Battery and manufacturing method thereof

Abstract

To decrease reduction of initial capacitance with addition of Fe.SOLUTION: A battery includes a cathode, an anode and an electrolyte. The cathode contains a cathode active material. The cathode active material contains a lithium nickel composite oxide. The lithium nickel composite oxide contains Fe. An XAFS spectrum of a K absorption end of Fe in the cathode has a peak top in a range of 7132±2 eV.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a battery and a method for producing a positive electrode active material. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2010-021125 (Patent Document 1) discloses a lithium composite metal oxide containing nickel, manganese, and iron. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-021125 Summary of the Invention [Problem to be solved by the invention]

[0004] The addition of iron (Fe) to lithium nickel composite oxide (LNO) has been investigated. Hereinafter, LNO with added Fe will also be referred to as "LNO-Fe." LNO-Fe can have higher output than LNO. However, LNO-Fe tends to have a lower initial capacity than LNO. Therefore, the present disclosure aims to reduce the decrease in initial capacity in LNO-Fe. [Means for solving the problem]

[0005] 1. The battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material. The positive electrode active material includes a lithium nickel composite oxide. The lithium nickel composite oxide includes iron. The X-ray absorption fine structure spectrum of the positive electrode at the iron K absorption edge has a peak top within the range of 7132±2 eV.

[0006] In LNO-Fe, Fe tends to become trivalent. When LNO-Fe contains trivalent Fe, it is thought that the divalent nickel (Ni) increases to compensate for the charge imbalance in the compound as a whole. Divalent Ni tends to occupy lithium (Li) sites. The phenomenon in which Ni, which should be on the Ni site, becomes mixed into the Li site is also called "cation mixing." It is thought that cation mixing reduces the initial capacity.

[0007] In LNO-Fe, the presence of Fe in a less than trivalent state can reduce cation mixing. The valence of Fe can be confirmed by X-ray absorption fine structure (XAFS) spectroscopy. That is, in XAFS measurements of the positive electrode, when the XAFS spectrum at the K absorption edge of Fe has a peak top within the range of 7132±2 eV, it is believed that Fe may exist in a less than trivalent state.

[0008] 2. In the battery described in the above item "1," the lithium nickel composite oxide may contain, for example, 1 to 2% by mass of iron.

[0009] When the Fe content is 1 to 2%, for example, there tends to be a good balance between output and initial capacity. Note that a numerical range such as "m to n%" includes both the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% but less than n%."

[0010] 3. In the battery according to the above item "1" or "2," the lithium nickel composite oxide may contain, for example, at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide and lithium nickel cobalt aluminum composite oxide.

[0011] In addition to Ni and Fe, LNO-Fe may contain, for example, cobalt (Co), manganese (Mn), aluminum (Al), and the like.

[0012] 4. A method for producing a positive electrode active material includes the following steps (a) to (c) in this order: (a) A lithium nickel composite oxide containing iron is prepared. (b) A mixture is formed by mixing a lithium nickel composite oxide with a reducing agent. (c) Heating the mixture in an inert atmosphere produces a positive electrode active material.

[0013] For example, the valence of Fe can be reduced to less than 3 by heat treating a mixture of LNO-Fe and a reducing agent under an inert atmosphere.

[0014] 5. In the method for producing a positive electrode active material described in "4" above, the lithium nickel composite oxide may contain, for example, at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide and lithium nickel cobalt aluminum composite oxide. The lithium nickel composite oxide may contain 1 to 2% by mass of iron. The reducing agent may contain, for example, ascorbic acid.

[0015] For example, ascorbic acid can be used as a reducing agent.

