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

Abstract

This positive electrode active material for a non-aqueous electrolyte secondary battery contains a lithium transition metal complex oxide capable of occluding and releasing Li. The lithium transition metal complex oxide is represented by general formula LixM1yOzFw (in the formula, 0.5≤x<3.1, 1≤y≤2, 2≤z+w≤4, and M1 is at least one element selected from Ni, Co, Mn, Ti, Fe, Al, Ge, Si, and Nb), and M2 (M2 being at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W) is included in the interior of secondary particles of the lithium transition metal complex oxide.

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] The positive electrode active material contained in a non-aqueous electrolyte secondary battery may cause a side reaction with the electrolyte, resulting in a decrease in battery capacity due to repeated charge and discharge. This tendency is particularly prominent in batteries using a positive electrode active material with a high energy density. Patent Document 1 discloses a positive electrode active material in which nanoparticles such as olivine-type lithium metal phosphate oxide are coated on the surface of a spinel-type lithium manganese-based oxide. Further, Patent Document 2 discloses a positive electrode active material in which fine particles of an oxide of a metal element such as Zr are attached to the surface of a lithium-containing composite oxide.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

[0004] The secondary battery using the positive electrode active material disclosed in Patent Document 1 and Patent Document 2 has improved durability compared to the secondary battery using the uncoated positive electrode active material, but the battery capacity is reduced. The positive electrode active materials disclosed in Patent Document 1 and Patent Document 2 still have room for improvement in terms of battery capacity.

[0005] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure contains a lithium transition metal composite oxide capable of occluding and releasing Li. The lithium transition metal composite oxide has the general formula Li x M1 y O z F w(wherein 0.5 ≦ x < 3.1, 1 ≦ y ≦ 2, 2 ≦ z + w ≦ 4, and M1 is at least one element selected from Ni, Co, Mn, Ti, Fe, Al, Ge, Si, and Nb), and M2 (M2 is at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W) is contained inside the secondary particles of the lithium transition metal composite oxide.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode containing the positive electrode active material for the non-aqueous electrolyte secondary battery, a negative electrode, and an electrolyte.

[0007] According to one aspect of the present disclosure, the durability and the battery capacity of the battery can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0009] According to a positive electrode active material obtained by coating the surface of a lithium transition metal composite oxide with an oxide or the like, side reactions such as decomposition of the electrolyte and elution of transition metals from the positive electrode active material during charge and discharge of the battery can be suppressed. However, coating may make it difficult for lithium ions to move, and the battery capacity may decrease. As a result of intensive studies on such problems, the present inventor has found that by using a positive electrode active material in which at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W is present inside the secondary particles of the lithium transition metal composite oxide, the durability and the battery capacity of the secondary battery can be improved. It is presumed that the presence of at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W inside the secondary particles of the lithium transition metal composite oxide makes it easier for lithium ions to move.

[0010] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical battery case will be exemplified. However, the electrode body is not limited to the wound type, and may be a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one with a separator interposed therebetween. Further, the battery case is not limited to a cylindrical shape, and may be, for example, a rectangular shape, a coin shape, etc., or a battery case composed of a laminate sheet including a metal layer and a resin layer.

[0011] FIG. 1 is a longitudinal sectional view of a cylindrical secondary battery 10 which is an example of the embodiment. In the secondary battery 10 shown in FIG. 1, an electrode body 14 and a non-aqueous electrolyte are housed in an exterior body 15. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. As the non-aqueous solvent (organic solvent) of the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, etc. can be used, and these solvents can be used as a mixture of two or more kinds. When using a mixture of two or more solvents, it is preferable to use a mixed solvent containing a cyclic carbonate and a chain carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc. can be used as the chain carbonate. As the electrolyte salt of the non-aqueous electrolyte, LiPF6, LiBF4, LiCF3SO3, etc. and mixtures thereof can be used. The dissolution amount of the electrolyte salt with respect to the non-aqueous solvent can be, for example, 0.5 to 2.0 mol / L. In the following, for convenience of explanation, the side of the sealing body 16 will be referred to as "upper" and the bottom side of the exterior body 15 will be referred to as "lower".

