Positive electrode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

The present invention relates to a positive electrode active material for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery. A positive electrode active material for a non-aqueous electrolyte secondary battery, which contains a lithium transition metal composite compound that is a Li excess system and is represented by the general formula LixMnyNizMe [alpha] OaFb (wherein 1 < = x < = 1.2, 0.4 < = y < = 0.8, 0 < = z < = 0.4, x + y + z = 2, 0 < alpha < = 0.05, 1.8 < = a < = 2, 1.8 < = a + b < = 2.2, Me being at least two elements selected from the group consisting of metal elements other than Li, Mn, and Ni, and the Me is an element having an ion radius of # imgabs0 # or more.

Description

[0001] This application is a divisional application of an application filed on October 13, 2020, with application number 202080089411.6, and invention name “Positive electrode active material for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery”. Technical Field

[0002] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery. Background Art

[0003] In the past, lithium transition metal composite compounds have been widely used as positive electrode active materials for secondary batteries such as lithium ion batteries, and Li-excess positive electrode active materials containing a large amount of Li for high-output secondary batteries have attracted much attention. However, batteries using Li-excess positive electrode active materials have the problem that the battery voltage decreases with repeated charge and discharge. Patent document 1 discloses a technology for suppressing the decrease in battery voltage caused by charge and discharge cycles by improving the composition of Li-excess positive electrode active materials.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6342161 Summary of the invention

[0007] The initial voltage of a battery using the Li-excess positive electrode active material disclosed in Patent Document 1 is as low as about 3.58V.

[0008] The positive electrode active material for a non-aqueous electrolyte secondary battery as one embodiment of the present disclosure includes a lithium transition metal composite compound. The lithium transition metal composite compound is represented by the general formula Li x Mn y Ni z Me α O a F b (wherein, 1≤x≤1.2, 0.4≤y≤0.8, 0≤z≤0.4, x+y+z=2, 0<α≤0.05, 1.8≤a≤2, 1.8≤a+b≤2.2, Me is at least two or more elements selected from metal elements other than Li, Mn, and Ni) means that Me contains at least one or more ionic radius of The above elements.

[0009] A nonaqueous electrolyte secondary battery as one embodiment of the present disclosure includes a positive electrode including the positive electrode active material for a nonaqueous electrolyte secondary battery, a negative electrode, and a nonaqueous electrolyte.

[0010] The positive electrode active material for a nonaqueous electrolyte secondary battery as one embodiment of the present disclosure can increase the initial voltage of the secondary battery and suppress a decrease in the battery voltage due to charge and discharge cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a longitudinal cross-sectional view of a cylindrical secondary battery as an example of an embodiment.

[0012] Description of Reference Numerals

[0013] 10 Secondary batteries

[0014] 11 Positive electrode

[0015] 12 Negative electrode

[0016] 13 Divider

[0017] 14 Electrode body

[0018] 15 Outer shell

[0019] 16 Sealing body

[0020] 17, 18 Insulation board

[0021] 19 Positive lead

[0022] 20 Negative lead

[0023] 21 Groove

[0024] 22 Metal plates with partial openings

[0025] 23 Lower valve body

[0026] 24 Insulation components

[0027] 25 Upper valve body

[0028] 26 Cover

[0029] 26a Opening

[0030] 27 Gasket DETAILED DESCRIPTION

[0031] Li-excess positive electrode active materials, which are formed by replacing part of the transition metal layer of a lithium transition metal composite compound having a layered rock salt structure with Li, have attracted much attention as materials for high-output secondary batteries. However, when charging and discharging are repeated, there is a problem of reduced battery output. The inventors of the present invention conducted in-depth research on this issue and found that: by replacing part of the transition metal layer of a lithium transition metal composite compound having a layered rock salt structure with Li, The structure of the lithium transition metal composite compound is stabilized by solid solution of the above metal elements. In addition, by including two or more metal elements with ionic radius of The above metal elements increase the configuration entropy and stabilize the solid solution. Therefore, a positive electrode active material for a non-aqueous electrolyte secondary battery in the form shown below is conceived, which can increase the initial voltage of the secondary battery and suppress the battery voltage drop caused by the charge and discharge cycle.

