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

Abstract

A positive electrode active material for nonaqueous electrolyte secondary batteries comprises a lithium transition metal composite oxide that has secondary particles each formed from aggregated primary particles and a surface modification layer that is formed on the surface of each of the primary particles of the lithium transition metal composite oxide, in which the lithium transition metal composite oxide contains at least Al and Ni in an amount of 80 mol% or more relative to the total number of moles of metal elements excluding Li, the surface modification layer contains W and at least one of Sr and Ca, and the content of W in the surface modification layer is 0.075 mol% or less relative to the total number of moles of the metal elements excluding Li in the lithium transition metal composite oxide.

Description

[Technical field]

[0001] The present disclosure relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, non-aqueous electrolyte secondary batteries have been widely used as high-output, high-capacity secondary batteries, which include a positive electrode, a negative electrode, and a non-aqueous electrolyte, and are charged and discharged by transferring Li ions between the positive electrode and the negative electrode. From the viewpoint of reducing the resistance and increasing the capacity of the battery, there is a demand for improving the characteristics of the positive electrode active material contained in the positive electrode of the battery.

[0003] For example, Patent Document 1 discloses a lithium metal composite oxide in which a tungsten-lithium-containing compound is formed on the surface of primary particles as a positive electrode active material from which a battery with low resistance and high capacity can be obtained. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP2016-225275A Summary of the Invention

[0005] In order to obtain a high discharge capacity in the lithium transition metal composite oxide contained in the positive electrode active material, it is possible to design it so that the Ni content is high. However, when the ratio of Ni to the total number of moles of metal elements other than Li is 80 mol % or more, the layered structure of the lithium transition metal composite oxide becomes unstable, and the battery capacity may decrease with charge / discharge cycles. The technology of Patent Document 1 does not take into consideration the decrease in battery capacity with charge / discharge cycles, and there is still room for improvement.

[0006] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a lithium transition metal composite oxide having secondary particles formed by aggregation of primary particles, and a surface modification layer formed on the surfaces of the primary particles of the lithium transition metal composite oxide, wherein the lithium transition metal composite oxide contains at least 80 mol % or more of Ni and Al relative to the total number of moles of metal elements excluding Li, the surface modification layer contains at least one of Sr and Ca, and W, and the content of W in the surface modification layer is 0.075 mol % or less relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

[0007] A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a positive electrode containing the above-described positive electrode active material for nonaqueous electrolyte secondary batteries, a negative electrode, and a nonaqueous electrolyte.

[0008] According to the positive electrode active material for a nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure, a nonaqueous electrolyte secondary battery having high output and improved charge / discharge cycle characteristics can be provided. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The layered structure of lithium transition metal composite oxides includes a transition metal layer such as Ni, a Li layer, and an oxygen layer, and the Li ions present in the Li layer reversibly enter and exit the Li layer, which allows the charge and discharge reaction of the battery to proceed. In the lithium transition metal composite oxide contained in the positive electrode active material, if the ratio of Ni to the total number of moles of metal elements other than Li is 80 mol % or more, many Li ions are extracted from the Li layer during charging of the battery, which may cause the layered structure to become unstable. On the surface of the lithium transition metal composite oxide whose layered structure has become unstable, an altered layer is formed by reaction with the electrolyte. The altered layer is the starting point for further structural changes in the lithium transition metal composite oxide, so the battery capacity gradually decreases with charging and discharging.

[0011] Therefore, the present inventors have conducted extensive research to solve the above problems, and have found that by forming a surface modification layer containing at least one of Sr and Ca, and W on the surface of a lithium transition metal composite oxide, the charge / discharge cycle characteristics and output characteristics of the battery are improved due to the synergistic effect of Sr or Ca and W. It is presumed that W facilitates the movement of Li ions between the electrolyte and the lithium transition metal composite oxide, while stabilizing the surface state of the lithium transition metal composite oxide through electronic interaction due to the coexistence of Sr and Ca, thereby specifically suppressing the formation of an altered layer. Note that when the content of W in the surface modification layer is more than 0.075 mol% with respect to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide, the surface modification layer becomes too thick, increasing the reaction resistance and decreasing the output characteristics.

[0012] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below. A cylindrical battery in which a wound electrode body is housed in a cylindrical battery case will be exemplified below, but the electrode body is not limited to the wound type, and may be a laminate type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated one by one with a separator interposed therebetween. In addition, the battery case is not limited to a cylindrical shape, and may be, for example, a square shape, a coin shape, or the like, or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0013] Fig. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As illustrated in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14, a nonaqueous electrolyte, and a battery case 15 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. The battery case 15 includes a cylindrical outer can 16 with a bottom and a sealing body 17 that closes the opening of the outer can 16.

[0014] The electrode body 14 is composed of a long positive electrode 11, a long negative electrode 12, two long separators 13, a positive electrode tab 20 joined to the positive electrode 11, and a negative electrode tab 21 joined to the negative electrode 12. The negative electrode 12 is formed to have a size slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. The two separators 13 are formed to have a size at least slightly larger than the positive electrode 11, and are arranged to sandwich the positive electrode 11, for example.

