Method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, and method for producing a non-aqueous electrolyte secondary battery

Abstract

The present invention provides a non-aqueous electrolyte secondary battery in which the proportion of Ni to the total number of moles of metal elements excluding Li is 80 mol% or more, thereby suppressing the decrease in battery capacity due to charging and discharging. [Solution] A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a first step of obtaining a composite oxide containing Al and Ni; a second step of mixing the composite oxide, a lithium compound, and a strontium compound to obtain a mixture; and a third step of calcining the mixture, wherein the third step includes a first calcination step of calcining the mixture to a first set temperature of 450°C to 680°C at a first heating rate under an oxygen stream, and a second calcination step of calcining the mixture to a second set temperature of over 680°C and 800°C at a second heating rate under an oxygen stream, the second heating rate being slower than the first heating rate, and the third step forming a surface modification layer on the surface of the primary particles of the lithium transition metal composite oxide.

Description

[Technical Field]

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

[0002] In recent years, non-aqueous electrolyte secondary batteries, which consist of a positive electrode, a negative electrode, and a non-aqueous electrolyte, and charge and discharge by moving lithium ions between the positive and negative electrodes, have been widely used as high-power, high-capacity secondary batteries. From the perspective of reducing battery resistance and increasing capacity, there is a need to improve the properties of the positive electrode active material contained in the positive electrode of the battery.

[0003] For example, Patent Document 1 discloses a lithium transition metal composite oxide having a layered structure and containing Mn, Ni, Co, Sr, and Mo, wherein the Mo content is 0.1 mol% to 1.5 mol%, and the Mo / Sr content ratio is 0.5 to 2.0 in molar ratio, thereby improving charge-discharge cycle characteristics while accommodating high capacity. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5245210 [Overview of the project]

[0005] Incidentally, in lithium transition metal composite oxides contained in positive electrode active materials, a design approach of increasing the Ni content is conceivable to obtain a high discharge capacity. However, when the proportion 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 charging and discharging. The technology described in Patent Document 1 does not take into account the decrease in battery capacity with charging and discharging in batteries with a high Ni content, and there is still room for improvement.

[0006] Therefore, the purpose of this disclosure is to provide a positive electrode active material in which the proportion of Ni is 80 mol% or more relative to the total number of moles of metal elements excluding Li, thereby suppressing the decrease in battery capacity associated with charging and discharging.

[0007] A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, according to one aspect of the present disclosure, comprises: a first step of obtaining a composite oxide containing Al and Ni; a second step of mixing the composite oxide obtained in the first step with a lithium compound and a strontium compound to obtain a mixture; and a third step of calcining the mixture to obtain a lithium transition metal composite oxide containing 80 mol% or more of Ni with respect to the total number of moles of metal elements excluding Li, and having a surface modification layer containing at least Sr on the lithium transition metal composite oxide, wherein the third step comprises: a first calcination step of calcining the mixture under an oxygen stream to a first set temperature of 450°C to 680°C at a first heating rate; and a second calcination step of calcining the mixture under an oxygen stream to a second set temperature of over 680°C and 800°C at a second heating rate, wherein the second heating rate is slower than the first heating rate; and the third step is characterized by forming a surface modification layer on the surface of the primary particles of the lithium transition metal composite oxide.

[0008] One aspect of the present disclosure is a method for manufacturing a non-aqueous electrolyte secondary battery, characterized in that a battery is manufactured using a positive electrode, a negative electrode, and a non-aqueous electrolyte, which are manufactured using the above-described method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0009] According to a positive electrode active material for a non-aqueous electrolyte secondary battery, which is one aspect of this disclosure, it is possible to provide a high-capacity non-aqueous electrolyte secondary battery that suppresses the decrease in battery capacity associated with charging and discharging. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. [Modes for carrying out the invention]

[0011] The layered structure of lithium transition metal composite oxides consists of a transition metal layer such as Ni, a Li layer, and an oxygen layer. The charge-discharge reaction of the battery proceeds as Li ions in the Li layer reversibly move in and out. However, in lithium transition metal composite oxides contained in positive electrode active materials, if the proportion of Ni to the total number of moles of metal elements other than Li is 80 mol% or more, a large number of Li ions are extracted from the Li layer during battery charging, which can destabilize the layered structure. On the surface of lithium transition metal composite oxides with an unstable layered structure, a modified layer is formed by reaction with the electrolyte. Further structural changes in the lithium transition metal composite oxide proceed starting from the modified layer, causing the battery capacity to gradually decrease with charging and discharging. However, by including predetermined amounts of Al and Sr, as in the positive electrode active material for non-aqueous electrolyte secondary batteries, one embodiment of this disclosure, the reaction with the electrolyte on the surface is suppressed due to the synergistic effect of Al and Sr, and the surface structure is stabilized, thereby suppressing the decrease in battery capacity with charging and discharging. Since Al does not undergo oxidation state changes during charging and discharging, it is presumed that its inclusion in the transition metal layer stabilizes the structure of the transition metal layer. Furthermore, it is presumed that Sr can alter the surface state of the lithium transition metal composite oxide through electronic interactions.

