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

Abstract

Provided is a positive electrode active material which contributes to an improvement in the durability of a non-aqueous electrolyte secondary battery. This positive electrode active material included in the non-aqueous electrolyte secondary battery comprises a lithium transition metal composite oxide, wherein: the lithium transition metal composite oxide contains Ni, Ca, and Sr, and contains secondary particles formed by aggregating primary particles; adhered particles including fibrous particles are present on the surfaces of the secondary particles; and the fibrous particles contain at least one among Ca and Sr.

Description

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

[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, and in particular to a positive electrode active material for a non-aqueous electrolyte secondary battery containing Ni at a high concentration, and a non-aqueous electrolyte secondary battery using this positive electrode active material for a non-aqueous electrolyte secondary battery.

[0002] Lithium nickel oxide (LiNiO ２ ) has a high energy density, and a lithium transition metal composite oxide in which part of the Ni is substituted with Co, Al, Mn, etc. is used as the positive electrode active material. However, because lithium transition metal composite oxides are prone to side reactions with non-aqueous electrolytes, they may deteriorate with repeated charge and discharge, resulting in a decrease in discharge capacity, and therefore, improved durability is required.

[0003] Patent Document 1 describes α-NaFeO ２ The present invention discloses a positive electrode active material for a non-aqueous electrolyte secondary battery having a structure in which the positive electrode active material contains one or more transition metal elements selected from the group consisting of Mn, Ni, and Co, and an alkaline earth metal and W are present on the particle surfaces of a lithium transition metal composite oxide.

[0004] JP 2018-129221 A

[0005] Demand for durability in secondary batteries is increasing, and surface protection technology for lithium transition metal composite oxides, which are positive electrode active materials, has become an important development issue. After extensive research, the present inventors have found that durability can be significantly improved by having fibrous particles containing at least one of Ca and Sr present on the surfaces of secondary particles of lithium transition metal composite oxides.

[0006] An object of the present disclosure is to provide a positive electrode active material that contributes to improving the durability of non-aqueous electrolyte secondary batteries.

[0007] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises a lithium transition metal composite oxide, the lithium transition metal composite oxide containing Ni, Ca, and Sr, and secondary particles formed by aggregation of primary particles, with adhered particles containing fibrous particles present on the surfaces of the secondary particles, and the fibrous particles containing at least one of Ca and Sr.

[0008] A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure is characterized by including a positive electrode containing the above-described positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

[0009] According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, the durability of the non-aqueous electrolyte secondary battery is improved.

[0010] 1 is a longitudinal cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention;

[0011] Lithium transition metal composite oxides have a layered structure, and the reversible movement of Li ions into and out of this layered structure promotes the charge / discharge reactions of the battery. Generally, lithium transition metal composite oxides primarily composed of Ni are known as high-capacity positive electrode active materials. However, such lithium transition metal composite oxides are susceptible to side reactions with non-aqueous electrolytes, which can cause the layered crystal structure to break down, leading to deterioration and a decrease in discharge capacity after repeated charge / discharge. Furthermore, even when charging / discharging at an increased charge voltage, the side reactions with non-aqueous electrolytes become more pronounced, which can accelerate deterioration and reduce discharge capacity.

[0012] Patent Document 1 discloses a positive electrode active material for non-aqueous electrolyte secondary batteries in which an alkaline earth metal and W are present on the particle surface of a lithium transition metal composite oxide from the viewpoint of improving durability. However, demands for durability of secondary batteries are increasing, and further technological development is required beyond the technology disclosed in Patent Document 1.

[0013] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that durability can be more significantly improved by having fibrous particles containing at least one of Ca and Sr present on the surfaces of secondary particles of a lithium transition metal composite oxide. It has been found that by having both Ca and Sr present on the surfaces of the secondary particles, rather than just one of Ca and Sr, and by having the particles containing at least one of Ca and Sr have a fibrous shape, it is possible to specifically improve durability while maintaining liquid permeability without covering the particle surfaces.

[0014] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below. Hereinafter, a cylindrical battery in which a wound electrode assembly is housed in a cylindrical exterior body will be exemplified. However, the electrode assembly is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are alternately stacked one by one with separators interposed therebetween. Furthermore, the exterior body is not limited to a cylindrical shape and may be, for example, prismatic or coin-shaped, or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0015] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. As shown in FIG. 1 , the secondary battery 10 includes a wound electrode assembly 14, an electrolyte, and an exterior body 16 that accommodates the electrode assembly 14 and the electrolyte. The electrode assembly 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 spirally wound with the separator 13 interposed therebetween. The exterior body 16 is a cylindrical metal container with a bottom and an opening on one axial side, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the battery will be referred to as the top, and the bottom side of the exterior body 16 will be referred to as the bottom.

[0016] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode assembly 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and alternately stacked in the radial direction of the electrode assembly 14. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal and lateral directions. The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The electrode assembly 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 assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the lateral direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the end faces in the lateral direction of the positive electrode 11 and the negative electrode 12 form the end faces in the axial direction of the electrode body 14 .

[0017] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom side of the exterior body 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and 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 bottom surface of the exterior body 16 by welding or the like, and the exterior body 16 serves as the negative electrode terminal.

[0018] A gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior body 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior body 16 by the grooved portion 22 and the open end of the exterior body 16 that is crimped to the sealing body 17.