[0015] The nonaqueous electrolyte secondary battery 10 includes insulating plates 18, 19 disposed above and below the electrode body 14. In the example shown in Fig. 1, a positive electrode tab 20 attached to the positive electrode 11 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode tab 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode tab 20 is connected to the lower surface of a bottom plate 23 of the sealing body 17 by welding or the like, and a cap 27 of the sealing body 17 electrically connected to the bottom plate 23 serves as a positive electrode terminal. The negative electrode tab 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

[0016] The exterior can 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the exterior can 16 and the sealing body 17, and the internal space of the battery case 15 is sealed. The exterior can 16 has a grooved portion 22 that supports the sealing body 17 and is formed, for example, by pressing the side portion from the outside. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its upper surface.

[0017] The sealing body 17 has a structure in which a bottom plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are laminated in this order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disk shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other 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 so as to push the upper valve body 26 toward the cap 27, and the current path between the lower valve body 24 and the upper valve body 26 is interrupted. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0018] The positive electrode 11, negative electrode 12, separator 13, and nonaqueous electrolyte that constitute the nonaqueous electrolyte secondary battery 10, and in particular the positive electrode active material contained in the positive electrode mixture layer 31 that constitutes the positive electrode 11, will be described in detail below.

[0019] [Positive electrode] The positive electrode 11 has a positive electrode current collector 30 and a positive electrode composite layer 31 formed on both sides of the positive electrode current collector 30. For the positive electrode current collector 30, a foil of a metal stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film having the metal disposed on the surface layer, can be used. The positive electrode composite layer 31 may contain a positive electrode active material, a conductive material, and a binder. The thickness of the positive electrode composite layer 31 is, for example, 10 μm to 150 μm on one side of the positive electrode current collector 30. The positive electrode 11 can be produced, for example, by applying a positive electrode slurry containing a positive electrode active material, a conductive material, a binder, and the like to the surface of the positive electrode current collector 30, drying the coating, and then compressing it to form the positive electrode composite layer 31 on both sides of the positive electrode current collector 30.

[0020] Examples of the conductive material contained in the positive electrode mixture layer 31 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. These resins may be used in combination with carboxymethylcellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like.

[0021] The positive electrode active material contained in the positive electrode mixture layer 31 includes a lithium transition metal composite oxide having secondary particles formed by aggregation of primary particles, and a surface modification layer formed on the surfaces of the primary particles of the lithium transition metal composite oxide. The surface modification layer suppresses side reactions between the lithium transition metal composite oxide and the electrolyte and suppresses the generation of an altered layer. Here, the surface modification layer formed on the surfaces of the primary particles means that the surface modification layer is present on the surfaces of the secondary particles or at the interface where the primary particles contact each other.

[0022] The secondary particles of the lithium transition metal composite oxide are particles having a volume-based median diameter (D50) of preferably 3 μm to 30 μm, more preferably 5 μm to 25 μm, and particularly preferably 7 μm to 15 μm. D50 means a particle diameter at which the cumulative frequency is 50% from the smallest particle diameter in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of the secondary particles of the lithium transition metal composite oxide can be measured using a laser diffraction type particle size distribution measuring device (e.g., MT3000II manufactured by Microtrack Bell Co., Ltd.) with water as a dispersion medium.

[0023] The particle size of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed by a scanning electron microscope (SEM).

[0024] The lithium transition metal composite oxide may have, for example, a layered structure belonging to the space group R-3m, a layered structure belonging to the space group C2 / m, etc. Among these, in terms of high capacity, stability of the crystal structure, etc., it is preferably 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, a Li layer, and an oxygen layer.

[0025] The lithium transition metal composite oxide contains at least 80 mol% of Ni and Al with respect to the total number of moles of metal elements excluding Li. By setting the ratio of Ni to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide to 80 mol% or more, a high-capacity battery can be obtained. The ratio of Ni to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide is preferably 90 mol% or more. Thereby, a higher-capacity battery can be obtained.

[0026] The lithium transition metal composite oxide has the general formula Li a Ni x Co y Al z Mn w M1 v O 2-b (where 0.95 ≦ a ≦ 1.05, 0.8 ≦ x ≦ 0.96, 0 ≦ y ≦ 0.15, 0 < z ≦ 0.10, 0 ≦ w ≦ 0.1, 0 ≦ v ≦ 0.1, 0 ≦ b ≦ 0.05, x + y + z + w + v = 1, and M1 contains at least one element selected from Fe, Ti, Si, Nb, Zr, Mo, and Zn). Note that the positive electrode active material may include a lithium transition metal composite oxide other than that represented by the above general formula, or other compounds, as long as the object of the present disclosure is not impaired. The molar fraction of the metal elements contained in the entire particles of the lithium transition metal composite oxide is measured by inductively coupled plasma (ICP) emission spectrometry.

[0027] The ratio a of Li in the lithium transition metal composite oxide preferably satisfies 0.95 ≦ a < 1.05, and more preferably satisfies 0.97 ≦ a ≦ 1.03. When a is less than 0.95, the battery capacity may decrease as compared with the case where a satisfies the above range. When a is 1.05 or more, it may lead to a decrease in charge-discharge cycle characteristics as compared with the case where a satisfies the above range.

[0028] The ratio z of Al to the total molar number of metal elements excluding Li in the lithium transition metal composite oxide preferably satisfies 0 < z ≦ 0.10, and more preferably satisfies 0.03 ≦ z ≦ 0.07. Since the oxidation number of Al does not change even during charge and discharge, it is considered that the structure of the transition metal layer is stabilized by being contained in the transition metal layer. On the other hand, when z exceeds 0.10, Al impurities may be generated and the battery capacity may decrease. Also, when z is 0.07 or less, the layered structure of the lithium transition metal composite oxide tends to become unstable, so the effect of improving the charge-discharge cycle characteristics by the surface modification layer described later is remarkable. Al may be uniformly dispersed in the layered structure of the lithium transition metal composite oxide, for example, or may be present in a part of the layered structure.