[0012] The opening end of the outer package 15 is blocked by the sealing body 16, so the interior of the secondary battery 10 is sealed. Insulating plates 17 and 18 are respectively provided above and below the electrode body 14. The positive electrode lead 19 extends upward through the through-hole of the insulating plate 17 and is welded to the lower surface of the filter 22 which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26 which is the top plate of the sealing body 16 and is electrically connected to the filter 22 serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through the through-hole of the insulating plate 18 to the bottom side of the outer package 15 and is welded to the inner surface of the bottom of the outer package 15. In the secondary battery 10, the outer package 15 serves as the negative electrode terminal. When the termination part of the negative electrode lead 20 is installed, the negative electrode lead 20 extends to the bottom side of the outer package 15 through the outside of the insulating plate 18 and is welded to the inner surface of the bottom of the outer package 15.

[0013] The outer package 15 is, for example, a bottomed cylindrical metal outer can. A gasket 27 is provided between the outer package 15 and the sealing body 16 to ensure the sealing property inside the secondary battery 10. The outer package 15 has, for example, a groove portion 21 formed by pressing the side surface from the outside to support the sealing body 16. The groove portion 21 is preferably formed in an annular shape along the circumferential direction of the outer package 15 and supports the sealing body 16 via the gasket 27 on its upper surface.

[0014] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 which are laminated in order from the side of the electrode body 14. Each member constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each member except the insulating member 24 is electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their central portions, and an insulating member 24 is interposed between the peripheral edges of each. When the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 breaks, and as a result, the upper valve body 25 bulges toward the cap 26 side and separates from the lower valve body 23, thereby cutting off their electrical connection. When the internal pressure further rises, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cap 26.

[0015] Hereinafter, the positive electrode 11, negative electrode 12, and separator 13 that constitute the secondary battery 10 will be described in detail, particularly the positive electrode active material contained in the positive electrode composite material layer that constitutes the positive electrode 11.

[0016] [Positive Electrode] The positive electrode 11 has, for example, a positive electrode core such as a metal foil, and a positive electrode composite material layer formed on the positive electrode core. As the positive electrode core, a foil of a metal stable within the potential range of the positive electrode such as aluminum, a film having the metal disposed on the surface layer, etc. can be used. The positive electrode composite material layer contains, for example, a positive electrode active material, a binder, a conductive material, etc. The positive electrode can be manufactured, for example, by applying a positive electrode composite material slurry containing a positive electrode active material, a binder, a conductive material, etc. onto the positive electrode core, drying to form the positive electrode composite material layer, and then rolling this positive electrode composite material layer.

[0017] Examples of the conductive material contained in the positive electrode composite material layer include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. These may be used alone or in combination of two or more.

[0018] Examples of the binder contained in the positive electrode composite material layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, polyolefin-based resins, etc. These may be used alone or in combination of two or more.

[0019] The positive electrode active material contains a lithium transition metal composite oxide capable of occluding and releasing Li. The lithium transition metal composite oxide may have a spinel structure. Whether the lithium transition metal composite oxide has a spinel structure can be confirmed by X-ray diffraction method (XRD).

[0020] The lithium transition metal composite oxide is, for example, a secondary particle formed by aggregation of a plurality of primary particles. The particle size of the primary particles constituting the secondary particle is, for example, 0.05 μm to 1 μm. The particle size of the primary particle is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM).

[0021] The volume-based median diameter (D50) of the secondary particles of the lithium transition metal composite oxide is, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, particularly preferably 7 μm to 15 μm. D50 means the particle size at which the cumulative frequency in the volume-based particle size distribution reaches 50% from the smaller particle size side, and is also called the median diameter. The particle size distribution of the composite oxide (Z) can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by Microtrac Bell Corporation) with water as the dispersion medium.