[0032] The positive electrode active material for a non-aqueous electrolyte secondary battery as one embodiment of the present disclosure includes a lithium transition metal composite compound. The lithium transition metal composite compound is represented by the general formula Li x Mn y Ni z Me α O a F b (wherein, 1≤x≤1.2, 0.4≤y≤0.8, 0≤z≤0.4, x+y+z=2, 0<α≤0.05, 1.8≤a≤2, 1.8≤a+b≤2.2, Me is at least two or more elements selected from metal elements other than Li, Mn, and Ni) means that Me contains at least one or more ionic radius of The above elements.

[0033] Hereinafter, an example of an embodiment of a cylindrical secondary battery disclosed in the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, values, directions, etc. are examples for easy understanding of the present invention and may be appropriately changed according to the specifications of the cylindrical secondary battery. In addition, the outer shell is not limited to a cylindrical shape, for example, it may be a square shape, etc. In addition, in the following description, when multiple embodiments and variations are included, it is initially envisioned that these characteristic parts will be appropriately combined and used.

[0034] Figure 1 It is an axial cross-sectional view of a cylindrical secondary battery 10 as an example of the embodiment. Figure 1 In the secondary battery 10 shown, an electrode body 14 and a nonaqueous electrolyte (not shown) are housed in an outer shell 15. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound via a separator 13. It should be noted that, for the sake of convenience, the following description will be made with the sealing body 16 side as the "upper" and the bottom side of the outer shell 15 as the "lower".

[0035] The open end of the outer shell 15 is sealed by the sealing body 16, thereby the interior of the secondary battery 10 is sealed. Insulating plates 17 and 18 are respectively provided on the upper and lower parts of the electrode body 14. The positive lead 19 extends upward through the through hole of the insulating plate 17 and is welded to the lower surface of the metal plate 22 which is partially opened as the bottom plate of the sealing body 16. In the secondary battery 10, the cover 26 which is the top plate of the sealing body 16 electrically connected to the partially opened metal plate 22 becomes the positive terminal. On the other hand, the negative lead 20 extends to the bottom side of the outer shell 15 through the through hole of the insulating plate 18 and is welded to the bottom inner surface of the outer shell 15. In the secondary battery 10, the outer shell 15 becomes the negative terminal. It should be noted that when the negative lead 20 is provided at the terminal part, the negative lead 20 extends to the bottom side of the outer shell 15 through the outside of the insulating plate 18 and is welded to the bottom inner surface of the outer shell 15.

[0036] The outer shell 15 is, for example, a metal outer can in a cylindrical shape with a bottom. A gasket 27 is provided between the outer shell 15 and the sealing body 16 to ensure the sealing property inside the secondary battery 10. The outer shell 15 has, for example, a groove 21 formed by pressing the side surface from the outside to support the sealing body 16. The groove 21 is preferably formed in an annular shape along the circumferential direction of the outer shell 15, and the sealing body 16 is supported by the gasket 27 on its upper surface.

[0037] The sealing body 16 has a partially open metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cover 26, which are stacked in sequence from the electrode body 14 side. The components constituting the sealing body 16 have, for example, a disc shape or a ring shape, and the components except the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, and the insulating member 24 is inserted between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat, for example, the lower valve body 23 will break, and the upper valve body 25 will expand toward the cover 26 side and away from the lower valve body 23, thereby cutting off the electrical connection between the two. As a result, the internal pressure rises, the upper valve body 25 will break, and the gas will be discharged from the opening 26a of the cover 26.

[0038] Hereinafter, the positive electrode 11 , the negative electrode 12 , the separator 13 , and the nonaqueous electrolyte constituting the secondary battery 10 , in particular, the positive electrode active material contained in the positive electrode composite material layer constituting the positive electrode 11 will be described in detail.

