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

Abstract

A positive electrode active material which has a crystal structure belonging to space group R-3m and is a composite oxide represented by the compositional formula Li1 + aNibMncXdOe wherein X is at least one element selected from transition metal elements other than Li, Ni, and Mn and typical elements, a < = 1.15, 0.35 < = b < = 0.70, 0.30 < = c < = 0.65, 0 < = d < = 0.07, and e is a value satisfying electroneutrality. The value (alpha * beta) obtained by multiplying the Ni mixing rate (alpha) obtained by the Rietveld analysis of the positive electrode active material by the strain (beta) obtained by the Williamson-Hall method is 0.090 or less.

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 secondary batteries, the positive electrode active material significantly influences battery performance, including input / output characteristics, capacity, and durability. Consequently, extensive research has been conducted on positive electrode active materials. Lithium-transition metal composite oxides containing transition metal elements such as Ni and Mn are commonly used as positive electrode active materials. The type and amount of elements contained in the lithium-transition metal composite oxide, as well as the composite oxide's crystal structure, significantly influence battery performance. Even slight changes in these properties can lead to failure to achieve target performance.

[0003] For example, Patent Documents 1 to 3 disclose that, in order to improve battery performance such as charge-discharge cycle characteristics, they focus on the lattice strain of the crystal structure of a positive electrode active material and control the strain within a specific range.

[0004] Prior art literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-253169

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2013-091581

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 2016-188168 Summary of the Invention

[0008] In recent years, nonaqueous electrolyte secondary batteries such as lithium-ion secondary batteries have been used as power sources for driving vehicles, and further increases in capacity are being demanded. From the perspective of increasing capacity, the positive electrode active materials described in Patent Documents 1 to 3 still have much room for improvement.

[0009] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery having a crystal structure belonging to the space group R-3m, characterized in that it is composed of the composition formula Li 1+a Ni b Mn c X d O eRepresented, wherein X is at least one selected from transition metal elements and typical elements other than Li, Ni, and Mn, a≤1.15, 0.35≤b≤0.70, 0.30≤c≤0.65, 0≤d≤0.07, e is a value satisfying electrical neutrality, and the product of the Ni mixing ratio α obtained by Rietveld analysis and the strain β obtained by the Williamson-Hall method (α×β) is less than 0.090.

[0010] The nonaqueous electrolyte secondary battery according to the present disclosure includes a positive electrode containing the above-mentioned positive electrode active material, a negative electrode, and a nonaqueous electrolyte.

[0011] According to the positive electrode active material according to the present disclosure, it is possible to increase the capacity of a non-aqueous electrolyte secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a longitudinal cross-sectional view of a nonaqueous electrolyte secondary battery as an example of an embodiment. DETAILED DESCRIPTION

[0013] The present inventors conducted intensive research to achieve higher capacity in non-aqueous electrolyte secondary batteries. They discovered that in positive electrode active materials with a crystal structure belonging to the space group R-3m, the battery's charge and discharge capacity significantly increased when the value (α×β)—the product of the mixing ratio α, which represents the proportion of Ni incorporated into Li sites in the crystal structure, and the strain β, which represents the unevenness of the spacing between lattice planes—is 0.090 or less. The present inventors discovered that in layered rock salt structures belonging to the space group R-3m, the mixing ratio α and strain β significantly influence the discharge capacity, and that controlling the α×β value to 0.090 or less significantly improves the discharge capacity.

[0014] In particular, when the Ni content is less than 70 mol% of the total molar number of metal elements other than Li, the influence of the mixing ratio α and the strain β on the discharge capacity becomes greater, and the effect produced by controlling the value of α×β to less than 0.090 becomes significant. From the perspective of reducing the material cost of the battery, it is required to reduce the Ni content of the positive electrode active material, but if the Ni content is reduced, it is difficult to achieve a high capacity of the battery. The positive electrode active material involved in the present disclosure is extremely useful in achieving both low cost and high capacity of the battery. In addition, since the value of α×β varies greatly depending on the synthesis conditions of the positive electrode active material, in order to adjust the value of α×β to the target value, it is necessary to focus on this value and strictly control the synthesis conditions.

[0015] Hereinafter, 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 with reference to the accompanying drawings. Furthermore, technical configurations formed by selectively combining the various components of the various embodiments and variations described below are also included within the scope of the present disclosure.

