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

Abstract

A positive electrode active material for nonaqueous electrolyte secondary batteries according to one embodiment of the present disclosure comprises first lithium nickel oxide particles that have an average particle diameter of 8 μm to 30 μm inclusive, and second lithium nickel oxide particles that have an average particle diameter of 6 μm or less. A sulfonic acid compound represented by general formula I is present on the surfaces of the second lithium nickel oxide particles. If X mass% is the ratio of the mass of a sulfonic acid compound that is present on the surfaces of the first lithium nickel oxide particles to the mass of the first lithium nickel oxide particles and Y mass% is the ratio of the mass of the sulfonic acid compound that is present on the surfaces of the second lithium nickel oxide particles to the mass of the second lithium nickel oxide particles, X and Y satisfy the relational expression Y > X. (In the formula, A represents a group 1 element or a group 2 element; R represents a hydrocarbon group; and n is 1 or 2.)

Description

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

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

[0002] Lithium-containing composite oxides containing transition metals such as Ni, Co, and Mn have been used as high-capacity positive electrode active materials. For example, Patent Document 1 discloses a technology for improving battery capacity and rate characteristics by using a positive electrode active material in which two lithium cobalt oxides having different compositions and average particle sizes are mixed in a predetermined volume ratio.

[0003] Japanese Patent Application Laid-Open No. 2006-156004

[0004] However, the technology disclosed in Patent Document 1 uses a positive electrode active material with a relatively small average particle size, which can cause gas generation inside the battery after storage in a high-temperature environment, resulting in issues with battery reliability. For example, forming a coating layer on the surface of the positive electrode active material to suppress gas generation can result in a decrease in charge capacity. Patent Document 1 does not consider achieving both high-temperature storage characteristics and charge capacity of the battery, and there is still room for improvement.

[0005] An object of the present disclosure is to provide a positive electrode active material that enables a battery to achieve both high-temperature storage characteristics and charge capacity.

[0006] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises first lithium nickel oxide particles having an average particle size of 8 μm or more and 30 μm or less, and second lithium nickel oxide particles having an average particle size of 6 μm or less, wherein a sulfonic acid compound represented by general formula I is present on the surface of the second lithium nickel oxide particles, and wherein, when the ratio of the mass of the sulfonic acid compound present on the surface of the first lithium nickel oxide particles to the mass of the first lithium nickel oxide particles is X% by mass, and the ratio of the mass of the sulfonic acid compound present on the surface of the second lithium nickel oxide particles to the mass of the second lithium nickel oxide particles is Y% by mass, X and Y satisfy the relationship Y>X. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by including a positive electrode containing the above-described positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte.

[0008] According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, it is possible to improve the high-temperature storage characteristics of the non-aqueous electrolyte secondary battery while suppressing a decrease in the charge capacity.

[0009] 1 is a longitudinal cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention;

[0010] In recent years, non-aqueous electrolyte secondary batteries have come to be used in a variety of applications, and there is an increasing demand for improved battery characteristics. As described in Patent Document 1, high capacity can be achieved by using a mixture of two types of lithium-containing composite oxides with different average particle sizes as a positive electrode active material. However, a positive electrode active material with a relatively small average particle size has a large surface area per mass, making it more susceptible to reaction with a non-aqueous electrolyte. This can lead to gas generation inside the battery after storage in a high-temperature environment, which can cause issues with battery reliability. After extensive research to solve the above problem, the inventors discovered that by using first lithium-nickel oxide particles with an average particle size of 8 μm to 30 μm and second lithium-nickel oxide particles with an average particle size of 6 μm or less, and disposing a larger amount of sulfonic acid compound in the second lithium-nickel oxide particles than in the first lithium-nickel oxide particles, both high-temperature storage characteristics and charge capacity of the battery can be achieved.

[0011] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below. Hereinafter, a cylindrical battery in which a wound electrode assembly is housed in a cylindrical exterior body will be exemplified. However, the electrode assembly is not limited to the wound type and may be a laminated type in which multiple positive electrodes and multiple negative electrodes are alternately stacked one by one with separators interposed therebetween. Furthermore, the exterior body is not limited to a cylindrical shape and may be, for example, prismatic or coin-shaped, or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0012] Fig. 1 is a longitudinal 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 (not shown), 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.

