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

Abstract

The positive electrode active material for a nonaqueous electrolyte secondary battery contains a lithium transition metal composite oxide capable of occluding and releasing Li. The lithium transition metal composite oxide is represented by 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 or more elements selected from the group consisting of Ni, Co, Mn, Ti, Fe, Al, Ge, Si, and Nb) indicates that M2 (M2 is at least one or more elements selected from the group consisting of Ca, Sr, Sc, Er, Y, Zr, and W) is contained in the interior of the secondary particles of the lithium transition metal composite oxide.

Description

Technical Field

[0001] This 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 Technology

[0002] In non-aqueous electrolyte secondary batteries, the positive electrode active material can cause side reactions with the electrolyte, sometimes leading to a decrease in battery capacity due to repeated charge-discharge cycles. This tendency is particularly pronounced in batteries using high-energy-density positive electrode active materials. 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 oxide. Patent Document 2 discloses a positive electrode active material in which particles of oxides of metal elements such as Zr are attached to the surface of a lithium-containing composite oxide.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2013-191540

[0006] Patent Document 2: Japanese Patent Application Publication No. 2012-138197 Summary of the Invention

[0007] Secondary batteries using the positive electrode active materials disclosed in Patent Documents 1 and 2 exhibit improved durability compared to secondary batteries using uncoated positive electrode active materials, but their battery capacity is lower. There is still room for improvement in battery capacity regarding the positive electrode active materials disclosed in Patent Documents 1 and 2.

[0008] One aspect of this disclosure is the positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a lithium transition metal composite oxide capable of absorbing, storing, and releasing Li. The lithium transition metal composite oxide uses 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) indicates that the secondary particles of the lithium transition metal composite oxide contain M2 (M2 is at least one element selected from Ca, Sr, Sc, Er, Y, Zr and W).

[0009] As one aspect of this disclosure, a non-aqueous electrolyte secondary battery comprises: a positive electrode, a negative electrode, and an electrolyte, all containing the aforementioned positive electrode active material for a non-aqueous electrolyte secondary battery.

[0010] According to one method of this disclosure, battery durability and battery capacity can be improved. Attached Figure Description

[0011] Figure 1 This is a longitudinal sectional view of a cylindrical secondary battery as an example of an implementation method.

[0012] Figure 2 The images show SEM images and EPMA analysis results of the cross-sections of the positive electrode active material for Example 1 and Comparative Example 1. Detailed Implementation

[0013] By coating the surface of a lithium transition metal composite oxide with an oxide or similar positive electrode active material, side reactions such as electrolyte decomposition and dissolution of the transition metal from the positive electrode active material during battery charging and discharging can be suppressed. However, lithium ions become less mobile due to the coating, sometimes resulting in a decrease in battery capacity. The inventors conducted in-depth research on the above-mentioned problems and discovered that by using a positive electrode active material containing at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W within the secondary particles of the lithium transition metal composite oxide, the durability and capacity of the secondary battery can be improved. It is speculated that this is because the presence of at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W within the secondary particles of the lithium transition metal composite oxide facilitates lithium ion movement.

[0014] The following describes in detail one embodiment of the non-aqueous electrolyte secondary battery of this disclosure. An example of a cylindrical battery is shown below, in which a wound electrode body is housed within a cylindrical battery casing. However, the electrode body is not limited to a wound type; it can be a stacked type, in which multiple positive electrodes and multiple negative electrodes are alternately stacked one by one, separated by separators. Furthermore, the battery casing is not limited to a cylindrical shape; for example, it can be square, coin-shaped, or a battery casing composed of a laminate containing a metal layer and a resin layer.

