Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery and Non-Aqueous Electrolyte Secondary Battery

Abstract

This positive electrode active material for nonaqueous electrolyte secondary batteries contains a lithium transition metal composite oxide that is represented by composition formula LixMnyNizPaMbO2-cFc (wherein M represents at least one element that is selected from among Ti, Co, Si, Sr, Nb, W, Mo, Ca, Mg, Sb, Na, B, V, Cr, Fe, Cu, Zn, Ge, Zr, Ru, K and Bi; 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).

Description

Technical Field

[0001] The present disclosure 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 greatly affects battery performance such as input / output characteristics, capacity, and cycle characteristics. Generally, lithium transition metal composite oxides containing metal elements such as Ni, Co, Mn, and Al are used as the positive electrode active material. Since the properties of lithium transition metal composite oxides vary greatly depending on their composition, many studies have been conducted on the types and amounts of additive elements.

[0003] For example, Patent Document 1 discloses an active material for a non-aqueous electrolyte secondary battery represented by the general formula Li a Co x Ni y Mn z O2X b (where X is one or more of 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). Patent Document 1 also describes the characteristics of the active material, such as a small BET specific surface area and a large discharge capacity.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Lithium-excess composite oxides with a molar ratio of Li to transition metal exceeding 1 are expected as next-generation high-capacity cathode active materials, but there are problems such as easy elution of transition metals. It is known that adding F to lithium-excess composite oxides suppresses the elution of transition metals and improves durability. However, in this case, there is a problem that the resistance increases and the capacity decreases.

[0006] The cathode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure has 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 、Al and is characterized by containing a lithium transition metal composite oxide represented by 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).

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a cathode containing the above cathode active material, an anode, a separator interposed between the cathode and the anode, and a non-aqueous electrolyte.

[0008] According to one aspect of the present disclosure, high capacity can be achieved in a highly durable lithium-excess cathode active material containing F. That is, the cathode active material according to one aspect of the present disclosure is highly durable and has a high capacity.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] As described above, when F is added to a lithium-excess type composite oxide, elution of transition metals is suppressed and durability is improved, but resistance increases and capacity decreases. As a result of intensive studies to solve this problem, the present inventors have found that high capacity can be achieved by adding at least one of P and a specific element M to a lithium-excess type F-containing composite oxide containing at least Mn as a transition metal. When P and the specific element M are present, the capacity is specifically improved as compared with the case where one or both of them are absent.

[0011] Even if only the element M is added without adding P to the lithium-excess type F-containing composite oxide, high capacity cannot be achieved. Further, when only P is added without adding the element M, the capacity rather decreases. Only when P and the element M are used in combination, a specific interaction can be obtained and high capacity can be realized. Furthermore, when two or more types of the element M are added together with P, the effect of increasing the capacity becomes more remarkable.

[0012] Hereinafter, with reference to the drawings, an example of 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 according to the present disclosure will be described in detail. It is assumed from the beginning that a plurality of embodiments and modifications described below can be selectively combined.

[0013] Hereinafter, a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer can 16 will be exemplified. However, the outer body is not limited to a cylindrical outer can. For example, it may be a rectangular outer can (rectangular battery), a coin-shaped outer can (coin-shaped battery), or an outer body (laminated battery) composed of a laminated sheet including a metal layer and a resin layer. Further, the electrode body is not limited to a wound type, and may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with a separator interposed therebetween.

[0014] FIG. 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 which is an example of an embodiment. As shown in FIG. 1, the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an exterior can 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has 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 wound in a spiral shape with the separator 13 interposed therebetween. The exterior can 16 is a bottomed cylindrical metal container having an opening on one side in the axial direction, and the opening of the exterior can 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the side of the battery where the sealing body 17 is located is regarded as the upper side, and the bottom side of the exterior can 16 is regarded as the lower side.

[0015] The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and a mixed solvent of two or more of these are used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. As the electrolyte salt, for example, a lithium salt such as LiPF6 is used. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte and may be a solid electrolyte.