[0012] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail. In the following, a cylindrical battery in which a wound electrode body is housed in a cylindrical battery case will be given as an example, but the electrode body is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are stacked alternately one by one with a separator in between. Furthermore, the battery case is not limited to a cylindrical shape and may be, for example, rectangular, coin-shaped, etc., or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0013] Figure 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment. As illustrated in Figure 1, the non-aqueous electrolyte secondary battery 10 comprises an electrode body 14, a non-aqueous electrolyte (not shown), and a battery case 15 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13. The battery case 15 consists of a bottomed cylindrical outer casing 16 and a sealing body 17 that closes the opening of the outer casing 16.

[0014] The electrode body 14 consists 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 be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and width (short-side) 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.

[0015] The non-aqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, a positive electrode tab 20 attached to the positive electrode 11 extends towards the sealing body 17 through a through-hole in the insulating plate 18, and a negative electrode tab 21 attached to the negative electrode 12 extends towards the bottom of the outer casing 16 through the outside of the insulating plate 19. The positive electrode tab 20 is connected to the lower surface of the bottom plate 23 of the sealing body 17 by welding or the like, and the cap 27 of the sealing body 17, which is electrically connected to the bottom plate 23, becomes the positive electrode terminal. The negative electrode tab 21 is connected to the inner surface of the bottom of the outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0016] The outer container 16 is, for example, a metal container with a bottomed cylindrical shape. A gasket 28 is provided between the outer container 16 and the sealing body 17, sealing the internal space of the battery case 15. The outer container 16 has a grooved portion 22 that supports the sealing body 17, which 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 outer container 16, and its upper surface supports the sealing body 17.

[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 stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, with the insulating member 25 interposed between their respective peripheries. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0018] The following describes in detail the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte that constitute the non-aqueous electrolyte secondary battery 10, with particular attention paid to the positive electrode active material contained in the positive electrode active material layer 31 that constitutes the positive electrode 11.

[0019] [Positive electrode] The positive electrode 11 comprises a positive electrode current collector 30 and a positive electrode active material layer 31 formed on both sides of the positive electrode current collector 30. The positive electrode current collector 30 can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode active material layer 31 contains a positive electrode active material, a conductive material, and a binder. The thickness of the positive electrode active material 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 manufactured by applying a positive electrode slurry containing a positive electrode active material, a conductive material, and a binder to the surface of the positive electrode current collector 30, drying the coating, and then compressing it to form the positive electrode active material layer 31 on both sides of the positive electrode current collector 30.

[0020] Examples of conductive materials included in the positive electrode active material layer 31 include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of binders included in the positive electrode active material 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 its salts, polyethylene oxide (PEO), etc.

[0021] The positive electrode active material includes a lithium transition metal composite oxide and 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% Ni and Al relative 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.

[0022] Lithium transition metal composite oxides have a layered structure. Examples of layered structures of lithium transition metal composite oxides include layered structures belonging to space group R-3m and layered structures belonging to space group C2 / m. Among these, a layered structure belonging to space group R-3m is preferred in terms of high capacity and crystal structure stability.

[0023] In lithium transition metal composite oxides, the ratio of Ni to the total number of moles of metal elements excluding Li is preferably 90 mol% or more. This allows for the production of batteries with higher capacity.

[0024] Lithium transition metal composite oxides have the general formula Li a Ni x Al y Co z M w O 2-b(Where 0.95 < a < 1.05, 0.8 ≤ x ≤ 0.96, 0 < y ≤ 0.10, 0 ≤ z ≤ 0.15, 0 ≤ w ≤ 0.1, 0 ≤ b < 0.05, x + y + z + w = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn), it can be a composite oxide. In addition, the positive electrode active material may contain 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 whole particles of the lithium transition metal composite oxide is measured by inductively coupled plasma (ICP) emission spectroscopic analysis.

[0025] It is preferable that a, which indicates the ratio of Li in the lithium transition metal composite oxide, 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, more Li compounds need to be added as compared with the case where a satisfies the above range, so it may not be economical from the viewpoint of production cost.

[0026] It is preferable that y, which indicates the ratio of Al to the total molar number of the metal elements excluding Li in the lithium transition metal composite oxide, satisfies 0 < y ≤ 0.10, and more preferably satisfies 0.03 ≤ y ≤ 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 y > 0.10, Al impurities are generated and the battery capacity decreases. Al may be uniformly dispersed in the layered structure of the lithium transition metal composite oxide, or may be present in a part of the layered structure.

[0027] Co and M (where M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn) are optional components. The ratios of Co and M to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide, z and w, preferably satisfy 0 ≤ z ≤ 0.15 and 0 ≤ w ≤ 0.1, respectively. Since Co is expensive, it is preferable to reduce the Co content from the viewpoint of manufacturing costs.