[0016] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. The present embodiment and the example are illustrative in all respects. The present embodiment and the example are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configuration may be extracted from the present embodiment and the example and that they may be arbitrarily combined. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a conceptual diagram of a battery according to this embodiment. [Figure 2]Figure 2 shows an example of an XAFS spectrum. [Figure 3] FIG. 3 is a schematic flowchart of the method for producing a positive electrode active material in this embodiment. [Figure 4] FIG. 4 is a table showing the manufacturing conditions and initial capacities of the positive electrode active materials. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Battery> FIG. 1 is a conceptual diagram of a battery according to this embodiment. The battery 100 is a lithium-ion battery. The battery 100 includes a power generating element 50. The power generating element 50 may be housed in an exterior body (not shown). The exterior body may have any shape. The exterior body may be, for example, a metal case or a pouch made of a metal foil laminate film. The case may be, for example, rectangular or cylindrical.

[0019] The power generating element 50 includes a positive electrode 10, a negative electrode 20, and an electrolyte 30. That is, the battery 100 includes the positive electrode 10, the negative electrode 20, and the electrolyte 30. The power generating element 50 may have any form. For example, the power generating element 50 may be a laminated type or a wound type.

[0020] 《Positive electrode》 The positive electrode 10 may be, for example, in the form of a sheet. The positive electrode 10 may include, for example, a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector may include, for example, Al foil or the like. The positive electrode active material layer may be disposed on the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. That is, the positive electrode 10 includes a positive electrode active material. The positive electrode active material layer may further include a conductive material, a binder, and the like in addition to the positive electrode active material. The conductive material can form an electron conduction path within the positive electrode active material layer. The conductive material may include, for example, at least one selected from the group consisting of carbon black (e.g., acetylene black (AB), Ketjen Black (registered trademark), etc.), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF). The amount of the conductive material may be, for example, 0.1 to 15 parts by mass per 100 parts by mass of the positive electrode active material. The binder can fix the positive electrode active material layer to the positive electrode current collector. The binder may contain, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA). The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material.

[0021] <Cathode active material> The positive electrode active material may be, for example, a particle group. The positive electrode active material may have, for example, a D50 of 1 to 30 μm. "D50" refers to the particle size at which the cumulative frequency of particles with smaller particle sizes reaches 50% in a volume-based particle size distribution. The particle size distribution can be measured using a laser diffraction particle size distribution analyzer.

[0022] The positive electrode active material can cause a positive electrode reaction. The positive electrode active material contains lithium nickel composite oxide (LNO). LNO contains Fe. That is, the positive electrode active material contains LNO-Fe. LNO-Fe can have any crystal structure. The crystal structure may be, for example, a layered rock salt type, a cubic rock salt type, etc. In LNO-Fe, Fe may be, for example, an interstitial solid solution atom or a substitutional solid solution atom. The content of Fe in LNO-Fe may be, for example, 0.1 to 3%, 0.1 to 2.5%, 1 to 2.5%, or 1 to 2% by mass fraction. When the content of Fe is 1 to 2%, for example, there is a tendency for a good balance between output and initial capacity.

[0023] LNO-Fe may contain, for example, at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide and lithium nickel cobalt aluminum composite oxide.

[0024] LNO-Fe may have, for example, a composition represented by the following general formula. Li , ,

[0027] ,

[0026] , , (Ni x M 1-x ) 1-y Fe y O2 In the above general formula, a, x, and y may satisfy, for example, the relationship of -0.5 ≤ a ≤ 0.5, 0 < x ≤ 1, 0.001 ≤ y ≤ 0.05. M may contain, for example, at least one selected from the group consisting of Co, Mn, and Al.

[0025] In the above general formula, x may satisfy, for example, the relationship of 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ , 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x ≤ 1.

[0026] In the above general formula, y may satisfy, for example, the relationship of 0.01 ≤ y ≤ 0.05, 0.01 ≤ y ≤ 0.04, or 0.02 ≤ y ≤ 0.04.

[0027] LNO-Fe may contain Fe less than trivalent. LNO-Fe may contain, for example, divalent Fe. When the valence of Fe is less than 3, the decrease in initial capacity due to the addition of Fe can be reduced. This is thought to be due to the reduction in cation mixing between the Ni site and the Li site.