[0019] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked, and functions as a safety valve. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and each component except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0020] The positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte that constitute the secondary battery 10 will be described in detail below, with the positive electrode 11 being particularly described below.

[0021] [Positive Electrode] The positive electrode 11 has, for example, a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer is preferably formed on both sides of the positive electrode current collector. The positive electrode current collector can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer. The thickness of the positive electrode current collector is, for example, 10 μm or more and 30 μm or less.

[0022] The positive electrode mixture layer contains, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode current collector. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, the conductive agent, etc. to the surface of the positive electrode current collector, drying the coating, and then rolling the coating to form positive electrode mixture layers on both sides of the positive electrode current collector.

[0023] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphene, graphite, and other carbon-based particles. These may be used alone 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 with respect to the total mass of the positive electrode mixture layer.

[0024] Examples of binders contained in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic-based resins, polyolefin-based resins, and polyacrylonitrile (PAN). These may be used alone or in combination of two or more. The content of the binder in the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less with respect to the total mass of the positive electrode mixture layer.

[0025] The positive electrode active material contained in the positive electrode mixture layer includes a lithium transition metal composite oxide, which contains Ni, Ca, and Sr.

[0026] The Ni content in the lithium transition metal composite oxide is preferably 50 mol% or more relative to the total number of moles of elements excluding Li and O. The Ni content in the lithium transition metal composite oxide may be, for example, 50 mol%≦Ni content≦95 mol%, 70 mol%≦Ni content≦95 mol%, or 75 mol%≦Ni content≦95 mol%, relative to the total number of moles of elements excluding Li and O. If the Ni content is 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%.

[0027] The Ca content in the lithium transition metal composite oxide is, for example, 0 mol% < Ca content ≦ 1 mol% relative to the total number of moles of elements excluding Li and O. The lower limit of the 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 number of moles of elements excluding Li and O. The lower limit of the Sr content is, for example, 0.01 mol%. The sum of the Ca content and Sr content is, for example, preferably 0 mol% < Ca content + Sr content ≦ 2 mol%, and more preferably 0.02 mol% ≦ Ca content + Sr content ≦ 2 mol%, relative to the total number of moles of elements excluding Li and O.

[0028] The lithium transition metal composite oxide is, for example, represented by the general formula Li ａ Ni ｘ M1 ｙ M2 ｚ Ca ｓ Sr ｔ O ２－ｂ (wherein 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) The proportion of metal elements contained in the lithium transition metal composite oxide can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0029] The lithium transition metal composite oxide contains secondary particles formed by 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 measured as the diameter of the circumscribed circle in a particle image observed with 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 volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0030] Adherent particles, including fibrous particles, are present on the surfaces of secondary particles of the lithium transition metal composite oxide. The adhered particles are particles smaller than the secondary particles adhered to the surfaces of the secondary particles of the lithium transition metal composite oxide. The fibrous particles are one type of adhered particles and are elongated fibrous particles. The fibrous particles may aggregate to form rod-shaped or spherical adhered particles. In addition to fibrous particles, the adhered particles include, for example, aggregated particles. The aggregated particles do not have an elongated shape like the fibrous particles, but have, for example, a plate-like or spherical shape.

[0031] The fibrous particles contain at least one of Ca and Sr. The durability can be improved by having the fibrous particles containing at least one of Ca and Sr present on the surface of the secondary particles of the lithium transition metal composite oxide. The composition of the fibrous particles is not particularly limited as long as the fibrous particles contain at least one of Ca and Sr, but examples thereof include oxides, hydroxides, carbonate compounds, etc. containing at least one of Ca and Sr. The fibrous particles may contain both Ca and Sr.

[0032] The aspect ratio of the fibrous particles is, for example, 10 or more. The higher the aspect ratio of the fibrous particles, the more the durability of the battery tends to improve. The aspect ratio of the fibrous particles is preferably 15 or more, more preferably 20 or more. The upper limit of the aspect ratio of the fibrous particles is not particularly limited, but is, 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, for each of 10 fibrous particles using the SEM image, the length of the major axis was divided by the length of the minor axis in the direction perpendicular to the major axis to obtain the aspect ratio, and these were averaged to calculate the aspect ratio of the fibrous particles. The major axis of the fibrous particles is, for example, 3 μm or less.

[0033] It is preferable that Ca and Sr are each uniformly present on the secondary particle surface. This makes the durability-enhancing effect of the fibrous particles more pronounced. That is, the uniform presence of fibrous particles containing at least one of Ca and Sr on the secondary particle surface can significantly suppress side reactions with the nonaqueous electrolyte. The distribution of Ca and Sr on the secondary particle surface can be confirmed, for example, by the Gini coefficient of each element on the secondary particle surface calculated from the results of element concentration analysis of the cross section of the secondary particle using a time-of-flight secondary ion mass spectrometer (TOF-SIMS). A smaller Gini coefficient on the secondary particle surface indicates that the element is more uniformly dispersed on the secondary particle surface, with the minimum value being 0. The Gini coefficient on the secondary particle surface of Ca and the Gini coefficient on the secondary particle surface of Sr are each preferably 0.7 or less. The Gini coefficients on the secondary particle surfaces of Ca and Sr are, for example, 0.1 or more.