[0022] The lithium transition metal composite oxide has the general formula Li x M1 y O z F w (where 0.5 ≦ x < 3.1, 1 ≦ y ≦ 2, 2 ≦ z + w ≦ 4, and M1 is at least one element selected from Ni, Co, Mn, Ti, Fe, Al, Ge, Si, and Nb). The molar fraction of each element constituting the lithium transition metal composite oxide can be measured, for example, for the elements excluding F by inductively coupled plasma (ICP) emission spectroscopic analysis, and for F by ion chromatography (IC) measurement.

[0023] The lithium transition metal composite oxide has the general formula Li 1+α Ni 0.5-β Mn 1.5-γ M2 β+γ O a F b (where 0 ≦ α ≦ 0.2, 0 ≦ β < 0.2, 0 ≦ γ < 0.5, 0 ≦ b ≦ 0.2, 3.8 ≦ a + b ≦ 4.2, and M2 is at least one element selected from Ti, Fe, Al, Ge, Si, and Nb).

[0024] In 1+α indicating the proportion of Li in the lithium transition metal composite oxide, α satisfies 0 ≦ α ≦ 0.2, and preferably satisfies 0 ≦ α ≦ 0.05. When α is less than 0, the battery capacity may decrease compared to the case where α satisfies the above range. When α exceeds 0.2, it may lead to a decrease in charge-discharge cycle characteristics compared to the case where α satisfies the above range.

[0025] In 0.5-β indicating the proportion of Ni to the total molar number of metal elements excluding Li in the lithium transition metal composite oxide, β satisfies 0 ≦ β < 0.2, preferably satisfies 0 ≦ β ≦ 0.15, and more preferably satisfies 0 ≦ β ≦ 0.1.

[0026] In 1.5-γ indicating the proportion of Mn to the total molar number of metal elements excluding Li in the lithium transition metal composite oxide, γ satisfies 0 ≦ γ < 0.5, preferably satisfies 0 ≦ γ ≦ 0.3, and more preferably satisfies 0 ≦ γ ≦ 0.1.

[0027] M (M is at least one element selected from Ti, Fe, Al, Ge, Si, Nb, Ta, Zr, W, Mo, Sc, Y, and Er) in the lithium transition metal composite oxide is an optional component with respect to the total molar number of metal elements excluding Li, and β + γ indicating its proportion satisfies β + γ ≧ 0.

[0028] In b indicating the proportion of F in the lithium transition metal composite oxide, b satisfies 0 ≦ b ≦ 0.2, and preferably satisfies 0 ≦ b ≦ 0.1. By containing F in the lithium transition metal composite oxide, the stability of the crystal structure of the lithium transition metal composite oxide is improved. When the crystal structure of the lithium transition metal composite oxide is stabilized, for example, the durability of the secondary battery is improved.

[0029] The positive electrode active material contains M2 (M2 is at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W) inside the secondary particles of the lithium transition metal composite oxide. By containing M2 inside the secondary particles of the lithium transition metal composite oxide, the durability and battery capacity of the secondary battery can be improved.

[0030] M2 preferably contains at least one element selected from Ca and Sr. By using a lithium transition metal composite oxide containing Ca or Sr inside the secondary particles, the durability and battery capacity of the secondary battery can be improved.

[0031] Hereinafter, for convenience of explanation, the above-mentioned lithium transition metal composite oxide and the positive electrode active material containing M2 contained inside the secondary particles of the lithium transition metal composite oxide are referred to as "composite oxide (Y)". In the present disclosure, the positive electrode active material contained in the secondary battery may be mainly composed of the composite oxide (Y) and may be substantially composed of only the composite oxide (Y). Note that the positive electrode active material may contain a composite oxide other than the composite oxide (Y) or other compounds as long as the object of the present disclosure is not impaired.