[0016] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode body 14 are all strip-shaped elongated bodies, and are alternately laminated in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger in size than the positive electrode 11 in order to prevent precipitation of lithium. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the longitudinal direction and the width direction (short side direction). The separator 13 is formed to be at least slightly larger in size than the positive electrode 11, and for example, two sheets are arranged so as to sandwich 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.

[0017] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. In the example shown in FIG. 1, the positive electrode lead 20 extends toward the sealing body 17 through the through-hole of the insulating plate 18, and the negative electrode lead 21 extends toward the bottom side of the outer can 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0018] A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the airtightness inside the battery. The outer can 16 is formed with a groove portion 22 that supports the sealing body 17, with a part of the side surface portion projecting inward. The groove portion 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 by the groove portion 22 and the open end portion of the outer can 16 that is caulked to the sealing body 17.

[0019] 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 cap 27 are laminated in order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and an insulating member 25 is interposed between the peripheral edges of each. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and breaks so as to push the upper valve body 26 toward the cap 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further rises, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0020] Hereinafter, the positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 will be described in detail, particularly the positive electrode active material constituting the positive electrode 11.

[0021] [Positive Electrode] The positive electrode 11 has a positive electrode core and a positive electrode composite layer provided on the surface of the positive electrode core. As the positive electrode core, a foil of a metal stable within the potential range of the positive electrode 11 such as aluminum or an aluminum alloy, a film having such a metal disposed on the surface layer, etc. can be used. The positive electrode composite layer contains a positive electrode active material, a conductive material, and a binder, and is preferably provided on both sides of the positive electrode core. The positive electrode 11 can be produced, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a conductive material, a binder, etc. on the positive electrode core, drying the coating film, and then compressing it to form the positive electrode composite layer on both sides of the positive electrode core.

[0022] Examples of the conductive material contained in the positive electrode composite layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode composite layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, etc. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0023] The positive electrode active material has the 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, 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, x + y + z + a + b ≤ 2), and contains a lithium transition metal composite oxide represented thereby. The composite oxide is a Li-excess type material in which the molar ratio of Li to the transition metal exceeds 1, and a predetermined amount of fluoride ions are introduced and a part of O is substituted by F.

[0024] The positive electrode active material is mainly composed of a composite oxide represented by the above compositional formula. Here, the main component means the component with the highest mass ratio among the constituent components of the composite oxide. In the positive electrode 11, as the positive electrode active material, a composite oxide other than the composite oxide represented by the above compositional formula (for example, a composite oxide that is not a Li-excess type or a composite compound that does not contain fluoride ions) may be used in combination, but the content of the above composite oxide is preferably 50% by mass or more, and may be substantially 100% by mass. The composition of the composite oxide can be measured using an ICP emission spectroscopic analyzer (iCAP6300 manufactured by Thermo Fisher Scientific).

[0025] The lithium transition metal composite oxide represented by the above compositional formula preferably contains Ni in addition to Li, Mn, and P. Ni contributes to increasing the capacity. Further, 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 preferable, and Ti, Co, Nb, and Sb are more preferable. When P is contained in the composite oxide and element M is not contained, the capacity decreases instead due to the addition of P. Also, the capacity improvement effect cannot be obtained by element M alone. The capacity is specifically improved only when P and element M are used in combination.

[0026] The lithium transition metal composite oxide represented by the above compositional formula more preferably contains two or more types of element M. Among them, it is preferably two or more elements selected from Ti, Co, Si, Sr, Nb, Mg, Sb, Ge, and Al. For example, among two or more types of element M, at least one is selected from Ti, Co, Nb, Sb, and Al. Also, the two or more types of element M may be selected from Ti, Co, Nb, Sb, and Al. By adding two or more types of element M, the capacity improvement effect becomes more remarkable.