[0028] <XAFS Measurement> In LNO-Fe, the fact that the valence of Fe is less than 3 can be confirmed by XAFS measurement of the positive electrode 10. Examples of facilities that can perform XAFS measurement include the beamline "BL11S2" at the "Aichi Synchrotron Light Center."

[0029] The positive electrode 10 (electrode plate, sheet) is cut to a predetermined size to prepare a measurement sample. The XAFS spectrum at the K absorption edge of Fe is measured by a fluorescence method. The measurement conditions are as follows:

[0030] Ring: 1.2 GeV Measurement range: 7073.26~7163.26eV Step width: 0.30eV Time: 1.00s

[0031] FIG. 2 shows an example of an XAFS spectrum. The horizontal axis of the graph represents X-ray energy. The vertical axis represents absorbance. The absorbance is normalized. The "peak top" indicates the point where the absorbance reaches its maximum value within the range of 7110 to 7160 eV. The XAFS spectrum of No. 5 has a peak top in the range of 7140 eV or higher. The valence of Fe contained in No. 5 is believed to be 3. LNO-Fe of No. 1 is obtained by subjecting LNO-Fe of No. 5 to a reduction treatment. The XAFS spectrum of No. 1 has a peak top in the range of 7132±2 eV (7130 to 7134 eV). The valence of Fe contained in No. 1 is believed to be less than 3. The valence of Fe contained in No. 1 may be 2. A battery 100 including a positive electrode 10 of No. 1 is expected to exhibit reduced initial capacity. The manufacturing conditions for Nos. 1 and 5 are described below.

[0032] As long as the XAFS spectrum at the K absorption edge of Fe has a peak top within the range of 7132 ± 2 eV, additional elements (dopants) may be added to LNO-Fe. The dopant may include, for example, at least one selected from the group consisting of B, C, N, halogen, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Sn, W, and lanthanoids. The surface of LNO-Fe (particles) may be coated with, for example, an oxide solid electrolyte (such as LiNbO3, Li3PO4, etc.).

[0033] 《Negative electrode》 The negative electrode 20 may be, for example, sheet-shaped. The negative electrode 20 may include, for example, a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector may include, for example, a Cu foil or the like. The negative electrode active material layer may be disposed on the surface of the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material may be powdery or sheet-shaped. The negative electrode active material may be, for example, natural graphite, artificial graphite, soft carbon, hard carbon, Si, SiO x (0 < x < 2), Si-based alloy, Sn, SnO x (0 < x < 2), Li, Li-based alloy, and Li4Ti5O 12 and may include at least one selected from the group consisting of. The negative electrode active material layer may further include a conductive material, a binder, and the like. The negative electrode active material layer may include, for example, VGCF, CMC, styrene-butadiene rubber (SBR), etc.

[0034] 《Electrolyte》 The electrolyte 30 can form an ion conduction path between the positive electrode 10 and the negative electrode 20. The electrolyte 30 can be a liquid, a polymer gel, or a solid. The liquid electrolyte can include, for example, a lithium salt and a solvent. The lithium salt can include, for example, LiPF6. The solvent can include, for example, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or the like. The gel electrolyte can include a liquid electrolyte and a polymer material. The polymer material can include, for example, PVdF-HFP, polyethylene oxide (PEO), or the like. The solid electrolyte can include, for example, a sulfide Li ion conductor (Li3PS4, etc.). The solid electrolyte can also function to separate the positive electrode 10 and the negative electrode 20.

[0035] <Separator> For example, when the battery 100 includes a liquid electrolyte or a gel electrolyte, the battery 100 may further include a separator (not shown). The separator may include, for example, a porous film. The separator is disposed between the positive electrode 10 and the negative electrode 20. The liquid electrolyte can permeate the separator. The separator may include, for example, a porous film made of polyolefin.

