 1 above. Scanning transmission electron micrographs of the structures of lithium iron phosphate obtained in Examples 1 and 2 and Comparative Example 1 are shown in FIGS. 3, 4, and 5, respectively.

From the fact that a peak was observed in the vicinity of 2θ = 41 ° in the XRD measurement shown in FIG. 2 and the element mapping analysis by EDX, the iron phosphide of different phases in the lithium iron phosphates of Examples 1 and 2 and Comparative Example 1 ( It was confirmed that Fe ₂ P) was present. As shown in FIGS. 3 to 5, the presence of iron phosphide particles (shown in black circles) was observed in the structure observation of lithium iron phosphate in Examples 1 and 2 and Comparative Example 1. . Also, as shown in FIGS. 3 and 4, in Examples 1 and 2, the oxygen-containing layer (iron phosphide particles) is coated so as to cover the surface of the iron phosphide particles (portions indicated by black circles). It was confirmed that a portion (shown in light gray) was present. In addition, element mapping analysis by EDX confirmed that the oxygen-containing layer contained iron. As shown in FIG. 5, in Comparative Example 1, the oxygen-containing layer (slightly lighter gray than the iron phosphide particles) is shown on the surface of the iron phosphide particles (portions shown in black circles). It is confirmed that there is no part).

As a result of evaluating the charge / discharge characteristics of the batteries produced in Examples 1 and 2 and Comparative Example 1, the ratio of the discharge capacity at the third cycle to the discharge capacity at the first cycle at a current value of 0.15 mA, That is, Table 1 shows the discharge capacity retention rate [%] (cycle characteristics).

From the results shown in Table 1, in the batteries of Examples 1 and 2 in which lithium iron phosphate containing iron phosphide particles and an oxygen-containing layer formed on the surface thereof was used as the positive electrode active material, only the iron phosphide particles were used. It turns out that cycling characteristics are more favorable than the battery of the comparative example 1 using the lithium iron phosphate containing as a positive electrode active material.

It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the claims.

According to the present invention, cycle characteristics can be improved in a non-aqueous electrolyte secondary battery using lithium iron phosphate as a positive electrode active material, and therefore the present invention is useful for manufacturing a non-aqueous electrolyte secondary battery. .

1: Coin-type non-aqueous electrolyte secondary battery, 11: case, 12: sealing plate, 13: gasket, 14: positive electrode, 15: negative electrode, 16: separator, 17: current collector plate, 18: spring member.

Claims (10)

A positive electrode active material mainly composed of lithium iron phosphate, comprising iron phosphide and an oxygen-containing layer formed on the surface of the iron phosphide. The positive electrode active material according to claim 1, wherein the oxygen-containing layer contains an iron oxide. A secondary battery comprising a positive electrode comprising the positive electrode active material according to claim 1. It is a manufacturing method of the positive electrode active material of any one of Claim 1 or Claim 2, Comprising:
A mixing step of mixing starting materials including a lithium-containing material, an iron-containing material and a phosphorus-containing material
A drying step of drying the mixture obtained in the mixing step in the air;
A firing step of firing the dried material obtained in the drying step,
The method for producing a positive electrode active material, wherein the mixing step includes a step of adding water to the starting material. The method for producing a positive electrode active material according to claim 4, wherein the mixing step includes a step of adding water having a mass ratio of 1.5 to 3.0 with respect to the total mass of the starting material. The method for producing a positive electrode active material according to claim 4, wherein the mixing step includes a step of adding an organic acid to the starting material. The method for producing a positive electrode active material according to claim 6, wherein the organic acid is ascorbic acid. The positive electrode active material according to any one of claims 4 to 7, wherein the lithium-containing raw material includes at least one selected from the group consisting of lithium hydroxide, lithium carbonate, and lithium acetate. Production method. The method for producing a positive electrode active material according to any one of claims 4 to 8, wherein the iron-containing raw material contains iron oxalate. The method for producing a positive electrode active material according to any one of claims 4 to 9, wherein the phosphorus-containing raw material contains at least one of diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

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