[0029] Co, Mn, and M1 (M1 is at least one element selected from Fe, Ti, Si, Nb, Zr, Mo, and Zn) are optional components. The ratios y, w, and v of Co, Mn, and M1 to the total molar number of metal elements excluding Li in the lithium transition metal composite oxide preferably satisfy 0 ≦ y ≦ 0.15, 0 ≦ w ≦ 0.1, and 0 ≦ v ≦ 0.1, respectively.

[0030] The surface modification layer is formed on the surface of the primary particles of the lithium transition metal composite oxide. The surface modification layer contains at least one of Sr and Ca and W. Due to the synergistic effect of Sr or Ca and W, the charge-discharge cycle characteristics and output characteristics of the battery can be specifically improved.

[0031] The surface modification layer may contain, for example, Sr or a compound containing Sr, or Ca or a compound containing Ca. Examples of the compound containing Sr include SrO and SrCO3. Examples of the compound containing Ca include CaO and CaCO3. The surface modification layer may also contain, for example, W or a compound containing W. Examples of the compound containing W include WO3.

[0032] The surface modification layer may further contain Al. The Al contained in the surface modification layer may be, for example, Al or a compound containing Al. An example of the compound containing Al is Al2O3. Also, the compound containing Al may be a compound containing Al, Sr, or Ca, and examples of the compound include SrAlO4 and CaAlO4. The surface modification layer may further contain Li. Examples of the compound containing Li are Li2O, LiOH, and Li2CO3. Also, the compound containing Li may be a compound containing W, and examples of the compound include lithium tungstate.

[0033] The content of Sr and Ca in the surface modification layer can be, for example, 0.05 mol% to 0.50 mol% based on the total number of moles of metal elements except Li in the lithium transition metal composite oxide. In this range, the surface state of the lithium transition metal composite oxide can be stabilized by electronic interaction. In addition, by coexisting with W, the formation of an altered layer can be suppressed, and the charge / discharge cycle characteristics of the battery can be specifically improved. The content of Sr in the surface modification layer is preferably 0.05 mol% to 0.30 mol%, more preferably 0.10 mol% to 0.20 mol%. In addition, the content of Ca in the surface modification layer is preferably 0.10 mol% to 0.50 mol%, more preferably 0.25 mol% to 0.50 mol%. In addition, when both Sr and Ca are contained in the surface modification layer, the total content of Sr and Ca may be 0.05 mol% to 0.50 mol%.

[0034] The content of W in the surface modification layer is 0.075 mol% or less with respect to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide. In this range, it is possible to reduce the reaction resistance of the battery while achieving a synergistic effect with Ca or Sr. In addition, the content of W in the surface modification layer with respect to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide is, for example, 0.01 mol% or more, preferably 0.02 mol% or more, and more preferably 0.04 mol% or more. Here, the presence of Sr, Ca, and W in the surface modification layer can be confirmed by energy dispersive X-ray spectroscopy (TEM-EDX). In addition, the contents of Sr, Ca, and W in the surface modification layer can be measured by inductively coupled plasma (ICP) emission spectroscopy of a solution obtained by dissolving the lithium transition metal composite oxide in a mixed solution of aqua regia and hydrofluoric acid.

[0035] The thickness of the surface modification layer is, for example, 0.1 nm or more. This can suppress the reaction between the surface of the lithium transition metal composite oxide and the electrolyte. The thickness of the surface modification layer may be, for example, 5 nm or less.

[0036] The content of the lithium transition metal composite oxide in the positive electrode active material is preferably 90 mass% or more, and more preferably 99 mass% or more, relative to the total mass of the positive electrode active material, from the standpoint of, for example, improving the battery capacity and effectively suppressing deterioration of the charge / discharge cycle characteristics.

[0037] The positive electrode active material of the present embodiment may contain other lithium transition metal composite oxides in addition to the lithium transition metal composite oxide of the present embodiment, such as lithium transition metal composite oxides having a Ni content of 0 mol % or more and less than 80 mol %.

[0038] Next, an example of a method for producing a positive electrode active material including a lithium transition metal composite oxide and a surface modification layer will be described.

[0039] The method for producing a positive electrode active material includes, for example, a first step of obtaining a composite oxide containing Ni, Al, and an arbitrary metal element, a second step of mixing the composite oxide, a Li compound, and a Sr compound or a Ca compound to obtain a mixture, a third step of firing the mixture to obtain a fired product, a fourth step of washing the fired product with water and then adding a W compound to obtain a W additive, and a fifth step of heat-treating the W additive to obtain a positive electrode active material. Parameters such as the composition of the surface modification layer in the finally obtained positive electrode active material can be adjusted by controlling, for example, the mixing ratio of the raw materials in the second and fourth steps, the firing temperature and time in the third step, and the heat treatment temperature and time in the fifth step.

[0040] In the first step, for example, while stirring a solution of a metal salt containing Ni, Al, and an arbitrary metal element (Co, Mn, Fe, etc.), an alkaline solution such as sodium hydroxide is dropped to adjust the pH to the alkaline side (e.g., 8.5 to 12.5), thereby precipitating (co-precipitating) a composite hydroxide containing Ni, Al, and the arbitrary metal element, and the composite hydroxide is calcined to obtain a composite oxide containing Ni, Al, and the arbitrary metal element. The calcination temperature is not particularly limited, but is, for example, in the range of 300°C to 600°C.