[0027] When the lithium transition metal composite oxide contains two or more elements M, examples of suitable 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, (7) Sb and Al, and the like. The lithium transition metal composite oxide may contain other elements M in addition to these two elements M. Examples of suitable combinations of three types of elements M include Co, Al, and Ti; Co, Sb, and Ti; Co, Sb, and Ge, and the like. The number of types of elements M contained in the lithium transition metal composite oxide is, for example, 5 or less or 4 or less.

[0028] Since Co is particularly rare and expensive, the lithium transition metal composite oxide may not substantially contain Co. Even if another element M is used instead of Co, an equivalent or better capacity improvement effect can be obtained.

[0029] In the above composition formula, the molar ratio (x) of Li is 1.0 < x ≤ 1.2, preferably 1.1 ≤ x ≤ 1.2. The molar ratio (y) of Mn is 0.4 ≤ y ≤ 0.8, preferably 0.45 ≤ y ≤ 0.6. If the molar ratios of Li and Mn are within this range, the capacity improvement effect will appear more significantly. Ni is an optional component, but for example, it is preferably contained in an amount less than that of Mn. A suitable content (molar ratio) of Ni is 0.05 ≤ z ≤ 0.3.

[0030] 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 type composite oxide and not a cation-excess type composite oxide. Also, the molar ratio (c) of F is 0 < c ≤ 0.1, preferably 0.05 ≤ c ≤ 0.085. By adding a predetermined amount of F, the elution of transition metals is suppressed and the durability is improved.

[0031] In the above compositional formula, the molar ratio (a) of P satisfies 0 < a < 0.01, preferably 0.002 ≤ a ≤ 0.01, or 0.002 ≤ a ≤ 0.005. Even a small amount of P exhibits an effect, but when it is present in an amount of 0.2 mol% or more based on the total molar amount of elements other than Li, O, and F, the capacity improvement effect becomes more significant. On the other hand, if the content of P is too high, the capacity improvement effect cannot be obtained, so the upper limit of the content is preferably set to 1 mol%. Also, the molar ratio (b) of element M satisfies 0 < b < 0.05, preferably 0 < b ≤ 0.035, or 0.002 ≤ b ≤ 0.01. When two or more types of element M are contained, the total thereof needs to be 5 mol% or less based on the total molar amount of elements other than Li, O, and F.

[0032] In the lithium transition metal composite oxide represented by the above compositional formula, the ratio of the contents of P and element M is not particularly limited, but the suitable ratio range varies somewhat depending on the type of element M, etc. For example, when containing one selected from Sb, Sr, Ti, Mg, Nb, and Si as element M, the content of P is set to be equal to or more than the content of element M, and when element M is Co or Al, the content of P is set to be equal to or less than the content of element M. Note that the lithium transition metal composite oxide may contain elements other than Li, Mn, Ni, P, element M, O, and F as long as the object of the present disclosure is not impaired.

[0033] The lithium transition metal composite oxide is, for example, secondary particles formed by aggregation of a plurality of primary particles. An example of the volume-based median diameter (D50) of the lithium transition metal composite oxide is 1 to 20 μm, or 2 to 15 μm. D50 is the particle diameter at which the volume integration value becomes 50% in the particle size distribution measured by the laser diffraction scattering method. The BET specific surface area of the lithium transition metal composite oxide is, for example, 1.0 to 4.0 mm 2 / g. If the BET specific surface area is within this range, it is easier 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.

[0034] The lithium transition metal composite oxide represented by the above compositional formula can be synthesized, for example, by mixing a carbonate containing Mn and Ni, a compound containing P, a compound containing element M, and lithium fluoride (LiF), and firing the mixture. An example of the firing conditions is 700 to 900 °C for 10 to 30 hours. Note that the compound containing P may be added to the fired product after mixing and firing the other components. In this case, P tends to be unevenly distributed on the particle surface of the lithium transition metal composite oxide.

[0035] Examples of the compound containing P include lithium phosphate and diphosphorus pentoxide. Examples of the compound containing element M include cobalt sulfate, antimony trioxide, aluminum oxide, titanium oxide, magnesium oxide, niobium oxide, silicon oxide, and germanium oxide.

