Positive electrode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

Abstract

The positive electrode active material for non-aqueous electrolyte secondary batteries comprises a composition formula Li x Mn y Ni z P a M b O 2‑c F c (wherein, M is at least one element selected from Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, and Bi, and 1.0<x≤1.2, 0.4≤y≤0.8, 0≤z≤0.4, 0<a<0.01, 0<b<0.05, 0<c<0.1, and x+y+z+a+b≤2) is a lithium transition metal composite oxide.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the positive electrode active material. Background Art

[0002] In non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, the positive electrode active material significantly influences battery performance, including input / output characteristics, capacity, and cycle characteristics. Lithium-transition metal composite oxides containing metal elements such as Ni, Co, Mn, and Al are commonly used as positive electrode active materials. Since the properties of lithium-transition metal composite oxides vary significantly depending on their composition, extensive research has been conducted on the types and amounts of added elements.

[0003] For example, Patent Document 1 discloses a general formula Li a Co x Ni y Mn z O2X b (wherein X is one or more selected from the group consisting of F, Cl, P, and S, a / (x+y+z) is 1.25 to 1.40, x / (x+y+z) is 0.02 to 0.23, z / (x+y+z) is 0.63 to 0.72, b / a is 0.01 to 0.1, and a+x+y+z=2) is described as an active material for a non-aqueous electrolyte secondary battery. Patent Document 1 also describes the characteristics of the active material as having a small BET specific surface area and a large discharge capacity.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 5946011 Summary of the Invention

[0007] Lithium-excess composite oxides, in which the molar ratio of lithium to transition metal exceeds 1, are highly anticipated as high-capacity, next-generation positive electrode active materials. However, they face challenges such as the susceptibility of transition metals to dissolution. Adding fluorine to lithium-excess composite oxides is known to suppress transition metal dissolution and improve durability, but this approach also increases resistance and reduces capacity.

[0008] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present invention comprises a composition formula Li x Mn y Ni z P a M b O 2-c F c(wherein, M is at least one element selected from Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi, and Al, and 1.0<x≤1.2, 0.4≤y≤0.8, 0≤z≤0.4, 0<a<0.01, 0<b<0.05, 0<c<0.1, and x+y+z+a+b≤2) is a lithium transition metal composite oxide.

[0009] A nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes a positive electrode containing the above-described positive electrode active material, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.

[0010] According to one embodiment of the present invention, a highly durable lithium-excess positive electrode active material containing F can achieve a high capacity. That is, the positive electrode active material as one embodiment of the present invention has both high durability and high capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment. DETAILED DESCRIPTION

[0012] As mentioned above, adding F to a lithium-excess composite oxide can suppress the dissolution of transition metals and improve durability, but on the other hand, it increases resistance and reduces capacity. The present inventors conducted intensive research to address this issue and discovered that adding P and at least one specific element M to a lithium-excess F-containing composite oxide containing at least Mn as a transition metal can achieve a higher capacity. The presence of P and the specific element M specifically improves capacity compared to the absence of either or both of them.

[0013] Even when only element M is added to a lithium-excess F-containing composite oxide without P, ​​the capacity cannot be increased. Furthermore, when only P is added without element M, the capacity actually decreases. Only when P and element M are used together can a specific interaction be achieved, leading to a higher capacity. Furthermore, when two or more elements M are added along with P, the capacity-enhancing effect is even more pronounced.

[0014] Hereinafter, an embodiment of a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the positive electrode active material of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that it was initially envisioned that the multiple embodiments and modifications described below could be selectively combined.