[0041] In the second step, the composite oxide obtained in the first step, a Li compound, and a Sr compound or a Ca compound are mixed to obtain a mixture. Examples of Li compounds include Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH·H2O, LiH, and LiF. Examples of Sr compounds include Sr(OH)2, Sr(OH)2·H2O, Sr(OH)2·8H2O, SrO, SrCo3, SrSO4, and Sr(NO3)2. Examples of Ca compounds include Ca(OH)2, CaO, CaCO3, CaSO4, and Ca(NO3)2. The particle size of the Sr compound or Ca compound is preferably, for example, 0.1 μm to 20 μm. When the Sr compound or Ca compound contains moisture, it may be used after dehydration treatment such as drying in order to suppress moisture generation during firing. The mixing ratio of the composite oxide obtained in the first step and the Li compound is preferably, for example, a ratio in which the molar ratio of metal elements other than Li:Li is in the range of 1:0.98 to 1:1.1, in order to easily adjust each of the parameters to the ranges specified above. The mixing ratio of the composite oxide obtained in the first step and at least one of the Sr compound and the Ca compound is preferably, for example, a ratio in which the molar ratio of metal elements other than Li:(Sr+Ca) is in the range of 1:0.0005 to 1:0.005, in order to easily adjust each of the parameters to the ranges specified above. In the second step, when the composite oxide obtained in the first step, the Li compound, and the Sr compound or the Ca compound are mixed, other metal raw materials may be added as necessary. The other metal raw materials are oxides containing metal elements other than the metal elements constituting the composite oxide obtained in the first step, etc.

[0042] In the third step, the mixture obtained in the second step is fired at a predetermined temperature and time to obtain a fired product. The firing of the mixture in the third step may include a multi-stage firing process including, for example, a first firing process in which the mixture is fired in a firing furnace under an oxygen stream at a first heating rate to a first set temperature of 450°C or more and 680°C or less, and a second firing process in which the mixture is fired in a firing furnace under an oxygen stream after the first firing process at a second heating rate to a second set temperature of more than 680°C and 800°C or less. Here, the first heating rate is in the range of 1.5°C / min to 5.5°C / min, and the second heating rate is slower than the first heating rate and may be in the range of 0.1°C / min to 3.5°C / min. The first heating rate may be in the range of 0.1°C / min to 5.5°C / min, or in the range of 0.2°C / min to 5.5°C / min. By such multi-stage calcination, the parameters such as the composition of the surface modification layer can be adjusted to the above-specified range in the finally obtained positive electrode active material of this embodiment. The first temperature increase rate and the second temperature increase rate may be set in a plurality of rates for each temperature region as long as they are within the above-specified range. The holding time of the first set temperature in the first calcination step is preferably 0 to 5 hours, more preferably 0 to 3 hours, from the viewpoint of adjusting each of the above-specified parameters of the lithium transition metal composite oxide to the above-specified range. The holding time of the first set temperature is the time for maintaining the first set temperature after reaching the first set temperature. The holding time of the second set temperature in the second calcination step is preferably 1 to 10 hours, more preferably 1 to 5 hours, from the viewpoint of adjusting each of the above-specified parameters of the lithium transition metal composite oxide to the above-specified range. The holding time of the second set temperature is the time for maintaining the second set temperature after reaching the second set temperature. When the mixture is fired, the above parameters are adjusted to fall within the above-specified ranges, for example, in an oxygen flow with an oxygen concentration of 60% or more, and the flow rate of the oxygen flow is set at 10 cm 3 The flow rate can be in the range of 0.2 mL / min to 4 mL / min per kg of the mixture and 0.3 L / min or more per kg of the mixture. Sr compounds or Ca compounds are present on the surfaces of the primary particles of the fired product after the third step.

[0043] In the fourth step, a W compound or a W-containing solution is added to the fired product obtained in the third step to obtain a W additive. First, the fired product is washed with water. This can remove impurities and the like in the product obtained in the third step. The method of washing with water may include, for example, mixing the fired product with water so that the slurry concentration is within the range of 500 g / L to 2000 g / L, stirring for 3 minutes to 1 hour, and then filtering. Li compounds remain in the fired product after washing with water, and these remaining Li compounds dissolve in the water contained in the fired product to generate an alkaline aqueous solution. When a W compound is added to the fired product, the W compound dissolves in the alkaline aqueous solution and spreads over the entire surface of the fired product. Examples of W compounds include tungsten oxide (WO3), lithium tungstate (Li2WO4, Li4WO5, Li6W2O9), and the like. The amount of W added may be 0.075 mol% or less with respect to the total mole number of metal elements other than Li in the lithium transition metal composite oxide. In addition, when a W-containing solution is added to the fired product, the W concentration in the W-containing solution is, for example, 0.05 mol / L or more, and preferably 0.1 mol / L to 1 mol / L. The W-containing solution is not particularly limited as long as it contains W, but is preferably a solution in which a W compound that is easily soluble in an alkaline solution, such as tungsten oxide, lithium tungstate, or ammonium tungstate, is dissolved in an aqueous solution of lithium hydroxide.