[0028] Lithium transition metal composite oxides are, for example, secondary particles formed by the aggregation of multiple primary particles. The particle size of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM). The surface modification layer exists on the surface of the primary particles. In other words, the surface modification layer exists on the surface of the secondary particles of the lithium transition metal composite oxide, or at the interface where the primary particles come into contact with each other.

[0029] Lithium transition metal composite oxides are particles with a volume-based median diameter (D50) of, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, and particularly preferably 7 μm to 15 μm. D50 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of lithium transition metal composite oxides can be measured using a laser diffraction particle size distribution analyzer (e.g., Microtrac-Bell MT3000II) with water as the dispersion medium.

[0030] Lithium transition metal composite oxides have a surface layer located from the surface inward and a main body located inside the surface layer. The thickness of the surface layer is, for example, 1 nm to 5 nm.

[0031] The ratio of Al to the total number of moles of metal elements excluding Li in the surface layer is 1.3 times or more than the ratio of Al to the total number of moles of metal elements excluding Li in the main body. As a result, the structure of the surface layer is more stable than that of the main body, and in synergy with the surface modification layer described later, the decrease in battery capacity due to charging and discharging can be suppressed. Note that the ratio of Al to the total number of moles of metal elements excluding Li in the surface layer can be, for example, 4 times or less than the ratio of Al to the total number of moles of metal elements excluding Li in the main body.

[0032] The surface modification layer contains at least Sr. The surface modification layer may contain, for example, Sr or a compound containing Sr. An example of a compound containing Sr is SrO2. The surface modification layer may further contain Al or a compound containing Al, and at least one selected from compounds containing both Sr and Al. An example of a compound containing Al is Al2O3. An example of a compound containing both Sr and Al is SrAlO4. The surface modification layer may further contain Li. Li present on the surface of the lithium transition metal composite oxide described later may be included in the surface modification layer.

[0033] The ratio of Al to the total number of moles of metal elements excluding Li in the surface modification layer can be made greater than the ratio of Al to the total number of moles of metal elements excluding Li in the main body of the lithium transition metal composite oxide.

[0034] Furthermore, it is preferable that the ratio of Al to the total number of moles of metal elements excluding Li in the surface modification layer is 1.9 times or more the ratio of Al to the total number of moles of metal elements excluding Li in the main body of the lithium transition metal composite oxide.

[0035] The proportion of Sr in the surface modification layer can be set to 0.05 mol% to 0.25 mol% relative to the total number of moles of metal elements excluding Li in the surface modification layer. Within this range, electronic interactions can alter the surface state of the lithium transition metal composite oxide.

[0036] The thickness of the surface modification layer is, for example, 0.1 nm to 2 nm. Within this range, the reaction with the electrolyte on the surface of the lithium transition metal composite oxide is suppressed, and in synergy with the aforementioned surface layer, the decrease in battery capacity due to charging and discharging can be suppressed.

[0037] The amount of Li remaining on the surface of the lithium transition metal composite oxide (hereinafter sometimes referred to as the amount of residual Li) can be 0.03 wt% to 0.08 wt%. The Li present on the surface of the lithium transition metal composite oxide includes Li contained in the surface modification layer, and Li present in forms other than the surface modification layer, such as Li compounds on top of the surface modification layer.

[0038] The positive electrode active material can be dispersed in water and eluted, and the amount of residual Li can be quantified by titration. The specific measurement method is as follows. (1) Add 1 g of positive electrode active material to 30 ml of pure water and stir to prepare a suspension in which the active material is dispersed in water. (2) Filter the suspension and add pure water to make up 70 ml to obtain a filtrate containing Li eluted from the active material. (3) While measuring the pH of the filtrate, hydrochloric acid is added dropwise in small amounts, and the amount of Li dissolved in the filtrate is calculated from the amount of hydrochloric acid consumed (titration volume) up to the first inflection point (around pH 8) and the second inflection point (around pH 4) of the pH curve.

[0039] The content of lithium transition metal composite oxide in the positive electrode active material is preferably 90% by mass or more, and more preferably 99% by mass or more, relative to the total mass of the positive electrode active material, for example, in terms of improving battery capacity and effectively suppressing the deterioration of charge-discharge cycle characteristics.

[0040] Furthermore, the positive electrode active material of this embodiment may contain other lithium transition metal composite oxides in addition to the lithium transition metal composite oxide of this embodiment. Examples of other lithium transition metal composite oxides include lithium transition metal composite oxides with a Ni content of 0 mol% or more and less than 85 mol%.

[0041] 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.

[0042] A 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 obtained in the first step with a lithium compound to obtain a mixture; and a third step of calcining the mixture. The composition and thickness parameters of the surface layer and surface modification layer in the finally obtained positive electrode active material are adjusted by controlling, for example, the mixing ratio of raw materials in the second step, the calcination temperature and time in the third step, etc.