[0016] In the embodiment described below, a non-aqueous electrolyte secondary battery 10 is illustrated as a cylindrical battery in which a wound electrode body 14 is housed in an outer can 16 having a bottomed cylindrical shape. However, the outer can of the battery is not limited to a cylindrical outer can. Other embodiments of the non-aqueous electrolyte secondary battery disclosed herein include, for example, a square battery having a square outer can, a coin-shaped battery having a coin-shaped outer can, and a pouch-type battery having an outer body composed of a laminated sheet including a metal layer and a resin layer. In addition, the electrode body is not limited to a wound type, and may also be a stacked type electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked with a separator.

[0017] Figure 1 FIG is a cross-sectional view of a non-aqueous electrolyte secondary battery 10 as an example of an embodiment. Figure 1 As shown, the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer can 16 for storing the electrode body 14 and the non-aqueous electrolyte. The non-aqueous electrolyte secondary battery 10 is, for example, a lithium-ion secondary battery. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a winding 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 outer can 16 is a metal container with a bottomed cylindrical shape that is open at one axial end, and the opening of the outer can 16 is blocked by a sealing body 17. In the following, for ease of explanation, the sealing body 17 side of the battery is set as the top, and the bottom side of the outer can 16 is set as the bottom.

[0018] The non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolyte) or a solid electrolyte.

[0019] Liquid electrolyte (electrolyte) contains non-aqueous solvent and electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvent can use esters, ethers, nitriles, amides and mixed solvents of two or more thereof, etc. As an example of non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and mixed solvents thereof, etc. can be cited. Non-aqueous solvent can contain halogen substitution (such as fluoroethylene carbonate, etc.) in which at least a portion of hydrogen of these solvents is substituted with halogen atoms such as fluorine. Electrolyte salt, for example, uses lithium salts such as LiPF6.

[0020] As a solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As an inorganic solid electrolyte, well-known materials in all-solid lithium-ion secondary batteries, etc. (such as oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte, for example, comprises a lithium salt and a matrix polymer, or comprises a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. As polymer materials, fluororesins, acrylic resins, polyether resins, etc. can be cited.

[0021] The positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode body 14 are all strip-shaped long bodies, which are alternately stacked in the radial direction of the electrode body 14 by being wound into a spiral. In order to prevent the precipitation of lithium, the negative electrode 12 is formed to be one circle larger than the positive electrode 11. In other words, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length direction and the width direction. The separator 13 is formed to be at least one circle larger than the positive electrode 11, for example, two sheets are arranged in a manner that sandwiches 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.

[0022] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. Figure 1 In the example shown, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 to the sealing body 17 side, while the negative electrode lead 21 extends through the outside of the insulating plate 19 to the bottom side of the outer can 16. 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. The top plate of the sealing body 17, or lid 27, which is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner 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.

[0023] A gasket 28 is provided between the outer can 16 and the sealing member 17 to ensure the airtightness of the battery interior. The outer can 16 is formed with a groove 22, which extends inward from a portion of its side surface and supports the sealing member 17. The groove 22 is preferably annular along the circumference of the outer can 16, and its upper surface supports the sealing member 17. The sealing member 17 is secured to the upper portion of the outer can 16 by the groove 22 and the open end of the outer can 16 riveted to the sealing member 17.

[0024] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating component 25, an upper valve body 26 and a cover 27 are stacked in order from the electrode body 14 side. The various components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the various components except the insulating component 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and an insulating component 25 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat, the lower valve body 24 is deformed and ruptured in a manner that pushes the upper valve body 26 toward the cover 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 ruptures, and the gas is discharged from the opening of the cover 27.

[0025] Hereinafter, the positive electrode 11 , the negative electrode 12 , and the separator 13 constituting the electrode assembly 14 , particularly the positive electrode 11 , will be described in detail.

[0026] [positive electrode]

[0027] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer arranged on the positive electrode core. The positive electrode core can be made of a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, titanium, or a thin film having the metal arranged on the surface. The positive electrode mixture layer preferably contains a positive electrode active material, a conductive agent, and a binder, and is provided on both sides of the positive electrode core. The positive electrode 11 can be produced, for example, as follows: a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder is applied to the positive electrode core, the coating is dried, and then compressed to form positive electrode mixture layers on both sides of the positive electrode core.