[0015] Figure 1 This is a longitudinal sectional view of a cylindrical secondary battery 10 as an example of an implementation. Figure 1In the secondary battery 10 shown, the electrode body 14 and the non-aqueous electrolyte are housed within the outer casing 15. The electrode body 14 has a wound structure formed by winding a positive electrode 11 and a negative electrode 12 together with a separator 13. The non-aqueous solvent (organic solvent) for the non-aqueous electrolyte can be carbonates, lactones, ethers, ketones, esters, etc., and two or more of these solvents can be mixed for use. When using two or more solvents, a mixed solvent containing cyclic carbonates and chain carbonates is preferred. For example, ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), etc., can be used as cyclic carbonates, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), etc., can be used as chain carbonates. The electrolyte salt for the non-aqueous electrolyte can be LiPF6, LiBF4, LiCF3SO3, etc., and mixtures thereof. The solubility of the electrolyte salt relative to the non-aqueous solvent can be, for example, set to 0.5 to 2.0 mol / L. It should be noted that, for ease of explanation, the side of the sealing body 16 will be referred to as "above" and the bottom side of the outer shell 15 as "below".

[0016] The opening of the outer casing 15 is blocked by the sealing body 16, thus sealing the interior of the secondary battery 10. 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 metal plate 22, which serves as a partial opening in the bottom plate of the sealing body 16. In the secondary battery 10, the top plate, i.e., the cover 26, of the sealing body 16, which is electrically connected to the partially open metal plate 22, becomes the positive terminal. On the other hand, the negative electrode lead 20 extends towards the bottom side of the outer casing 15 through the through hole of the insulating plate 18 and is welded to the inner bottom surface of the outer casing 15. In the secondary battery 10, the outer casing 15 becomes the negative terminal. It should be noted that when the negative electrode lead 20 is provided at the terminal, the negative electrode lead 20 extends towards the bottom side of the outer casing 15 through the outside of the insulating plate 18 and is welded to the inner bottom surface of the outer casing 15.

[0017] The outer casing 15 is, for example, a bottomed cylindrical metal can. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure the internal airtightness of the secondary battery 10. The outer casing 15 has, for example, a grooved portion 21 formed by applying pressure to the side from the outside to support the sealing body 16. The grooved portion 21 is preferably formed in a ring shape along the circumference of the outer casing 15, and the sealing body 16 is supported by the gasket 27 on its upper surface.

[0018] The sealing body 16 comprises, sequentially stacked from the electrode body 14 side, a partially open metal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cover 26. Each component constituting the sealing body 16 has, for example, a circular or annular shape, and all components except the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, with the insulating member 24 sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat release, for example, the lower valve body 23 breaks, causing the upper valve body 25 to expand towards the cover 26 and detach from the lower valve body 23, thereby breaking the electrical connection between the two. When the internal pressure rises further, the upper valve body 25 breaks, and gas is discharged from the opening 26a of the cover 26.

[0019] The following describes in detail the positive electrode 11, negative electrode 12, and separator 13 constituting the secondary battery 10, and especially the positive electrode active material contained in the positive electrode composite material layer constituting the positive electrode 11.

[0020] [positive electrode]

[0021] The positive electrode 11, for example, comprises: a positive electrode core such as a metal foil, and a positive electrode composite material layer formed on the positive electrode core. The positive electrode core may be a foil of a metal stable within the potential range of the positive electrode, such as aluminum, or a thin film of the metal disposed on its surface. The positive electrode composite material layer may include, for example, a positive electrode active material, a binder material, and a conductive material. The positive electrode may be manufactured, for example, by coating a positive electrode composite material slurry containing a positive electrode active material, a binder material, and a conductive material onto the positive electrode core and drying it to form a positive electrode composite material layer, and then calendering the positive electrode composite material layer.

[0022] Examples of conductive materials included in the positive electrode composite layer include carbon black (CB), acetylene black (AB), Ketjen black, and graphite particles. They can be used individually or in combination of two or more.

[0023] Examples of binders used in the cathode composite material layer include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. They can be used alone or in combination of two or more.

[0024] The positive electrode active material includes a lithium transition metal composite oxide capable of absorbing, storing, and releasing Li. This lithium transition metal composite oxide can possess a spinel structure. The spinel structure of the lithium transition metal composite oxide can be confirmed by X-ray diffraction (XRD).

[0025] Lithium transition metal composite oxides are, for example, secondary particles formed by the aggregation of multiple primary particles. The particle size of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is determined in the form of the diameter of the circumcircle of the particle image observed using a scanning electron microscope (SEM).