[0013] The electrode assembly 14 is composed of a strip-shaped positive electrode 11, a strip-shaped negative electrode 12, two strip-shaped 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 in the longitudinal direction and width direction (short direction) than the positive electrode 11. The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11, for example.

[0014] The nonaqueous electrolyte secondary battery 10 includes insulating plates 18, 19 disposed above and below the electrode assembly 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, while a negative electrode tab 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom of the outer can 16. The positive electrode tab 20 is connected to the underside 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 the 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 the negative electrode terminal.

[0015] The outer can 16 is, for example, a cylindrical metal container with a bottom. A gasket 28 is provided between the outer can 16 and the sealing body 17, sealing the internal space of the battery case 15. The outer can 16 has a groove 22 that supports the sealing body 17, formed, for example, by pressing the side surface from the outside. The groove 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its upper surface.

[0016] The sealing body 17 has a structure in which, in order from the electrode body 14 side, a bottom plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for 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, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0017] The positive electrode 11, negative electrode 12, separator 13, and nonaqueous electrolyte that constitute the nonaqueous electrolyte secondary battery 10 will be described in detail below, particularly the positive electrode active material contained in the positive electrode mixture layer 31 that constitutes the positive electrode 11.

[0018] [Positive Electrode] The positive electrode 11 includes, for example, a positive electrode current collector 30 and a positive electrode mixture layer 31 formed on the surface of the positive electrode current collector 30. The positive electrode mixture layer 31 is preferably formed on both sides of the positive electrode current collector 30. The positive electrode current collector 30 may be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on its surface. The positive electrode mixture layer 31 may include a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture 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 mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like to the surface of the positive electrode current collector 30, drying the coating, and then rolling the coating to form the positive electrode mixture layer 31 on both sides of the positive electrode current collector 30.

[0019] Examples of the conductive agent contained in the positive electrode mixture layer 31 include carbon-based materials such as carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphene, and graphite. These may be used alone or in combination of two or more. The content of the conductive agent in the positive electrode mixture layer 31 is, for example, 0.1 mass % or more and 10 mass % or less with respect to the total mass of the positive electrode mixture layer 31.

[0020] Examples of the binder contained in the positive electrode mixture layer 31 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, and polyolefin-based resins. These may be used alone or in combination of two or more. The content of the binder in the positive electrode mixture layer 31 is, for example, 0.1% by mass or more and 10% by mass or less with respect to the total mass of the positive electrode mixture layer 31.

[0021] The positive electrode active material contained in the positive electrode mixture layer 31 includes first lithium nickel oxide particles and second lithium nickel oxide particles having an average particle size smaller than that of the first lithium nickel oxide particles. This increases the packing density of the positive electrode active material in the positive electrode mixture layer 31, thereby improving battery capacity. The average particle size refers to the volume-based median diameter (D50) of the secondary particles. D50 refers to the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, and is also called the median diameter. The particle size distribution of the lithium nickel oxide particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0022] The first lithium nickel oxide particles have an average particle size of 8 μm to 30 μm, preferably 8 μm to 25 μm, and more preferably 10 μm to 20 μm, and the second lithium nickel oxide particles have an average particle size of 6 μm or less, preferably 0.5 μm to 6 μm, and more preferably 1 μm to 6 μm.

[0023] In the first lithium nickel oxide particles, the value of (D90 - D10) / average particle size is, for example, 0.6 or less. As a result, the first lithium nickel oxide particles have a sharp particle size distribution. In the second lithium nickel oxide particles, the value of (D90 - D10) / average particle size is, for example, 1.0 or less. As a result, the second lithium nickel oxide particles have a sharp particle size distribution. When both the first lithium nickel oxide particles and the second lithium nickel oxide particles have a sharp particle size distribution, the effects of the present disclosure become more pronounced. The D10 and D90 of the lithium nickel oxide particles refer to the particle sizes at which the cumulative frequency in the volume-based particle size distribution is 10% and 90%, respectively, from the smallest particle size. The D10 and D90 of the lithium nickel oxide particles can be calculated from the particle size distribution of the lithium nickel oxide particles in the same manner as the above-mentioned average particle size (D50).