[0036] <Method of manufacturing positive electrode active material> 3 is a schematic flowchart of a method for producing a cathode active material according to this embodiment. Hereinafter, the "method for producing a cathode active material according to this embodiment" may be abbreviated as "this production method." This production method includes "(a) preparation of LNO-Fe," "(b) addition of a reducing agent," and "(c) second heat treatment."

[0037] (a) Preparation of LNO-Fe The production method includes preparing LNO-Fe. LNO-Fe may be synthesized or commercially available. For example, LNO-Fe may be synthesized by coprecipitation. That is, the production method may include, for example, "(a1) preparation of a raw material solution," "(a2) crystallization," and "(a3) first heat treatment."

[0038] (a1) Preparation of raw material solution For example, a raw material solution can be prepared by dissolving various raw materials in water. For example, a raw material solution can be prepared by dissolving NiSO4, CoSO4, MnSO4, Al2(SO4)3, FeSO4, etc. in ion-exchanged water. The concentration of the raw material solution can be, for example, 10 to 40% by mass fraction.

[0039] <(a2) Crystallization> For example, ammonia water is placed in a reaction vessel. While the ammonia water is being stirred, the atmosphere in the vessel is replaced with nitrogen. NaOH is mixed with the ammonia water to form a reaction solution. The reaction solution is alkaline. The pH of the reaction solution can be adjusted by the amount of NaOH added.

[0040] The raw material solution and aqueous ammonia are added dropwise to the reaction solution so that the pH of the reaction solution is maintained within a predetermined range. This produces a coprecipitate. The coprecipitate contains a metal hydroxide. The metal hydroxide is a precursor of LNO-Fe. The coprecipitate can be recovered, for example, by filtration. For example, the coprecipitate may be washed with ion-exchanged water. After washing, the coprecipitate is dried to form a dried product.

[0041] (a3) First Heat Treatment For example, the dried material and a Li raw material are mixed in a mortar to form a mixture. The Li raw material may include, for example, LiOH, Li2CO3, etc. For example, the mixture is subjected to a first heat treatment in a muffle furnace or the like. LNO-Fe can be synthesized by the first heat treatment. The first heat treatment may also be referred to as a "first firing." The heat treatment temperature may be, for example, 800 to 1100°C. The heat treatment time may be, for example, 8 to 16 hours. After the first heat treatment, the LNO-Fe may be crushed to adjust the particle size of the LNO-Fe. For example, the LNO-Fe may be crushed using a jet mill or the like.

[0042] (b) Addition of a reducing agent The method includes mixing LNO-Fe with a reducing agent to form a mixture. For example, the LNO-Fe and reducing agent may be mixed in a mortar. The reducing agent may be solid or liquid. For example, the reducing agent may include at least one selected from the group consisting of L-ascorbic acid, isoascorbic acid, catechin, dibutylhydroxytoluene, tocopherol, and butylhydroxyanisole.

[0043] (c) Second Heat Treatment The method includes producing a positive electrode active material by heating a mixture (LNO-Fe and a reducing agent) in an inert atmosphere. The second heat treatment can reduce Fe in the LNO-Fe. The second heat treatment can also be referred to as "second calcination." In the second heat treatment, trivalent Fe can be reduced to Fe less than trivalent. In the second heat treatment, trivalent Fe can be reduced to divalent Fe.

[0044] The second heat treatment may be carried out in a muffle furnace or the like. The inert atmosphere may be, for example, an argon atmosphere (Ar) or a nitrogen atmosphere (N2). The heat treatment temperature may be, for example, 800 to 1100°C. The heat treatment time may be, for example, 8 to 16 hours. After the second heat treatment, the positive electrode active material may be crushed to adjust the particle size of the positive electrode active material. For example, the positive electrode active material may be crushed using a jet mill or the like. [Example]

[0045] <Sample preparation> Positive electrode active materials Nos. 1 to 11 were produced as follows. Hereinafter, for example, "positive electrode active material No. 1" may be abbreviated as "No. 1".