[0036] As described above, the positive electrode active material mainly comprises a lithium transition metal composite oxide represented by the compositional formula Li x Mn y Ni z P a M b O 2-c F c Element M is at least one 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, preferably two or more. An example of the suitable range of the content of P is 0.2 to 1 mol%, and an example of the suitable range of the content of element M is 2 mol% or less with respect to the total number of moles of elements other than Li, O, and F.

[0037] [Negative electrode] The negative electrode 12 has a negative electrode core and a negative electrode composite layer provided on the surface of the negative electrode core. For the negative electrode core, a foil of a metal stable within the potential range of the negative electrode 12 such as copper, or a film having the metal disposed on the surface layer can be used. The negative electrode composite layer contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core. The negative electrode 12 can be manufactured, for example, by applying a negative electrode composite slurry containing a negative electrode active material, a conductive material, a binder, etc. on the surface of the negative electrode core, drying the coating film, and then compressing it to form the negative electrode composite layer on both sides of the negative electrode core.

[0038] The negative electrode composite layer contains, as the negative electrode active material, for example, a carbon-based active material that reversibly occludes and releases lithium ions. Suitable carbon-based active materials are graphite such as flake graphite, massive graphite, and earthy graphite, artificial graphite such as massive artificial graphite (MAG), and mesophase carbon microbeads (MCMB). Further, as the negative electrode active material, a Si-based active material composed of at least one of Si and Si-containing compounds may be used, or a carbon-based active material and a Si-based active material may be used in combination.

[0039] As the conductive material contained in the negative electrode composite 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 binder contained in the negative electrode composite layer, fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc. can also be used as in the case of the positive electrode 11, but it is preferable to use styrene-butadiene rubber (SBR). Further, the negative electrode composite layer preferably further contains CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. Among them, it is preferable to use SBR in combination with CMC or its salt, and PAA or its salt.

[0040] [Separator] For the separator 13, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin 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-olefin, cellulose, and the like are suitable. The separator 13 may have either a single-layer structure or a laminated structure. On the surface of the separator 13, a heat-resistant layer containing inorganic particles, a heat-resistant layer composed of a resin with high heat resistance such as aramid resin, polyimide, or polyamideimide, may be formed.

[0041] <Example> Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0042] <Example 1> [Synthesis of Lithium Transition Metal Composite Oxide] A carbonate containing Mn and Ni in a molar ratio of 2:1, lithium phosphate (a compound containing P), antimony trioxide (a compound containing element M), and lithium fluoride were mixed, and the mixture was calcined at 800 °C for 20 hours under an oxygen stream to obtain a lithium transition metal composite oxide represented by the composition formula Li 1.167 Mn 0.55 Ni 0.275 P 0.0065 Sb 0.001 O 1.92 F 0.08 O

[0043] [Fabrication of Positive Electrode] The above lithium transition metal composite oxide was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a solid content mass ratio of 7:2:1, and a positive electrode composite material slurry was prepared using N-methyl-2-pyrrolidone (NMP) as the dispersion medium. Next, the positive electrode composite material slurry was applied onto a positive electrode core made of aluminum foil, and after drying and compressing the coating film, it was cut into a predetermined electrode size to obtain a positive electrode.

[0044] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a predetermined volume ratio. LiPF6 was added to the mixed solvent to obtain a non-aqueous electrolyte solution.

[0045] [Fabrication of Test Cell] An electrode body was constructed by oppositely disposing a positive electrode and a negative electrode made of a lithium metal foil with a separator in between, and the electrode body was housed in a coin-shaped exterior can. After injecting the non-aqueous electrolyte solution into the exterior can, the exterior can was sealed to obtain a coin-shaped test cell (non-aqueous electrolyte secondary battery).

[0046] For the test cell, the initial capacity 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.