[0028] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black such as acetylene black and Ketjen black, graphite, carbon nanotubes (CNTs), carbon nanofibers, graphene, metal fibers, metal powders, and conductive whiskers. A conductive agent may be used alone or in combination. The content of the conductive agent relative to the mass of the positive electrode mixture layer is, for example, 0.1% by mass or more and 5% by mass or less.

[0029] As the binder contained in the positive electrode mixture layer, fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, ethylene-propylene-butadiene copolymer, polyacrylonitrile (PAN), polyimide, polyamide, acrylic resins such as ethylene-acrylic acid copolymer, etc. can be cited. In addition, these resins can also be used in combination with carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. The binder can be used alone or in combination with multiple types. The content of the binder is, for example, 0.1% by mass or more and 5% by mass or less relative to the mass of the positive electrode mixture layer.

[0030] The positive electrode active material has a crystal structure belonging to the space group R-3m and is composed of the formula Li 1+a Ni b Mn c X d O e A lithium transition metal composite oxide represented by . In the composition formula, X is at least one selected from transition metal elements and typical elements other than Li, Ni, and Mn, a≤1.15, 0.35≤b≤0.70, 0.30≤c≤0.65, 0≤d≤0.07, and e is a value that satisfies electrical neutrality. The composite oxide constituting the positive electrode active material contains Li, Ni, and Mn as essential elements. In addition, the composition of the positive electrode active material can be measured using an ICP emission spectrophotometer (for example, iCAP6300 manufactured by Thermo Fisher Scientific).

[0031] The positive electrode active material is characterized by having a layered rock salt structure belonging to the space group R-3m and having a composition that satisfies the above composition formula. At the same time, the product of the mixing ratio α, which indicates the proportion of Ni incorporated into the Li site of the crystal structure, obtained by Rietveld analysis, and the strain β, which indicates the unevenness of the spacing between the lattice planes, obtained by the Williamson-Hall method (α×β), is 0.090 or less. When the value of α×β is 0.090 or less, the charge and discharge capacity is particularly improved.

[0032] In the composition formula Li 1+a Ni b Mn c X d O e , the molar ratio (b) of Ni is greater than or equal to 0.35 and less than or equal to 0.70 (0.35≤b≤0.70). In addition, the molar ratio (c) of Mn is greater than or equal to 0.30 and less than or equal to 0.65 (0.30≤c≤0.65). In this case, it is possible to achieve both low cost and high capacity of the battery, and an improvement in discharge capacity can be achieved by controlling the value of α×β to less than or equal to 0.090. The content of Ni is greater than or equal to 35 mol% and less than or equal to 70 mol% relative to the total molar number of metal elements other than Li, and is preferably greater than or equal to the content of Mn.

[0033] From the viewpoint of further increasing the capacity, the molar ratio (b) of Ni is preferably 0.40 or more, more preferably 0.45 or more, and particularly preferably 0.50 or more. In addition, from the viewpoint of reducing material costs, the molar ratio (b) of Ni is preferably 0.65 or less, more preferably 0.60 or less. An example of a preferred range of the molar ratio (b) of Ni is 0.45 ≤ b ≤ 0.65 or 0.50 ≤ b ≤ 0.60. In this case, it is possible to more highly achieve both low cost and high capacity.

[0034] The molar ratio (c) of Mn is preferably 0.35 or more, more preferably 0.40 or more. Furthermore, the molar ratio (c) of Mn is preferably 0.60 or less. An example of a preferred range of the molar ratio (c) of Mn is 0.35 ≤ b ≤ 0.60 or 0.40 ≤ b ≤ 0.60. In this case, both low cost and high capacity can be achieved to a greater extent.

[0035] In the composition formula Li 1+a Ni b Mn c X d O e In the formula ( ), X represents, for example, at least one element selected from Mg, Ca, Sr, Ba, Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, Sb, B, Ga, In, P, Zr, Hf, Nb, Ta, Mo, W, Co, and Al. When a small amount of X is added, the improvement in charge and discharge capacity becomes more significant. Among them, at least one element selected from Al and Co is preferred. The molar ratio (d) of X is preferably 0.07 or less (0 ≤ d ≤ 0.07), more preferably 0.05 or less, and particularly preferably 0.03 or less.