[0034] The Gini coefficient of Ca on the secondary particle surface is the normalized intensity I Ｃａ＿ＯＵＴ When the cumulative rate is expressed in order of intensity, this is twice the area enclosed between the diagonal line and the Lorenz curve.

[0035] Normalized intensity I of Ca on the secondary particle surface Ｃａ＿ＯＵＴ is obtained by measurement under the following conditions using a time-of-flight secondary ion mass spectrometer (TOF-SIMS5 manufactured by IONTOF). Primary ions: Bi ３＋ Ion voltage: 30 kV Ion current: 0.03 pA @ 100 us Observation range: 50 μm x 50 μm Mass range: 60 us (up to 310 amu) Detection: 4 frames / scan, 150 scans

[0036] The image showing the concentration distribution of Ni and Ca obtained by the above measurement is divided into 256 × 256 pixels, and the detected intensities of Ni and Ca are calculated for each pixel. Furthermore, the ratio of the detected intensity of Ca to the detected intensity of Ni is defined as the normalized intensity I of Ca. Ｃａ It is calculated as follows.

[0037] The area from the surface of the secondary particle recognized from the image to the inside by 0.5 μm is defined as the surface of the secondary particle, and the pixels included in the surface of this secondary particle (hereinafter referred to as surface pixels) are determined. Ｃａ The set of Ｃａ＿ＯＵＴ It becomes. Ｃａ＿ＯＵＴ The Gini coefficient on the surface of the secondary particles of Ca is calculated from the normalized intensity I on the surface of the secondary particles of Sr. The sample for cross-sectional observation may be a sample in which a lithium transition metal composite oxide is embedded in a resin or the like, or a positive electrode mixture layer containing a lithium transition metal composite oxide. Ｓｒ＿ＯＵＴ I Ｃａ＿ＯＵＴ Alternatively, Ca and Sr may be uniformly present inside the secondary particles.

[0038] The lithium transition metal composite oxide may have a layered structure. Examples of the layered structure of the lithium transition metal composite oxide include a layered structure belonging to the space group R-3m and a layered structure belonging to the space group C2 / m. From the viewpoints of increasing capacity and crystalline structure stability, the lithium transition metal composite oxide preferably has a layered structure belonging to the space group R-3m. The layered structure of the lithium transition metal composite oxide may include a transition metal layer and a Li layer.

[0039] The positive electrode mixture layer may contain other positive electrode active materials in addition to the positive electrode active material of the present embodiment, such as lithium transition metal composite oxides that do not contain Ca or Sr.

[0040] Next, an example of a method for producing a positive electrode active material according to the present embodiment will be described. The method for producing a positive electrode active material includes, for example, a lithium transition metal composite oxide synthesis step of mixing a Ni-containing metal oxide, a Li compound, a Ca compound, and a Sr compound, and calcining the mixture to obtain a calcined product, a washing step of washing the calcined product with water and dehydrating it under predetermined conditions to obtain a cake-like composition, and a drying step of drying the cake-like composition to obtain a powder-like composition.

[0041] A metal oxide containing at least Ni can be produced by separately dropping a solution of a metal salt containing Ni, Co, Al, Mn, etc. and an alkaline solution such as sodium hydroxide into a reaction vessel in which a pH-adjusted solution is being stirred, adjusting the pH to the alkaline side (e.g., 8.5 to 12.5) to precipitate (co-precipitate) a composite hydroxide, and then heat-treating the metal hydroxide. The calcination temperature is not particularly limited, but is, for example, in the range of 250°C to 600°C.

[0042] Next, a mixture is obtained by mixing a metal oxide containing at least Ni, a Li compound, a Ca compound, and a Sr compound. ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２ Examples of Ca compounds include Ca(OH) ２ , CaHPO ４ , Ca(H ２ P.O. ４ ) ２ , Ca ３ (P.O. ４ ) ２ , CaO, CaCO ３ , CaSO ４ , Ca(NO ３ ) ２、 CaCl ２ , CaAlO ４ Examples of Sr compounds include Sr(OH) ２ , SrHPO４ , Sr(H ２ P.O. ４ ) ２ , Sr ３ (P.O. ４ ) ２ , SrO, SrCO ３ , SrSO ４ , Sr(NO ３ ) ２、 SrCl ２ , SrAlO ４ In addition, an M2 compound may be mixed during mixing. Examples of the Me compound include ZrO ２ , Nb ２ O ５ , Nb ２ O ５ ・nH ２ O, TiO ２ , Ti(OH) ４ , SiO, SiO ２ , Li ２ MoO ４ , MoO ３ , H ２ MoO ４ , W.O. ３ , Li ２ WO ４ , Fe(OH) ２ , Fe ２ O ３ , SnO ２ , Bi(OH) ３ , Bi ２ O ３ , H ３ BO ３ , B ２ O ３ , Sb ２ O ３ etc.