[0039] [positive electrode]

[0040] The positive electrode 11 has a positive electrode core and a positive electrode composite material layer disposed on the surface of the positive electrode core. The positive electrode core can be made of a foil of a metal such as aluminum that is stable within the potential range of the positive electrode 11, a thin film having the metal disposed on the surface, and the like. The positive electrode composite material layer preferably includes a positive electrode active material, a binding material, and a conductive material, and is disposed on both sides of the positive electrode core except for the portion connected to the positive electrode lead 19. The positive electrode 11 can be manufactured, for example, by coating a positive electrode composite material slurry including a positive electrode active material, a binding material, and a conductive material on the surface of the positive electrode core, drying the coating, and then compressing it to form the positive electrode composite material layer on both sides of the positive electrode core.

[0041] As the conductive material included in the positive electrode composite material layer, carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be exemplified. As the binding material included in the positive electrode composite material layer, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, etc. can be exemplified. These resins can also be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0042] The positive electrode active material includes a lithium transition metal composite compound. The lithium transition metal composite compound preferably has a crystal structure of an O3 structure. For example, from the perspective of the stability of the crystal structure, the O3 structure preferably accounts for more than 50% by volume of the crystal structure of the lithium transition metal composite compound, more preferably more than 90% by volume, further preferably more than 98% by volume, and particularly preferably 100% by volume. Here, the O3 structure refers to a layered crystal structure in which lithium is present at the center of an oxygen octahedron, and the overlapping manner of oxygen and transition metal is a layered crystal structure in which there are three types per unit lattice, and belongs to the space group R-3m or C2 / m.

[0043] Lithium transition metal complex compounds are represented by the general formula Li x Mn y Ni z Me α O a F b (wherein, 1≤x≤1.2, 0.4≤y≤0.8, 0≤z≤0.4, x+y+z=2, 0<α≤0.05, 1.8≤a≤2, 1.8≤a+b≤2.2, Me is at least two or more elements selected from metal elements other than Li, Mn, and Ni) means that Me contains at least one or more ionic radius of The above elements. A secondary battery having a positive electrode containing such a positive electrode active material can increase the initial voltage of the secondary battery and suppress the reduction of the battery voltage caused by the charge and discharge cycle. The molar fraction of each element constituting the lithium transition metal composite compound can be determined, for example, by inductively coupled plasma (ICP) emission spectrometry. The positive electrode active material has a lithium transition metal composite compound as a main component, or it can be composed only of a lithium transition metal composite compound. It should be noted that, without prejudice to the purpose of the present disclosure, the positive electrode active material may also contain a composite compound other than the lithium transition metal composite compound.

[0044] Me may also contain at least one element selected from K, Sr, Ba, Bi, Ca, La, Pr, Y, Dy, Sn, and Zn. The ionic radii of these elements are shown in Table 1. In addition, from the viewpoint of the difficulty of solid solution in the lithium transition metal composite compound, the ionic radius of Me is preferably the following.

[0045] [Table 1]

[0046]

[0047] Me may contain at least one element selected from Sr, Ca, Y, and Sn. This can suppress the voltage drop caused by the charge and discharge cycle and improve the initial voltage.

[0048] Me is preferably substantially composed of at least three or more elements selected from Sr, Ca, Y, and Sn. Thus, the voltage drop caused by the charge-discharge cycle can be more reliably suppressed, and the initial voltage can be improved. Here, "substantially composed of A" means that A is the main component, and other than A can be included within the scope that does not damage the purpose of the present disclosure.

[0049] Me preferably contains at least an alkaline earth metal element. Alkaline earth metal elements are cheap and easily available, and therefore are ideal. From the viewpoint of the ease of solid solution, Sr and Ca are more preferred.

[0050] The molar fraction α of Me preferably satisfies 0.01≤α≤0.03. By setting α≥0.01 or more, the voltage drop caused by the charge and discharge cycle can be more reliably suppressed. In addition, by setting α≤0.03, the molar fractions of Mn and Ni can be increased, so that the battery can have a high capacity.