[0044] In the fifth step, the W additive obtained in the fourth step is heat-treated to prepare a positive electrode active material. The heat treatment conditions are not particularly limited, but may be, for example, in a vacuum atmosphere, at a heat treatment temperature of 150°C to 400°C, and for a heat treatment time of 0.5 hours to 15 hours. This allows a surface modification layer containing at least one of Sr and Ca, and W, to be formed on the surface of the lithium transition metal composite oxide.

[0045] The molar fraction of the metal element contained in the positive electrode active material obtained above was measured by inductively coupled plasma (ICP) emission spectrometry and was expressed by the general formula Li a Ni x Co y Al z Mn w M1v M2 α W β O 2-b (wherein 0.95 ≤ a ≤ 1.05, 0.8 ≤ x ≤ 0.96, 0 ≤ y ≤ 0.15, 0 < z ≤ 0.10, 0 ≤ w ≤ 0.1, 0 ≤ v ≤ 0.1, 0.0005 ≤ α ≤ 0.005, β ≤ 0.00075, 0 ≤ b < 0.05, x + y + z + w + v = 1, M1 contains at least one element selected from Fe, Ti, Si, Nb, Zr, Mo, and Zn, and M2 is at least one of Sr and Ca). Note that M2 and W are not dissolved in the lithium transition metal composite oxide, but are contained in a surface modification layer present on the surface of the lithium transition metal composite oxide. Also, a part of Al may be contained in the surface modification layer.

[0046] [Negative electrode] The negative electrode 12 has a negative electrode current collector 40 and a negative electrode composite layer 41 formed on both surfaces of the negative electrode current collector 40. As the negative electrode current collector 40, a foil of a metal stable in the potential range of the negative electrode 12 such as copper or a copper alloy, or a film having the metal disposed on the surface layer can be used. The negative electrode composite layer 41 may contain a negative electrode active material and a binder. The thickness of the negative electrode composite layer 41 is, for example, 10 μm to 150 μm on one side of the negative electrode current collector 40. The negative electrode 12 can be produced, for example, by applying a negative electrode slurry containing a negative electrode active material, a binder, etc. to the surface of the negative electrode current collector 40, drying the coating film, and then rolling to form the negative electrode composite layer 41 on both surfaces of the negative electrode current collector 40.

[0047] The negative electrode active material contained in the negative electrode composite layer 41 is not particularly limited as long as it can reversibly occlude and release lithium ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, artificial massive graphite, and artificial graphite such as graphitized mesophase carbon microbeads. Also, as the negative electrode active material, a metal that alloys with Li such as Si and Sn, a metal compound containing Si, Sn, etc., or a lithium titanium composite oxide may be used. Further, those provided with a carbon coating may be used. For example, a Si-containing compound represented by SiO x (0.5 ≤ x ≤ 1.6), or Li 2ySiO (2+y) Si-containing compounds 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] As the binder contained in the negative electrode composite material layer 41, fluorine-containing resins such as PTFE and PVdF, PAN, polyimide, acrylic resin, polyolefin, etc. may be used as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) is used. Further, the negative electrode composite material layer 41 may contain CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc.

[0049] [Separator] For the separator 13, for example, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, etc. As the material of the separator, polyolefins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator 13 may have a single-layer structure or a laminated structure. Further, a resin layer with high heat resistance such as aramid resin or a filler layer containing an inorganic compound filler may be provided on the surface of the separator 13.

[0050] [Non-aqueous electrolyte] The non-aqueous electrolyte contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these can be used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. Examples of the halogen-substituted product include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0051] 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 carboxylates such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylates such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0052] 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, methyl phenyl ether, and the like. and chain ethers such as 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.

[0053] The electrolyte salt is preferably a lithium salt. Examples of lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 , LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borates such as Li2B4O7, Li(B(C2O4)F2), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 0 or more}, and the like. The lithium salt may be used alone or in combination of plural kinds. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is, for example, 0.8 mol to 1.8 mol per 1 L of the non-aqueous solvent. Further, vinylene carbonate or a propane sultone-based additive may be added.

[0054] <Example> 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.

[0055] [Preparation of Cathode Active Material] <Example 1> The composite hydroxide represented by [Ni 0.82 Co 0.13 Al 0.05 (OH)2 obtained by the coprecipitation method was calcined at 500 ° C for 8 hours to obtain a composite oxide (Ni 0.82 Co 0.13 Al 0.05 O2) (first step). Next, LiOH, the above composite oxide, and Sr(OH)2 were mixed so that the molar ratio of Li, the total amount of Ni, Co, and Al, and Sr was 1.03:1:0.0008 to obtain a mixture (second step). This mixture was under an oxygen stream with an oxygen concentration of 95% (10 cm 3The mixture was fired from room temperature to 650°C at a temperature rise rate of 2.0°C / min with a flow rate of 2 mL / min per kg of mixture and 5 L / min per kg of mixture, and then fired from 650°C to 780°C at a temperature rise rate of 0.5°C / min to obtain a fired product (third step). Water was added to the fired product so that the slurry concentration was 1500g / L, and the mixture was stirred for 15 minutes and filtered, and then WO3 was added to obtain a W additive. The amount of WO3 added was such that W was 0.05 mol% with respect to the total moles of metal elements other than Li in the W additive (fourth step). Furthermore, the W additive was heat-treated at 300°C for 8 hours to obtain the positive electrode active material of Example 1 (fifth step). The composition of the positive electrode active material was analyzed by an ICP emission spectrometer (manufactured by Thermo Fisher Scientific, product name "iCAP6300"), and the results were LiNi 0.822 Co 0.127 Al 0.051 Sr 0.0008 W 0.0005 It was O2.