[0043] The mixture is fired in an oxygen stream having an oxygen concentration of 60% or more, for example, at a flow rate of 10 cm 3 of the firing furnace. ３The mixture is fired at a flow rate of 0.1 to 4 L / min per kg of the mixture, or at a flow rate of 1 L / min or more per kg of the mixture. The firing conditions include a first set temperature of 450°C or less, a holding time at the first set temperature of 0 to 8 hours, and a temperature rise rate at 450°C or less of more than 1.5°C / min and less than 6.0°C / min. The second set temperature is set at 450°C or more and 680°C or less, a holding time at the second set temperature of 0 to 8 hours, and a temperature rise rate at 450°C or more and 680°C or less of more than 1.0°C / min and less than 4.5°C / min. The maximum temperature is in the range of 690°C or more and 900°C or less. The temperature rise rate from above 680°C to the maximum temperature may be, for example, 0.1 to 3.5°C / min. The holding time at the maximum temperature may be 1 to 10 hours. This firing step may be a multi-stage firing, and multiple firing steps may be set for each temperature range as long as they are within the above-specified range.

[0044] The fired product is washed with water, dehydrated, and dried to obtain a lithium transition metal composite oxide as a positive electrode active material. The water washing step is performed, for example, using a 3 L reaction vessel under conditions such as a solid-liquid ratio of 500 g / L to 2000 g / L, a water washing time of 5 minutes to 1 hour, and a stirring speed of 200 rpm or higher. When the size of the reaction vessel is changed, the water washing time and stirring speed may also be changed. The moisture content of the cake-like composition obtained by dehydration is, for example, 10% or less, or may be 8% or less. The drying step is performed, for example, under conditions of a pressure of 1 kPa or less, a temperature of 120°C to 300°C, and a time of 1 hour to 10 hours. More preferred conditions for the drying step are a pressure of 100 Pa or less, a temperature of 150°C to 250°C, and a time of 1 hour to 5 hours.

[0045] The lithium transition metal composite oxide may further be subjected to a heat treatment process. The heat treatment process is carried out, for example, in a vacuum, in an oxygen stream, or in the atmosphere at a temperature of 150°C to 600°C. During the heat treatment process, for example, tungsten oxide (WO ３ ), lithium tungstate (Li ２ WO ４ , Li ４ WO ５ , Li ６ W ２O ９ ), boric acid (H ３ BO ３ ), lithium borate (Li ２ B ４ O ７ , Li ３ BO ３ , LiB ３ O ５ , LiBO ２ ), lithium phosphate (Li ３－ｘ H ｘ P.O. ４ 0≦x≦3) may be added.

[0046] [Negative Electrode] The negative electrode 12 may have, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector, or a metal Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode current collector, and lithium metal may be deposited on the surface of the negative electrode current collector upon charging. When the negative electrode 12 has a negative electrode mixture layer, the negative electrode mixture 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 film with such a metal disposed on the surface. The thickness of the negative electrode current collector is, for example, 5 μm to 30 μm. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm to 150 μm on one side of the negative electrode current collector. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and the like to the surface of a negative electrode current collector, drying the coating, and then rolling the coating to form a negative electrode mixture layer on both sides of the negative electrode current collector.

[0047] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, carbon materials such as graphite are used. Graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, metals that alloy with Li, such as Si and Sn, metal compounds containing Si, Sn, and lithium-titanium composite oxides may also be used as the negative electrode active material. Furthermore, those provided with a carbon coating may also be used. For example, SiO ｘ(0.5≦x≦1.6) or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2) may be used in combination with graphite.

[0048] Examples of binders contained in the negative electrode mixture layer include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0049] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0050] 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 inorganic fillers include oxides and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg. The filler layer can 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.

[0051] [Non-aqueous electrolyte] The non-aqueous electrolyte has, for example, lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0052] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0053] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl 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).

[0054] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as ethyl 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, and tetraethylene glycol dimethyl ether.

[0055] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less, per 1 L of the non-aqueous solvent.

[0056] The non-aqueous electrolyte may contain an additive such as an unsaturated carbonate ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, a sulfate compound, a borate ester compound, a phosphate ester compound, or a phosphite ester compound.

[0057] 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, vinylethylene carbonate, and divinylethylene carbonate. One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. Some of the hydrogen atoms in the unsaturated cyclic carbonate may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by intermolecular condensation of multiple carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0058] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0059] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanatomethylcyclohexane (BIMCH). Examples of sultone compounds include propane sultone and propene sultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethyl phosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethyl phosphite and tris(trimethylsilyl)phosphite.

[0060] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0061] Hereinafter, the present disclosure will be further described with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0062] Example 1-1 [Preparation of Positive Electrode Active Material] [Ni ０．９１ Co ０．０４ Al ０．０５ ](OH) ２The composite hydroxide represented by the formula (1) was calcined at 400°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. Next, the metal oxide, Ca(OH) ２ , and Sr(OH) ２ and further, lithium hydroxide monohydrate (LiOH·H ) was added so that the molar ratio of Li to the total amount of Ni, Co, Al, Ca, and Sr was 103 mol %. ２ O) was mixed to obtain a mixture. This mixture was heated from room temperature to 400 ° C. under an oxygen stream with an oxygen concentration of 95% (flow rate of 3 L / min per 1 kg of mixture) at a temperature increase rate of 4 ° C. / min, and then heated from 400 ° C. to 650 ° C. at a temperature increase rate of 2 ° C. / min. Thereafter, the temperature was increased from 650 ° C. to 740 ° C. at a temperature increase rate of 1 ° C. / min, and then maintained for 6 hours to obtain a fired product. This fired product was added to water using a 3 L reaction vessel so that the solid-liquid ratio was 500 g / L, and then washed with water at a stirring speed of 300 rpm for 10 minutes, and then dehydrated. Furthermore, the mixture was dried at a temperature of 180 ° C. and a pressure of 10 Pa in a vacuum atmosphere for 2 hours to obtain the positive electrode active material of Example 1-1.