[0026] The median particle size (D50) of secondary particles of lithium transition metal composite oxides on a volume basis is, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, and particularly preferably 7 μm to 15 μm. D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution reaches 50% from the smallest particle size; it is also known as the median diameter. The particle size distribution of the composite oxide (Z) can be determined using a laser diffraction-based particle size distribution measuring device (e.g., MicrotracBEL Corp., MT3000II) with water as the dispersion medium.

[0027] Lithium transition metal composite oxides using the general formula Li x M1 y O z F w (In the formula, 0.5≤x<3.1, 1≤y≤2, 2≤z+w≤4, and M1 is an element selected from Ni, Co, Mn, Ti, Fe, Al, Ge, Si, and Nb). The mole fraction of each element constituting the lithium transition metal complex oxide can be determined, for example, as follows: elements other than F can be determined by inductively coupled plasma (ICP) emission spectrophotometry, and F can be determined by ion chromatography (IC).

[0028] Lithium transition metal composite oxides can also be represented by the general formula Li 1+α Ni 0.5-β Mn 1.5-γ M2 β+γ O a F b (In the formula, 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 an element selected from Ti, Fe, Al, Ge, Si and Nb)

[0029] In lithium transition metal composite oxides, the α in 1+α, representing the proportion of Li, satisfies 0 ≤ α ≤ 0.2, preferably 0 ≤ α ≤ 0.05. When α is less than 0, the battery capacity sometimes decreases compared to when α satisfies the above range. When α exceeds 0.2, it sometimes leads to a decrease in charge-discharge cycle characteristics compared to when α satisfies the above range.

[0030] The β in 0.5-β, representing the proportion of Ni, relative to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide, satisfies 0 ≤ β < 0.2, preferably 0 ≤ β ≤ 0.15, and more preferably 0 ≤ β ≤ 0.1.

[0031] The γ in 1.5-γ, representing the proportion of Mn, relative to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide, satisfies 0 ≤ γ < 0.5, preferably 0 ≤ γ ≤ 0.3, and more preferably 0 ≤ γ ≤ 0.1.

[0032] M (where M is an element selected from at least one of Ti, Fe, Al, Ge, Si, Nb, Ta, Zr, W, Mo, Sc, Y, and Er) is an arbitrary composition relative to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide, and the proportion β+γ satisfies β+γ≥0.

[0033] In lithium transition metal composite oxides, the proportion b representing the amount of F satisfies 0 ≤ b ≤ 0.2, preferably 0 ≤ b ≤ 0.1. The presence of F in the lithium transition metal composite oxide improves the stability of its crystal structure. This crystal structure stability leads to improved durability, for example, in secondary batteries.

[0034] The positive electrode active material contains M2 (M2 is an element selected from Ca, Sr, Sc, Er, Y, Zr and W) within the secondary particles of the lithium transition metal composite oxide. By including M2 within the secondary particles of the lithium transition metal composite oxide, the durability and capacity of the secondary battery can be improved.

[0035] 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 capacity of the secondary battery can be improved.

[0036] For ease of explanation, the positive electrode active material comprising the aforementioned lithium transition metal composite oxide and M2 contained within the secondary particles of the lithium transition metal composite oxide will be referred to as "composite oxide (Y)". In this disclosure, the positive electrode active material contained in the secondary battery is mainly composed of composite oxide (Y), or may be substantially composed solely of composite oxide (Y). It should be noted that, without prejudice to the purpose of this disclosure, the positive electrode active material may contain composite oxides other than composite oxide (Y), or other compounds.

[0037] The mole fraction of M2 is preferably 0.2% to 10%, more preferably 0.2% to 2%, relative to the total number of moles of metal elements other than Li contained in the lithium transition metal composite oxide. The mole fraction of M2 in the composite oxide (Y) can be determined by XRD.