[0024] The first lithium nickel oxide particles and the second lithium nickel oxide particles each include, for example, secondary particles formed by aggregation of primary particles. The particle size of the primary particles constituting the secondary particles of the first lithium nickel oxide particles is, for example, 0.02 μm or more and 1 μm or less. The particle size of the primary particles constituting the secondary particles of the second lithium nickel oxide particles is, for example, 0.02 μm or more and 1 μm or less. The particle size of the primary particles of the lithium nickel oxide particles is calculated by measuring the diameters of the circumscribed circles of 100 primary particles extracted by analyzing SEM images of the cross sections of the secondary particles and averaging the measured values.

[0025] The second lithium nickel oxide particles may be single primary particles (single crystal particles) or secondary particles formed by agglomeration of 2 to 5 primary particles.

[0026] The mass ratio of the first lithium-nickel oxide particles to the second lithium-nickel oxide particles contained in the positive electrode mixture layer 31 is, for example, 50:50. The mass ratio (X) of the first lithium-nickel oxide particles to the second lithium-nickel composite oxide is not limited to 50:50, but it is preferable that there is not much difference in the added amounts from the viewpoint of increasing capacity, etc. Specifically, the mass ratio (X) is preferably 90:10≦X≦50:50, and more preferably 80:20≦X≦60:40.

[0027] The lithium nickel oxide particles 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, a layered structure belonging to the space group R-3m is preferred in terms of high capacity, stability of the crystal structure, etc.

[0028] The first lithium-nickel oxide particles and the second lithium-nickel oxide particles each preferably contain 50 mol% or more of Ni, more preferably 80 mol% or more, and even more preferably 90% or more, relative to the total molar amount of metal elements excluding Li. The Co content is preferably low. This enhances the effects of the present application. The compositions of the first lithium-nickel oxide particles and the second lithium-nickel oxide particles may differ from each other. For example, the difference in Ni content between the large particles and the small particles may be within 20%, the difference in Co content may be within 20%, and the difference in Mn content may be within 20%. For example, the Ni content of the small particles may be changed by 2 to 10% and the Co content may be changed by 2 to 10% relative to the large particles. By reducing the Ni content of the small particles by 2 to 10% and increasing the Co content by 2 to 10% relative to the large particles, for example, by substituting 5% Ni for Co, durability during cycling and the amount of gas generation during high-temperature storage may be reduced. Reducing the Ni content of small particles by 2 to 10% and increasing the Mn content by 2 to 10% compared to large particles can improve the thermal stability of the battery. Increasing the Ni content of small particles by 2 to 10% and decreasing the Co content by 2 to 10% compared to large particles can improve capacity. Increasing the Ni content of small particles by 2 to 10% and decreasing the Mn content by 2 to 10% compared to large particles can improve capacity. When changing the Ni content of small particles compared to large particles, the Co and Mn contents may be changed simultaneously, or may be replaced with Me, etc., as described below. For large particles, the Mn and Co contents may be changed without changing the Ni content of small particles. For example, replacing Co with Mn (e.g., 5%) can improve safety. Replacing Mn with Co (e.g., 2%) can improve output.

[0029] The lithium nickel oxide particles can be, for example, of the general formula Li ａ Ni ｘ Co ｙMn ｚ Me ｗ O ｂ (wherein 0.8≦a≦1.2, 0.5≦x≦0.96, 0≦y≦0.3, 0≦z≦0.4, 0≦w≦0.1, 1.9≦b≦2.1, x+y+z+w=1, and Me represents one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, Ca, Sr, and B. The mole fraction of the metal elements contained in the lithium nickel oxide particles can be measured, for example, by inductively coupled plasma (ICP) atomic emission spectrometry.

[0030] The sulfonic acid compound represented by general formula I is present on the surface of the second lithium nickel oxide particles. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0031] When the ratio of the mass of the sulfonic acid compound present on the surface of the first lithium nickel oxide particles to the mass of the first lithium nickel oxide particles is X% by mass, and the ratio of the mass of the sulfonic acid compound present on the surface of the second lithium nickel oxide particles to the mass of the second lithium nickel oxide particles is Y% by mass, X and Y satisfy the relationship Y>X. The sulfonic acid compound does not have to be present on the surface of the first lithium nickel oxide particles. This can improve the high-temperature storage characteristics while suppressing a decrease in the charge capacity of the non-aqueous electrolyte secondary battery. By disposing a large amount of the sulfonic acid compound on the surface of the second lithium nickel oxide particles, which have higher activity than the first lithium nickel oxide particles, gas generation can be suppressed. Furthermore, by reducing the amount of the sulfonic acid compound present on the surface of the first lithium nickel oxide particles to a level that does not adversely affect the amount of gas generation, a decrease in charge capacity can be suppressed.