[0051] The lithium transition metal composite compound can be manufactured, for example, as follows: adding / mixing raw materials such as Li compounds, Mn compounds, Ni compounds, and Me compounds in a prescribed molar ratio, crushing / mixing the obtained mixture by mechanochemical treatment using a ball mill, etc., and calcining the crushed / mixed mixture to manufacture it. The calcination temperature of the mixture is preferably in the range of 700°C to 1000°C. The calcination atmosphere is preferably in an oxygen atmosphere or in the air. In addition, the mixture to which each raw material is added / mixed may be calcined without mechanochemical treatment, thereby manufacturing the lithium transition metal composite compound, but from the perspective of easy solid solution of Me, it is desirable to perform mechanochemical treatment.

[0052] The Li compound is not particularly limited, and may be, for example, LiF, Li2CO3, LiOH, etc. The Mn compound is not particularly limited, and may be, for example, LiMnO2, Li2MnO3, Mn2O3, MnO, Mn3O4, etc. The Ni compound is not particularly limited, and may be, for example, LiNiO2, NiO, etc. The Me compound is not particularly limited, and may be, for example, an oxide of Me, specifically, MeO, Me2O3, MeO2, etc.

[0053] [negative electrode]

[0054] The negative electrode 12 has a negative electrode core and a negative electrode composite material layer disposed on the surface of the negative electrode core. The negative electrode core can be made of a foil of a metal such as copper that is stable within the potential range of the negative electrode, a thin film having the metal disposed on the surface, or the like. The negative electrode composite material layer preferably contains a negative electrode active material and a binding material, and is disposed on both sides of the negative electrode core except for the portion connected to the negative electrode lead 20. The negative electrode 12 can be manufactured, for example, by coating a negative electrode composite material slurry containing a negative electrode active material and a binding material on the surface of the negative electrode core, drying the coating, and then compressing the negative electrode composite material layer to form the negative electrode composite material layer on both sides of the negative electrode core.

[0055] In the negative electrode composite material layer, as the negative electrode active material, for example, a carbon-based active material capable of reversibly storing and releasing lithium ions is included. Ideal carbon-based active materials are natural graphites such as flaky graphite, blocky graphite, and earthy graphite, blocky artificial graphite (MAG), and graphitized mesophase carbon microbeads (MCMB) and other artificial graphites. In addition, the negative electrode active material may also use a Si-based active material composed of at least one of Si and a Si-containing compound, and may also use a carbon-based active material and a Si-based active material in combination.

[0056] The binding material included in the negative electrode composite material layer is the same as that of the positive electrode, and fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc. can also be used, but styrene-butadiene rubber (SBR) is preferably used. In addition, the negative electrode composite material layer preferably also includes CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. Among them, it is ideal to use SBR and CMC or its salt, PAA or its salt in combination.

[0057] [Separator]

[0058] The separator 13 may be, for example, a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, nonwoven fabrics, and the like. As the material of the separator, olefin resins such as polyethylene and polypropylene, cellulose, and the like are ideal. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, it may be a multilayer separator including a polyethylene layer and a polypropylene layer, or a separator 13 having a surface coated with materials such as aramid resins and ceramics may be used.

[0059] [Non-aqueous electrolyte]

[0060] The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (electrolyte), and may also be a solid electrolyte using a gel-like polymer or the like. The non-aqueous solvent may use, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of these. The non-aqueous solvent may also contain a halogen substituted product obtained by replacing at least a portion of the hydrogen of these solvents with a halogen atom such as fluorine.

[0061] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylates such as γ-butyrolactone and γ-valerolactone; and chain carboxylates such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, and γ-butyrolactone.

[0062] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diisopropyl ... Hexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and other chain ethers, etc.

[0063] As the halogen-substituted product, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylates such as fluoromethyl propionate (FMP), and the like are preferably used.