[0015] The following example illustrates a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer can 16. However, the outer can is not limited to a cylindrical outer can and may, for example, be a rectangular outer can (prismatic battery), a coin-shaped outer can (coin battery), or an outer can composed of a laminate sheet including a metal layer and a resin layer (laminated battery). Furthermore, the electrode body is not limited to a wound type and may also be a stacked type in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0016] Figure 1 FIG is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 as an example of an embodiment. Figure 1 As shown, the nonaqueous electrolyte secondary battery 10 includes a wound electrode body 14, a nonaqueous electrolyte, and an outer can 16 that houses the electrode body 14 and the nonaqueous electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 is a metal container with a bottom and a cylindrical shape that is open at one axial end. The opening of the outer can 16 is sealed by a sealing member 17. For ease of description, the battery's sealing member 17 side is referred to as the top, and the bottom side of the outer can 16 is referred to as the bottom.

[0017] The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more thereof. The non-aqueous solvent may also contain a halogen-substituted product in which at least a portion of the hydrogen atoms in these solvents are replaced by halogen atoms such as fluorine. Examples of the electrolyte salt include lithium salts such as LiPF6. It should be noted that the non-aqueous electrolyte is not limited to a liquid electrolyte and may also be a solid electrolyte.

[0018] The positive electrode 11, the negative electrode 12, and the separator 13 constituting the electrode body 14 are all strip-shaped elongated bodies, which are alternately stacked in the radial direction of the electrode body 14 by being wound into a spiral shape. In order to prevent the precipitation of lithium, the negative electrode 12 is formed to be one circle larger than the positive electrode 11. That is, the negative electrode 12 is formed in a manner that is longer than the positive electrode 11 in the length direction and the width direction (short side direction). The separator 13 is formed to be at least one circle larger than the positive electrode 11, for example, two pieces are arranged in a manner that clamps the positive electrode 11. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0019] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14 . Figure 1In the example shown, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 toward the sealing body 17, while the negative electrode lead 21 extends through the outside of the insulating plate 19 toward the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of an internal terminal plate 23 of the sealing body 17 by welding or other means. The top plate of the sealing body 17, or lid 27, which is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or other means, and the outer can 16 serves as the negative electrode terminal.

[0020] A gasket 28 is provided between the outer can 16 and the sealing member 17 to ensure airtightness within the battery. A groove 22 is formed in the outer can 16, with a portion of the side surface protruding inward, to support the sealing member 17. The groove 22 is preferably formed in an annular shape along the circumference of the outer can 16, and supports the sealing member 17 on its upper surface. The sealing member 17 is secured to the upper portion of the outer can 16 by means of the groove 22 and the open end of the outer can 16, where the sealing member 17 is caulked.

[0021] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26 and a cover 27 are stacked in order from the electrode body 14 side. The components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is sandwiched between their respective peripheral portions. If the internal pressure of the battery rises due to abnormal heat, the lower valve body 24 is deformed and broken in a manner that pushes the upper valve body 26 upward toward the cover 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks, and the gas is discharged from the opening of the cover 27.

[0022] The positive electrode 11 , the negative electrode 12 , and the separator 13 constituting the electrode body 14 , and in particular, the positive electrode active material constituting the positive electrode 11 , will be described in detail below.

[0023] [positive electrode]

[0024] The positive electrode 11 has a positive electrode core and a positive electrode composite material layer provided on the surface of the positive electrode core. The positive electrode core can be made of a foil of a metal such as aluminum or aluminum alloy that is stable within the potential range of the positive electrode 11, or a film in which the metal is arranged on the surface. Preferably, the positive electrode composite material layer comprises a positive electrode active material, a conductive material, and a binding material, and is provided on both sides of the positive electrode core. For example, the positive electrode 11 can be manufactured by coating a positive electrode composite material slurry comprising a positive electrode active material, a conductive material, and a binding material on the positive electrode core, drying the coating, and then compressing it to form a positive electrode composite material layer on both sides of the positive electrode core.