[0032] For example, Y satisfies Y≦1. The lower limit of Y is, for example, 0.1. Furthermore, X satisfies, for example, 0≦X≦0.5. Y / X preferably satisfies 1.5≦Y / X, and more preferably 10≦Y / X. The upper limit of Y / X is, for example, 50.

[0033] X and Y are measured, for example, as follows: (1) The total amount of S element contained in the positive electrode mixture layer 31 is quantified by ICP. (2) The surface of the positive electrode mixture layer 31 is observed by an electron probe microanalyzer (EPMA), and the diameters of the first lithium nickel oxide particles and the second lithium nickel oxide particles and the amount of sulfonic acid compound present on the surfaces of the first lithium nickel oxide particles and the second lithium nickel oxide particles are calculated. Thirty first lithium nickel oxide particles and 30 second lithium nickel oxide particles are measured. (3) The ratio of sulfonic acid compound present on the surfaces of the first lithium nickel oxide particles and the second lithium nickel oxide particles is calculated from the results of the EPMA analysis, and this is multiplied by the total amount of S element obtained from the ICP analysis results to calculate X and Y.

[0034] In the above general formula I, A is preferably a Group 1 element, more preferably Li. This can further suppress the decrease in charge capacity. When A is a Group 1 element, n=1.

[0035] In general formula I, R is preferably an alkyl group. R is more preferably an alkyl group having 5 or less carbon atoms, even more preferably an alkyl group having 3 or less carbon atoms, and particularly preferably a methyl group. In addition, in R, some of the hydrogen atoms bonded to the carbon may be substituted with fluorine. However, in R, not all of the hydrogen atoms bonded to the carbon atoms are substituted with fluorine. The smaller the molecular weight of R, the more effectively the decrease in charging capacity can be suppressed.

[0036] Examples of sulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, magnesium methanesulfonate, and lithium fluoromethanesulfonate.

[0037] The presence of the sulfonic acid compound on the surface of the lithium nickel oxide particles can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectrum obtained by FT-IR, the lithium nickel oxide particles exhibit a peak at 1238 cm －１, 1175 cm －１ , 1065 cm －１ , 785 cm －１ It may have an absorption peak at at least one point in the vicinity.

[0038] In the infrared absorption spectrum obtained by FT-IR, for example, lithium nickel oxide particles containing lithium methanesulfonate have a peak at 1238 cm －１ , 1175 cm －１ , 1065 cm －１ , 785 cm －１ It has an absorption peak around 1238 cm －１ , 1175 cm －１ , 1065 cm －１ The peak around 785 cm is an absorption peak due to the SO stretching vibration of lithium methanesulfonate. －１ The peak in the vicinity is an absorption peak due to the C-S stretching vibration derived from lithium methanesulfonate.

[0039] In lithium nickel oxide particles containing sulfonic acid compounds other than lithium methanesulfonate, absorption peaks derived from the sulfonic acid compounds contained in the lithium nickel oxide particles can be identified, similar to lithium nickel oxide particles containing lithium methanesulfonate. The presence of sulfonic acid compounds on the surface of the lithium nickel oxide particles can also be confirmed by ICP, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), synchrotron XRD measurement, TOF-SIMS, etc.

[0040] A metal compound may be present on the surface of the lithium nickel oxide particles. The metal compound contains, for example, one or more metal elements selected from the group consisting of Sr, Ca, W, Zr, rare earth elements, and Al. Examples of the Sr-containing compound include SrO, Sr(OH), and the like. ２ and SrCO ３ Examples of compounds containing Ca include CaO and Ca(OH). ２ and CaCO ３ Examples of compounds containing W include WO ３ Examples of the compound containing Al include Al ２ O ３Examples of compounds containing Zr include ZrO ２ , Zr(OH) ４ , Zr(CO ３ ) ２ and Zr(SO ４ ) ２ ・4H ２ Examples of rare earth-containing compounds include oxides, hydroxides, carbonates, sulfates, nitrates, and phosphates of rare earth elements. The metal compound may contain a plurality of types of these metal elements, and examples thereof include CaWO ４ , SrWO ４ , SrAlO ４ , CaAlO ４ The metal compound may further contain Li, and an example thereof is lithium tungstate.