[0064] The electrolyte salt is preferably a lithium salt. Examples of lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1<x<6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lower aliphatic carboxylic acid lithium, Li2B4O7, Li(B(C2O4)F2) and other borates, LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2) {l, m is an integer greater than 1} and other imide salts. The lithium salt may be used alone or in combination. Among these, LiPF6 is preferably used from the viewpoint of ion conductivity, electrochemical stability, etc. The concentration of the lithium salt is preferably set to 0.8 to 1.8 mol per 1 L of solvent.

[0065] <Example>

[0066] Hereinafter, the present disclosure will be further described using examples, but the present disclosure is not limited to these examples.

[0067] <Example 1>

[0068] [Synthesis of positive electrode active material]

[0069] LiMnO2, Li2MnO3, LiNiO2, SrO, CaO, and Y2O3 were mixed in a stoichiometric ratio of 3:4:3:0.04:0.04:0.02, and the mixture was placed in a zirconia can with a volume of 45cc containing zirconia balls with a diameter of 5mm. The mixture was installed in a planetary ball mill (manufactured by FRITSCH, trade name "PLP-7") and pulverized / mixed at a revolution speed of 600rpm for 12 hours. The mixture was placed in a calcining furnace and calcined at 900°C in the atmosphere for 1 hour to obtain a positive electrode active material.

[0070] The composition of the obtained positive electrode active material was analyzed using an inductively coupled plasma (ICP) emission spectrometer (manufactured by Thermo Fisher Scientific, trade name "iCAP6300"), and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.01 Ca 0.01 Y 0.01 O 2.035 .

[0071] [Production of positive electrode]

[0072] The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) are mixed in a mass ratio of 92:5:3, and N-methyl-2-pyrrolidone (NMP) is used as a dispersion medium to prepare a positive electrode composite material slurry. Next, the positive electrode composite material slurry is applied to the surface of a positive electrode core formed of aluminum foil, the coating is dried, compressed, and cut into a specified electrode size to produce a positive electrode having a positive electrode composite material layer formed on the positive electrode core.

[0073] [Preparation of non-aqueous electrolyte]

[0074] LiPF6 was dissolved at a concentration of 1 mol / L in a mixed solvent of fluoroethylene carbonate (FEC) and methyl 3,3,3-trifluoropropionate (FMP) at a mass ratio of 1:3 to prepare a non-aqueous electrolyte.

[0075] [Production of test battery cells]

[0076] Leads were attached to the positive electrode and the counter electrode made of Li metal, and the positive electrode and the counter electrode were arranged opposite to each other via a polyolefin separator to produce an electrode body. The electrode body and the nonaqueous electrolyte were sealed in an outer casing made of an aluminum laminate film to produce a test battery cell.

[0077] <Example 2>

[0078] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, SrO, CaO, and SnO were mixed in a stoichiometric ratio of 3:4:3:0.04:0.04. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.01 Ca 0.01 Sn 0.01 O 2.03 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0079] <Example 3>

[0080] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, SrO, CaO, Y2O3, and SnO were mixed in a stoichiometric ratio of 3:4:3:0.03:0.03:0.015:0.03. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.0075 Ca 0.0075 Y 0.0075 Sn 0.0075 O 2.03375 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0081] <Example 4>

[0082] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, SrO, CaO, Y2O3, and ZnO were mixed in a stoichiometric ratio of 3:4:3:0.03:0.03:0.015:0.03. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.0075 Ca 0.0075 Y 0.0075 Zn 0.0075 O 2.03375 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0083] <Example 5>

[0084] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, SrO, CaO, and Y2O3 were mixed in a stoichiometric ratio of 3:4:3:0.02:0.02:0.01. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.005 Ca 0.005 Y 0.005 O 2.0175 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0085] <Example 6>

[0086] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, SrO, and CaO were mixed in a stoichiometric ratio of 3:4:3:0.04:0.04. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.01 Ca 0.01 O 2.02 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0087] <Example 7>

[0088] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, SrO, CaO, and SnO were mixed in a stoichiometric ratio of 3:4:3:0.02:0.02:0.02. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.005 Ca 0.005 Sn 0.005 O 2.015 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0089] <Example 8>