[0038] The distribution of M2 in the composite oxide (Y) can be confirmed in a two-dimensional manner using electron beam microscopy (EPMA). Specifically, using EPMA, after confirming the shape of the secondary particles of the lithium transition metal composite oxide in the same reflected electron image as SEM, compositional analysis at the same location can confirm the presence of a large amount of Sr inside the secondary particles of the lithium transition metal composite oxide.

[0039] The composite oxide (Y) can be synthesized, for example, by adding a Li source and an M2 source to a Li-free composite compound (X), mixing them, and calcining them at 200°C to 1050°C. Examples of composite compounds (X) include composite oxides, hydroxides, and carbonates containing Ni, Mn, etc. Examples of Li sources include LiOH. Examples of M2 sources include hydroxides, carbonates, and nitrates of M2. Examples of M2 sources include Ca(OH)2, CaCO3, Ca(NO3)2, Sr(OH)2, SrCO3, and Sr(NO3)2. The M2 source can be a powdered solid or an aqueous solution containing the M2 source. From the viewpoint of dispersing M2 inside or outside the secondary particles of the lithium transition metal composite oxide, adding an aqueous solution is preferred. When adding an aqueous solution, from the viewpoint of facilitating the adjustment of the aqueous solution, the preferred M2 source is Ca(NO3)2 or Sr(NO3)2, which have high water solubility.

[0040] [negative electrode]

[0041] The negative electrode 12, for example, comprises a negative electrode core such as a metal foil, and a negative electrode composite material layer disposed on the surface of the negative electrode core. The negative electrode core may be a foil of a metal stable within the negative electrode potential range, such as copper, or a thin film of the metal disposed on its surface. The negative electrode composite material layer, for example, includes a negative electrode active material and a binder material. The negative electrode may be manufactured, for example, by coating a negative electrode composite material slurry containing a negative electrode active material and a binder material onto the negative electrode core and drying it to form a negative electrode composite material layer, and then calendering the negative electrode composite material layer.

[0042] In the negative electrode composite material layer, the negative electrode active material may include, for example, a carbon-based active material that reversibly absorbs, stores, and releases lithium ions. Suitable carbon-based active materials include natural graphite such as flake graphite, block graphite, and amorphous graphite, as well as artificial graphite such as block graphite (MAG) and graphitized mesophase carbon microspheres (MCMB). Alternatively, the negative electrode active material may be a Si-based active material composed of at least one of Si and Si-containing compounds, or a combination of carbon-based and Si-based active materials may be used.

[0043] Similar to the case of the positive electrode, the binder material contained in the negative electrode composite layer can also be fluoropolymer, PAN, polyimide, acrylic resin, polyolefin, etc., with styrene-butadiene rubber (SBR) being preferred. Furthermore, the negative electrode composite layer preferably also contains CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. Suitablely, SBR is used in combination with CMC or its salts, and PAA or its salts.

[0044] [Separator]

[0045] The separator uses porous sheets with ion-permeable and insulating properties. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator include polyolefins such as polyethylene and polypropylene, and cellulose. The separator can be a single-layer structure or a multilayer structure. A heat-resistant layer can be formed on the surface of the separator.

[0046] <Example>

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

[0048] <Example 1>

[0049] Synthesis of positive electrode active materials

[0050] The Ni composition obtained through coprecipitation 0.5 Mn 1.5 The nickel-manganese composite hydroxide of (OH)4 was calcined at 500°C to obtain nickel-manganese composite oxide (X).

[0051] Next, an aqueous solution of nickel-manganese composite oxide (X), LiOH, and Sr(NO3)2 was mixed with a total Ni and Mn molar ratio of Li to Sr of 1:0.5:0.002. This mixture was calcined at 900°C for 10 hours and then pulverized to obtain lithium composite oxide (Y). The XRD results showed that the molar fraction of Sr was 0.16% relative to the total moles of metal elements other than Li in the lithium transition metal composite oxide.