[0056] [Preparation of positive electrode] The positive electrode active material of Example 1 was mixed in a ratio of 91 parts by mass, 7 parts by mass of acetylene black as a conductive material, and 2 parts by mass of polyvinylidene fluoride as a binder, and this was mixed with N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. Next, the slurry was applied to a positive electrode current collector made of aluminum foil with a thickness of 15 μm, and the coating film was dried. After that, the coating film was rolled with a rolling roller and cut into a predetermined electrode size to obtain a positive electrode in which a positive electrode composite layer was formed on both sides of the positive electrode core. In addition, an exposed portion in which the surface of the positive electrode core was exposed was provided in a part of the positive electrode.

[0057] [Preparation of negative electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethylcellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution at a solid content mass ratio of 100:1:1 to prepare a negative electrode slurry. The negative electrode slurry was applied to both sides of a negative electrode core made of copper foil, and the coating film was dried. The coating film was then rolled using a rolling roller and cut to a predetermined electrode size to obtain a negative electrode in which a negative electrode composite layer was formed on both sides of the negative electrode core. An exposed portion was provided in part of the negative electrode, where the surface of the negative electrode core was exposed.

[0058] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0059] [Preparation of test cell] An aluminum lead was attached to the exposed portion of the positive electrode containing the positive electrode active material of Example 1, a nickel lead was attached to the exposed portion of the negative electrode, and the positive electrode and the negative electrode were spirally wound with a polyolefin separator interposed therebetween to prepare a wound electrode body. This electrode body was housed in an exterior body, and the nonaqueous electrolyte was injected, and then the opening of the exterior body was sealed to obtain a test cell.

[0060] [Measurement of reaction resistance] The above test cell was charged at a constant current of 0.3 It under a temperature condition of 25°C until the cell voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 1 / 50 It. Subsequently, a constant current discharge was performed at 0.5 It until the cell voltage reached 2.5 V. Thereafter, again under a temperature condition of 25°C, a constant current charge was performed at 0.3 It until the cell voltage reached 4.2 V, and then a constant voltage charge was performed at 4.2 V until the current value reached 1 / 50 It. Next, the test cell was measured for AC impedance from 20 kHz to 0.01 Hz using an AC impedance measuring device, and a Nyquist diagram was drawn from the measured data, and the reaction resistance was calculated from the size of the arc between 10 Hz and 0.1 Hz.

[0061] [Evaluation of capacity retention rate] The test cell was subjected to the following cycle test. The discharge capacity at the first cycle and the discharge capacity at the 100th cycle of the cycle test were determined, and the capacity retention rate was calculated by the following formula.

[0062] Capacity retention rate (%) = (100th cycle discharge capacity ÷ 1st cycle discharge capacity) × 100 <Cycle test> The test cell was charged at a constant current of 0.3 It in a temperature environment of 45°C until the battery voltage reached 4.2 V, and then charged at a constant voltage until the current value reached 1 / 50 It at 4.2 V. Then, the test cell was discharged at a constant current of 0.5 It until the battery voltage reached 2.5 V. This charge / discharge cycle was repeated 100 times.

[0063] <Example 2> A positive electrode active material was obtained in the same manner as in Example 1, except that in the second step, Sr(OH)2 was added so that Sr was 0.10 mol % relative to the total number of moles of Ni, Co, and Al, and in the fourth step, WO3 was added so that W was 0.075 mol % relative to the total number of moles of metal elements other than Li in the W additive.

[0064] <Example 3> In the second step, a positive electrode active material was obtained in the same manner as in Example 1, except that Ca(OH)2 was added in an amount of 0.50 mol % based on the total number of moles of Ni, Co, and Al, instead of Sr.

[0065] <Comparative Example 1> A positive electrode active material was obtained in the same manner as in Example 1, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was not added.

[0066] <Comparative Example 2> A positive electrode active material was obtained in the same manner as in Example 1, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was added so that W was 0.075 mol% relative to the total moles of metal elements excluding Li in the W additive.

[0067] <Comparative Example 3> In the fourth step, a positive electrode active material was obtained in the same manner as in Example 1, except that WO3 was not added.

[0068] <Comparative Example 4> In the second step, Ca(OH)2 was added instead of Sr so that Ca was 0.25 mol% relative to the total mole number of Ni, Co, and Al, and in the fourth step, WO3 was not added. In the same manner as in Example 1, a positive electrode active material was obtained.

[0069] <Example 4> In the first step, [Ni 0.91 Co 0.05 Al 0.04 ](OH)2 was used to obtain a composite oxide (Ni 0.91 Co 0.05 Al 0.04 A positive electrode active material was obtained in the same manner as in Example 1, except that LiNiO2) was obtained. 0.911 Co 0.050 Al 0.039 Sr 0.0008 W 0.0005 It was O2.

[0070] <Example 5> In the second step, a positive electrode active material was obtained in the same manner as in Example 4, except that Sr(OH)2 was added so that Sr was 0.10 mol % relative to the total number of moles of Ni, Co, and Al.

[0071] <Example 6> A positive electrode active material was obtained in the same manner as in Example 4, except that in the second step, Sr(OH)2 was added so that Sr was 0.10 mol% relative to the total number of moles of Ni, Co, and Al, and in the fourth step, WO3 was added so that W was 0.075 mol% relative to the total number of moles of metal elements other than Li in the W additive.

