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

Abstract

Provided is a positive electrode active material that contributes to improvement in durability of a nonaqueous electrolyte secondary battery. The positive electrode active material contained in the nonaqueous electrolyte secondary battery includes a lithium transition metal complex oxide containing Ni, Ca, and Sr, and includes secondary particles formed by aggregation of primary particles, and an attached particle including a fibrous particle is present on a surface of the secondary particle, the fibrous particle including at least one of Ca and Sr.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials for non-aqueous electrolyte secondary batteries and non-aqueous electrolyte secondary batteries, particularly to positive electrode active materials for non-aqueous electrolyte secondary batteries containing high concentrations of Ni and non-aqueous electrolyte secondary batteries using such positive electrode active materials. Background Technology

[0002] Lithium nickel oxide (LiNiO2) has a high energy density, and lithium transition metal composite oxides, in which a portion of Ni is replaced by Co, Al, Mn, etc., are used as positive electrode active materials. However, lithium transition metal composite oxides are prone to side reactions with non-aqueous electrolytes, and therefore sometimes deteriorate due to repeated charge-discharge cycles, resulting in reduced discharge capacity and requiring improvements in durability.

[0003] Patent document 1 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery, which has an α-NaFeO2 structure and contains one or more transition metal elements selected from the group consisting of Mn, Ni and Co. Alkali earth metals and W are present on the surface of the lithium transition metal composite oxide particles.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-129221 Summary of the Invention

[0007] With increasingly stringent requirements for the durability of secondary batteries, surface protection technology for lithium transition metal composite oxides (LiMe) as positive electrode active materials has become an important development topic. Through repeated and in-depth research, the inventors have discovered that the presence of fibrous particles containing at least one of Ca and Sr on the surface of secondary particles in lithium transition metal composite oxides can significantly improve durability.

[0008] The purpose of this disclosure is to provide a positive electrode active material that helps improve the durability of non-aqueous electrolyte secondary batteries.

[0009] As one aspect of this disclosure, the positive electrode active material for a non-aqueous electrolyte secondary battery is characterized in that it comprises a lithium transition metal composite oxide containing Ni, Ca, and Sr, and includes secondary particles formed by the aggregation of primary particles, with attached particles containing fibrous particles on the surface of the secondary particles, the fibrous particles containing at least one of Ca and Sr.

[0010] As one aspect of this disclosure, the non-aqueous electrolyte secondary battery is characterized by comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, which include the aforementioned positive electrode active material for a non-aqueous electrolyte secondary battery.

[0011] According to the positive electrode active material for non-aqueous electrolyte secondary batteries as one aspect of this disclosure, the durability of non-aqueous electrolyte secondary batteries is improved. Attached Figure Description

[0012] Figure 1 This is a longitudinal cross-sectional view of a non-aqueous electrolyte secondary battery as an example of an implementation method. Detailed Implementation

[0013] Lithium transition metal composite oxides possess a layered structure in which Li ions can reversibly enter and exit, facilitating the charge-discharge reactions in the battery. Typically, Ni-based lithium transition metal composite oxides are known as high-capacity positive electrode active materials. However, such lithium transition metal composite oxides undergo side reactions with non-aqueous electrolytes, and their layered crystal structure is easily disrupted, sometimes leading to degradation and reduced discharge capacity due to repeated charge-discharge cycles. Furthermore, even with increased charging voltages, the side reactions with non-aqueous electrolytes become significant, sometimes accelerating degradation and further reducing discharge capacity.

[0014] Patent Document 1 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery, containing alkaline earth metals and W on the particle surface of a lithium transition metal composite oxide, from the viewpoint of improving durability. However, the requirements for the durability of secondary batteries are increasing, and the technology disclosed in Patent Document 1 is not limited to this, requiring further technological development.

[0015] To address the aforementioned issues, the inventors conducted in-depth research and discovered that the durability can be significantly improved by including fibrous particles containing at least one of Ca and Sr on the surface of secondary particles of lithium transition metal composite oxides. It has been determined that not only is either Ca or Sr present on the surface of the secondary particles, but both Ca and Sr are present on the surface of the secondary particles, and the particles containing at least one of Ca and Sr are fibrous in shape. This maintains liquid permeability without covering the particle surface and specifically improves durability.

[0016] The following is a detailed description of an embodiment of the non-aqueous electrolyte secondary battery disclosed herein. Hereinafter, a cylindrical battery in which a wound electrode body is housed within a cylindrical outer casing is illustrated. However, the electrode body is not limited to a wound type; it can also be a stacked type, in which multiple positive electrodes and multiple negative electrodes are alternately stacked one by one with separators. Furthermore, the outer casing is not limited to a cylindrical shape; for example, it can be square, coin-shaped, or a battery casing made of laminates comprising metal layers and resin layers.

[0017] Figure 1This is an axial cross-sectional view of a cylindrical secondary battery 10 as an example of an implementation. Figure 1 As shown, the secondary battery 10 includes a wound electrode body 14, an electrolyte, and an outer casing 16 for housing the electrode body 14 and the electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound into a spiral shape with the separator 13 in between. The outer casing 16 is a bottomed cylindrical metal container with an opening on one axial side, and the opening of the outer casing 16 is sealed by a sealing body 17. Hereinafter, for ease of explanation, the sealing body 17 side of the battery is referred to as the upper side, and the bottom side of the outer casing 16 is referred to as the lower side.

[0018] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all rectangular strips, which are alternately stacked radially in the electrode body 14 by being wound into a spiral shape in the length direction. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. To prevent lithium deposition, the negative electrode 12 is formed to be one size larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the length and width directions. Two separators 13 are formed to be at least one size larger than the positive electrode 11, for example, arranged to sandwich the positive electrode 11. The electrode body 14 includes 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. In the electrode body 14, the length direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the end faces of the positive electrode 11 and the negative electrode 12 in the width direction form the axial end faces of the electrode body 14.

[0019] Insulating plates 18 and 19 are respectively disposed above and below the electrode body 14. Figure 1 In the example shown, the positive lead 20 extends to the sealing body 17 through the through hole in the insulating plate 18, and the negative lead 21 extends to the bottom side of the outer casing 16 through the outer side of the insulating plate 19. The positive lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the top plate, i.e., the cover 27, of the sealing body 17, which is electrically connected to the internal terminal plate 23, becomes the positive terminal. The negative lead 21 is connected to the bottom inner surface of the outer casing 16 by welding or the like, and the outer casing 16 becomes the negative terminal.

[0020] A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure the airtightness of the battery interior. A groove 22 is formed in the outer casing 16, a portion of which protrudes inward and supports the sealing body 17. The groove 22 is preferably formed in a ring shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the groove 22 and the open end of the outer casing 16 that fits relative to the sealing body 17.