[0025] As the conductive material contained in the positive electrode composite material layer, carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be listed. As the binding material contained in the positive electrode composite material layer, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. can be listed. These resins can also be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0026] The positive electrode active material contains the composition formula Li x Mn y Ni z P a M b O 2-c F c A lithium transition metal composite oxide represented by (wherein M is at least one element selected from Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi, and Al, 1.0 < x ≤ 1.2, 0.4 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.4, 0 < a < 0.01, 0 < b < 0.05, 0 < c < 0.1, and x + y + z + a + b ≤ 2). This composite oxide is a lithium-excess material in which the molar ratio of lithium to transition metal exceeds 1, a predetermined amount of fluoride ions is introduced, and a portion of the oxygen atoms are replaced by fluorine atoms.

[0027] The positive electrode active material is mainly composed of the composite oxide shown in the above composition formula. Here, the main component refers to the component with the highest mass ratio among the constituents of the composite oxide. In the positive electrode 11, as the positive electrode active material, a composite oxide other than the composite oxide shown in the above composition formula (for example, a composite oxide of a non-Li excess system, a composite compound not containing fluoride ions) can also be used, but the content of the above composite oxide is preferably 50% by mass or more, and can actually be 100% by mass. It should be noted that the composition of the composite oxide can be measured using an ICP emission spectrometer (iCAP6300 manufactured by ThermoFisher Scientific).

[0028] The lithium transition metal composite oxide shown in the above composition formula preferably contains Ni in addition to Li, Mn, and P. Ni contributes to high capacity. Furthermore, it contains at least one element M selected from Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi, and Al as an essential component. Among them, Ti, Co, Si, Sr, Nb, Mg, Sb, Ge, and Al are preferred, and Ti, Co, Nb, and Sb are more preferred. When the composite oxide contains P and does not contain element M, the capacity will decrease due to the addition of P. In addition, the capacity improvement effect cannot be achieved by element M alone. Only when P and element M are used together can the capacity be specifically improved.

[0029] The lithium transition metal composite oxide represented by the above composition formula more preferably contains two or more elements M. Among them, preferably two or more elements are selected from Ti, Co, Si, Sr, Nb, Mg, Sb, Ge, and Al. For example, at least one of the two or more elements M is selected from Ti, Co, Nb, Sb, and Al. In addition, the two or more elements M may also be selected from Ti, Co, Nb, Sb, and Al. By adding two or more elements M, the capacity improvement effect becomes more significant.

[0030] When the lithium transition metal composite oxide contains two or more elements M, examples of preferred combinations of the elements M include (1) Ti and Co, (2) Ti and Nb, (3) Ti and Sb, (4) Co and Nb, (5) Co and Sb, (6) Nb and Sb, and (7) Sb and Al. The lithium transition metal composite oxide may contain other elements M in addition to these two elements M. Examples of preferred combinations of three elements M include Co and Al and Ti, Co and Sb and Ti, and Co and Sb and Ge. The number of elements M contained in the lithium transition metal composite oxide is, for example, 5 or less or 4 or less.

[0031] Note that Co is particularly rare and expensive, so the lithium transition metal composite oxide may not substantially contain Co. Using other elements M in place of Co can also achieve an equivalent or greater capacity improvement effect.

[0032] In the above composition formula, the molar ratio of Li (x) is 1.0 < x ≤ 1.2, preferably 1.1 ≤ x ≤ 1.2. The molar ratio of Mn (y) is 0.4 ≤ y ≤ 0.8, preferably 0.45 ≤ y ≤ 0.6. When the molar ratio of Li and Mn is within this range, a more significant capacity improvement effect is exhibited. Ni is an optional component, but is preferably contained in an amount less than Mn, for example. The preferred content (molar ratio) of Ni is 0.05 ≤ z ≤ 0.3.

[0033] In the above composition formula, the total molar amount (x+y+z+a+b) of Li, Mn, Ni, P, and element M is 2 or less, preferably 2. That is, the composite oxide is preferably a Li-excess composite oxide and not a cation-excess composite oxide. Furthermore, the molar ratio (c) of F is 0 < c ≤ 0.1, preferably 0.05 ≤ c ≤ 0.085. Adding a specified amount of F can suppress the dissolution of transition metals and improve durability.