[0036] In the composition formula Li 1+a Ni b Mn c X d O e The molar ratio (e) of O is a value that satisfies electrical neutrality. In other words, it is a value that satisfies the atomic valence of O in the positive electrode active material. The molar ratio (e) of O is, for example, 2.00 or more and 2.15 or less (2.00 ≤ e ≤ 2.15).

[0037] The positive electrode active material has a composition represented by the above composition formula, and has as its main component a composite oxide (hereinafter referred to as "Li-Ni-Mn composite oxide") having the above α×β value of 0.090 or less. Here, the main component refers to the component with the highest mass ratio among the constituent components of the positive electrode active material. In the mixture layer of the positive electrode 11, a composite oxide other than the Li-Ni-Mn composite oxide may be used as the positive electrode active material, but the content of the Li-Ni-Mn composite oxide is preferably 50% by mass or more, and may be substantially 100% by mass.

[0038] Li-Ni-Mn composite oxide is, for example, a secondary particle formed by the aggregation of multiple primary particles. An example of the volume-based median particle size (D50) of the Li-Ni-Mn composite oxide is 1 μm or more and 30 μm or more and 20 μm or less. The D50 of the composite oxide is the particle size at which the volume cumulative value is 50% in the particle size distribution measured by the laser diffraction scattering method. The BET specific surface area of the Li-Ni-Mn composite oxide is, for example, 0.1 m 2 / g or more and 10m 2 / g or less, or 0.5m 2 / g or more and 5m 2 The BET specific surface area of the composite oxide is measured according to the BET method (nitrogen adsorption method) described in JIS R 1626. When D50 and the BET specific surface area are within this range, high capacity can be easily achieved.

[0039] As mentioned above, the Li-Ni-Mn composite oxide has a layered rock salt structure belonging to the space group R-3m, and the value of the Ni mixing ratio α multiplied by the strain β (α×β) is less than 0.090. The Ni mixing ratio α is the ratio of the Ni content in the Li layers occupying the layered rock salt structure to the total Ni content, and is calculated using Rietveld analysis. The strain β represents the unevenness of the crystal lattice spacing and is calculated using the Williamson-Hall method.

[0040] The powder X-ray diffraction pattern of the Li-Ni-Mn composite oxide was obtained using a desktop X-ray diffractometer (manufactured by Rigaku Corporation, trade name "MiniFlex600"). The diffracted X-rays were detected by a high-speed one-dimensional detector (D / teX Ultra 2).

[0041] The measurement conditions of the above-mentioned X-ray diffraction apparatus are as follows.

[0042] X-ray source: CuKα rays

[0043] Tube voltage: 40kV

[0044] Tube current: 15mA

[0045] Divergence slit (DS): 1 / 4°

[0046] Scattering slit (SS): 13mm (open)

[0047] Receiving slit (RS): 8mm

[0048] Scan axis: 2θ / θ

[0049] Scanning method: continuous

[0050] 2θ scanning range: 10-80°

[0051] Scanning speed: 10° / min

[0052] Step size: 0.02°

[0053] The mixing ratio α in the crystal structure of the Li-Ni-Mn composite oxide is calculated by dividing the Ni amount in the Li site refined by the Rietveld analysis of the analysis software "Smartlab Studio 2" made by Rigaku Corporation by the total Ni amount in the structure. In this specification, the Li site in the Rietveld analysis is the 3b site (0, 0, 0.5) in the layered rock salt structure (R-3m), and the transition metal site is the 3a site (0, 0, 0). In addition, the strain β of the crystal structure of the Li-Ni-Mn composite oxide is calculated by the Williamson-Hall method in Smartlab Studio 2 using the 003, 101, 104, 015, and 113 diffraction lines.

[0054] In the Li-Ni-Mn composite oxide, the value of the product of the mixing ratio α and the strain β (α×β) is preferably 0.090 or less, preferably 0.072 or less, and more preferably 0.055 or less. The lower limit of the value of α×β is not particularly limited, but is preferably 0.002 or more, and more preferably 0.005 or more. An example of a preferred range of the value of α×β is 0.002 or more and 0.072 or less, or 0.005 or more and 0.055 or less. In this case, it is possible to achieve both low cost and high capacity at a higher level.

[0055] If the Ni content in the Li-Ni-Mn composite oxide changes, the preferred value of α×β also changes to some extent. 1+a Ni b Mn c X d O e When the molar ratio (b) of Ni is 0.35 or more and 0.55 or less, the value of α×β is, for example, 0.035 or more and 0.090 or less, or 0.040 or more and 0.055 or less. When the molar ratio (b) of Ni is greater than 0.55 and 0.70 or less, the value of α×β is, for example, 0.002 or more and 0.040 or less, or 0.005 or more and 0.035 or less.