[0021] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cover 27 are stacked sequentially from the electrode body 14 side, functioning as a safety valve. Each component constituting the sealing body 17 has, for example, a circular or annular shape, and all components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected through their respective central portions, and the insulating member 25 is located between the peripheral portions. When the internal pressure of the battery rises due to abnormal heating, the lower valve body 24 deforms and breaks by pushing the upper valve body 26 upwards towards 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 breaks, and gas is discharged from the opening of the cover 27.

[0022] The following is a detailed description of the positive electrode 11, negative electrode 12, separator 13 and non-aqueous electrolyte constituting the secondary battery 10, especially the positive electrode 11.

[0023] [positive electrode]

[0024] The positive electrode 11, for example, has a positive current collector and a positive electrode flux layer formed on the surface of the positive current collector. The positive electrode flux layer is preferably formed on both sides of the positive current collector. For the positive current collector, a metal foil stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a thin film formed by depositing this metal on the surface, can be used. The thickness of the positive current collector is, for example, 10 μm or more and 30 μm or less.

[0025] The positive electrode binder layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode binder layer is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode current collector. The positive electrode 11 can be manufactured, for example, by coating the surface of the positive electrode current collector with a positive electrode binder slurry containing a positive electrode active material, a conductive agent, etc., allowing the coating to dry, and then calendering it to form positive electrode binder layers on both sides of the positive electrode current collector.

[0026] Examples of conductive agents included in the positive electrode mixture layer include acetylene black (AB), carbon black (CB) such as Ketjen black, carbon nanotubes (CNT), graphene, graphite, and other carbon-based particles. These can be used individually or in combination of two or more. The content of the conductive agent in the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less relative to the total mass of the positive electrode mixture layer.

[0027] Examples of binders included in the positive electrode binder layer include fluorinated resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These can be used individually or in combination of two or more. The binder content in the positive electrode binder layer is, for example, 0.1% by mass or more and 10% by mass or less relative to the total mass of the positive electrode binder layer.

[0028] The positive electrode active material contained in the positive electrode binder layer includes lithium transition metal complex oxide. This lithium transition metal complex oxide contains Ni, Ca, and Sr.

[0029] The Ni content in the lithium transition metal composite oxide is preferably 50 mol% or more relative to the total moles of elements other than Li and O. For example, the Ni content in the lithium transition metal composite oxide can be 50 mol% ≤ Ni content ≤ 95 mol%, 70 mol% ≤ Ni content ≤ 95 mol%, or 75 mol% ≤ Ni content ≤ 95 mol%. If the Ni content falls within this range, both high capacity and structural stability can be achieved. The lower limit of the Ni content is more preferably 80 mol%, and even more preferably 85 mol%.

[0030] The Ca content in the lithium transition metal composite oxide is, for example, 0 mol% < Ca content ≤ 1 mol% relative to the total moles of elements other than Li and O. The lower limit for Ca content is, for example, 0.01 mol%. The Sr content in the lithium transition metal composite oxide is, for example, 0 mol% < Sr content ≤ 1 mol% relative to the total moles of elements other than Li and O. The lower limit for Sr content is, for example, 0.01 mol%. The sum of the Ca and Sr contents relative to the total moles of elements other than Li and O is preferably 0 mol% < Ca content + Sr content ≤ 2 mol%, more preferably 0.02 mol% ≤ Ca content + Sr content ≤ 2 mol.

[0031] Lithium transition metal composite oxides, for example, are of the general formula Li a Ni x M1 y M2 z Ca s Sr t O 2-b(where 0.8≤a≤1.2, 0.50≤x≤0.95, 0≤y<0.50, 0≤z≤0.05, 0<s≤0.01, 0<t≤0.01, 0≤b≤0.05, x+y+z+s+t=1, M1 is at least one element selected from the group consisting of Co, Mn, and Al, and M2 is at least one element selected from the group consisting of W, Nb, Ti, Zr, B, Sb, Si, Fe, Mo, Sn, and Bi) is the composite oxide shown. The proportion of metal elements contained in the lithium transition metal composite oxide can be determined, for example, by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0032] Lithium transition metal composite oxides contain secondary particles formed by the aggregation of primary particles. The particle size of the primary particles is, for example, 0.02 μm or more and 2 μm or less. The particle size of the primary particles is determined as the diameter of the circumscribed circle in a particle image observed by a scanning electron microscope (SEM). The average particle size of the secondary particles is, for example, 2 μm or more and 30 μm or less. Here, the average particle size refers to the median particle size (D50) on a volumetric basis. D50 refers to the particle size at which the cumulative frequency in the volumetric particle size distribution reaches 50% from the smallest end, also known as the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction-type particle size distribution measuring device (e.g., Microtrac BEL Co., Ltd., MT3000II) with water as the dispersion medium.

[0033] Adhesive particles, including fibrous particles, exist on the surface of secondary particles of lithium transition metal composite oxides. These adhesive particles are smaller than the secondary particles adhering to the surface of the lithium transition metal composite oxides. Fibrous particles are one type of adhesive particle, and are elongated, fibrous particles. Fibrous particles can aggregate to form rod-shaped or spherical adhesive particles. Besides fibrous particles, adhesive particles may also include, for example, blocky particles. Blocky particles do not have the elongated shape of fibrous particles; for example, they may have plate-like or spherical shapes.

[0034] The fibrous particles contain at least one of Ca and Sr. Durability can be improved by having fibrous particles containing at least one of Ca and Sr on the surface of secondary particles of lithium transition metal composite oxides. The composition of the fibrous particles is not particularly limited as long as they contain at least one of Ca and Sr; for example, they can be oxides, hydroxides, carbonates, etc., containing at least one of Ca and Sr. The fibrous particles can contain both Ca and Sr.

[0035] The aspect ratio of the fibrous particles is, for example, 10 or more. A higher aspect ratio tends to improve battery durability. The aspect ratio of the fibrous particles is preferably 15 or more, more preferably 20 or more. There is no particular upper limit to the aspect ratio of the fibrous particles, for example, 100. The aspect ratio of the fibrous particles can be calculated from images of the fibrous particles obtained using a scanning electron microscope (SEM). Specifically, using SEM images, for 10 fibrous particles, the aspect ratio is obtained by dividing the length of the major axis by the length of the minor axis in the direction perpendicular to the major axis, and these are averaged to calculate the aspect ratio of the fibrous particles. The major axis of the fibrous particles is, for example, 3 μm or less.

[0036] Preferably, Ca and Sr are uniformly distributed on the surface of the secondary particles. This makes the improved durability effect of the fibrous particles more significant. Specifically, by ensuring that fibrous particles containing at least one of Ca and Sr are uniformly distributed on the surface of the secondary particles, side reactions with non-aqueous electrolytes can be significantly suppressed. The distribution of Ca and Sr on the surface of the secondary particles can be determined, for example, by calculating the Gini coefficients of each element on the surface of the secondary particles from the elemental concentration analysis results of the cross-section of the secondary particles using a time-of-flight secondary ion mass spectrometry (TOF-SIMS) device. A smaller Gini coefficient indicates a more uniform dispersion of the element on the surface of the secondary particles, with a minimum value of 0. The Gini coefficients of Ca and Sr on the surface of the secondary particles are preferably 0.7 or less. The Gini coefficients of Ca and Sr on the surface of the secondary particles are, for example, 0.1 or more.