[0034] In the above composition formula, the molar ratio (a) of P is 0<a<0.01, preferably 0.002≤a≤0.01 or 0.002≤a≤0.005. Although a small amount of P can exert an effect, when it is present at 0.2 mol% or more relative to the total molar number of elements other than Li, O, and F, the capacity improvement effect becomes more significant. On the other hand, even if the content of P is excessively increased, the capacity improvement effect cannot be obtained, so it is preferred to set the upper limit of the content to 1 mol%. In addition, the molar ratio (b) of the element M is 0<b<0.05, preferably 0<b≤0.035 or 0.002≤b≤0.01. When containing two or more elements M, it is necessary to make their sum less than 5 mol% relative to the total molar number of elements other than Li, O, and F.

[0035] In the lithium transition metal composite oxide represented by the above composition formula, the ratio of the content of P to the element M is not particularly limited, and the preferred ratio range varies slightly depending on the type of element M. For example, when the element M contains one selected from Sb, Sr, Ti, Mg, Nb, and Si, the content of P is set to be greater than the content of element M. When the element M is Co or Al, the content of P is set to be less than the content of element M. It should be noted that the lithium transition metal composite oxide may contain elements other than Li, Mn, Ni, P, element M, O, and F within the scope of not impairing the purpose of the present invention.

[0036] The lithium transition metal composite oxide is, for example, a secondary particle formed by the aggregation of a plurality of primary particles. An example of a volume-based median particle size (D50) of the lithium transition metal composite oxide is 1 to 20 μm or 2 to 15 μm. D50 is a particle size at which the volume cumulative value in the particle size distribution measured by laser diffraction scattering is 50%. The BET specific surface area of ​​the lithium transition metal composite oxide is, for example, 1.0 to 4.0 mm 2 When the BET specific surface area is within this range, it is easy to achieve both high durability and high capacity. The BET specific surface area is measured according to the BET method (nitrogen adsorption method) described in JIS R1626.

[0037] The lithium transition metal composite oxide shown in the above composition formula can be synthesized by, for example, mixing a carbonate containing Mn and Ni, a compound containing P, a compound containing element M, and lithium fluoride (LiF), and calcining the mixture. An example of calcination conditions is 700-900°C for 10-30 hours. It should be noted that the compound containing P can also be added to the calcined product after mixing and calcining the other components. In this case, P is easily concentrated on the particle surface of the lithium transition metal composite oxide.

[0038] Examples of the compound containing P include lithium phosphate and phosphorus pentoxide. Examples of the compound containing the element M include cobalt sulfate, antimony trioxide, aluminum oxide, titanium oxide, magnesium oxide, niobium oxide, silicon oxide, and germanium oxide.

[0039] As mentioned above, the positive electrode active material has the composition formula Li x Mn y Ni z P a M b O 2-c F c The lithium transition metal composite oxide shown above is the main component. The element M is at least one, preferably two or more, selected from the group consisting of Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi, and Al. A preferred range of the P content is 0.2 to 1 mol%, and a preferred range of the element M content is 2 mol% or less, relative to the total molar number of elements excluding Li, O, and F.

[0040] [negative electrode]

[0041] The negative electrode 12 comprises a negative electrode core and a negative electrode composite material layer disposed on the surface of the negative electrode core. The negative electrode core may be made of a metal foil such as copper that is stable within the potential range of the negative electrode 12, or a film having the metal disposed on the surface. Preferably, the negative electrode composite material layer comprises a negative electrode active material and a binding material and is disposed on both sides of the negative electrode core. The negative electrode 12 can be manufactured, for example, by coating the surface of the negative electrode core with a negative electrode composite material slurry comprising a negative electrode active material, a conductive material, and a binding material, drying the coating, and then compressing the coating to form the negative electrode composite material layers on both sides of the negative electrode core.