[0052] [The production of the positive electrode]

[0053] The above-mentioned positive electrode active material was mixed with acetylene black and polyvinylidene fluoride (PVdF) at a solid component mass ratio of 96.3:2.5:1.2. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added, and the mixture was then kneaded to prepare a positive electrode composite slurry. This positive electrode composite slurry was coated onto both sides of a positive electrode core formed from aluminum foil. After the coating dried, it was calendered using rollers and cut into specified electrode sizes, resulting in a positive electrode with a positive electrode composite layer formed on both sides of the positive electrode core. It should be noted that a portion of the positive electrode has an exposed portion where the surface of the positive electrode core is exposed.

[0054] [Making the negative electrode]

[0055] Natural graphite was used as the negative electrode active material. The negative electrode active material was mixed with sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR) in an aqueous solution at a solid component mass ratio of 100:1:1 to prepare a negative electrode composite slurry. This negative electrode composite slurry was coated onto both sides of a negative electrode core formed from copper foil. After the coating dried, it was calendered using rollers and cut into specified electrode sizes, resulting in a negative electrode with a negative electrode composite layer formed on both sides of the negative electrode core. It should be noted that a portion of the negative electrode has an exposed portion where the surface of the negative electrode core is exposed.

[0056] [Preparation of non-aqueous electrolytes]

[0057] Fluorinated ethylene carbonate (FEC), ethylene carbonate (EC), and methyl ethyl carbonate (EMC) were mixed in a volume ratio of 1:1:6 to obtain a non-aqueous solvent. LiPF6 was then dissolved in this non-aqueous solvent at a concentration of 1.0 mol / L to obtain a non-aqueous electrolyte.

[0058] [Battery Manufacturing]

[0059] Aluminum leads are installed on the exposed portion of the positive electrode, and nickel leads are installed on the exposed portion of the negative electrode. The positive and negative electrodes are wound in a spiral shape with a polyolefin separator in between, and then pressed radially to form a flat, wound electrode body. This electrode body is then housed in a casing made of aluminum laminate, and the non-aqueous electrolyte is injected. The opening of the casing is then sealed to obtain a non-aqueous electrolyte secondary battery with a designed capacity of 650mAh.

[0060] [Evaluation of Capacity Maintenance Rate]

[0061] First, the battery prepared above is charged at a constant current of 0.2C at a temperature of 25°C until the battery voltage reaches 4.9V, and then charged at a constant voltage of 4.9V until the current value reaches 0.02C. Afterward, it is discharged at a constant current of 0.2C until the battery voltage reaches 3.0V. The battery after repeating this charge-discharge cycle 5 times is used as the initial battery.

[0062] For the initial battery, perform the following cycle test. Calculate the discharge capacity of the 3rd cycle and the discharge capacity of the 26th cycle, and then calculate the capacity retention rate using the following formula.

[0063] Capacity retention (%) = (Discharge capacity at 26th cycle ÷ Discharge capacity at 3rd cycle) × 100

[0064] <Circular Test>

[0065] For the test battery cell, it was charged at a constant current of 0.2C at 25°C until the battery voltage reached 4.9V, and then charged at a constant voltage of 4.9V until the current reached 0.02C. Afterwards, it was discharged at a constant current of 0.2C until the battery voltage reached 3.0V. This charge-discharge cycle was repeated 26 times.

[0066] <Example 2>

[0067] An aqueous solution of nickel-manganese composite oxide (X), LiOH, and Sr(NO3)2 was mixed in a molar ratio of Ni and Mn to Li and Sr of 1:0.5:0.02. Otherwise, a battery was fabricated and evaluated in the same manner as in Example 1. The XRD results showed that the molar fraction of Sr was 0.96% relative to the total moles of metals other than Li contained in the lithium transition metal composite oxide.

[0068] <Example 3>

[0069] The battery was prepared and evaluated in the same manner as in Example 1, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0070] <Example 4>

[0071] The battery was prepared and evaluated in the same manner as in Example 2, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0072] <Comparative Example 1>

[0073] Similar to Example 1, nickel-manganese composite oxide (X) was obtained by co-precipitation. Next, nickel-manganese composite oxide (X) and LiOH were mixed in a molar ratio of Ni, Mn, and Li of 1:0.5. This mixture was calcined at 900°C for 10 hours to obtain a calcined product. Then, an aqueous solution of Sr(NO3)2 was mixed and added to the calcined product to achieve a molar ratio of Ni, Mn, and Sr of 1:0.002. After calcining at 900°C for 10 hours, the product was pulverized to synthesize lithium composite oxide (Z), which was used as the positive electrode active material. A battery was fabricated and evaluated using the obtained positive electrode active material (lithium composite oxide (Z)) in the same manner as in Example 1.