[0041] A non-metallic compound may be present on the surface of the lithium nickel oxide particles. The non-metallic compound contains, for example, one or more non-metallic elements selected from the group consisting of P and B. Examples of the P-containing compound include Li, ３－ｘ H ｘ P.O. ４ (0≦x≦3) can be exemplified. ３ BO ３ , Li ３ BO ３ , Li ２ B ４ O ７ , LiBO ２ In particular, it is preferable that a boron compound is present on the surface.

[0042] Next, an example of a method for producing the positive electrode active material according to this embodiment will be described. The method for producing the positive electrode active material includes, for example, a synthesis step, a washing step, a drying step, and an addition step.

[0043] In the synthesis step, a metal oxide containing 25 mol% to 96 mol% of Ni, 15 mol% to 40 mol% of Co, and 5 mol% to 50 mol% of Mn is mixed with a Li compound and calcined to obtain lithium nickel oxide. The average particle size of the first lithium nickel oxide particles and the second lithium nickel oxide particles can be adjusted by the size of the metal hydroxide and conditions such as the temperature and time during calcination.

[0044] The metal oxide can be obtained, for example, by adding an alkaline solution such as sodium hydroxide dropwise to a stirred solution of a metal salt containing Ni, Co, Mn, and an optional metal element (e.g., Al, Fe), adjusting the pH to the alkaline side (e.g., 8.5 to 12.5), thereby precipitating (co-precipitating) a composite hydroxide containing Ni, Co, Mn, and the optional metal element, and then heat-treating the composite hydroxide. The heat-treatment temperature is not particularly limited, but is, for example, in the range of 300°C to 600°C.

[0045] Examples of Li compounds include Li ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２ Examples of suitable metal materials include O, LiH, and LiF. The mixing ratio of the metal oxide and the Li compound is preferably such that the molar ratio of metal elements excluding Li to Li is in the range of 1:0.98 to 1:1.1, in order to facilitate adjustment of the above-mentioned parameters to the ranges specified above. When mixing the metal oxide and the Li compound, other metal materials may be added as needed. Here, the other metal materials refer to oxides or the like containing metal elements other than the metal elements constituting the metal oxide.

[0046] The mixture of metal oxide and Li compound is fired, for example, in an oxygen atmosphere. The firing conditions may include a heating rate of more than 1.0°C / min and less than 5.5°C / min from 450°C to 680°C, and a maximum temperature of 700°C to 850°C. The heating rate from over 680°C to the maximum temperature may be, for example, 0.1°C / min to 3.5°C / min. The maximum temperature may be maintained for 1 hour to 10 hours. This firing process may be a multi-stage firing process, and multiple first and second heating rates may be set for each temperature range as long as they are within the above-specified ranges.

[0047] In the washing step, the first lithium-nickel oxide particles and the second lithium-nickel oxide particles prepared in the synthesis step are washed with water and dehydrated to obtain a cake-like composition. The washing and dehydration can be performed by a known method and under known conditions, as long as they are performed within a range that does not cause lithium to leach out of the lithium-nickel oxide particles and deteriorate the battery characteristics.

[0048] In the drying step, the cake-like composition obtained in the washing step is dried to obtain a powdery composition. The drying step may be performed under a vacuum atmosphere. The drying conditions are, for example, 150°C to 400°C and 0.5 hours to 15 hours. When preparing a second lithium nickel oxide composed of single particles, the powdery composition may be further pulverized using a jet mill or the like.