[0056] The mixing ratio α is preferably 0.05 to 0.20. The strain β is preferably 0.02 to 0.50, more preferably 0.05 to 0.30. When the value of α×β is within the above range and the values of the mixing ratio α and strain β are within this range, the improvement effect of the charge and discharge capacity becomes more significant.

[0057] Li-Ni-Mn composite oxide can be synthesized, for example, by mixing a composite hydroxide or composite oxide containing Ni, Mn, etc. with a lithium raw material and calcining. The composite hydroxide containing Ni, Mn, etc. is prepared by stirring a solution of a metal salt containing Ni, Mn, etc. while dropping an alkaline solution such as sodium hydroxide, adjusting the pH to alkaline (e.g., 8.5 or more and 12.5 or less) to thereby precipitate (coprecipitate). In addition, by calcining the composite hydroxide, a composite oxide containing Ni, Mn, etc. can be obtained.

[0058] Examples of lithium raw materials include Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH·H2O, LiH, and LiF. A composite hydroxide or composite oxide containing Ni, Mn, and the like is preferably mixed with the lithium raw material in a molar ratio of the total amount of metal elements such as Ni and Mn to Li of 1:1.01 to 1:1.12.

[0059] In the control of the above-mentioned α×β value, for example, the calcination conditions are important. That is, in the synthesis process of the Li-Ni-Mn composite oxide, the mixture of the above-mentioned raw materials needs to be calcined in such a way that the value of α×β becomes 0.090 or less. The mixture of raw materials is calcined in the atmosphere or in an oxygen flow using a calcination furnace. When the Ni content is about 50 mol% relative to the total molar number of metal elements in the composite oxide, the calcination temperature is preferably a high temperature of 800°C or more. However, the necessary calcination temperature varies depending on the composition of the raw materials, such as the Ni content. For example, when the Ni content becomes higher, the calcination temperature can be lowered. Therefore, in order to adjust the value of α×β to the target value, it is necessary to focus on this value and strictly control the conditions to achieve it.

[0060] When the Ni content is about 50 mol%, the calcination temperature is preferably 800°C or higher and 1100°C or lower. In addition, the heating rate is, for example, 0.3°C / minute or higher and 3.0°C / minute or lower, or 0.5°C / minute or higher and 2.0°C / minute or lower. The calcination time can be 3 hours or higher and 10 hours or lower. Here, the calcination time refers to the time from when the temperature of the calcination furnace reaches the maximum temperature of the calcination process until the calcination is completed and cooling begins. The calcined product can be taken out of the calcination furnace and quenched in the atmosphere. Li-Ni-Mn composite oxide can be obtained, for example, by quenching the calcined product in the atmosphere, washing it with water, drying it as needed, and pulverizing it using a known method.

[0061] When the Ni content in the composite hydroxide or composite oxide containing Ni, Mn, etc. is 35 mol% or more and 55 mol% or less, the calcination temperature is preferably 900° C. or more and 1000° C. or less. In this case, for example, if the calcination temperature is 850° C., the value of α×β cannot be reduced to 0.090 or less, and a high capacity cannot be achieved.

[0062] [negative electrode]

[0063] The negative electrode 12 includes a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode core can be made of a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, with a thin film of the metal disposed on the surface. The negative electrode mixture layer preferably contains a negative electrode active material and a binder, and is disposed on both sides of the negative electrode core. The negative electrode 12 can be manufactured, for example, as follows: a negative electrode mixture slurry containing a negative electrode active material and a binder is applied to the negative electrode core, the coating is dried, and then compressed to form a negative electrode mixture layer on both sides of the negative electrode core. In addition, the negative electrode mixture layer may also contain a conductive agent such as CNT.

[0064] Negative electrode active materials generally use carbon materials that reversibly absorb and release lithium ions. Alternatively, elements such as Si and Sn that alloy with Li, or materials containing these elements, may be used as negative electrode active materials. Silicon-containing materials containing Si are preferred. Alternatively, materials such as lithium titanate, which have a higher charge and discharge potential relative to metallic lithium than carbon materials, may be used as negative electrode active materials. Negative electrode active materials may be used singly or in combination.