[0043] In the first step, for example, an alkaline solution such as sodium hydroxide is added dropwise while stirring a solution of a metal salt containing Ni, Al, and an arbitrary metal element (Co, Mn, Fe, etc.) to adjust the pH to the alkaline side (e.g., 8.5 to 12.5), thereby precipitating (coprecipitation) a composite hydroxide containing Ni, Al, and an arbitrary metal element. The composite hydroxide is then calcined to obtain a composite oxide containing Ni, Al, and an arbitrary metal element. The calcination temperature is not particularly limited, but for example, it is in the range of 300°C to 600°C.

[0044] In the second step, the composite oxide obtained in the first step is mixed with a lithium compound and a strontium compound to obtain a mixture. Examples of lithium compounds include Li2CO3, LiOH, Li2O2, Li2O, LiNO3, LiNO2, Li2SO4, LiOH·H2O, LiH, and LiF. Examples of strontium compounds include Sr(OH)2, Sr(OH)2·8H2O, SrO, SrCo3, SrSO4, and Sr(NO3)2. The mixing ratio of the composite oxide obtained in the first step and the lithium compound is preferably such that, for example, the molar ratio of metal elements other than Li to Li is in the range of 1:0.98 to 1:1.1, as this facilitates adjusting each of the above parameters to the specified range. Furthermore, the mixing ratio of the composite oxide obtained in the first step and the strontium compound is preferably such that, for example, the molar ratio of metal elements other than Li to Sr is in the range of 1:0.0005 to 1:0.0018, in order to facilitate the adjustment of each of the above parameters to the range specified above. In the second step, when mixing the composite oxide obtained in the first step with the lithium compound and the strontium compound, other metal raw materials may be added as needed. Other metal raw materials are oxides containing metal elements other than the metal elements that constitute the composite oxide obtained in the first step.

[0045] In the third step, the mixture obtained in the second step is fired at a predetermined temperature and for a predetermined time to obtain the positive electrode active material according to the present embodiment. The firing of the mixture in the third step includes, for example, a first firing step of firing in a firing furnace under an oxygen stream at a first heating rate to a first set temperature of 450°C or higher and 680°C or lower, and a second firing step of firing the fired product obtained by the first firing step in the firing furnace under an oxygen stream at a second heating rate to a second set temperature of higher than 680°C and 800°C or lower. Here, the first heating rate is in the range of 1.5°C / min or higher and 5.5°C / min or lower, and the second heating rate is slower than the first heating rate and is in the range of 0.1°C / min or higher and 3.5°C / min or lower. By such multi-step firing, in the finally obtained positive electrode active material of the present embodiment, parameters such as the composition and thickness of the surface layer and the surface modification layer can be adjusted to the above-specified ranges. Note that the first heating rate and the second heating rate may be set in plural for each temperature region as long as they are within the above-specified ranges. The holding time of the first set temperature in the first firing step is preferably 0 hours or more and 5 hours or less, more preferably 0 hours or more and 3 hours or less, in terms of adjusting the above parameters of the lithium transition metal composite oxide to the above-specified ranges. 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 firing step is preferably 1 hour or more and 10 hours or less, more preferably 1 hour or more and 5 hours or less, in terms of adjusting the above parameters of the lithium transition metal composite oxide to the above-specified ranges. The holding time of the second set temperature is the time for maintaining the second set temperature after reaching the second set temperature. When firing the mixture, in terms of adjusting the above parameters to the above-specified ranges, for example, it is performed in an oxygen stream with an oxygen concentration of 60% or higher, and the flow rate of the oxygen stream can be in the range of 0.2 mL / min to 4 mL / min per 10 cm of the firing furnace and 0.3 L / min or higher per 1 kg of the mixture. 3 per, it can be in the range of 0.2 mL / min to 4 mL / min and 0.3 L / min or higher per 1 kg of the mixture.

[0046] <� The molar fraction of the metal elements contained in the positive electrode active material obtained above is measured by inductively coupled plasma (ICP) emission spectroscopic analysis, and the general formula is Li a Ni x Al y Coz M w Sr α O 2-b (where 0.95 < a < 1.05, 0.8 ≤ x ≤ 0.96, 0 < y ≤ 0.10, 0 ≤ z ≤ 0.15, 0 ≤ w ≤ 0.1, 0.05 ≤ α ≤ 0.18, 0 ≤ b < 0.05, x + y + z + w = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn). Note that Sr is not dissolved in the lithium transition metal composite oxide but is contained in the 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.)

[0047] In addition, the composition of the interior and surface layer of the lithium transition metal composite oxide in the positive electrode active material, as well as the composition of the surface modification layer, can be measured for the ratio of Ni, Co, Al, and M by analyzing each location in the cross-section of the primary particles of the positive electrode active material using energy dispersive X-ray spectroscopy (TEM-EDX). Note that since the surface modification layer is thinner than the spot diameter of the electron beam irradiated, the composition of the surface modification layer is affected by the composition of the adjacent surface layer. Even if Ni, Co, and Mn are detected in the measurement results of the surface layer, it is considered that Ni, Co, and M do not actually exist in the surface layer. Also, since the addition amount of Sr is small like α above, the presence or absence can be confirmed but it cannot be quantitatively measured.)