[0046] No. 1 A raw material solution was formed by dissolving NiSO4, CoSO4, MnSO4, and FeSO4 in ion-exchanged water. The molar ratio of Ni, Co, and Mn in the raw material solution was "Ni / Co / Mn = 1 / 1 / 1." The solute concentration in the raw material solution was 30% (mass fraction).

[0047] Ammonia water was placed in a reaction vessel. While stirring the ammonia water with a stirrer, the atmosphere in the reaction vessel was replaced with nitrogen. NaOH was then added to the reaction vessel to form a reaction liquid.

[0048] A coprecipitate was formed by adding the raw material solution and aqueous ammonia dropwise to the reaction solution so that the pH of the reaction solution remained within a certain range. The coprecipitate was recovered by filtering the reaction solution. The coprecipitate was dispersed in ion-exchanged water to form a dispersion. The dispersion was thoroughly stirred with a spatula. That is, the coprecipitate was washed with water. After washing with water, the dispersion was filtered to recover the coprecipitate. The coprecipitate was dried at 120°C for 16 hours to form a dried product.

[0049] The dried material was mixed with Li2CO3 in a mortar. This formed a mixture. The mixture was subjected to a first heat treatment in a muffle furnace to synthesize LNO-Fe. LNO-Fe is a crystalline solid obtained by the synthesis of Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 ) 1-y Fe y The LNO-Fe had a composition of 0.02. The Fe content was 1% by mass. The heat treatment temperature was 950°C. The heat treatment time was 10 hours. After the first heat treatment, the LNO-Fe was crushed using a jet mill.

[0050] LNO-Fe and a reducing agent (ascorbic acid) were mixed to form a mixture. The mixture was subjected to a second heat treatment in a muffle furnace to produce a positive electrode active material. The heat treatment atmosphere was a nitrogen atmosphere. The heat treatment temperature was 950°C. The heat treatment time was 10 hours. After the second heat treatment, the positive electrode active material was crushed using a jet mill.

[0051] No.2~4 4 is a table showing the manufacturing conditions and initial capacity of the positive electrode active material. The positive electrode active material was manufactured in the same manner as No. 1, except that the content (addition amount) of Fe in LNO-Fe was changed.

[0052] No.5 A coprecipitate containing no Fe was synthesized. The coprecipitate was subjected to the first heat treatment to synthesize LNO. LNO was synthesized by adding Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 The LNO had a composition of 0.02g / L. The LNO was crushed using a jet mill to produce a positive electrode active material. The LNO was not subjected to a second heat treatment.

[0053] No.6 A coprecipitate containing Fe was synthesized. The coprecipitate was subjected to the first heat treatment to synthesize LNO-Fe. LNO-Fe is a Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 ) 1-y Fe y The LNO-Fe had a composition of 0. The Fe content in the LNO-Fe was 1% by mass. The LNO-Fe was crushed to produce a positive electrode active material. The LNO-Fe was not subjected to a second heat treatment.

[0054] No.7 The LNO No. 5 was subjected to a second heat treatment. The second heat treatment was carried out in an air atmosphere. The heat treatment temperature was 950°C. The heat treatment time was 10 hours. After the second heat treatment, the LNO was crushed to produce a positive electrode active material.

[0055] No.8 The LNO-Fe of No. 6 was subjected to a second heat treatment. The second heat treatment was carried out in an air atmosphere. The heat treatment temperature was 950°C. The heat treatment time was 10 hours. After the second heat treatment, the LNO-Fe was crushed to produce a positive electrode active material.

[0056] No.9 No. 6 LNO-Fe was mixed with a reducing agent (ascorbic acid) to form a mixture. The mixture was subjected to a second heat treatment. The second heat treatment was carried out in an air atmosphere. The heat treatment temperature was 950°C. The heat treatment time was 10 hours. After the second heat treatment, the LNO-Fe was crushed to produce a positive electrode active material.