[0047] [Evaluation of Initial Capacity] The test cell was charged at a constant current of 0.05C to a battery voltage of 5.2V under a normal temperature environment, then rested for 20 minutes, and discharged at a constant current of 0.05C to a battery voltage of 2.5V, and the discharge capacity was measured.

[0048] <Examples 2 to 15, Comparative Examples 1 to 6> In the synthesis of the lithium transition metal composite oxide, except that the types of raw materials and the mixing ratio of the raw materials were changed so that the contents of P and element M were as shown in Table 1 (the contents of Li, Ni, Mn, O, and F were the same as in Example 1), test cells were fabricated in the same manner as in Example 1, and the initial capacity was evaluated. Oxides were used for the compounds containing Co, Sr, Al, Ti, Mg, Nb, Si, and Ge, respectively.

[0049]

Table 1

[0050] As shown in Table 1, the test cells of all the examples have a significantly improved initial capacity compared to the test cells of the comparative examples. In the test cells of the examples and the comparative examples, as described above, only the composition of the positive electrode active material is different, and the other configurations are common. The positive electrode active material of the example is a lithium-excess type composite oxide represented by the composition formula Li x Mn y Ni z P a M b O 2-c F c (where 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), while the positive electrode active material used in the test cell of the comparative example is not represented by this composition formula. Therefore, it is understood that the capacity is specifically improved by using the composite oxide represented by this composition formula.

[0051] When a positive electrode active material containing neither P nor element M was used, the initial capacity of the test cell was 4070 Wh / L (Comparative Example 1). And when a positive electrode active material containing only P and not containing element M was used, the initial capacity of the test cell decreased compared to the case where a positive electrode active material containing neither P nor element M was used (Comparative Examples 2 and 3). That is, adding only P to the composite oxide will rather decrease the capacity. Also, when a positive electrode active material with only element M added was used, no capacity improvement effect was observed compared to the case where a positive electrode active material containing neither P nor element M was used (Comparative Examples 4 to 6).

[0052] In contrast, when a positive electrode active material in which a predetermined amount of P and one or more kinds of element M are added to a composite oxide (a lithium-excess type F-containing composite oxide containing Mn and Ni as transition metals) is used, the initial capacity of the test cell is significantly improved compared to the case where the positive electrode active material of Comparative Example 1 is used. And when two or more kinds of element M are added together with P, the capacity improvement effect appears more significantly (Examples 11 to 15).

[0053] In the examples, the case where Co, Sb, Sr, Al, Ti, Mg, Nb, Si, and Ge are used as element M was shown. However, in addition to or instead of these elements, the same capacity improvement effect can also be obtained when W, Mo, Ca, Na, B, V, Cr, Fe, Cu, Zn, Zr, Ru, K, and Bi are used.

Explanation of Symbols

[0054] 10 Non-aqueous electrolyte secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Electrode body 16 Outer can 17 Sealing body 18, 19 Insulating plate 20 Positive electrode lead 21 Negative electrode lead 22 Grooved portion 23 Internal terminal board 24 Lower valve body 25 Insulating member 26 Upper valve body 27 Cap 28 Gasket

Claims

1. Compositional formula Li ｘ Mn ｙ Ni ｚ P ａ M ｂ O ２－ｃ F ｃ (In the formula, 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, 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, x + y + z + a + b ≤ 2), a positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide represented by the formula.)

2. Compositional Li ｘ Mn ｙ Ni ｚ P ａ M ｂ O ２－ｃ F ｃ In this case, 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. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1.

3. Compositional Li ｘ Mn ｙ Ni ｚ P ａ M ｂ O ２－ｃ F ｃ In this case, two or more types of M are selected from Ti, Co, Nb, Sb, and Al, and the molar ratio (b) of M is 0 < b < 0.

035. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2.

4. Compositional Li ｘ Mn ｙ Ni ｚ P ａ M ｂ O ２－ｃ F ｃ In this case, the molar ratio (a) of P is 0.002 < a < 0.005, and the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.

5. A non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material according to any one of Claims 1 to 4, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

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