[0063] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (iCAP6300, manufactured by Thermo Fisher Scientific), and the elements shown in Table 1 below were confirmed as elements excluding Li and O. In addition, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.3 μm and an aspect ratio of 40 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.60 and 0.58, respectively.

[0064] [Preparation of Positive Electrode] 95 parts by mass of the above positive electrode active material, 3 parts by mass of acetylene black (AB), and 2 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil, and after drying the coating, the coating was rolled with a rolling roller and cut to a predetermined electrode size to prepare a positive electrode. Note that an exposed portion was provided in part of the positive electrode where the surface of the positive electrode current collector was exposed.

[0065] [Preparation of Negative Electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, carboxymethyl cellulose sodium (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution at a solids mass ratio of 100:1:1 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and after drying the coating, the coating was rolled with a rolling roller and cut to a predetermined electrode size to prepare a negative electrode. Note that an exposed portion was provided in part of the negative electrode, where the surface of the negative electrode current collector was exposed.

[0066] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluorophosphate (LiPF ６ ) was dissolved in the solution to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0067] [Preparation of Test Cell] A positive electrode lead was attached to the exposed portion of the positive electrode, and a negative electrode lead was attached to the exposed portion of the negative electrode. The positive and negative electrodes were spirally wound with a polyolefin separator interposed therebetween, and then pressed radially to prepare a flat wound electrode assembly. This electrode assembly was housed in an exterior body made of an aluminum laminate sheet, and the nonaqueous electrolyte was poured into it. The opening of the exterior body was then sealed to obtain a test cell.

[0068] [Evaluation of durability] At an ambient temperature of 45°C, the test cell was charged at a constant current of 0.3 C to 4.2 V, and then at a constant voltage of 4.2 V to 0.02 C. It was then discharged at a constant current of 0.5 C to 2.5 V. This charge / discharge cycle was counted as one cycle, and 200 cycles were performed. The durability of the test cell was calculated using the following formula: Durability = (discharge capacity at 200th cycle / discharge capacity at 1st cycle) x 100

[0069] Example 1-2 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a positive electrode active material was prepared as follows. In the element concentration distribution measurement of the surface of the positive electrode active material by TOF-SIMS, Al was detected along with Ca and Sr. (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, Sr, and Zr relative to the total amount of metal elements was 0.3 mol %, 0.1 mol %, and 0.1 mol %, respectively. ２ , Sr(OH) ２ , and ZrO ２ (2) The solid-liquid ratio in the water washing step was changed to 750 g / L.

[0070] Example 1-3 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 0.3 mol %, 0.1 mol %, and 0.1 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ (2) The solid-liquid ratio in the water washing step was changed to 1000 g / L.

[0071] Example 1-4 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of W were 0.3 mol %, 0.1 mol %, and 0.1 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and W.O. ３ (2) The solid-liquid ratio in the water washing step was changed to 1500 g / L.

[0072] Example 1-5 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.3 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, and the water washing time was changed to 20 minutes.

[0073] Comparative Example 1-1 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements in the firing step was 0.5 mol %. ２ A test cell was produced and evaluated in the same manner as in Example 1-1, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 0.5 μm and an aspect ratio of 1 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0074] Comparative Example 1-2 In the preparation of the positive electrode active material, Ca was not added, and Sr(OH) was added so that the molar ratio of Sr to the total amount of metal elements in the firing step was 0.2 mol %. ２ A test cell was prepared in the same manner as in Example 1-1 except that the above was added, and evaluation was carried out.

[0075] Example 2-1 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows. (1) [Ni ０．９０ Co ０．０５ Mn ０．０５ ](OH) ２ (2) In the calcination step, a metal oxide containing Ni, Co, and Mn was obtained by using a composite hydroxide represented by the formula: Ca(OH) ２ , Sr(OH) ２and lithium hydroxide was mixed in such that the molar ratio of Li to the total amount of Ni, Co, Mn, Ca, and Sr was 105 mol %.

[0076] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (iCAP6300, manufactured by Thermo Fisher Scientific). As a result, the elements shown in Table 2 below were confirmed as elements excluding Li and O. Furthermore, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.27 μm and an aspect ratio of 30 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.59 and 0.58, respectively.

[0077] Example 2-2 In the firing step of producing a positive electrode active material, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Zr were 0.5 mol %, 0.2 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and ZrO ２ A test cell was prepared in the same manner as in Example 2-1 except that the above was added, and evaluation was carried out.

[0078] Example 2-3 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.5 mol %, 0.2 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) The solid-liquid ratio in the water washing step was changed to 750 g / L.

[0079] Example 2-4 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 1.0 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, and the water washing time was changed to 20 minutes.

[0080] Example 2-5 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 0.5 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1500 g / L and the water washing time was changed to 20 minutes. (3) H was added to the lithium transition metal composite oxide obtained in the water washing step so that the molar ratio of B to the total amount of Ni, Co, Mn, Ca, Sr, and Ti was 0.5 mol %. ３ BO ３ The mixture was mixed and heat-treated at 300° C. in an oxygen stream.