[0037] The Gini coefficient of the secondary particle surface of Ca is: for the normalized intensity I of Ca on the secondary particle surface Ca_OUT When the cumulative rate is expressed in order of intensity, it is twice the area enclosed between the diagonal and the Lorenz curve.

[0038] Normalized intensity I of Ca on the surface of secondary particles Ca_OUT The results were obtained using a time-of-flight secondary ion mass spectrometer (IONTOF-SIMS5) under the following conditions.

[0039] Primary ion: Bi3 ＋

[0040] Ionization voltage: 30kV

[0041] Ion current: 0.03pA@100us

[0042] Observation range: 50μm × 50μm

[0043] Quality range: 60µs (~310amu)

[0044] Detection: 4 frames / scan, 150 scans

[0045] The image representing the concentration distributions of Ni and Ca obtained from the above measurements was segmented into 256×256 pixels, and the detection intensity of Ni and Ca was calculated for each pixel. Then, the ratio of the detection intensity of Ca to the detection intensity of Ni was calculated as the normalized intensity I of Ca. Ca .

[0046] The area from the surface of the secondary particle identified in the above image to within 0.5 μm is defined as the surface of the secondary particle, and the pixels contained on the surface of this secondary particle (hereinafter referred to as surface pixels) are determined. I corresponds to each surface pixel. Ca The set is I Ca_OUT . byI Ca_OUT Calculate the Gini coefficient of the secondary particle surface of Ca. The specimen for cross-sectional observation can be a sample in which lithium transition metal composite oxide is embedded in resin, or a cathode composite layer containing lithium transition metal composite oxide. The normalized intensity I of the secondary particle surface of Sr is calculated. Sr_OUT with I Ca_OUT Similarly, Ca and Sr can also exist uniformly within the secondary particles.

[0047] Lithium transition metal composite oxides can have a layered structure. Examples of layered structures for lithium transition metal composite oxides include those belonging to space group R-3m and those belonging to space group C2 / m. From the viewpoints of high capacity and crystal structure stability, lithium transition metal composite oxides preferably have a layered structure belonging to space group R-3m. The layered structure of lithium transition metal composite oxides can include a transition metal layer and a Li layer.

[0048] In addition to the positive electrode active material described in this embodiment, the positive electrode additive layer may also contain other positive electrode active materials. Examples of other positive electrode active materials include lithium transition metal composite oxides that do not contain Ca or Sr.

[0049] Next, an example of a method for manufacturing the positive electrode active material according to this embodiment will be described. The method for manufacturing the positive electrode active material includes, for example, a lithium transition metal composite oxide synthesis step, in which a metal oxide containing Ni, a Li compound, a Ca compound, and a Sr compound are mixed and calcined to obtain a calcined product; a washing step, in which the calcined product is washed with water and dehydrated under specified conditions to obtain a cake-like composition; and a drying step, in which the cake-like composition is dried to obtain a powder-like composition.

[0050] Metal oxides containing at least Ni can be prepared by adding dropwise solutions of metal salts such as Ni, Co, Al, and Mn, and an alkaline solution such as sodium hydroxide, to a stirred reaction vessel containing a pH-adjusted solution. The pH is then adjusted to alkaline (e.g., 8.5–12.5), causing the composite hydroxide to precipitate (co-precipitate). This metal hydroxide is then heat-treated. There are no particular limitations on the firing temperature, for example, a range of 250°C to 600°C.

[0051] Next, a mixture is obtained by mixing a metal oxide containing at least Ni, a Li compound, a Ca compound, and a Sr compound. Examples of Li compounds include: Li₂CO₃, LiOH, Li₂O₂, Li₂O, LiNO₃, LiNO₂, Li₂SO₄, LiOH·H₂O, LiH, and LiF. Examples of Ca compounds include: Ca(OH)₂, CaHPO₄, Ca(H₂PO₄)₂, Ca₃(PO₄)₂, CaO, CaCO₃, CaSO₄, Ca(NO₃)₂, CaCl₂, and CaAlO₄. Examples of Sr compounds include: Sr(OH)₂, SrHPO₄, Sr(H₂PO₄)₂, Sr₃(PO₄)₂, SrO, SrCO₃, SrSO₄, Sr(NO₃)₂, SrCl₂, and SrAlO₄. Additionally, an M₂ compound may also be mixed during the mixing process. Examples of Me compounds include: ZrO2, Nb2O5, Nb2O5·nH2O, TiO2, Ti(OH)4, SiO, SiO2, Li2MoO4, MoO3, H2MoO4, WO3, Li2WO4, Fe(OH)2, Fe2O3, SnO2, Bi(OH)3, Bi2O3, H3BO3, B2O3, Sb2O3, etc.

[0052] By firing the above mixture, a fired product can be obtained. The firing process is, for example, carried out in an oxygen stream with an oxygen concentration of 60% or higher, at a flow rate of 10 cm³ / s. 3Firing is performed in a firing furnace at a rate ranging from 0.1 L / min to 4 L / min, or at a rate of 1 L / min or more per 1 kg of mixture. The first set temperature in the firing conditions is set to 450°C or below, the holding time at the first set temperature is between 0 and 8 hours, and the heating rate at 450°C or below is between 1.5°C / min and 6.0°C / min. The second set temperature is set to 450°C or above and 680°C or below, the holding time at the second set temperature is between 0 and 8 hours, and the heating rate at 450°C or above and 680°C is between 1.0°C / min and 4.5°C / min. Furthermore, the maximum temperature is reached in the range of 690°C or above and 900°C or below. The heating rate from above 680°C to reaching the maximum temperature can be set, for example, to 0.1°C / min to 3.5°C / min. Additionally, the holding time at the maximum temperature can be between 1 hour and 10 hours. In addition, the firing process can also be a multi-stage firing process. As long as it is within the range specified above, multiple temperature zones can be set.

[0053] By washing, dehydrating, and drying the calcined material described above, a lithium transition metal composite oxide, which serves as a positive electrode active material, can be obtained. The washing process is performed, for example, using a 3L reaction vessel, under conditions of a solid-liquid ratio of 500 g / L or more and 2000 g / L or less, a washing time of 5 minutes or more and 1 hour or less, and a stirring speed of 200 rpm or more. The washing time and stirring speed can be varied by changing the size of the reaction vessel. The moisture content of the cake-like composition obtained by dehydration is, for example, 10% or less, and can be 8% or less. The drying process is performed, for example, under conditions of a pressure of 1 kPa or less, a temperature of 120°C or more and 300°C or less, and a time of 1 hour or more and 10 hours or less. More preferably, the drying conditions are a pressure of 100 Pa or less, a temperature of 150°C or more and 250°C or less, and a time of 1 hour or more and 5 hours or less.