[0042] In the negative electrode composite material layer, as the negative electrode active material, for example, a carbon-based active material that reversibly absorbs and releases lithium ions is included. Preferred carbon-based active materials are natural graphites such as flaky graphite, block graphite, and earthy graphite, and graphites such as block artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB). In addition, the negative electrode active material can use a Si-based active material composed of at least one of Si and a Si-containing compound, or a carbon-based active material and a Si-based active material can be used in combination.

[0043] As the conductive material contained in the negative electrode composite material layer, carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be used, as in the case of the positive electrode 11. As the binding material contained in the negative electrode composite material layer, as in the case of the positive electrode 11, fluororesins, PAN, polyimide, acrylic resins, polyolefins, etc. can be used, preferably styrene-butadiene rubber (SBR). In addition, the negative electrode composite material layer preferably further includes CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among them, SBR, CMC or a salt thereof, and PAA or a salt thereof are preferably used in combination.

[0044] [Separator]

[0045] The separator 13 can use a porous sheet with ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. As the material of the separator 13, polyolefins such as polyethylene, polypropylene, and copolymers of ethylene and α-olefins, cellulose, and the like are preferred. The separator 13 can be any of a single-layer structure and a laminated structure. A heat-resistant layer containing inorganic particles, a heat-resistant layer composed of a heat-resistant resin such as an aromatic polyamide resin, polyimide, or polyamide-imide, and the like can also be formed on the surface of the separator 13.

[0046] <Example>

[0047] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0048] <Example 1>

[0049] [Synthesis of lithium transition metal composite oxides]

[0050] A carbonate containing Mn and Ni, lithium phosphate (a compound containing P), antimony trioxide (a compound containing element M), and lithium fluoride are mixed in a molar ratio of 2:1, and the mixture is calcined at 800°C under an oxygen flow for 20 hours to obtain a composition formula Li 1.167 Mn 0.55 Ni 0.275 P 0.0065 Sb 0.001 O 1.92 F0.08 The lithium transition metal composite oxide shown.

[0051] [Production of positive electrode]

[0052] The aforementioned lithium transition metal composite oxide was used as the positive electrode active material. A positive electrode composite material slurry was prepared by mixing the positive electrode active material, acetylene black, and polyvinylidene fluoride at a solids mass ratio of 7:2:1, using N-methyl-2-pyrrolidone (NMP) as the dispersion medium. The positive electrode composite material slurry was then applied to a positive electrode core formed of aluminum foil. The coating was dried, compressed, and then cut into the specified electrode size to obtain the positive electrode.

[0053] [Preparation of non-aqueous electrolyte]

[0054] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed at a predetermined volume ratio. LiPF6 is added to the mixed solvent to obtain a non-aqueous electrolyte solution.

[0055] [Fabrication of test battery]

[0056] The positive electrode and the negative electrode formed of lithium metal foil were arranged opposite each other with a separator interposed therebetween to form an electrode assembly, which was then housed in a coin-shaped outer can. The non-aqueous electrolyte solution was then injected into the outer can, and the outer can was sealed to obtain a coin-shaped test cell (non-aqueous electrolyte secondary battery).

[0057] The initial capacity of the test battery was evaluated by the following method, and the evaluation results are shown in Table 1 together with the contents of P and element M in the positive electrode active material.

[0058] [Evaluation of initial capacity]

[0059] At room temperature, the test battery was CC charged at a constant current of 0.05 C until the battery voltage reached 5.2 V. The battery was then rested for 20 minutes and CC discharged at a constant current of 0.05 C until the battery voltage reached 2.5 V. The discharge capacity was measured.

[0060] <Examples 2 to 15, Comparative Examples 1 to 6>

[0061] In the synthesis of the lithium transition metal composite oxide, the types of raw materials and the mixing ratio of the raw materials were changed so that the contents of P and the element M were the same as those shown in Table 1. (The contents of Li, Ni, Mn, O, and F were the same as those in Example 1.) Test cells were prepared in the same manner as in Example 1, and the initial capacities were evaluated. It should be noted that oxides were used as the compounds containing Co, Sr, Al, Ti, Mg, Nb, Si, and Ge, respectively.