[0081] Example 2-6 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows. In the element concentration distribution measurement of the surface of the positive electrode active material by TOF-SIMS, B was detected along with Ca and Sr. (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, Sr, and Zr relative to the total amount of metal elements was 0.5 mol %, 0.1 mol %, and 0.3 mol %. ２ , Sr(OH) ２ , and ZrO ２(2) In the water washing step, the solid-liquid ratio was changed to 1500 g / L and the water washing time was changed to 20 minutes. (3) H was added to the lithium transition metal composite oxide obtained in the water washing step so that the molar ratio of B to the total amount of Ni, Co, Mn, Ca, Sr, and Zr was 0.5 mol %. ３ BO ３ The mixture was mixed and heat-treated at 300° C. in an oxygen stream.

[0082] Comparative Example 2-1 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements in the firing step was 0.5 mol %. ２ A test cell was produced and evaluated in the same manner as in Example 2-1, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 0.5 μm and an aspect ratio of 1.5 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0083] Comparative Example 2-2 In the preparation of the positive electrode active material, Ca was not added, and Sr(OH) was added so that the molar ratio of Sr to the total amount of metal elements in the firing step was 0.5 mol %. ２ A test cell was prepared in the same manner as in Example 2-1 except that the above was added, and evaluation was carried out.

[0084] Comparative Example 2-3 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.5 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) In the water washing step, the washing time was changed to 1 minute and the stirring speed was changed to 100 rpm.

[0085] Comparative Example 2-4 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 0.5 mol %, 0.2 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２, Sr(OH) ２ , and TiO ２ (2) The washing time in the washing step was changed to 1 minute.

[0086] Comparative Example 2-5 A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Zr were 1 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and ZrO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L and the stirring speed was changed to 100 rpm.

[0087] Example 3-1 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows. (1) [Ni ０．９０ Mn ０．１０ ](OH) ２ (2) In the calcination step, a composite hydroxide represented by the formula (1) was used to obtain a metal oxide containing Ni and Mn. Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements was 0.5 mol % and the molar ratio of Sr was 0.2 mol %. ２ , Sr(OH) ２ and lithium hydroxide was mixed in such that the molar ratio of Li to the total amount of Ni, Mn, Ca, and Sr was 109 mol %.

[0088] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (iCAP6300, manufactured by Thermo Fisher Scientific). As a result, the elements shown in Table 3 below were confirmed as elements excluding Li and O. In addition, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.4 μm and an aspect ratio of 12 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.55 and 0.62, respectively.

[0089] Example 3-2 In the firing step of producing a positive electrode active material, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of W were 0.5 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and W.O. ３ A test cell was prepared in the same manner as in Example 3-1 except that the above was added, and evaluation was carried out.

[0090] Example 3-3 A test cell was prepared and evaluated in the same manner as in Example 3-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.5 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) The solid-liquid ratio in the water washing step was changed to 750 g / L.

[0091] Example 3-4 A test cell was prepared and evaluated in the same manner as in Example 3-1, except that a positive electrode active material was prepared as follows. In the element concentration distribution measurement of the surface of the positive electrode active material by TOF-SIMS, B was detected along with Ca and Sr. (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, Sr, and Ti relative to the total amount of metal elements was 1 mol %, 0.2 mol %, and 0.3 mol %. ２ , Sr(OH) ２ , and TiO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L and the water washing time was changed to 20 minutes. (3) H was added to the lithium transition metal composite oxide obtained in the water washing step so that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr, and Ti was 1 mol %. ３ BO ３ The mixture was mixed and heat-treated at 300° C. in an oxygen stream.

[0092] Example 3-5 A test cell was prepared and evaluated in the same manner as in Example 3-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Zr were 0.5 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and ZrO ２ (2) The solid-liquid ratio in the water washing step was changed to 1500 g / L. (3) H was added to the lithium transition metal composite oxide obtained in the water washing step so that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr, and Zr was 0.5 mol %. ３ BO ３ The mixture was mixed and heat-treated at 300° C. in an oxygen stream.

[0093] Comparative Example 3-1 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca and Zr relative to the total amount of metal elements in the firing step was 0.5 mol % and 0.2 mol %, respectively. ２ and ZrO ２ A test cell was produced and evaluated in the same manner as in Example 3-1, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 0.5 μm and an aspect ratio of 1.2 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0094] Comparative Example 3-2 A test cell was prepared and evaluated in the same manner as in Example 3-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of W were 0.5 mol %, 0.2 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and W.O. ３ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0095] Comparative Example 3-3 A test cell was prepared and evaluated in the same manner as in Example 3-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 1 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0096] Comparative Example 3-4 A test cell was prepared and evaluated in the same manner as in Example 3-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 0.5 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm. (3) H was added to the lithium transition metal composite oxide obtained in the water washing step so that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr, and Ti was 1.5 mol %. ３ BO ３ The mixture was mixed and heat-treated at 300° C. in an oxygen stream.

[0097] Comparative Example 3-5 A test cell was prepared and evaluated in the same manner as in Example 3-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Zr were 1.0 mol %, 0.3 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and ZrO ２(2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm. (3) H was added to the lithium transition metal composite oxide obtained in the water washing step so that the molar ratio of B to the total amount of Ni, Mn, Ca, Sr, and Zr was 1.0 mol %. ３ BO ３ The mixture was mixed and heat-treated at 300° C. in an oxygen stream.