[0054] Lithium transition metal composite oxides can be further subjected to a heat treatment process. This heat treatment process can be carried out, for example, in a vacuum, in an oxygen stream, or in atmosphere, at temperatures ranging from 150°C to 600°C. During this heat treatment process, for example, tungsten oxide (WO3), lithium tungstate (Li2WO4, Li4WO5, Li6W2O9), boric acid (H3BO3), lithium borate (Li2B4O7, Li3BO3, LiB3O5, LiBO2), or lithium phosphate (Li...) can be added. 3-x H x PO40≤x≤3), etc.

[0055] [negative electrode]

[0056] The negative electrode 12 may, for example, have a negative electrode current collector and a negative electrode binder layer formed on the surface of the negative electrode current collector, or a metallic Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may also have a negative electrode current collector, on which lithium metal is deposited during charging. When the negative electrode 12 has a negative electrode binder layer, the binder layer is preferably formed on both sides of the negative electrode current collector. The negative electrode current collector may be a foil of a metal stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a thin film of the metal disposed on its surface. The thickness of the negative electrode current collector is, for example, 5 μm or more and 30 μm or less. The negative electrode binder layer, for example, includes a negative electrode active material and a binder. The thickness of the negative electrode binder layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode current collector. The negative electrode 12 can be manufactured, for example, by coating the surface of the negative electrode current collector with a negative electrode mixture slurry containing negative electrode active material, binder, etc., allowing the coating to dry, and then calendering to form a negative electrode mixture layer on both sides of the negative electrode current collector.

[0057] As the negative electrode active material contained in the negative electrode coating layer, there are no particular limitations on the material as long as it can reversibly absorb, store, and release lithium ions; carbon materials such as graphite are commonly used. Graphite can be any of the following: natural graphite such as flake graphite, block graphite, and amorphous graphite; artificial graphite such as block graphite; and artificial graphite such as graphitized mesophase carbon microspheres. Additionally, as the negative electrode active material, metals alloyed with Li such as Si and Sn, metal compounds containing Si and Sn, and lithium-titanium composite oxides can also be used. Furthermore, materials with a carbon coating can also be used. For example, SiO₂... x (0.5≤x≤1.6) represents Si-containing compounds, or compounds composed of Li 2y SiO (2＋y) Si-containing compounds, such as those containing Si particles dispersed in the lithium silicate phase (0<y<2), can be used in combination with graphite.

[0058] Examples of binders contained in the negative electrode binder layer include: styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and also partially neutralized salts), polyvinyl alcohol (PVA), etc. These can be used individually or in combination of two or more.

[0059] [Separator]

[0060] The separator 13 can be a porous sheet with ion permeability and insulation. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably a polyolefin such as polyethylene or polypropylene, or cellulose. 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 an aromatic polyamide resin, can be formed on the surface of the separator 13.

[0061] A filler layer containing inorganic filler can 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 inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. The filler layer can be formed by coating a slurry containing the filler onto the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0062] [Non-aqueous electrolytes]

[0063] Non-aqueous electrolytes, for example, have lithium-ion conductivity. Non-aqueous electrolytes can be liquid electrolytes (electrolytes) or solid electrolytes.

[0064] Liquid electrolytes (electrolytes) may include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Non-aqueous solvents may include, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted derivatives formed by substituting at least a portion of the hydrogen atoms of these solvents with halogen atoms such as fluorine. Examples of halogen-substituted derivatives include fluorocyclic carbonates such as fluoroethylene carbonate (FEC), fluorochain carbonates, and fluorochain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0065] Examples of the aforementioned esters include: cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate; chain carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0066] Examples of the aforementioned ethers include: 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eucalyptol, crown ethers and other cyclic ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, and dihexyl ether. Ethers, including ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and other chain ethers.

[0067] The preferred electrolyte salt is a lithium salt. Examples of lithium salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, and LiB. 10 Cl 10 Examples of lithium salts include lower aliphatic carboxylic acids such as lithium Cl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO₂F₂), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium tetrafluoro(oxalate)phosphate. Examples of borates include lithium bis(oxalate)borate (LiBOB) and lithium difluoro(oxalate)borate (LiDFOB). Examples of imide salts include lithium difluorosulfonylimide (LiN(FSO₂)₂), lithium bis(trifluoromethanesulfonate)imide (LiN(CF₃SO₂)₂), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF₃SO₂)(C₄F₉SO₂)), and lithium bis(pentafluoroethanesulfonate)imide (LiN(C₂F₅SO₂)₂). Among these, LiPF₆ is preferred from the perspectives of ionic conductivity and electrochemical stability. The concentration of lithium salt can be, for example, less than 4 moles per 1 L of non-aqueous solvent, less than 3 moles, preferably less than 1.8 moles, and more preferably more than 0.8 moles and less than 1.8 moles.

[0068] Non-aqueous electrolytes may contain additives. Examples of additives include unsaturated carbonates, acid anhydrides, phenolic compounds, benzene compounds, nitrile compounds, isocyanate compounds, sulpholactone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0069] Examples of unsaturated cyclic carbonates include: vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, etc. Unsaturated cyclic carbonates can be used alone or in combination of two or more. A portion of the hydrogen atoms in an unsaturated cyclic carbonate can be replaced by fluorine atoms. The anhydride can be an anhydrous product formed by the intermolecular condensation of multiple carboxylic acid molecules, preferably an anhydride of a polycarboxylic acid. Examples of anhydrides of polycarboxylic acids include: succinic anhydride, maleic anhydride, phthalic anhydride, etc.

[0070] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0071] Examples of nitrile compounds include adiponitrile, heptanonitrile, propionitrile, and succinic anionizer. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and methylcyclohexane diisocyanate (BIMCH). Examples of sulcolone compounds include propane sulcolone and propenyl sulcolone. Examples of sulfuric acid compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate compounds include trimethyl phosphate and tris(trimethylsilyl) phosphate. Examples of phosphite compounds include trimethyl phosphite and tris(trimethylsilyl) phosphite.

[0072] As a solid electrolyte, polymer electrolytes, inorganic solid electrolytes, etc., in solid or gel form can be used. As an inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Polymer electrolytes, for example, contain lithium salts and matrix polymers, or contain non-aqueous solvents, lithium salts, and matrix polymers. As a matrix polymer, for example, a polymer material that gels by absorbing non-aqueous solvents is used. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins.

[0073] Example

[0074] The present disclosure is further illustrated below by way of examples and comparative examples, but the present disclosure is not limited to the following examples.