[0072] <Example 7> In the second step, Ca(OH)2 was added so that Ca was 0.05 mol% based on the total number of moles of Ni, Co, and Al instead of Sr, and in the fourth step, WO3 was added so that W was 0.075 mol% based on the total number of moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 4.

[0073] <Example 8> In the second step, Ca(OH)2 was added so that Ca was 0.10 mol% based on the total moles of Ni, Co, and Al instead of Sr, and in the fourth step, WO3 was added so that W was 0.075 mol% based on the total moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 4.

[0074] <Example 9> In the second step, a positive electrode active material was obtained in the same manner as in Example 4, except that Ca(OH)2 was added in an amount of 0.25 mol % based on the total number of moles of Ni, Co, and Al, instead of Sr.

[0075] <Example 10> A positive electrode active material was obtained in the same manner as in Example 4, except that in the second step, Ca(OH)2 was added in an amount of 0.50 mol % based on the total mole number of Ni, Co, and Al, instead of Sr.

[0076] <Example 11> In the second step, Ca(OH)2 was added so that Ca was 0.50 mol% based on the total number of moles of Ni, Co, and Al instead of Sr, and in the fourth step, WO3 was added so that W was 0.075 mol% based on the total number of moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 4.

[0077] <Comparative Example 5> A positive electrode active material was obtained in the same manner as in Example 4, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was not added.

[0078] <Comparative Example 6> A positive electrode active material was obtained in the same manner as in Example 4, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was added so that W was 0.075 mol% relative to the total moles of metal elements excluding Li in the W additive.

[0079] <Comparative Example 7> In the fourth step, a positive electrode active material was obtained in the same manner as in Example 4, except that WO3 was not added.

[0080] <Comparative Example 8> A positive electrode active material was obtained in the same manner as in Example 4 except that in the second step, Ca(OH)2 was added so that Ca was 0.25 mol% based on the total mole number of Ni, Co, and Al instead of Sr, and in the fourth step, WO3 was not added.

[0081] <Comparative Example 9> In the second step, Sr(OH)2 was added so that Sr was 0.10 mol% relative to the total number of moles of Ni, Co, and Al, and in the fourth step, WO3 was added so that W was 0.080 mol% relative to the total number of moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 4.

[0082] <Comparative Example 10> In the second step, Ca(OH)2 was added so that Ca was 0.50 mol% based on the total number of moles of Ni, Co, and Al instead of Sr, and in the fourth step, WO3 was added so that W was 0.080 mol% based on the total number of moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 4.

[0083] <Example 12> In the first step, [Ni 0.925 Al 0.05 Mn 0.025 ](OH)2 was used to obtain a composite oxide (Ni 0.925 Al 0.05 Mn 0.025 In the second step, Sr(OH)2 was added so that Sr was 0.10 mol% relative to the total number of moles of Ni, Al, and Mn, and in the fourth step, WO3 was added so that W was 0.020 mol% relative to the total number of moles of metal elements other than Li in the W additive. A positive electrode active material was obtained in the same manner as in Example 1. The composition of the obtained positive electrode active material was LiNi 0.925 Al 0.054 Mn 0.021 Sr 0.0010 W 0.0002 It was O2.

[0084] <Example 13> In the second step, Sr(OH)2 was added so that Sr was 0.15 mol% relative to the total number of moles of Ni, Al, and Mn, and in the fourth step, WO3 was added so that W was 0.040 mol% relative to the total number of moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 12.

[0085] <Example 14> In the fourth step, a positive electrode active material was obtained in the same manner as in Example 12, except that WO3 was added so that W was 0.075 mol % relative to the total number of moles of metal elements other than Li in the W additive.

[0086] <Comparative Example 11> A positive electrode active material was obtained in the same manner as in Example 12, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was not added.

[0087] <Comparative Example 12> A positive electrode active material was obtained in the same manner as in Example 12, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was added so that W was 0.050 mol% relative to the total moles of metal elements other than Li in the W additive.

[0088] <Comparative Example 13> In the second step, Sr(OH)2 was added so that Sr was 0.08 mol% relative to the total number of moles of Ni, Al, and Mn, and in the fourth step, a positive electrode active material was obtained in the same manner as in Example 12, except that WO3 was not added.

[0089] <Comparative Example 14> In the second step, Sr(OH)2 was added so that Sr was 0.20 mol% relative to the total number of moles of Ni, Al, and Mn, and in the fourth step, WO3 was added so that W was 0.080 mol% relative to the total number of moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 12.

[0090] <Example 15> In the first step, [Ni 0.94 Al 0.06 ](OH)2 was used to obtain a composite oxide (Ni 0.94 Al 0.06 A positive electrode active material was obtained in the same manner as in Example 1, except that LiNiO2) was obtained. 0.939 Al 0.061 Sr 0.0008 W 0.0005 It was O2.

[0091] <Example 16> In the second step, Sr(OH)2 was added so that Sr was 0.10 mol% relative to the total number of moles of Ni and Al, and in the fourth step, WO3 was added so that W was 0.075 mol% relative to the total number of moles of metal elements other than Li in the W additive, except that a positive electrode active material was obtained in the same manner as in Example 15.