[0032] The molar fraction of M2 with respect to the total molar number of metal elements other than Li contained in the lithium transition metal composite oxide is preferably 0.2% to 10%, and more preferably 0.2% to 2%. The molar fraction of M2 in the composite oxide (Y) can be measured by XRD.

[0033] The distribution of M2 in the composite oxide (Y) can be two-dimensionally confirmed by an electron probe microanalyzer (EPMA). Specifically, after confirming the shape of the secondary particles of the lithium transition metal composite oxide with a backscattered electron image similar to SEM by EPMA, when performing a composition analysis at the same location, it can be confirmed that Sr is present in a large amount inside the secondary particles of the lithium transition metal composite oxide.

[0034] The composite oxide (Y) can be synthesized, for example, by adding a Li source and an M2 source to a composite compound (X) that does not contain Li, mixing them, and firing at 200°C to 1050°C. Examples of the composite compound (X) include composite oxides, hydroxides, and carbonate compounds containing Ni, Mn, etc. Examples of the Li source include LiOH, etc. Examples of the M2 source include hydroxides, carbonate compounds, and nitrate compounds of M2. Examples of the M2 source include Ca(OH)2, CaCO3, Ca(NO3)2, Sr(OH)2, SrCO3, Sr(NO3)2, etc. The M2 source may be either a powdery solid or an aqueous solution in which the M2 source is dissolved. From the viewpoint of dispersing M2 inside or outside the secondary particles of the lithium transition metal composite oxide, the method of adding an aqueous solution is preferred. When adding an aqueous solution, from the viewpoint of facilitating the preparation of the aqueous solution, Ca(NO3)2 and Sr(NO3)2, which have high solubility in water, are preferred as the M2 source.

[0035] [Negative electrode] The negative electrode 12 has, for example, a negative electrode core body such as a metal foil, and a negative electrode composite material layer provided on the surface of the negative electrode core body. For the negative electrode core body, a foil of a metal stable within the potential range of the negative electrode such as copper, or a film having the metal disposed on the surface layer can be used. The negative electrode composite material layer contains, for example, a negative electrode active material and a binder. The negative electrode can be produced, for example, by applying a negative electrode composite material slurry containing a negative electrode active material, a binder, etc. onto the negative electrode core body, drying to form a negative electrode composite material layer, and then rolling this negative electrode composite material layer.

[0036] The negative electrode composite material layer contains, as the negative electrode active material, for example, a carbon-based active material that can reversibly occlude and release 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) that have been graphitized. Also, 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.

[0037] As the binder contained in the negative electrode composite layer, similar to the case of the positive electrode, fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc. can be used, 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.

[0038] [Separator] For the separator, 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, etc. As the material of the separator, polyolefins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator.

[0039] <Example> Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0040] <Example 1> [Synthesis of Positive Electrode Active Material] The nickel-manganese composite hydroxide having the composition of Ni 0.5 Mn 1.5 (OH)4 obtained by coprecipitation was calcined at 500 °C to obtain a nickel-manganese composite oxide (X).

[0041] Next, an aqueous solution of nickel-manganese composite oxide (X), LiOH, and Sr(NO3)2 was mixed so that the molar ratio of the total amount of Ni and Mn, Li, and Sr was 1:0.5:0.002. After calcining this mixture at 900 °C for 10 hours and then pulverizing, a lithium composite oxide (Y) was obtained. As a result of XRD, the molar fraction of Sr with respect to the total number of moles of metal elements contained in the lithium transition metal composite oxide excluding Li was 0.16%.

[0042] [Fabrication of the Positive Electrode] The above positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were mixed at a solid content mass ratio of 96.3:2.5:1.2. After adding an appropriate amount of N-methyl-2-pyrrolidone (NMP), this was kneaded to prepare a positive electrode composite slurry. The positive electrode composite slurry was applied to both sides of a positive electrode core made of aluminum foil. After drying the coating film, the coating film was rolled using a roller and cut to a predetermined electrode size to obtain a positive electrode with positive electrode composite layers formed on both sides of the positive electrode core. Note that an exposed portion where the surface of the positive electrode core was exposed was provided on a part of the positive electrode.