[0065] The carbon material that functions as the negative electrode active material is, for example, at least one selected from natural graphite, artificial graphite, soft carbon and hard carbon. Among them, artificial graphite such as blocky artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB), natural graphite such as flaky graphite, blocky graphite, and earthy graphite, or a mixture thereof, is preferably used. Silicon-containing materials that function as negative electrode active materials include, for example, silicon alloys, silicon compounds, and composite materials containing Si. Suitable silicon-containing materials are composite particles comprising an ion-conducting phase and a Si phase dispersed in the ion-conducting phase.

[0066] As in the case of the positive electrode 11, the binder contained in the negative electrode mixture layer can use fluororesins, olefin resins, PAN, polyimide, polyamide, acrylic resins, etc., and can also use polyvinyl acetate, styrene-butadiene rubber (SBR), etc. Among them, SBR is preferably used. The binder can be used alone or in combination. In addition, the negative electrode mixture layer preferably contains CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. They function as thickeners in the negative electrode mixture slurry. The content of the binder is, for example, 0.1% by mass or more and 5% by mass or less relative to the mass of the negative electrode mixture layer.

[0067] [Diaphragm]

[0068] The separator 13 uses a porous sheet with ion permeability and insulation. As specific examples of porous sheets, microporous films, woven fabrics, non-woven fabrics, etc. can be cited. As the material of the separator 13, polyolefins such as polyethylene and polypropylene, cellulose, etc. are preferred. The separator 13 can be a single-layer structure or a multi-layer structure. In addition, a resin layer with high heat resistance such as aromatic polyamide resin can also be formed on the surface of the separator 13.

[0069] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of the inorganic filler include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. The filler layer may be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0070] Example

[0071] Hereinafter, the present disclosure will be further described with reference to examples, but the present disclosure is not limited to these examples.

[0072] <Example 1>

[0073] [Preparation of positive electrode active material]

[0074] A hydroxide containing Ni and Mn at a molar ratio of 1:1 and lithium hydroxide at a molar ratio of Ni:Mn:Li = 0.5:0.5:1.05 were mixed, and the resulting mixture was heated at a temperature increase rate of 1°C / minute and calcined at 950°C in air for 10 hours. Subsequently, the calcined product was quenched in air to obtain a Li-Ni-Mn composite oxide. The composition of the obtained Li-Ni-Mn composite oxide was analyzed using an ICP emission spectrometer (iCAP6300 manufactured by Thermo Fisher Scientific).

[0075] [Production of positive electrode]

[0076] As the positive electrode active material, the above-mentioned Li-Ni-Mn composite oxide is used. The positive electrode active material, acetylene black and polyvinylidene fluoride are mixed in a solid content mass ratio of 92:5:3, and N-methyl-2-pyrrolidone (NMP) is used as a dispersion medium to prepare a positive electrode mixture slurry. The positive electrode slurry is applied to a positive electrode core composed of aluminum foil. After the coating film is dried, the coating film is rolled using a calendering roller to obtain a positive electrode having a positive electrode mixture layer formed on the positive electrode core.

[0077] [Preparation of non-aqueous electrolyte]

[0078] A non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF 6 ) at a concentration of 1 mol / L in a mixed solvent of fluoroethylene carbonate (FEC) and methyl propionate (FMP) at a volume ratio of 1:3.

[0079] [Preparation of test unit]

[0080] A lithium metal foil was used as the negative electrode. The positive and negative electrodes were placed opposite each other with a separator interposed therebetween to form an electrode assembly. This electrode assembly and the non-aqueous electrolyte were housed in a coin-shaped outer can. The opening of the outer can was sealed with a gasket and a sealing member to produce a test cell (non-aqueous electrolyte secondary battery).

[0081] <Example 2>

[0082] In the synthesis process of Li-Ni-Mn composite oxide, a hydroxide containing Ni and Mn in a molar ratio of 1:1 and lithium hydroxide in a molar ratio of Ni:Mn:Li = 0.5:0.5:1.11 were mixed, and the resulting mixture was heated at a heating rate of 1°C / min and calcined at 900°C in air for 3 hours. Otherwise, a positive electrode active material and a test unit were prepared in the same manner as in Example 1.

[0083] <Example 3>

[0084] A positive electrode active material and a test cell were produced in the same manner as in Example 2 except that the calcination temperature was changed to 1000° C. and the calcination time was changed to 10 hours in the synthesis step of the Li—Ni—Mn composite oxide.