[0092] <Example 17> In the second step, a positive electrode active material was obtained in the same manner as in Example 15, except that Ca(OH)2 was added in an amount of 0.50 mol % based on the total mole number of Ni and Al, instead of Sr.

[0093] <Comparative Example 15> A positive electrode active material was obtained in the same manner as in Example 15, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was not added.

[0094] <Comparative Example 16> A positive electrode active material was obtained in the same manner as in Example 15, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was added so that W was 0.075 mol% relative to the total moles of metal elements excluding Li in the W additive.

[0095] <Comparative Example 17> In the fourth step, a positive electrode active material was obtained in the same manner as in Example 15, except that WO3 was not added.

[0096] <Comparative Example 18> In the second step, Ca(OH)2 was added instead of Sr so that Ca was 0.25 mol% relative to the total moles of Ni and Al, and in the fourth step, WO3 was not added. A positive electrode active material was obtained in the same manner as in Example 15, except that.

[0097] <Reference example 1> [Ni 0.595 Co 0.21 Mn 0.195 ](OH)2 was used to obtain a composite oxide (Ni 0.595 Co 0.21 Mn0.195 A positive electrode active material was obtained in the same manner as in Example 1, except that in the second step, Sr(OH)2 was not added, and in the fourth step, WO3 was not added. The composition of the obtained positive electrode active material was found to be LiNi 0.594 Co 0.211 Mn 0.195 It was O2.

[0098] <Reference example 2> In the fourth step, a positive electrode active material was obtained in the same manner as in Reference Example 1, except that WO3 was added so that W was 0.050 mol % relative to the total number of moles of metal elements other than Li in the W additive.

[0099] <Reference example 3> A positive electrode active material was obtained in the same manner as in Reference Example 1, except that in the second step, Sr(OH)2 was added so that Sr was 0.10 mol% relative to the total number of moles of Ni, Co, and Mn, and in the fourth step, WO3 was added so that W was 0.075 mol% relative to the total number of moles of metal elements other than Li in the W additive.

[0100] <Reference example 4> A positive electrode active material was obtained in the same manner as in Reference Example 1, except that in the second step, Ca(OH)2 was added so that Ca was 0.50 mol% relative to the total number of moles of Ni, Co, and Mn, and in the fourth step, WO3 was added so that W was 0.050 mol% relative to the total number of moles of metal elements other than Li in the W additive.

[0101] The reaction resistances and capacity retention rates of the Examples, Comparative Examples, and Reference Examples are shown in Tables 1 to 5. The results of ICP optical emission spectroscopy of the obtained positive electrode active materials are also shown in Tables 1 to 5. The reaction resistances and capacity retention rates of the test cells of Examples 1 to 3 and Comparative Examples 2 to 4 shown in Table 1 are shown relative to the reaction resistances and capacity retention rates of the test cell of Comparative Example 1, which are set to 100.

[0102] The reaction resistance and capacity retention rate of the test cells of Examples 4 to 11 and Comparative Examples 6 to 10 shown in Table 2 are shown relative to the reaction resistance and capacity retention rate of the test cell of Comparative Example 5, which is set to 100.

[0103] The reaction resistance and capacity retention rate of the test cells of Examples 12 to 14 and Comparative Examples 12 to 14 shown in Table 3 are shown relative to the reaction resistance and capacity retention rate of the test cell of Comparative Example 11, which is set to 100.

[0104] The reaction resistance and capacity retention rate of the test cells of Examples 15 to 17 and Comparative Examples 16 to 18 shown in Table 4 are shown relatively to the reaction resistance and capacity retention rate of the test cell of Comparative Example 15, which is set to 100.

[0105] The reaction resistance and capacity retention rate of the test cells of Reference Examples 2 to 4 shown in Table 5 are shown relatively to the reaction resistance and capacity retention rate of the test cell of Reference Example 1, which is set to 100.

[0106] [Table 1]

[0107] [Table 2]

[0108] [Table 3]

[0109] [Table 4]

[0110] [Table 5]

[0111] In all of Tables 1 to 4, the Examples had lower reaction resistance and higher capacity retention than the Comparative Examples. In Table 5, the lithium transition metal composite oxides in all of Reference Examples 1 to 4 did not contain 80% or more Ni and did not contain Al, so there was no change in reaction resistance and capacity retention even when they had a surface modification layer containing a predetermined amount of Sr or Ca and W. [Explanation of symbols]

[0112] 10 Nonaqueous electrolyte secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Electrode body 15 Battery case 16 Outer can 17 Sealing body 18,19 Insulating plate 20 Positive tab 21 Negative electrode tab 22 Grooved part 23 Bottom plate 24 Lower valve body 25 Insulating materials 26 Upper valve 27 Cap 28 Gasket 30 Positive electrode current collector 31 Positive electrode mixture layer 40 Negative electrode current collector 41 Negative electrode composite layer

Claims

1. a lithium transition metal composite oxide having secondary particles formed by aggregation of primary particles; a surface modification layer formed on the surface of the primary particles of the lithium transition metal composite oxide, The lithium transition metal composite oxide contains at least 80 mol % or more of Ni and Al based on the total number of moles of metal elements excluding Li, the surface modification layer contains at least one of Sr and Ca, and W; a content of W in the surface modification layer is 0.075 mol % or less relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the surface modification layer further contains Al.

3. 3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of Sr and Ca in the surface modification layer is 0.05 mol % to 0.50 mol % with respect to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

4. 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 3, a negative electrode, and a non-aqueous electrolyte.

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