[0062] [Table 1]

[0063]

[0064] As shown in Table 1, the initial capacity of the test battery of the embodiment is greatly improved compared with the test battery of the comparative example. As mentioned above, the test batteries of the embodiment and the comparative example are the same except that the composition of the positive electrode active material is different. The positive electrode active material of the embodiment is the composition formula Li x Mn y Ni z P a M b O 2-c F c (wherein, 1.0 < x ≤ 1.2, 0.4 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.4, 0 < a < 0.01, 0 < b < 0.05, 0 < c < 0.1, x + y + z + a + b ≤ 2). The positive electrode active material used in the test battery of the comparative example cannot be represented by this composition formula. Therefore, it is believed that the capacity is specifically improved by using the composite oxide represented by this composition formula.

[0065] When a positive electrode active material that does not contain P and element M is used, the initial capacity of the test battery is 4070Wh / L (Comparative Example 1). Moreover, compared with the case where a positive electrode active material that does not contain both P and element M is used, the initial capacity of the test battery decreases when a positive electrode active material that contains only P but not element M is used (Comparative Examples 2 and 3). That is, when only P is added to the composite oxide, the capacity decreases. In addition, compared with the case where a positive electrode active material that does not contain both P and element M is used, no capacity improvement effect is observed when a positive electrode active material that only element M is added is used (Comparative Examples 4 to 6).

[0066] When a positive electrode active material was used in which a predetermined amount of P and one or more elements M were added to a composite oxide (a lithium-excess F-containing composite oxide containing Mn and Ni as transition metals), the initial capacity of the test cell was significantly improved compared to the positive electrode active material of Comparative Example 1. Furthermore, when two or more elements M were added together with P, an even more significant capacity improvement effect was demonstrated (Examples 11 to 15).

[0067] It should be noted that in the embodiments, Co, Sb, Sr, Al, Ti, Mg, Nb, Si, and Ge are used as the element M. However, the same capacity improvement effect can be obtained when W, Mo, Ca, Na, B, V, Cr, Fe, Cu, Zn, Zr, Ru, K, and Bi are used in addition to or instead of these elements.

[0068] Description of Reference Numerals

[0069] 10Non-aqueous electrolyte secondary battery

[0070] 11 positive electrode

[0071] 12 negative electrode

[0072] 13 Dividers

[0073] 14 Electrode body

[0074] 16 outer cans

[0075] 17 Sealing body

[0076] 18, 19 insulation board

[0077] 20 Positive lead

[0078] 21 Negative lead

[0079] 22 groove part

[0080] 23 Internal terminal board

[0081] 24 Lower valve body

[0082] 25 Insulation components

[0083] 26 Upper valve body

[0084] 27 Cover

[0085] 28 Sealing gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a composition formula Li x Mn y Ni z P a M b O 2-c F c The lithium transition metal composite oxide shown in the formula, wherein M is at least one element selected from Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi, and Al, 1.0<x≤1.2, 0.4≤y≤0.8, 0≤z≤0.4, 0.002<a≤0.01, 0<b<0.05, 0.05<c<0.1, x+y+z+a+b≤2.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein Composition formula Li x Mn y Ni z P a M b O 2-c F c Here, M is two or more elements selected from Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K, Bi, and Al.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein Composition formula Li x Mn y Ni z P a M b O 2-c F c In the embodiment, two or more M are selected from Ti, Co, Nb, Sb, and Al, and the molar ratio (b) of M is 0<b<0.

035.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein Composition formula Li x Mn y Ni z P a M b O 2-c F c In the embodiment, the molar ratio (a) of P is 0.002<a<0.

005. 5 . A non-aqueous electrolyte secondary battery comprising: a positive electrode containing the positive electrode active material according to claim 1 , a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

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