[0074] <Comparative Example 2>

[0075] An aqueous solution of Sr(NO3)2 was mixed into the calcined material and added so that the molar ratio of the total amount of Ni and Mn to Sr was 1:0.02. Otherwise, the battery was prepared and evaluated in the same manner as in Comparative Example 1.

[0076] <Comparative Example 3>

[0077] The battery was prepared and evaluated in the same manner as in Comparative Example 1, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0078] <Comparative Example 4>

[0079] The battery was prepared and evaluated in the same manner as in Comparative Example 2, except that Ca(NO3)2 was used instead of Sr(NO3)2.

[0080] Table 1 summarizes the discharge capacity (initial capacity) and capacity retention of the initial batteries for the examples and comparative examples. Additionally, Table 1 also shows the M2 element, the amount of M2 added, and the presence or absence of M2 within the secondary particles of the lithium transition metal composite oxide.

[0081] [Table 1]

[0082]

[0083] The battery of Example 1 has higher discharge capacity and capacity retention rate compared to the battery of Comparative Example 1. Similarly, in Examples 2-4 and Comparative Examples 2-4, the batteries of the examples also have higher discharge capacity and capacity retention rate compared to the batteries of the comparative examples. Furthermore, Figure 2The figures show SEM images and EPMA analysis results of the cross-sections of the positive electrode active materials of Example 1 and Comparative Example 1. In Example 1, Sr is predominantly located within the secondary particles of the lithium transition metal composite oxide, while in Comparative Example 1, Sr is predominantly located between the secondary particles of the lithium transition metal composite oxide. The same tendency is also observed in Example 2 and Comparative Example 2. Furthermore, in Examples 3 and 4, Ca is predominantly located within the secondary particles of the lithium transition metal composite oxide, while in Comparative Examples 3 and 4, Ca is predominantly located between the secondary particles of the lithium transition metal composite oxide.

[0084] Explanation of reference numerals in the attached figures

[0085] 10 Secondary batteries

[0086] 11 Positive electrode

[0087] 12 Negative electrode

[0088] 12a Volume Terminal

[0089] 13. Separators

[0090] 14 Electrode bodies

[0091] 15. Outer shell

[0092] 16 Sealing body

[0093] 17, 18 Insulation Boards

[0094] 19 Positive lead

[0095] 20 Negative lead

[0096] 21. Grooved section

[0097] 22. Metal plate with partial openings

[0098] 23 Lower valve body

[0099] 24 Insulating components

[0100] 25 Upper valve body

[0101] 26 covers

[0102] 26a Opening

[0103] 27 Gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium transition metal composite oxide capable of absorbing, storing, and releasing Li. The lithium transition metal composite oxide uses the general formula Li x M1 y O z F w In this 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. M2 is located within the secondary particles of the lithium transition metal composite oxide, and M2 is at least one element selected from Ca, Sr, Sc, Er, Y, Zr, and W. The lithium transition metal composite oxide uses the general formula Li 1+α Ni 0.5-β Mn 1.5-γ M β+γ O a F b The formula represents the expression where 0≤α≤0.2, 0≤β<0.2, 0≤γ<0.5, 0≤b≤0.2, 3.8≤a+b≤4.2, and M is at least one element selected from Ti, Fe, Al, Ge, Si, and Nb.

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

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The mole fraction of M2 is 0.2% to 10% relative to the total number of moles of metal elements other than Li contained in the lithium transition metal composite oxide.

4. A non-aqueous electrolyte secondary battery, comprising: A positive electrode comprising the positive electrode active material for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 3; Negative electrode; and Electrolytes.

Images