[0075] <Example 1-1>

[0076] [Preparation of positive electrode active material]

[0077] [Ni] obtained by coprecipitation method 0.91 Co 0.04 Al 0.05 The composite hydroxide represented by [OH]2 was calcined at 400°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. Next, the above metal oxide, Ca(OH)2, and Sr(OH)2 were mixed in a molar ratio of 0.3 mol% for Ca and 0.1 mol% for Sr relative to the total amount of metal elements. Lithium hydroxide monohydrate (LiOH·H2O) was further mixed in a molar ratio of Li relative to the total amount of Ni, Co, Al, Ca, and Sr of 103 mol% to obtain a mixture. This mixture was heated from room temperature to 400°C at a heating rate of 4°C / min under an oxygen flow of 95% oxygen concentration (flow rate of 3 L / min per kg of mixture), and then heated from 400°C to 650°C at a heating rate of 2°C / min. Finally, the temperature was increased from 650°C to 740°C at a heating rate of 1°C / min and held for 6 hours to obtain the calcined product. For this calcined material, a 3L reaction vessel was used. The calcined material was added to water at a solid-liquid ratio of 500 g / L. After washing with water for 10 minutes with stirring at 300 rpm, it was dehydrated. Then, it was dried under a vacuum atmosphere at 180°C and 10 Pa for 2 hours to obtain the positive electrode active material of Example 1-1.

[0078] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 1 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.3 μm and an aspect ratio of 40 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, detecting Ca and Sr, with Gini coefficients of 0.60 and 0.58, respectively, on the secondary particle surface.

[0079] [The production of the positive electrode]

[0080] 95 parts by mass of the above-mentioned positive electrode active material, 3 parts by mass of acetylene black (AB), and 2 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and N-methyl-2-pyrrolidone (NMP) was added in appropriate amount to prepare a positive electrode slurry. Next, the positive electrode slurry was coated onto both sides of a positive electrode current collector made of aluminum foil. After the coating was dried, it was calendered using calendering rollers and cut into specified electrode sizes to manufacture the positive electrode. It should be noted that an exposed portion of the positive electrode is provided, exposing the surface of the positive electrode current collector.

[0081] [Making the negative electrode]

[0082] 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 component mass ratio of 100:1:1 to prepare a negative electrode slurry. Next, the negative electrode slurry was coated onto both sides of a negative electrode current collector made of copper foil. After the coating was dried, it was calendered using calendering rollers and cut into specified electrode sizes to fabricate the negative electrode. It should be noted that a portion of the negative electrode is provided with an exposed portion that exposes the surface of the negative electrode current collector.

[0083] [Preparation of non-aqueous electrolytes]

[0084] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. A non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) in this mixed solvent at a concentration of 1.2 mol / L.

[0085] [Fabrication of the Experimental Battery Cell]

[0086] A positive electrode lead is installed on the exposed portion of the positive electrode, and a negative electrode lead is installed on the exposed portion of the negative electrode. The positive and negative electrodes are wound into a spiral shape with a polyolefin separator in between, and then pressed radially to form a flat, wound electrode body. This electrode body is housed in an outer casing made of aluminum laminate, and after injecting the aforementioned non-aqueous electrolyte, the opening of the outer casing is sealed to obtain the experimental battery cell.

[0087] [Durability Evaluation]

[0088] At an ambient temperature of 45°C, the test battery cell was charged to 4.2V at a constant current of 0.3C, and then charged to 0.02C at a constant voltage of 4.2V. It was then discharged to 2.5V at a constant current of 0.5C. This charge-discharge cycle was counted as one cycle, and 200 cycles were performed. The durability of the test battery cell was calculated using the following formula.

[0089] Durability = (Discharge capacity at 200th cycle / Discharge capacity at 1st cycle) × 100

[0090] <Example 1-2>

[0091] The positive electrode active material was prepared as follows. Otherwise, test battery cells were prepared in the same manner as in Examples 1-1 for evaluation. It should be noted that in the TOF-SIMS-based determination of the elemental concentration distribution on the surface of the positive electrode active material, Al was detected along with Ca and Sr.

[0092] (1) In the firing process, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.3 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Zr is 0.1 mol%.

[0093] (2) Change the solid-liquid ratio in the water washing process to 750 g / L.

[0094] <Examples 1-3>

[0095] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0096] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.3 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Ti is 0.1 mol%.

[0097] (2) Change the solid-liquid ratio in the water washing process to 1000g / L.

[0098] <Examples 1-4>

[0099] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0100] (1) In the firing process, Ca(OH)2, Sr(OH)2 and WO3 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.3 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of W is 0.1 mol%.

[0101] (2) Change the solid-liquid ratio in the water washing process to 1500g / L.

[0102] <Examples 1-5>

[0103] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0104] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added in a manner that the molar ratio of Ca is 0.3 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Nb is 0.3 mol%, relative to the total amount of metal elements.

[0105] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L and the water washing time is changed to 20 minutes.

[0106] <Comparative Example 1-1>

[0107] In the fabrication of the positive electrode active material, no Sr was added. During the firing process, Ca(OH)₂ was added at a molar ratio of 0.5 mol% relative to the total amount of metal elements. Otherwise, test battery cells were fabricated and evaluated in the same manner as in Examples 1-1. SEM observation confirmed that blocky particles with a length diameter of 0.5 μm and an aspect ratio of 1 were attached to the surface of the secondary particles of the positive electrode active material.

[0108] <Comparative Examples 1-2>

[0109] In the preparation of the positive electrode active material, no Ca was added. In the firing process, Sr(OH)2 was added in a molar ratio of 0.2 mol% to the total amount of metal elements. Otherwise, the test battery cells were prepared in the same manner as in Examples 1-1 and evaluated.

[0110] <Example 2-1>

[0111] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0112] (1) Using [Ni 0.90 Co 0.05 Mn 0.05 The complex hydroxide shown in ](OH)2 yields a metal oxide containing Ni, Co, and Mn.

[0113] (2) In the calcination process, Ca(OH)2 and Sr(OH)2 are added in a molar ratio of 0.5 mol% and 0.1 mol% relative to the total amount of metal elements, and lithium hydroxide is mixed in a molar ratio of Li to the total amount of Ni, Co, Mn, Ca and Sr of 105 mol%.

[0114] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 2 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.27 μm and an aspect ratio of 30 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, and Ca and Sr were detected, with Gini coefficients of 0.59 and 0.58, respectively, on the secondary particle surface.

[0115] <Example 2-2>

[0116] In the firing process of the positive electrode active material, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in the manner of Ca molar ratio of 0.5 mol%, Sr molar ratio of 0.2 mol%, and Zr molar ratio of 0.5 mol%. Otherwise, test battery cells are made in the same manner as in Example 2-1 and evaluated.

[0117] <Example 2-3>

[0118] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated.

[0119] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added in a manner that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of Nb is 0.5 mol%, relative to the total amount of metal elements.

[0120] (2) Change the solid-liquid ratio in the water washing process to 750 g / L.

[0121] <Example 2-4>

[0122] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated.

[0123] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 1.0 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Ti is 0.5 mol%.

[0124] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L and the water washing time is changed to 20 minutes.