[0048] [Negative Electrode] The negative electrode 12 has a negative electrode current collector 40 and negative electrode active material layers 41 formed on both sides of the negative electrode current collector 40. For the negative electrode current collector 40, a foil of a metal stable within the potential range of the negative electrode 12 such as copper or a copper alloy, a film having the metal disposed on the surface layer, etc. can be used. The negative electrode active material layer 41 contains a negative electrode active material and a binder. The thickness of the negative electrode active material 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 by applying a negative electrode slurry containing a negative electrode active material, a binder, etc. on the surface of the negative electrode current collector 40, drying the coating film, and then rolling to form the negative electrode active material layers 41 on both sides of the negative electrode current collector 40.)

[0049] The negative electrode active material contained in the negative electrode active material layer 41 is not particularly limited as long as it can reversibly occlude and release lithium ions, and generally carbon materials such as graphite are used. Graphite may be any of natural graphite such as flaky graphite, massive graphite, and earthy graphite, artificial massive graphite, and artificial graphite such as graphitized mesophase carbon microbeads. Further, as the negative electrode active material, metals that alloy with Li such as Si and Sn, metal compounds containing Si, Sn, etc., lithium titanium composite oxides, etc. may be used. Further, those provided with a carbon coating may 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), etc. may be used in combination with graphite.

[0050] For the binder contained in the negative electrode active material layer 41, similar to the case of the positive electrode 11, fluorine-containing resins such as PTFE and PVdF, PAN, polyimide, acrylic resin, polyolefin, etc. may be used, but preferably styrene-butadiene rubber (SBR) is used. Further, the negative electrode active material layer 41 may contain CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc.

[0051] [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 an aramid resin, a filler layer containing an inorganic compound filler may be provided on the surface of the separator 13.

[0052] [Non-aqueous electrolyte] Non-aqueous electrolytes include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted solvents include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0053] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters 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 linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0054] Examples of the above ethers include cyclic ethers such as 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, crown ether, etc.; and chain ethers such as 1,2 - dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o - dimethoxybenzene, 1,2 - diethoxyethane, 1,2 - dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1 - dimethoxymethane, 1,1 - diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0055] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-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, borate salts such as Li2B4O7, Li(B(C2O4)F2), etc.; LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1Examples include imide salts such as SO2){l,m are integers greater than or equal to 0}. Lithium salts may be used individually or in mixtures of multiple types. Of these, LiPF6 is preferred from the viewpoint of ionic conductivity and electrochemical stability. The concentration of the lithium salt is, for example, 0.8 moles to 1.8 moles per liter of non-aqueous solvent. Furthermore, vinylene carbonate or propane-sultone additives may be added. [Examples]

[0056] The present disclosure will be further explained below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0057] [Fabrication of positive electrode active material] <Example 1> [Ni obtained by coprecipitation method] 0.82 Al 0.05 Co 0.13 The composite hydroxide represented by ](OH)2 is calcined at 500°C for 8 hours, and the composite oxide (Ni 0.82 Al 0.05 Co 0.13 O2) was obtained. LiOH, Sr(OH)2, and the above composite oxide were mixed so that the molar ratio of Li, Ni, Al, and Co to Sr was 1.03:1:0.0005 to obtain a mixture. Under an oxygen stream with an oxygen concentration of 95% (10 cm 3 The mixture was calcined at a flow rate of 2 mL / min per unit area and 5 L / min per kg of mixture at a heating rate of 2.0 °C / min from room temperature to 650 °C, and then calcined again at a heating rate of 0.5 °C / min from 650 °C to 780 °C. Impurities were removed from the calcined material by washing with water to obtain the positive electrode active material. The composition of the obtained positive electrode active material was measured using an ICP emission spectrometer (Thermo Fisher Scientific, product name "iCAP6300"), and the composition was found to be LiNi 0.82 Al 0.05 Co 0.13 Sr 0.0005 It was O2. This was used as the positive electrode active material in Example 1.

[0058] <Comparative Example 1> LiOH and composite oxides (Ni 0.82 Al 0.05 Co 0.13 A positive electrode active material was obtained in the same manner as in Example 1, except that O2) was mixed with Li so that the molar ratio of the total amount of Li, Ni, Al, and Co was 1.03:1. The composition of the obtained positive electrode active material was LiNi 0.82 Al 0.05 Co 0.13 It was O2. This was used as the positive electrode active material for Comparative Example 1.