[0090] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, SrO, and CaO were mixed in a stoichiometric ratio of 3:4:3:0.04:0.08. The composition of the obtained positive electrode active material was analyzed and the result was Li1.17 Mn 0.58 Ni 0.25 Sr 0.01 Ca 0.02 O 2.03 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0091] <Example 9>

[0092] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, LiNiO2, CaO, and SnO were mixed in a stoichiometric ratio of 3:4:3:0.04:0.08. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Ca 0.01 Sn 0.02 O 2.03 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0093] <Example 10>

[0094] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiF, LiMnO2, Li2MnO3, LiNiO2, SrO, CaO, and SnO were mixed in a stoichiometric ratio of 0.18:1:1:1:0.036:0.036:0.036. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 Sr 0.01 Ca 0.01 Sn 0.01 O 2.025 F 0.005 Furthermore, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0095] <Comparative Example>

[0096] The positive electrode active material was synthesized in the same manner as in Example 1 except that LiMnO2, Li2MnO3, and LiNiO2 were mixed in a stoichiometric ratio of 3:4:3. The composition of the obtained positive electrode active material was analyzed and the result was Li 1.17 Mn 0.58 Ni 0.25 O2. In addition, a test battery cell was prepared in the same manner as in Example 1 using this positive electrode active material.

[0097] [Evaluation of initial voltage and voltage maintenance rate during charge and discharge cycles]

[0098] Under a temperature environment of 25° C., the test battery cells of the example and the comparative example were charged at a constant current of 0.2 C to 4.7 V and then discharged at a constant current of 0.5 C to 2.5 V. From the discharge curve at this time, the initial voltage was calculated using the following formula.

[0099] Initial voltage = (discharge energy as the sum of the quantities at each voltage) / (discharge capacity at 2.5 V)

[0100] As described above, 50 charge and discharge cycles were performed, in which the battery was charged to 4.7 V at a constant current of 0.2 C and then discharged to 2.5 V. The battery voltage at the 50th cycle was calculated from the discharge curve of the 50th cycle in the same manner as above, and the voltage maintenance rate was calculated using the following formula.

[0101] Voltage maintenance rate = (battery voltage at the 50th cycle) / (initial voltage)

[0102] The results of the initial voltage and voltage maintenance rate of the test battery cells of the embodiment and the comparative example are summarized in Table 2. In addition, the elements contained in Me and their molar fractions are summarized in Table 2. It should be noted that the higher the value of the voltage maintenance rate, the more the decrease in battery voltage caused by the charge and discharge cycle can be suppressed.

[0103] [Table 2]

[0104]

[0105] *The numerical value in the brackets of Me represents the mole fraction (mol %).

[0106] ** Example 10 contains 0.05 mol % F as anion.

[0107] Compared with the test cell of the comparative example not containing Me, the initial voltage of the test cells of Examples 1 to 10 was maintained at the same level, and the voltage maintenance rate was higher. The initial voltage of Examples 1 to 3 was also higher than that of the comparative example.

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium transition metal composite compound, The lithium transition metal composite compound is a Li excess system, and is of the general formula Li x Mn y Ni z Me α O a F b In the formula, 1≤x≤1.2, 0.4≤y≤0.8, 0≤z≤0.4, x+y+z=2, 0<α≤0.05, 1.8≤a≤2, 1.8≤a+b≤2.2, Me is at least two or more elements selected from metal elements other than Li, Mn and Ni, The Me is an ionic radius of The above elements.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein The Me contains at least one element selected from the group consisting of K, Sr, Ba, Bi, Ca, La, Pr, Y, Dy, Sn, and Zn.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein The Me contains at least one element selected from the group consisting of Sr, Ca, Y, and Sn.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein The Me is substantially formed of at least three elements selected from the group consisting of Sr, Ca, Y, and Sn.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein The Me contains at least an alkaline earth metal element.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein The α satisfies 0.01≤α≤0.

03. 7 . A non-aqueous electrolyte secondary battery comprising: a positive electrode comprising the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , a negative electrode, and a non-aqueous electrolyte.

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