[0125] <Examples 2-5>

[0126] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated.

[0127] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Ti is 0.5 mol%.

[0128] (2) In the water washing process, the solid-liquid ratio is changed to 1500g / L and the water washing time is changed to 20 minutes.

[0129] (3) H3BO3 is mixed in the lithium transition metal composite oxide obtained in the water washing process with the molar ratio of B to the total amount of Ni, Co, Mn, Ca, Sr and Ti being 0.5 mol%, and then heat-treated in an oxygen stream at 300°C.

[0130] <Examples 2-6>

[0131] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated. It should be noted that in the TOF-SIMS-based determination of the elemental concentration distribution on the surface of the positive electrode active material, B was detected along with Ca and Sr.

[0132] (1) In the firing process, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Zr is 0.3 mol%.

[0133] (2) In the water washing process, the solid-liquid ratio is changed to 1500g / L and the water washing time is changed to 20 minutes.

[0134] (3) H3BO3 is mixed in the lithium transition metal composite oxide obtained in the water washing process in such a way that the molar ratio of B to the total amount of Ni, Co, Mn, Ca, Sr and Zr is 0.5 mol%, and then heat-treated in an oxygen stream at 300°C.

[0135] <Comparative Example 2-1>

[0136] In the fabrication of the positive electrode active material, no Sr was added. During the firing process, Ca(OH)₂ was added at a molar ratio of 0.5 mol% relative to the total amount of metal elements. Otherwise, test battery cells were fabricated and evaluated in the same manner as in Example 2-1. SEM observation confirmed that blocky particles with a length diameter of 0.5 μm and an aspect ratio of 1.5 were attached to the surface of the secondary particles of the positive electrode active material.

[0137] <Comparative Example 2-2>

[0138] In the preparation of the positive electrode active material, no Ca was added. In the firing process, Sr(OH)2 was added in a molar ratio of 0.5 mol% to the total amount of metal elements. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated.

[0139] <Comparative Examples 2-3>

[0140] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated.

[0141] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Nb is 0.5 mol%.

[0142] (2) Change the washing time in the washing process to 1 minute and change the stirring speed to 100 rpm.

[0143] <Comparative Examples 2-4>

[0144] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated.

[0145] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of Ti is 0.5 mol%.

[0146] (2) Change the water washing time in the water washing process to 1 minute.

[0147] <Comparative Examples 2-5>

[0148] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 2-1 and evaluated.

[0149] (1) In the firing process, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 1 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Zr is 0.5 mol%.

[0150] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L and the stirring speed is changed to 100rpm.

[0151] <Example 3-1>

[0152] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0153] (1) Using [Ni 0.90 Mn 0.10 The composite hydroxide shown in ](OH)2 yields a metal oxide containing Ni and Mn.

[0154] (2) In the calcination process, Ca(OH)2 and Sr(OH)2 are added in a molar ratio of 0.5 mol% and 0.2 mol% relative to the total amount of metal elements, and lithium hydroxide is mixed in a molar ratio of Li relative to the total amount of Ni, Mn, Ca and Sr of 109 mol%.

[0155] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 3 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.4 μm and an aspect ratio of 12 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, detecting Ca and Sr, with Gini coefficients of 0.55 and 0.62, respectively, on the secondary particle surface.

[0156] <Example 3-2>

[0157] In the firing process of the positive electrode active material, Ca(OH)2, Sr(OH)2 and WO3 are added relative to the total amount of metal elements in the form of 0.5 mol% of Ca, 0.1 mol% of Sr, and 0.5 mol% of W. Otherwise, test battery cells are made in the same manner as in Example 3-1 and evaluated.

[0158] <Example 3-3>

[0159] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 3-1 and evaluated.

[0160] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Nb is 0.5 mol%.

[0161] (2) Change the solid-liquid ratio in the water washing process to 750 g / L.

[0162] <Example 3-4>

[0163] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 3-1 and evaluated. It should be noted that in the TOF-SIMS-based determination of the elemental concentration distribution on the surface of the positive electrode active material, B was detected along with Ca and Sr.

[0164] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 1 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of Ti is 0.3 mol%.

[0165] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L and the water washing time is changed to 20 minutes.

[0166] (3) H3BO3 is mixed in the lithium transition metal composite oxide obtained in the water washing process in such a way that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr and Ti is 1 mol%, and then heat-treated in an oxygen stream at 300°C.

[0167] <Examples 3-5>

[0168] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 3-1 and evaluated.

[0169] (1) In the firing process, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Zr is 0.3 mol%.

[0170] (2) Change the solid-liquid ratio in the water washing process to 1500g / L.

[0171] (3) H3BO3 is mixed in the lithium transition metal composite oxide obtained in the water washing process in such a way that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr and Zr is 0.5 mol%, and then heat-treated in an oxygen stream at 300°C.

[0172] <Comparative Example 3-1>

[0173] In the fabrication of the positive electrode active material, Sr was not added. During the calcination process, Ca(OH)₂ and ZrO₂ were added in a molar ratio of 0.5 mol% for Ca and 0.2 mol% for Zr, relative to the total amount of metal elements. Otherwise, test battery cells were fabricated and evaluated in the same manner as in Example 3-1. SEM observation confirmed that blocky particles with a length diameter of 0.5 μm and an aspect ratio of 1.2 were attached to the surface of the secondary particles of the positive electrode active material.

[0174] <Comparative Example 3-2>

[0175] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 3-1 and evaluated.

[0176] (1) In the firing process, Ca(OH)2, Sr(OH)2 and WO3 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of W is 0.5 mol%.

[0177] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0178] <Comparative Example 3-3>

[0179] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 3-1 and evaluated.

[0180] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 1 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Nb is 0.3 mol%.

[0181] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0182] <Comparative Examples 3-4>

[0183] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 3-1 and evaluated.

[0184] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Ti is 0.3 mol%.

[0185] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0186] (3) H3BO3 is mixed in the lithium transition metal composite oxide obtained in the water washing process in such a way that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr and Ti is 1.5 mol%, and then heat-treated in an oxygen stream at 300°C.

[0187] <Comparative Examples 3-5>

[0188] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 3-1 and evaluated.

[0189] (1) In the firing process, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 1.0 mol%, the molar ratio of Sr is 0.3 mol%, and the molar ratio of Zr is 0.5 mol%.

[0190] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0191] (3) H3BO3 is mixed in the lithium transition metal composite oxide obtained in the water washing process in such a way that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr and Zr is 1.0 mol%, and then heat-treated in an oxygen stream at 300°C.

[0192] <Example 4-1>

[0193] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0194] (1) Using [Ni 0.89 Co 0.04 Mn 0.05 Al 0.02 The complex hydroxide shown in ](OH)2 yields metal oxides containing Ni, Co, Mn and Al.

[0195] (2) In the firing process, Ca(OH)2 and Sr(OH)2 are added in a molar ratio of 0.5 mol% and 0.2 mol% relative to the total amount of metal elements.