[0059] <Example 2> [Ni 0.87 Al 0.04 Co 0.09 Using a composite hydroxide represented by ](OH)2, a composite oxide (Ni 0.87 Al 0.04 Co 0.09 A positive electrode active material was obtained in the same manner as in Example 1, except that O2 was obtained and LiOH, Sr(OH)2, and the above composite oxide were mixed so that the molar ratio of Li, Ni, Al, and Co to Sr was 1.03:1:0.001. The composition of the obtained positive electrode active material was LiNi 0.87 Al 0.04 Co 0.09 Sr 0.001 It was O2. This was used as the positive electrode active material in Example 2.

[0060] <Comparative Example 2> LiOH and composite oxides (Ni 0.87 Al 0.04 Co 0.09 A positive electrode active material was obtained in the same manner as in Example 2, except that O2) was mixed with Li so that the molar ratio of Li to the total amount of Ni, Al, and Co was 1.03:1. The composition of the obtained positive electrode active material was LiNi 0.87 Al 0.04 Co 0.09 It was O2. This was used as the positive electrode active material for Comparative Example 2.

[0061] <Example 3> [Ni 0.92 Al 0.05 Co 0.01 Mn 0.02(OH)₂ complex hydroxide was used to obtain a complex oxide (Ni 0.92 Al 0.05 Co 0.01 Mn 0.02 O₂). A positive electrode active material was obtained in the same manner as in Example 1, except that LiOH, Sr(OH)₂, and the above complex oxide were mixed so that the molar ratio of Li, the total amount of Ni, Al, Co, and Mn, and Sr was 1.03:1:0.0007 to obtain a mixture. The composition of the obtained positive electrode active material was LiNi 0.92 Al 0.05 Co 0.01 Mn 0.02 Sr 0.0007 O₂. This was used as the positive electrode active material of Example 3.

[0062] <Comparative Example 3> LiOH and a complex oxide (Ni 0.92 Al 0.05 Co 0.01 Mn 0.02 O₂) were mixed to obtain a mixture in the same manner as in Example 3, except that the molar ratio of Li to the total amount of Ni, Al, Co, and Mn was adjusted to 1.03:1. The composition of the obtained positive electrode active material was LiNi 0.92 Al 0.05 Co 0.01 Mn 0.02 O₂. This was used as the positive electrode active material of Comparative Example 3.

[0063] <Example 4> [Ni 0.91 Al 0.05 Mn 0.04 (OH)₂ complex hydroxide was used to obtain a complex oxide (Ni 0.91 Al 0.05 Mn 0.04 O₂). A positive electrode active material was obtained in the same manner as in Example 1, except that LiOH, Sr(OH)₂, and the above complex oxide were mixed so that the molar ratio of Li, the total amount of Ni, Al, and Mn, and Sr was 1.03:1:0.0015 to obtain a mixture. The composition of the obtained positive electrode active material was LiNi 0.91 Al 0.05 Mn 0.04 Sr 0.0015It was O2. This was used as the positive electrode active material of Example 4.

[0064] <Comparative Example 4> LiOH and composite oxide (Ni 0.91 Al 0.05 Mn 0.04 O2) were mixed so that the molar ratio of Li to the total amount of Ni, Al, and Mn was 1.03:1 to obtain a mixture, and then a positive electrode active material was obtained in the same manner as in Example 4. The composition of the obtained positive electrode active material was LiNi 0.91 Al 0.05 Mn 0.04 O2. This was used as the positive electrode active material of Comparative Example 4.

[0065] <Example 5> [Ni 0.92 Al 0.06 Mn 0.02 (OH)2-represented composite hydroxide was used to obtain a composite oxide (Ni 0.92 Al 0.06 Mn 0.02 O2), and LiOH, Sr(OH)2, and the above composite oxide were mixed so that the molar ratio of Li to the total amount of Ni, Al, and Mn and Sr was 1.03:1:0.0018 to obtain a mixture, and then 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 0.92 Al 0.06 [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​ [Ni 0.60 Co 0.21 Mn 0.19 Using a composite hydroxide represented by ](OH)2, a composite oxide (Ni 0.60 Co 0.21 Mn 0.19 A positive electrode active material was obtained in the same manner as in Example 1, except that O2 was obtained and LiOH, Sr(OH)2, and the above composite oxide were mixed so that the molar ratio of the total amount of Li, Ni, Co, and Mn to Sr was 1.03:1:0.001. The composition of the obtained positive electrode active material was LiNi 0.60 Co 0.21 Mn 0.19 Sr 0.001 It was O2. This was used as the positive electrode active material for Comparative Example 6.

[0068] <Comparative Example 7> LiOH and composite oxides (Ni 0.60 Co 0.21 Mn 0.19 A positive electrode active material was obtained in the same manner as in Comparative Example 6, except that O2) was mixed with Li so that the molar ratio of Li to the total amount of Ni, Co, and Mn was 1.03:1. The composition of the obtained positive electrode active material was LiNi 0.60 Co 0.21 Mn 0.19 It was O2. This was used as the positive electrode active material for Comparative Example 7.