[0098] Example 4-1 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows. (1) [Ni ０．８９ Co ０．０４ Mn ０．０５ Al ０．０２ ](OH) ２ (2) In the calcination step, a composite hydroxide represented by the formula (1) was used to obtain a metal oxide containing Ni, Co, Mn, and Al. Ca(OH) was added so that the molar ratio of Ca and the molar ratio of Sr were 0.5 mol % and 0.2 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ was added.

[0099] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (iCAP6300, manufactured by Thermo Fisher Scientific). As a result, the elements shown in Table 4 below were confirmed as elements excluding Li and O. In addition, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.4 μm and an aspect ratio of 12 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.63 and 0.57, respectively.

[0100] Example 4-2 In the firing step of producing a positive electrode active material, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of W were 1.0 mol %, 0.2 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and W.O. ３A test cell was prepared in the same manner as in Example 4-1 except that the above was added, and evaluation was carried out.

[0101] Example 4-3 A test cell was prepared and evaluated in the same manner as in Example 4-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.5 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) The solid-liquid ratio in the water washing step was changed to 750 g / L.

[0102] Example 4-4 A test cell was prepared and evaluated in the same manner as in Example 4-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 1.0 mol %, 0.2 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, and the water washing time was changed to 20 minutes.

[0103] Example 4-5 A test cell was prepared and evaluated in the same manner as in Example 4-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Zr were 0.5 mol %, 0.1 mol %, and 0.6 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and ZrO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1500 g / L, and the water washing time was changed to 20 minutes.

[0104] Comparative Example 4-1 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements in the firing step was 1 mol %. ２A test cell was produced and evaluated in the same manner as in Example 4-1, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 0.5 μm and an aspect ratio of 1.4 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0105] Comparative Example 4-2 A test cell was prepared and evaluated in the same manner as in Example 4-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of W were 0.5 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and W.O. ３ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0106] Comparative Example 4-3 A test cell was prepared and evaluated in the same manner as in Example 4-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.5 mol %, 0.2 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0107] Comparative Example 4-4 A test cell was prepared and evaluated in the same manner as in Example 4-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 0.5 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0108] Comparative Example 4-5 A test cell was prepared and evaluated in the same manner as in Example 4-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Zr were 0.5 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and ZrO ２ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0109] Example 5-1 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows. (1) [Ni ０．９０ Mn ０．０５ Al ０．０５ ](OH) ２ (2) In the calcination step, a metal oxide containing Ni, Mn, and Al was obtained by using a composite hydroxide represented by the formula: Ca(OH) ２ , Sr(OH) ２ was added.

[0110] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (iCAP6300, manufactured by Thermo Fisher Scientific). As a result, the elements shown in Table 5 below were confirmed as elements excluding Li and O. Furthermore, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.7 μm and an aspect ratio of 10 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.63 and 0.66, respectively.

[0111] Example 5-2 In the firing step of producing a positive electrode active material, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of W were 0.7 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH)２ , and W.O. ３ A test cell was prepared in the same manner as in Example 5-1 except that the above was added, and evaluation was carried out.

[0112] Example 5-3 In the firing step of producing a positive electrode active material, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.7 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ A test cell was prepared in the same manner as in Example 5-1 except that the above was added, and evaluation was carried out.

[0113] Example 5-4 In the firing step of producing a positive electrode active material, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 0.7 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ A test cell was prepared in the same manner as in Example 5-1 except that the above was added, and evaluation was carried out.

[0114] Example 5-5 In the firing step of producing a positive electrode active material, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Zr were 0.7 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and ZrO ２ A test cell was prepared in the same manner as in Example 5-1 except that the above was added, and evaluation was carried out.

[0115] Comparative Example 5-1 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements in the firing step was 1.0 mol %. ２ A test cell was produced and evaluated in the same manner as in Example 5-1, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 0.5 μm and an aspect ratio of 1.5 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0116] Comparative Example 5-2 A test cell was prepared and evaluated in the same manner as in Example 5-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of W were 0.7 mol %, 0.2 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and W.O. ３ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0117] Comparative Example 5-3 A test cell was prepared and evaluated in the same manner as in Example 5-1, except that a positive electrode active material was prepared as follows: (1) In the firing step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.7 mol %, 0.2 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ (2) In the water washing step, the solid-liquid ratio was changed to 1000 g / L, the water washing time was changed to 1 minute, and the stirring speed was changed to 100 rpm.

[0118] Example 6 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows. (1) [Ni ０．８０ Mn ０．２０ ](OH) ２ (2) In the calcination step, a metal oxide containing Ni and Mn was obtained by using a composite hydroxide represented by the formula (1). In the calcination step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Nb were 0.5 mol %, 0.1 mol %, and 0.3 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and Nb ２ O ５ Lithium hydroxide was added so that the molar ratio of Li to the total amount of Ni, Mn, Ca, Sr, and Nb was 113 mol %.

[0119] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (manufactured by Thermo Fisher Scientific, iCAP6300). As a result, the elements shown in Table 6 below were confirmed as elements excluding Li and O. In addition, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.3 μm and an aspect ratio of 10 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.63 and 0.62, respectively.