[0196] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 4 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.4 μm and an aspect ratio of 12 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, detecting Ca and Sr, with Gini coefficients of 0.63 and 0.57, respectively, on the secondary particle surface.

[0197] <Example 4-2>

[0198] In the firing process for preparing the positive electrode active material, Ca(OH)2, Sr(OH)2, and WO3 are added relative to the total amount of metal elements in the manner of Ca molar ratio of 1.0 mol%, Sr molar ratio of 0.2 mol%, and W molar ratio of 0.5 mol%. Otherwise, test battery cells are prepared in the same manner as in Example 4-1 and evaluated.

[0199] <Example 4-3>

[0200] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 4-1 and evaluated.

[0201] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added in a manner that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Nb is 0.3 mol%, relative to the total amount of metal elements.

[0202] (2) Change the solid-liquid ratio in the water washing process to 750 g / L.

[0203] <Example 4-4>

[0204] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 4-1 and evaluated.

[0205] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 1.0 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of Ti is 0.3 mol%.

[0206] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L and the water washing time is changed to 20 minutes.

[0207] <Example 4-5>

[0208] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 4-1 and evaluated.

[0209] (1) In the firing process, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Zr is 0.6 mol%.

[0210] (2) In the water washing process, the solid-liquid ratio is changed to 1500g / L and the water washing time is changed to 20 minutes.

[0211] <Comparative Example 4-1>

[0212] In the fabrication of the positive electrode active material, no Sr was added. During the firing process, Ca(OH)₂ was added at a molar ratio of 1 mol% relative to the total amount of metal elements. Otherwise, the test battery cells were fabricated and evaluated in the same manner as in Example 4-1. SEM observation confirmed that blocky particles with a length diameter of 0.5 μm and an aspect ratio of 1.4 were attached to the surface of the secondary particles of the positive electrode active material.

[0213] <Comparative Example 4-2>

[0214] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 4-1 and evaluated.

[0215] (1) In the firing process, Ca(OH)2, Sr(OH)2 and WO3 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of W is 0.3 mol%.

[0216] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0217] <Comparative Example 4-3>

[0218] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 4-1 and evaluated.

[0219] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of Nb is 0.3 mol%.

[0220] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0221] <Comparative Example 4-4>

[0222] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 4-1 and evaluated.

[0223] (1) In the firing process, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Ti is 0.5 mol%.

[0224] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0225] <Comparative Examples 4-5>

[0226] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 4-1 and evaluated.

[0227] (1) In the firing process, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.5 mol%, the molar ratio of Sr is 0.1 mol%, and the molar ratio of Zr is 0.3 mol%.

[0228] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0229] <Example 5-1>

[0230] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0231] (1) Using [Ni 0.90 Mn 0.05 Al0.05 The complex hydroxide shown in ](OH)2 yields a metal oxide containing Ni, Mn and Al.

[0232] (2) In the firing process, Ca(OH)2 and Sr(OH)2 are added relative to the total amount of metal elements, with the molar ratio of Ca being 0.5 mol% and the molar ratio of Sr being 0.1 mol%.

[0233] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 5 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.7 μm and an aspect ratio of 10 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, and Ca and Sr were detected, with Gini coefficients of 0.63 and 0.66, respectively, on the secondary particle surface.

[0234] <Example 5-2>

[0235] In the firing process of the positive electrode active material, Ca(OH)2, Sr(OH)2 and WO3 are added relative to the total amount of metal elements in the form of 0.7 mol% Ca, 0.1 mol% Sr, and 0.3 mol% W. Otherwise, test battery cells are made in the same manner as in Example 5-1 and evaluated.

[0236] <Example 5-3>

[0237] In the firing process for preparing the positive electrode active material, Ca(OH)2, Sr(OH)2 and Nb2O5 were added relative to the total amount of metal elements in the manner of Ca molar ratio of 0.7 mol%, Sr molar ratio of 0.1 mol%, and Nb molar ratio of 0.3 mol%. Otherwise, test battery cells were prepared in the same manner as in Example 5-1 and evaluated.

[0238] <Example 5-4>

[0239] In the firing process for preparing the positive electrode active material, Ca(OH)2, Sr(OH)2 and TiO2 are added relative to the total amount of metal elements in the form of 0.7 mol%, 0.1 mol%, and 0.3 mol% molar ratios of Ca. Otherwise, test battery cells are prepared in the same manner as in Example 5-1 and evaluated.

[0240] <Example 5-5>

[0241] In the firing process of the positive electrode active material, Ca(OH)2, Sr(OH)2 and ZrO2 are added relative to the total amount of metal elements in the manner of Ca molar ratio of 0.7 mol%, Sr molar ratio of 0.1 mol%, and Zr molar ratio of 0.5 mol%. Otherwise, test battery cells are made in the same manner as in Example 5-1 and evaluated.

[0242] <Comparative Example 5-1>

[0243] In the fabrication of the positive electrode active material, no Sr was added. During the firing process, Ca(OH)₂ was added at a molar ratio of 1.0 mol% relative to the total amount of metal elements. Otherwise, the test battery cells were fabricated and evaluated in the same manner as in Example 5-1. SEM observation confirmed that blocky particles with a length diameter of 0.5 μm and an aspect ratio of 1.5 were attached to the surface of the secondary particles of the positive electrode active material.

[0244] <Comparative Example 5-2>

[0245] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 5-1 and evaluated.

[0246] (1) In the firing process, Ca(OH)2, Sr(OH)2 and WO3 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.7 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of W is 0.3 mol%.

[0247] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0248] <Comparative Example 5-3>

[0249] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 5-1 and evaluated.

[0250] (1) In the firing process, Ca(OH)2, Sr(OH)2 and Nb2O5 are added relative to the total amount of metal elements in such a way that the molar ratio of Ca is 0.7 mol%, the molar ratio of Sr is 0.2 mol%, and the molar ratio of Nb is 0.3 mol%.

[0251] (2) In the water washing process, the solid-liquid ratio is changed to 1000g / L, the water washing time is changed to 1 minute, and the stirring speed is changed to 100rpm.

[0252] <Example 6>

[0253] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0254] (1) Using [Ni 0.80 Mn 0.20 The composite hydroxide shown in ](OH)2 yields a metal oxide containing Ni and Mn.

[0255] (2) In the calcination process, Ca(OH)2, Sr(OH)2, and Nb2O5 are added in a molar ratio of 0.5 mol%, 0.1 mol%, and 0.3 mol% relative to the total amount of metal elements. Lithium hydroxide is mixed in a molar ratio of 113 mol% relative to the total amount of Ni, Mn, Ca, Sr, and Nb.

[0256] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 6 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.3 μm and an aspect ratio of 10 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, detecting Ca and Sr, with Gini coefficients of 0.63 and 0.62, respectively, on the secondary particle surface.