[0069] TEM-EDX measurements were performed on the positive electrode active materials of Examples 1-5 and Comparative Examples 1-7, and compositional analysis was conducted on the internal and surface layers of the lithium transition metal composite oxide, as well as the surface modification layer. Since Sr could not be quantified, its presence or absence was analyzed based on the presence or absence of peaks. In addition, the residual Li content of the positive electrode active materials of Examples 1-5 and Comparative Examples 1-7 was measured. The results are shown in Table 1.

[0070] [Table 1]

[0071] In Examples 1-5, the Al content of the surface modification layer was higher than that of the main body and the surface layer. On the other hand, this trend was not observed in Comparative Examples 1-5. In Examples 1-5, the Al content of the surface modification layer was higher than that of the surface layer, indicating the presence of Al in the surface modification layer. However, in Comparative Examples 1-5, the Al content of the surface modification layer and the surface layer were similar, suggesting that the Al content was influenced by the composition of the adjacent surface layer, and therefore Al is not present in the surface modification layer. Furthermore, in Examples 1-5 and Comparative Example 6, where Sr was added, Sr was detected only in the surface modification layer and not in the surface layer or the main body. In all samples, the composition of the surface modification layer was influenced by the composition of the adjacent surface layer, and it is considered that Ni, Co, and Mn are not present in the surface modification layer. In addition, residual Li was detected in all samples.

[0072] Next, test cells were prepared using the positive electrode active materials of Examples 1-5 and Comparative Examples 1-7 as follows.

[0073] [Fabrication of the positive electrode] 91 parts by mass of the positive electrode active materials from Examples 1-5 and Comparative Examples 1-7, 7 parts by mass of acetylene black as a conductive material, and 2 parts by mass of polyvinylidene fluoride as a binder were mixed, and this mixture was then 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 15 μm thick aluminum foil, and after the coating film was dried, the coating film was rolled using a rolling mill and cut to 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. An exposed portion was provided on a part of the positive electrode in which the surface of the positive electrode core was exposed. Positive electrodes were prepared in the same manner for the other examples and comparative examples.

[0074] [Fabrication of the 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 in a solid content mass ratio of 100:1:1 to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, and after the coating film was dried, the coating film was rolled using a rolling mill and cut to a predetermined electrode size to obtain a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core. An exposed portion was provided on a part of the negative electrode in which the surface of the negative electrode core was exposed.

[0075] [Preparation of non-aqueous electrolytes] Ethylene carbonate (EC), methyl ethyl carbonate (MEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluoride phosphate (LiPF6) was dissolved in this mixed solvent to a concentration of 1.2 mol / liter to prepare a non-aqueous electrolyte.

[0076] [Preparation of test cells] Aluminum leads were attached to the exposed portion of the positive electrode containing the positive electrode active material of Examples 1-5 and Comparative Examples 1-7, and nickel leads were attached to the exposed portion of the negative electrode. The positive and negative electrodes were then wound in a spiral shape via a polyolefin separator to create a wound electrode body. This electrode body was housed in an outer casing, the non-aqueous electrolyte was injected, and the opening of the outer casing was sealed to obtain a test cell.

[0077] [Evaluation of capacity retention rate] The following cycle tests were performed on batteries fabricated by incorporating the positive electrodes containing the positive electrode active materials of Examples 1-5 and Comparative Examples 1-7. The discharge capacity at the first cycle and the discharge capacity at the 100th cycle were determined, and the capacity retention rate was calculated using the following formula.

[0078] Capacity retention rate (%) = (Discharge capacity at 100 cycles ÷ Discharge capacity at 1 cycle) amount)×100 <Cycle Testing> The test cell was charged with a constant current of 0.5It at a temperature of 45°C until the battery voltage reached 4.2V, and then charged with a constant voltage until the current value was 1 / 50It at 4.2V. After that, it was discharged with a constant current of 0.5It until the battery voltage reached 2.5V. This charge-discharge cycle was repeated 100 times.

[0079] The volume retention rates for Examples 1-5 and Comparative Examples 1-7 are shown in Tables 2-7. The residual Li content is also listed in Tables 2-7. The volume retention rate of the test cell in Example 1 shown in Table 2 is expressed relatively, with the volume retention rate of the test cell in Comparative Example 1 set to 100%.

[0080] The capacity retention rates of the test cells in Example 2, shown in Table 3, are expressed relatively, with the capacity retention rate of the test cells in Comparative Example 2 set to 100%.

[0081] The capacity retention rates of the test cells in Example 3 shown in Table 4 are expressed relatively, with the capacity retention rate of the test cells in Comparative Example 3 set to 100%.

[0082] The capacity retention rates of the test cells in Example 4, shown in Table 5, are expressed relatively, with the capacity retention rate of the test cells in Comparative Example 4 set to 100%.

[0083] The volume retention rates of the test cells in Example 5 shown in Table 6 are expressed relatively, with the volume retention rate of the test cells in Comparative Example 5 set to 100%.