[0043] [Fabrication of the Negative Electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution at a solid content mass ratio of 100:1:1 to prepare a negative electrode composite slurry. The negative electrode composite slurry was applied to both sides of a negative electrode core made of copper foil. After drying the coating film, the coating film was rolled using a roller and cut to a predetermined electrode size to obtain a negative electrode with negative electrode composite layers formed on both sides of the negative electrode core. Note that an exposed portion where the surface of the negative electrode core was exposed was provided on a part of the negative electrode.

[0044] [Fabrication of the Non-aqueous Electrolyte] Fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1:1:6 to obtain a non-aqueous solvent. A non-aqueous electrolyte was obtained by dissolving LiPF6 in this non-aqueous solvent at a concentration of 1.0 mol / L.

[0045] [Fabrication of the Battery] An aluminum lead was attached to the exposed portion of the above positive electrode, and a nickel lead was attached to the exposed portion of the above negative electrode. After winding the positive electrode and the negative electrode spirally through a separator made of polyolefin, it was press-molded in the radial direction to fabricate a flat spiral wound electrode body. This electrode body was housed in an exterior body composed of an aluminum laminate sheet. After injecting the above non-aqueous electrolyte, the opening of the exterior body was sealed to obtain a non-aqueous electrolyte secondary battery with a design capacity of 650 mAh.

[0046] [Evaluation of capacity retention rate] First, for the battery fabricated above, constant current charging was performed at a constant current of 0.2C until the battery voltage reached 4.9V under a temperature environment of 25°C, and then constant voltage charging was performed until the current value reached 0.02C at 4.9V. Thereafter, constant current discharging was performed at a constant current of 0.2C until the battery voltage reached 3.0V. After repeating this charge-discharge cycle 5 times, the battery was used as the initial battery.

[0047] For the initial battery, the following cycle test was conducted. The discharge capacity at the 3rd cycle and the discharge capacity at the 26th cycle of the cycle test were determined, and the capacity retention rate was calculated according to the following formula.

[0048] Capacity retention rate (%) = (Discharge capacity at the 26th cycle ÷ Discharge capacity at the 3rd cycle) × 100 <Cycle test> The test cell was subjected to constant current charging at a constant current of 0.2C until the battery voltage reached 4.9V under a temperature environment of 25°C, and then constant voltage charging was performed until the current value reached 0.02C at 4.9V. Thereafter, constant current discharging was performed at a constant current of 0.2C until the battery voltage reached 3.0V. This charge-discharge cycle was repeated 26 times.

[0049] <Example 2> A battery was fabricated and evaluated in the same manner as in Example 1, except that an aqueous solution of nickel manganese composite oxide (X), LiOH, and Sr(NO3)2 was mixed so that the molar ratio of the total amount of Ni and Mn, Li, and Sr was 1:0.5:0.02. As a result of XRD, the molar fraction of Sr with respect to the total molar number of metal elements contained in the lithium transition metal composite oxide excluding Li was 0.96%.

[0050] <Example 3> A battery was fabricated and evaluated in the same manner as in Example 1, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0051] <Example 4> A battery was fabricated and evaluated in the same manner as in Example 2, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0052] <Comparative Example 1> A nickel-manganese composite oxide (X) was obtained by coprecipitation in the same manner as in Example 1. Next, the nickel-manganese composite oxide (X) and LiOH were mixed so that the molar ratio of the total amount of Ni and Mn to Li was 1:0.5, and this mixture was calcined at 900 °C for 10 hours to obtain a calcined product. Further, an aqueous solution of Sr(NO3)2 was mixed and added to this calcined product so that the molar ratio of the total amount of Ni and Mn to Sr was 1:0.002, and after calcination at 900 °C for 10 hours, it was pulverized to synthesize a lithium composite oxide (Z), which was used as a positive electrode active material. A battery was fabricated and evaluated for the obtained positive electrode active material (lithium composite oxide (Z)) in the same manner as in Example 1.