[0257] <Comparative Example 6>

[0258] In the fabrication of the positive electrode active material, no Sr was added. During the firing process, Ca(OH)₂ was added at a molar ratio of 1.0 mol% relative to the total amount of metal elements. Otherwise, the test battery cells were fabricated and evaluated in the same manner as in Example 6. SEM observation confirmed that blocky particles with a length diameter of 1.5 μm and an aspect ratio of 1.5 were attached to the surface of the secondary particles of the positive electrode active material.

[0259] <Example 7>

[0260] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0261] (1) Using [Ni 0.80 Co 0.10 Mn 0.10 The complex hydroxide shown in ](OH)2 yields a metal oxide containing Ni, Co, and Mn.

[0262] (2) In the calcination process, Ca(OH)2, Sr(OH)2 and TiO2 are added in a molar ratio of 0.5 mol%, Sr 0.1 mol%, and Ti 0.5 mol%, relative to the total amount of metal elements, and lithium hydroxide is mixed in a molar ratio of Li to the total amount of Ni, Co, Mn, Ca, Sr and Ti of 105 mol%.

[0263] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 7 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.5 μm and an aspect ratio of 10 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, detecting Ca and Sr, with Gini coefficients of 0.53 and 0.59, respectively, on the secondary particle surface.

[0264] <Comparative Example 7>

[0265] In the fabrication of the positive electrode active material, no Sr was added. During the firing process, Ca(OH)2 was added at a molar ratio of 0.7 mol% relative to the total amount of metal elements. Otherwise, the test battery cells were fabricated and evaluated in the same manner as in Example 7. SEM observation confirmed that blocky particles with a major diameter of 2 μm and an aspect ratio of 1.0 were attached to the surface of the secondary particles of the positive electrode active material.

[0266] <Example 8>

[0267] The positive electrode active material was prepared as follows. Otherwise, the test battery cells were prepared in the same manner as in Example 1-1 and evaluated.

[0268] (1) Using [Ni 0.50 Co 0.20 Mn 0.30 The complex hydroxide shown in ](OH)2 yields a metal oxide containing Ni, Co, and Mn.

[0269] (2) In the calcination process, Ca(OH)2, Sr(OH)2 and TiO2 are added in a molar ratio of 0.5 mol%, Sr 0.2 mol%, and Ti 1.0 mol%, relative to the total amount of metal elements, and lithium hydroxide is mixed in a molar ratio of Li to the total amount of Ni, Co, Mn, Ca, Sr and Ti of 115 mol%.

[0270] The obtained positive electrode active material was analyzed using an ICP emission spectrometer (Thermo Fisher Scientific, iCAP6300), and the elements other than Li and O were confirmed as shown in Table 8 below. Furthermore, scanning electron microscopy (SEM) confirmed the presence of fibrous particles with a major diameter of 0.7 μm and an aspect ratio of 15 attached to the surface of the secondary particles of the positive electrode active material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to determine the elemental concentration distribution on the surface of the positive electrode active material, detecting Ca and Sr, with Gini coefficients of 0.51 and 0.55, respectively, on the secondary particle surface.

[0271] <Comparative Example 8>

[0272] In the fabrication of the positive electrode active material, no Sr was added. During the firing process, Ca(OH)2 was added in a molar ratio of 1.0 mol% relative to the total amount of metal elements. Otherwise, the test battery cells were fabricated and evaluated in the same manner as in Example 8. SEM observation confirmed that blocky particles with a major diameter of 3 μm and an aspect ratio of 1.0 were attached to the surface of the secondary particles of the positive electrode active material.

[0273] The evaluation results of the test battery cells of the Examples and Comparative Examples are shown in Tables 1 to 8. The durability of the test battery cells in Tables 1 to 8 is expressed relative to the durability of the test battery cells used as the benchmark in each table, which is set to 100. The benchmark test battery cells in Tables 1 to 8 are Comparative Examples 1-1, 2-5, 3-4, 4-4, 5-3, 6, 7, and 8, respectively.

[0274] [Table 1]

[0275]

[0276] [Table 2]

[0277]

[0278] [Table 3]

[0279]

[0280] [Table 4]

[0281]

[0282] [Table 5]

[0283]

[0284] [Table 6]

[0285]

[0286] [Table 7]

[0287]

[0288] [Table 8]

[0289]

[0290] In any of Tables 1 to 8, the durability of the test battery cells in the Examples is higher than that of the test battery cells in the Comparative Examples. This demonstrates that the battery durability is improved by the presence of fibrous particles containing Ca and Sr on the surface of the secondary particles of the lithium transition metal composite oxide.

[0291] This disclosure is further illustrated by the following embodiments.

[0292] Option 1:

[0293] A positive electrode active material for non-aqueous electrolyte secondary batteries.

[0294] It contains lithium transition metal complex oxides.

[0295] The aforementioned lithium transition metal composite oxide contains Ni, Ca, and Sr, and also includes secondary particles formed by the aggregation of primary particles.

[0296] The surface of the aforementioned secondary particles contains attached particles comprising fibrous particles, wherein the fibrous particles comprise at least one of Ca and Sr.

[0297] Option 2:

[0298] According to the positive electrode active material for non-aqueous electrolyte secondary batteries described in Scheme 1, the content of Ni in the above-mentioned lithium transition metal composite oxide is 50 mol% or more relative to the total molar number of elements other than Li and O.

[0299] Option 3:

[0300] According to Scheme 1 or 2, the positive electrode active material for non-aqueous electrolyte secondary batteries, wherein the major diameter of the fibrous particles is less than 3 μm.

[0301] Option 4:

[0302] According to any one of Schemes 1 to 3, the positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the aspect ratio of the fibrous particles is 10 or more.

[0303] Option 5:

[0304] The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Schemes 1 to 4, wherein Ca and Sr are each uniformly present on the surface of the secondary particles.

[0305] Option 6:

[0306] A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte, including any one of embodiments 1 to 5, for use as a positive electrode active material in a non-aqueous electrolyte secondary battery.

[0307] Explanation of reference numerals in the attached figures

[0308] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive lead, 21 Negative lead, 22 Groove, 23 Internal terminal block, 24 Lower valve body, 25 Insulating component, 26 Upper valve body, 27 Cover, 28 Gasket.

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, It contains lithium transition metal complex oxides. The lithium transition metal composite oxide contains Ni, Ca, and Sr, and includes secondary particles formed by the aggregation of primary particles. The secondary particles have attached particles containing fibrous particles on their surface, the fibrous particles containing at least one of Ca and Sr.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The content of Ni in the lithium transition metal composite oxide is more than 50 mol% relative to the total molar number of elements other than Li and O.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The major diameter of the fibrous particles is less than 3 μm.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, The aspect ratio of the fibrous particles is 10 or more.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein, Ca and Sr are each uniformly present on the surface of the secondary particles.

6. A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and a non-aqueous electrolyte, all comprising the positive electrode active material for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 5.

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