[0085] <Example 4>

[0086] In the synthesis process of Li-Ni-Mn composite oxide, a hydroxide containing Ni and Mn in a molar ratio of 6:4 and lithium hydroxide in a molar ratio of Ni:Mn:Li = 0.6:0.4:1.00 are mixed, and the resulting mixture is heated at a heating rate of 1°C / min and calcined at 900°C in air for 10 hours. The calcined product is washed with a sufficient amount of water and then heat-treated at 180°C in a vacuum for 2 hours. Otherwise, a positive electrode active material and a test unit are prepared in the same manner as in Example 1.

[0087] <Example 5>

[0088] In the synthesis process of Li-Ni-Mn composite oxide, a hydroxide containing Ni and Mn in a molar ratio of 7:3 and lithium hydroxide in a molar ratio of Ni:Mn:Li = 0.7:0.3:1.05 are mixed, and the resulting mixture is heated at a heating rate of 1°C / min and calcined at 800°C in air for 3 hours. The calcined product is washed with a sufficient amount of water and then heat-treated at 180°C in a vacuum for 2 hours. Otherwise, a positive electrode active material and a test unit are prepared in the same manner as in Example 1.

[0089] <Example 6>

[0090] In the synthesis process of Li-Ni-Mn composite oxide, a hydroxide containing Ni and Mn in a molar ratio of 7:3 and lithium hydroxide in a molar ratio of Ni:Mn:Li=0.7:0.3:1.09 are mixed, and the resulting mixture is heated at a heating rate of 1°C / min and calcined at 900°C in air for 3 hours. The calcined product is washed with a sufficient amount of water and then heat-treated at 180°C in a vacuum for 2 hours. Otherwise, a positive electrode active material and a test unit are prepared in the same manner as in Example 1.

[0091] <Example 7>

[0092] In the synthesis process of Li-Ni-Mn composite oxide, a hydroxide containing Ni, Mn and Co in a molar ratio of 60:35:5 and lithium hydroxide in a molar ratio of Ni:Mn:Co:Li = 0.60:0.35:0.05:1.05 are mixed, and the resulting mixture is heated at a heating rate of 1°C / min and calcined at 850°C in air for 3 hours. The calcined product is washed with a sufficient amount of water and then heat-treated at 180°C in a vacuum for 2 hours. Otherwise, a positive electrode active material and a test unit are prepared in the same manner as in Example 1.

[0093] Comparative Example 1

[0094] A positive electrode active material and a test cell were produced in the same manner as in Example 1 except that the calcination temperature was changed to 850° C. and the calcination time was changed to 5 hours in the synthesis step of the Li—Ni—Mn composite oxide.

[0095] Comparative Example 2

[0096] A positive electrode active material and a test cell were produced in the same manner as in Example 2 except that the calcination temperature was changed to 850° C. and the calcination time was changed to 10 hours in the synthesis step of the Li—Ni—Mn composite oxide.

[0097] Comparative Example 3

[0098] A positive electrode active material and a test cell were produced in the same manner as in Example 2 except that the calcination temperature was changed to 850° C. and the calcination time was changed to 3 hours in the synthesis step of the Li—Ni—Mn composite oxide.

[0099] For each of the Li-Ni-Mn composite oxides of Examples and Comparative Examples, the Ni mixing ratio α and the strain β were determined by the above-described method, and Table 1 shows these values and the value of α×β.

[0100] [Evaluation of discharge capacity]

[0101] Each test cell of the Examples and Comparative Examples was charged at 25°C at a constant current of 0.2C until the battery voltage reached 4.5V. It was then charged at a constant voltage of 4.65V until the current reached 0.02C. After a 20-minute pause, the cells were discharged at a constant current of 0.2C until the battery voltage reached 2.5V. The discharge capacity was then determined. The discharge capacity measurement results are shown in Table 1, along with the composition of the positive electrode active material, the mixing ratio α, and the strain β.

[0102] Table 1

[0103]

[0104] As shown in Table 1, the test cells of the Examples all had higher capacities than the test cells of the Comparative Examples. Specifically, in the layered rock salt structure of the Li-Ni-Mn composite oxide, the battery capacity can be significantly improved when the value of the product of the mixing ratio α and the strain β (α×β) is set to 0.090 or less. When the value of α×β exceeds 0.090, as in the positive electrode active material of the Comparative Examples, the higher capacity achieved using the positive electrode active material of the Examples cannot be achieved.