[0053] <Comparative Example 2> A battery was fabricated and evaluated in the same manner as in Comparative Example 1, except that an aqueous solution of Sr(NO3)2 was mixed and added to the calcined product so that the molar ratio of the total amount of Ni and Mn to Sr was 1:0.02.

[0054] <Comparative Example 3> A battery was fabricated and evaluated in the same manner as in Comparative Example 1, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0055] <Comparative Example 4> A battery was fabricated and evaluated in the same manner as in Comparative Example 2, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0056] Table 1 summarizes the discharge capacities (initial capacities) and capacity retention rates of the initial batteries of the examples and comparative examples. Table 1 also shows the M2 element, the addition amount of M2, and the presence or absence of M2 inside the secondary particles of the lithium transition metal composite oxide.

[0057]

Table 1

[0058] The battery of Example 1 had a higher discharge capacity and capacity retention rate than the battery of Comparative Example 1. Similarly, among the batteries of Examples 2 to 4 and Comparative Examples 2 to 4, the batteries of the examples also had a higher discharge capacity and capacity retention rate than the batteries of the comparative examples. Further, FIG. 2 shows the SEM photographs and EPMA analysis results of the cross section of the positive electrode active material in Example 1 and Comparative Example 1. In Example 1, Sr was unevenly distributed inside the secondary particles of the lithium transition metal composite oxide, while in Comparative Example 1, Sr was unevenly distributed between the secondary particles of the lithium transition metal composite oxide. A similar tendency was also observed between Example 2 and Comparative Example 2. Further, in Examples 3 and 4, Ca was unevenly distributed inside the secondary particles of the lithium transition metal composite oxide, while in Comparative Examples 3 and 4, Ca was unevenly distributed between the secondary particles of the lithium transition metal composite oxide.

Description of Reference Numerals

[0059] 10 Secondary battery 11 Positive electrode 12 Negative electrode 12a End portion of winding 13 Separator 14 Electrode body 15 Outer package 16 Sealing body 17, 18 Insulating plate 19 Positive electrode lead 20 Negative electrode lead 21 Grooved portion 22 Filter 23 Lower valve body 24 Insulating member 25 Upper valve body 26 Cap 26a Opening 27 Gasket

Claims

1. A positive electrode active material containing a lithium transition metal composite oxide capable of occluding and releasing Li, The lithium transition metal composite oxide has a general formula Li ｘ M1 ｙ O ｚ F ｗ (where 0.5 ≦ x < 3.1, 1 ≦ y ≦ 2, 2 ≦ z + w ≦ 4, and M1 is at least one element selected from Ni, Co, Mn, Ti, Fe, Al, Ge, Si, and Nb), and is represented by wherein at least one element M2 (M2 is at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W) is contained inside the secondary particles of the lithium transition metal composite oxide, and a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, by mixing a composite compound not containing Li, a Li source, and an aqueous solution in which an M2 source is dissolved and firing, the M2 is unevenly distributed inside the secondary particles of the lithium transition metal composite oxide, A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

2. The lithium transition metal composite oxide has the general formula Li １＋α Ni ０．５－β Mn １．５－γ M2 β＋γ O ａ F ｂ (where 0 ≦ α ≦ 0.2, 0 ≦ β < 0.2, 0 ≦ γ < 0.5, 0 ≦ b ≦ 0.2, 3.8 ≦ a + b ≦ 4.2, and M2 is at least one element selected from Ti, Fe, Al, Ge, Si, and Nb), the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1.

3. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the M2 contains at least one element selected from Ca and Sr.

4. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the molar fraction of M2 with respect to the total molar number of metal elements excluding Li contained in the lithium transition metal composite oxide is 0.2% to 10%.

5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, wherein the aqueous solution in which the M2 source is dissolved is at least one aqueous solution selected from Ca(NO3)2 and Sr(NO3)2.

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