[0049] In the addition step, at least one of a sulfonic acid compound and a sulfonic acid solution is added to the cake-like composition obtained in the washing step or the powder-like composition obtained in the drying step. This allows the sulfonic acid compound to adhere to the surfaces of the lithium nickel oxide particles. It is preferable to add at least one of a sulfonic acid compound and a sulfonic acid solution to the cake-like composition. The sulfonic acid compound may be in either powder or solution form. The sulfonic acid solution is, for example, a methanesulfonic acid solution obtained by dissolving methanesulfonic acid in water. Li compounds remain in the cake-like composition, and these remaining Li compounds are dissolved in the water contained in the cake-like composition. Therefore, even when a sulfonic acid solution is added, a Li-containing sulfonic acid compound is formed. From the viewpoint of more easily achieving the effects of the present application, a Li compound or a Li compound solution may be added to the cake-like composition or the powder-like composition together with the sulfonic acid solution. Alternatively, a mixed solution in which a sulfonic acid solution and a Li compound or a Li compound solution are premixed may be added to the cake-like composition or the powder-like composition. The Li compound is, for example, LiOH, and the Li compound solution is, for example, a LiOH solution obtained by dissolving LiOH in water. The amounts of the Li compound and sulfonic acid solution added to the cake-like composition preferably satisfy the relationship of 0≦Li compound / sulfonic acid≦1.3 in molar ratio. The amount of sulfonic acid compound or sulfonic acid added is preferably 0.1% by mass or more and 1% by mass or less relative to the mass of lithium nickel oxide. The concentrations of the sulfonic acid solution and the sulfonic acid compound solution are, for example, 0.5% by mass or more and 40% by mass or less. The addition step may be performed during the washing step, after the washing step, during the drying step, or after the drying step, and the timing of the addition can be changed as appropriate.

[0050] A metal compound containing one or more metal elements selected from the group consisting of Sr, Ca, W, Zr, rare earth elements, and Al, and a nonmetallic compound containing one or more nonmetallic elements selected from the group consisting of P and B can be attached to the surface of lithium nickel oxide particles by adding the raw material of the metal compound or nonmetallic compound during or after the synthesis process, during or after the washing process, during or after the drying process, or during the addition process. The Sr raw material is Sr(OH). ２ , Sr(OH) ２ ・8H ２ O, SrO, SrCo ３ , SrSO ４ , Sr(NO ３ ) ２、 SrCl ２ , SrAlO ４ Examples of Ca raw materials include Ca(OH) ２ , CaO, CaCO ３ , CaSO ４ , Ca(NO ３ ) ２、 CaCl ２ , CaAlO ４ The Zr raw material is Zr(OH) ４ , ZrO ２ , Zr(CO ３ ) ２ , Zr(SO ４ ) ２ ・4H ２ These metal compounds may be pulverized to appropriately change the particle size, and the amount of water, including hydrates, may be adjusted before use. Examples of rare earth raw materials include oxides, hydroxides, carbonates, etc. of rare earth elements. Examples of W raw materials include tungsten oxide (WO ３ ), lithium tungstate (Li ２ WO ４ , Li ４ WO ５ , Li ６ W ２ O ９ As the W raw material, a solution containing W may be used. As the Al raw material, Al ２ O ３、 Al(OH) ３、 Al２ (SO ４ ) ３ The P raw material may be Al derived from lithium nickel oxide. ３－ｘ H ｘ P.O. ４ (0≦x≦3) and the like. ３ BO ３ , Li ３ BO ３ , Li ２ B ４ O ７ , LiBO ２ In addition, when the liquid raw material is added after the drying step, a heat treatment may be carried out to evaporate the water.

[0051] [Negative Electrode] The negative electrode 12 includes, for example, a negative electrode current collector 40 and a negative electrode mixture layer 41 formed on the surface of the negative electrode current collector 40. The negative electrode mixture layer 41 is preferably formed on both sides of the negative electrode current collector 40. The negative electrode current collector 40 may be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film having such a metal disposed on the surface. The negative electrode mixture layer 41 may include a negative electrode active material and a binder. The thickness of the negative electrode mixture 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 mixture slurry containing a negative electrode active material, a binder, etc. to the surface of the negative electrode current collector 40, drying the coating, and then rolling the coating to form the negative electrode mixture layer 41 on both sides of the negative electrode current collector 40.

[0052] The negative electrode active material contained in the negative electrode mixture layer 41 is not particularly limited as long as it can reversibly absorb 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, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, as the negative electrode active material, metals that alloy with Li, such as Si and Sn, metal compounds containing Si, Sn, and lithium-titanium composite oxides, may also be used. Furthermore, these may be provided with a carbon coating. For example, SiO ｘ (0.5≦x≦1.6) or Li ２ｙSiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2) may be used in combination with graphite.