[0105] Furthermore, the α×β value of Li-Ni-Mn composite oxides varies significantly depending on the synthesis conditions of the composite oxides. For example, Example 2 and Comparative Example 3 show that for Li-Ni-Mn composite oxides of the same composition, a 50°C change in calcination temperature results in a significant change in the α×β value (Example 2: 0.0872, Comparative Example 3: 0.1100). Consequently, the discharge capacity also differs significantly (Example 2: 174.0 mAh / g, Comparative Example 3: 153.9 mAh / g). Furthermore, increasing the calcination temperature to 1000°C and extending the calcination time results in a α×β value of 0.0423, and a discharge capacity of 189.9 mAh / g (see Example 3).

[0106] The present disclosure is further illustrated by the following embodiments.

[0107] Technical composition 1: A positive electrode active material for a non-aqueous electrolyte secondary battery having a crystal structure belonging to the space group R-3m and a composition formula Li 1+a Ni b Mn c X d O e Represented, wherein X is at least one selected from transition metal elements and typical elements other than Li, Ni, and Mn, a≤1.15, 0.35≤b≤0.70, 0.30≤c≤0.65, 0≤d≤0.07, e is a value satisfying electrical neutrality, and the product of the Ni mixing ratio α obtained by Rietveld analysis and the strain β obtained by the Williamson-Hall method (α×β) is less than 0.090.

[0108] Technical Configuration 2: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Technical Configuration 1, wherein a value obtained by multiplying the mixing ratio α by the strain β (α×β) is 0.002 or more and 0.072 or less.

[0109] Technical Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Technical Configuration 1 or 2, wherein the mixing ratio α is 0.05 or more and 0.20 or less.

[0110] Technical configuration 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of technical configurations 1 to 3, wherein the composition formula is Li 1+a Ni b Mn c X d O e In the embodiment, the molar ratio (b) of Ni is 0.50≤b≤0.60.

[0111] Technical configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the composition formula is Li 1+a Ni b Mn c X d O e wherein X is at least one selected from Mg, Ca, Sr, Ba, Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, Sb, B, Ga, In, P, Zr, Hf, Nb, Ta, Mo, W, Co, and Al.

[0112] Technical configuration 6: The positive electrode active material for the non-aqueous electrolyte secondary battery according to technical configuration 5, wherein the composition formula is Li 1+a Ni b Mn c X d O e wherein X is at least one selected from Al and Co.

[0113] Technical Configuration 7: A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode comprises the positive electrode active material according to any one of Technical Configurations 1 to 6.

[0114] Description of Reference Numerals

[0115] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 External can, 17 Sealing body, 18, 19 Insulating plates, 20 Positive electrode lead, 21 Negative electrode lead, 22 Slotted portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cover, 28 Gasket.

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery having a crystal structure belonging to the space group R-3m and a composition formula Li 1+a Ni b Mn c X d O e express, Wherein, X is at least one selected from transition metal elements and typical elements other than Li, Ni, and Mn, a≤1.15, 0.35≤b≤0.70, 0.30≤c≤0.65, 0≤d≤0.07, and e is a value satisfying electrical neutrality. The value α×β obtained by multiplying the Ni mixing ratio α obtained by the Rietveld analysis by the strain β obtained by the Williamson-Hall method is 0.090 or less.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, A value α×β obtained by multiplying the mixing ratio α by the strain β is equal to or greater than 0.002 and equal to or less than 0.

072.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, The mixing ratio α is 0.05 or more and 0.20 or less.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, In the composition formula Li 1+a Ni b Mn c X d O e In the embodiment, the molar ratio b of Ni is 0.50≤b≤0.

60.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 3, In the composition formula Li 1+a Ni b Mn c X d O e wherein X is at least one selected from Mg, Ca, Sr, Ba, Sn, Ti, Si, V, Cr, Fe, Cu, Zn, Bi, Sb, B, Ga, In, P, Zr, Hf, Nb, Ta, Mo, W, Co, and Al.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, In the composition formula Li 1+a Ni b Mn c X d O e wherein X is at least one selected from Al and Co.

7. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, The positive electrode includes the positive electrode active material according to any one of claims 1 to 6.

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