[0084] The volume retention rates of the test cells in Comparative Example 7, shown in Table 7, are expressed relatively, with the volume retention rate of the test cells in Comparative Example 6 set to 100%.

[0085] [Table 2]

[0086] [Table 3]

[0087] [Table 4]

[0088] [Table 5]

[0089] [Table 6]

[0090] [Table 7]

[0091] In all of Tables 2 to 6, the examples containing Sr in the surface modification layer had a higher capacity retention rate than the comparative examples that did not contain Sr in the surface modification layer. It is also presumed that Al is contained in greater amounts in the surface layer than in the main body, and that some of the Al is contained in the surface modification layer. In Table 7, since neither Comparative Example 6 nor Comparative Example 7 contained Al in the lithium transition metal composite oxide, there was no change in capacity retention rate with or without the addition of Sr. [Explanation of Symbols]

[0092] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Outer casing, 17 Sealing body, 18,19 Insulating plate, 20 Positive electrode tab, 21 Negative electrode tab, 22 Grooved section, 23 Bottom plate, 24 Lower valve body, 25 Insulating material, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 31 Positive electrode active material layer, 40 Negative electrode current collector, 41 Negative electrode active material layer

Claims

1. A first step to obtain a composite oxide containing Al and Ni, A second step involves mixing the composite oxide obtained in the first step with a lithium compound and a strontium compound to obtain a mixture. A third step is to calcine the mixture in order to obtain a lithium transition metal composite oxide having a surface modification layer containing at least Sr on the lithium transition metal composite oxide, which contains 80 mol% or more of Ni relative to the total number of moles of metal elements other than Li, A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: The third step is, A first firing step in which the mixture is fired under an oxygen stream to a first set temperature of 450°C to 680°C at a first heating rate, A second firing step in which the mixture is fired under an oxygen stream to a second set temperature of over 680°C and up to 800°C at a second heating rate, Includes, The second heating rate is slower than the first heating rate. The third step is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the surface modification layer is formed on the surface of primary particles of a lithium transition metal composite oxide.

2. In the second step described above, the strontium compound is Sr(OH) ２ , Sr(OH) ２ 8H ２ O, SrO, SrCo ３ , SrSO ４ , and Sr(NO ３ ) ２ A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is selected from at least one of the following.

3. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein in the second step, the mixing ratio of the composite oxide obtained in the first step and the strontium compound is such that the molar ratio of metal elements excluding Li to Sr is in the range of 1:0.0005 to 1:0.0018.

4. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the third step further comprises washing the calcined product with water after the first calcination step and the second calcination step.

5. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein in the third step, the first heating rate is in the range of 1.5°C / min or more and 5.5°C / min or less.

6. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein in the third step, the second heating rate is in the range of 0.1°C / min or more and 3.5°C / min or less.

7. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein in the third step, after reaching the first set temperature, the first set temperature is maintained for 0 hours or more and 5 hours or less.

8. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein in the third step, after reaching the second set temperature, the second set temperature is maintained for 1 hour or more and 10 hours or less.

9. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, wherein the Sr is not solid-dissolved in the lithium transition metal composite oxide.

10. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 9, wherein the surface modification layer further contains Al.

11. The lithium transition metal composite oxide has the general formula Li ａ Ni ｘ Al ｙ Co ｚ M ｗ O ２－ｂ (where 0.95 < a < 1.05, 0.8 ≤ x ≤ 0.96, 0 < y ≤ 0.10, 0 ≤ z ≤ 0.15, 0 ≤ w ≤ 0.1, 0 ≤ b < 0.05, x + y + z + w = 1, and M is at least one element selected from Mn, Fe, Ti, Si, Nb, Zr, Mo, and Zn). A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 10.

12. The lithium transition metal composite oxide comprises a surface layer located on the interior side of the surface and a main body located on the interior side of the surface layer, wherein the ratio of Al to the total number of moles of metal elements excluding Li in the surface modification layer is greater than the ratio of Al to the total number of moles of metal elements excluding Li in the main body, according to any one of claims 1 to 11.

13. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 12, wherein the ratio of Al to the total number of moles of metal elements excluding Li in the surface layer is 1.3 times or more the ratio of Al to the total number of moles of metal elements excluding Li in the main body.

14. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 13, wherein the proportion of Sr in the surface modification layer is 0.05 mol% to 0.25 mol% with respect to the total number of moles of metal elements excluding Li in the surface modification layer.

15. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 14, wherein the ratio of Ni to the total number of moles of metal elements other than Li in the lithium transition metal composite oxide is 90 mol% or more.

16. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 15, wherein the amount of Li remaining on the surface of the lithium transition metal composite oxide is 0.03 wt% to 0.08 wt%.

17. A method for manufacturing a non-aqueous electrolyte secondary battery, comprising manufacturing a battery using a positive electrode prepared by the method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 16, a negative electrode, and a non-aqueous electrolyte.

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