[0057] No.10 The LNO No. 5 was subjected to a second heat treatment. The second heat treatment was carried out in a nitrogen atmosphere. The heat treatment temperature was 950°C. The heat treatment time was 10 hours. After the second heat treatment, the LNO was crushed to produce a positive electrode active material.

[0058] No. 11 The LNO-Fe of No. 6 was subjected to a second heat treatment. The second heat treatment was carried out in a nitrogen atmosphere. The heat treatment temperature was 950°C. The heat treatment time was 10 hours. After the second heat treatment, the LNO-Fe was crushed to produce a positive electrode active material.

[0059] <Evaluation> Test batteries containing positive electrode active materials Nos. 1 to 11 were fabricated, respectively. The initial capacities of the test batteries were measured. In the table of FIG. 4, the initial capacity values ​​are relative to the value of No. 1.

[0060] The test battery configuration was as follows: Cylindrical lithium-ion battery Power generating element: Wound type Positive electrode: Positive electrode active material / AB / PVDF=88 / 10 / 2 (mass ratio) Negative electrode: Negative electrode active material (natural graphite), CMC, SBR Electrolyte: LiPF6 (1 mol / L), EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0061] The positive and negative electrodes were manufactured by coating the surface of a current collector (metal foil) with the slurry. An Allgood film applicator (with a film thickness adjustment function) was used as the coating device. After coating the slurry, the coating was dried at 80°C for 5 minutes.

[0062] <Result> In the table of FIG. 4, for example, in a comparison between No. 5 and No. 6, it can be seen that the addition of Fe to LNO tends to decrease the initial capacity.

[0063] In Nos. 1 to 4, the decrease in initial capacity due to the addition of Fe was reduced. This is thought to be because Fe was reduced to a valence of less than three by the second heat treatment (reducing agent and inert atmosphere).

[0064] The initial capacity of No. 9 decreased. The second heat treatment of No. 9 was not performed in an inert atmosphere.

[0065] The initial capacity of No. 11 decreased. No reducing agent was used in the second heat treatment of No. 11.

[0066] XAFS measurements were carried out on the positive electrodes. For Nos. 1 to 4, the XAFS spectra at the K absorption edge of Fe had peak tops within the range of 7132±2 eV. For Nos. 5 to 11, the XAFS spectra at the K absorption edge of Fe had peak tops outside the range of 7132±2 eV. The XAFS spectra at the K absorption edge of Fe for Nos. 1 and 5 are shown in FIG. 2. [Explanation of symbols]

[0067] 10 positive electrodes, 20 negative electrodes, 30 electrolytes, 50 power generating elements, 100 batteries.

Claims

1. a positive electrode, a negative electrode, and an electrolyte; the positive electrode includes a positive electrode active material, the positive electrode active material contains a lithium nickel composite oxide, the lithium nickel composite oxide contains 0.1 to 2% by mass of iron, The X-ray absorption fine structure spectrum at the iron K absorption edge of the positive electrode has a peak top within a range of 7132 ± 2 eV. battery.

2. The lithium nickel composite oxide contains 1 to 2% iron by mass fraction. The battery of claim 1 .

3. The lithium nickel composite oxide includes at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide and lithium nickel cobalt aluminum composite oxide. The battery of claim 1 .

4. A method for manufacturing the battery according to claim 1, comprising: (a) preparing a lithium nickel composite oxide containing iron; (b) mixing the lithium nickel composite oxide with a reducing agent to form a mixture; and (c) heating the mixture under an inert atmosphere to produce a positive electrode active material; in this order, How batteries are manufactured.

5. the lithium nickel composite oxide includes at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide and lithium nickel cobalt aluminum composite oxide, the lithium nickel composite oxide contains 1 to 2% by mass of iron, The reducing agent includes ascorbic acid. The method for manufacturing the battery according to claim 4 .

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