[0120] Comparative Example 6 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements in the firing step was 1.0 mol %. ２ A test cell was produced and evaluated in the same manner as in Example 6, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 1.5 μm and an aspect ratio of 1.5 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0121] Example 7 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows. (1) [Ni ０．８０ Co ０．１０ Mn ０．１０ ](OH) ２ (2) In the calcination step, a metal oxide containing Ni, Co, and Mn was obtained by using a composite hydroxide represented by the formula (1). In the calcination step, Ca(OH) was added so that the molar ratio of Ca, the molar ratio of Sr, and the molar ratio of Ti were 0.5 mol %, 0.1 mol %, and 0.5 mol %, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ and lithium hydroxide was mixed in such that the molar ratio of Li to the total amount of Ni, Co, Mn, Ca, Sr, and Ti was 105 mol %.

[0122] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (manufactured by Thermo Fisher Scientific, iCAP6300). As a result, the elements shown in Table 7 below were confirmed as elements excluding Li and O. Furthermore, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.5 μm and an aspect ratio of 10 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.53 and 0.59, respectively.

[0123] Comparative Example 7 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements in the firing step was 0.7 mol %. ２ A test cell was produced and evaluated in the same manner as in Example 7, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 2 μm and an aspect ratio of 1.0 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0124] Example 8 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that the positive electrode active material was prepared as follows. (1) [Ni ０．５０ Co ０．２０ Mn ０．３０ ](OH) ２ (2) In the calcination step, a metal oxide containing Ni, Co, and Mn was obtained by using a composite hydroxide represented by the formula (1). In the calcination step, Ca(OH) was added so that the molar ratio of Ca, Sr, and Ti was 0.5 mol%, 0.2 mol%, and 1.0 mol%, respectively, relative to the total amount of metal elements. ２ , Sr(OH) ２ , and TiO ２ and lithium hydroxide was mixed in such that the molar ratio of Li to the total amount of Ni, Co, Mn, Ca, Sr, and Ti was 115 mol %.

[0125] The obtained positive electrode active material was measured using an ICP optical emission spectrometer (manufactured by Thermo Fisher Scientific, iCAP6300). As a result, the elements shown in Table 8 below were confirmed as elements excluding Li and O. In addition, observation using a scanning electron microscope (SEM) confirmed that fibrous particles with a major axis of 0.7 μm and an aspect ratio of 15 were attached to the surface of the secondary particles of the positive electrode active material. As a result of measuring the element concentration distribution on the surface of the positive electrode active material using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Ca and Sr were detected, and the Gini coefficients of Ca and Sr on the secondary particle surfaces were 0.51 and 0.55, respectively.

[0126] Comparative Example 8 In the preparation of a positive electrode active material, Sr was not added, and Ca(OH) was added so that the molar ratio of Ca to the total amount of metal elements in the firing step was 1.0 mol %. ２ A test cell was produced and evaluated in the same manner as in Example 8, except that the secondary particles of the positive electrode active material were added. SEM observation confirmed that aggregated particles with a major axis of 3 μm and an aspect ratio of 1.0 were attached to the surfaces of the secondary particles of the positive electrode active material.

[0127] The evaluation results of the test cells of the examples and comparative examples are shown in Tables 1 to 8. The durability of the test cells in Tables 1 to 8 is expressed relative to the durability of the reference test cell in each table, which is set to 100. The reference test cells in Tables 1 to 8 are Comparative Example 1-1, Comparative Example 2-5, Comparative Example 3-4, Comparative Example 4-4, Comparative Example 5-3, Comparative Example 6, Comparative Example 7, and Comparative Example 8, respectively.

[0128]

[0129]

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

[0136] In all of Tables 1 to 8, the test cells of the examples have higher durability than the test cells of the comparative examples. This shows that the presence of fibrous particles containing Ca and Sr on the surfaces of the secondary particles of the lithium transition metal composite oxide improves the durability of the battery.

[0137] The present disclosure is further described by the following embodiments. Aspect 1: A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide contains Ni, Ca, and Sr and includes secondary particles formed by aggregation of primary particles, and wherein attached particles including fibrous particles are present on the surfaces of the secondary particles, and the fibrous particles include at least one of Ca and Sr. Aspect 2: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Aspect 1, wherein the Ni content in the lithium transition metal composite oxide is 50 mol % or more relative to the total number of moles of elements excluding Li and O. Aspect 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Aspect 1 or 2, wherein the major axis of the fibrous particles is 3 μm or less. Aspect 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Aspects 1 to 3, wherein the aspect ratio of the fibrous particles is 10 or more. Configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein Ca and Sr are each uniformly present on the surface of the secondary particles. Configuration 6: A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, a negative electrode, and a non-aqueous electrolyte.

[0138] REFERENCE SIGNS LIST 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Exterior body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide contains Ni, Ca, and Sr, and includes secondary particles formed by aggregation of primary particles, and there are adhering particles containing fibrous particles on the surface of the secondary particles, and the fibrous particles contain at least one of Ca and Sr, the positive electrode active material for a non-aqueous electrolyte secondary battery.

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 50 mol% or more based on the total number of moles of elements excluding Li and O.

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

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 each of Ca and Sr is uniformly present on the surface of the secondary particles.

6. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, a negative electrode, and a non-aqueous electrolyte.

Images