[0053] Examples of the binder contained in the negative electrode mixture layer 41 include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0054] [Separator] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a laminated structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin, or a filler layer containing an inorganic compound filler may be provided on the surface of the separator 13.

[0055] [Non-aqueous electrolyte] The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0056] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0057] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0058] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as ethyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0059] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２ Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 to 1.8 mol per liter of the non-aqueous solvent.

[0060] The non-aqueous electrolyte may contain an additive such as an unsaturated carbonate ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, a sulfate compound, a borate ester compound, a phosphate ester compound, or a phosphite ester compound.

[0061] Examples of unsaturated cyclic carbonates include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. Some of the hydrogen atoms in the unsaturated cyclic carbonate may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by intermolecular condensation of multiple carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0062] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0063] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanatomethylcyclohexane (BIMCH). Examples of sultone compounds include propane sultone and propene sultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethyl phosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethyl phosphite and tris(trimethylsilyl)phosphite.

[0064] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0065] 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.

[0066] <Example 1> [Preparation of Positive Electrode Active Material] <Preparation of First Lithium Nickel Oxide Particles> The average particle size (D50) was 16 μm and the composition was LiNi ０．８５ Co ０．０５ Mn ０．１０ O ２Lithium nickel oxide particles represented by the formula (1) were prepared. The lithium nickel oxide particles had a (D90-D10) / average particle size ratio of 0.47 and a sharp particle size distribution. Water was added to the above to give a slurry concentration of 1500 g / L, and the mixture was stirred for 15 minutes and filtered to obtain a cake-like composition (washing step). Powdered lithium methanesulfonate was added to this cake-like composition (addition step). The amount of lithium methanesulfonate added was 0.1% by mass relative to the mass of the lithium nickel oxide particles. After the addition step, a drying step was performed under conditions of 180°C for 2 hours in a vacuum atmosphere to obtain first lithium nickel oxide particles. Note that the presence of lithium methanesulfonate on the surface of the first lithium nickel oxide particles was confirmed by Fourier transform infrared spectroscopy (FT-IR).

[0067] <Preparation of second lithium nickel oxide particles> The average particle size (D50) is 4 μm and the composition is LiNi ０．８５ Co ０．０５ Mn ０．１０ O ２ Lithium nickel oxide particles represented by the formula (1) were prepared. The lithium nickel oxide particles had a (D90-D10) / average particle size ratio of 0.90 and a sharp particle size distribution. Water was added to the above to adjust the slurry concentration to 1500 g / L, and the mixture was stirred for 15 minutes and filtered to obtain a cake-like composition (washing step). Powdered lithium methanesulfonate was added to this cake-like composition (addition step). The amount of lithium methanesulfonate added was 0.5% by mass relative to the mass of the lithium nickel oxide particles. After the addition step, a drying step was performed under conditions of 180°C for 2 hours in a vacuum atmosphere to obtain second lithium nickel oxide particles. The presence of lithium methanesulfonate on the surface of the positive electrode active material was confirmed by Fourier transform infrared spectroscopy (FT-IR).

[0068] [Preparation of Positive Electrode] The first lithium nickel oxide particles and the second lithium nickel oxide particles were mixed in a mass ratio of 5:5 to form a positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 92:5:3, and a positive electrode mixture slurry was prepared using N-methyl-2-pyrrolidone (NMP) as a dispersion medium. The positive electrode mixture slurry was then applied to a positive electrode current collector made of aluminum foil. The coating was dried and compressed, and the positive electrode current collector was then cut to a predetermined electrode size to obtain a positive electrode having a positive electrode mixture layer disposed on both sides of the positive electrode current collector. An exposed portion was provided in a portion of the positive electrode, exposing the surface of the positive electrode current collector. Furthermore, Y / X = 5.

[0069] [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 (LiPF ６ ) was dissolved in the solution to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0070] [Preparation of Test Cell] The above-mentioned positive electrode and a negative electrode made of lithium metal were stacked facing each other with a separator interposed therebetween to prepare an electrode assembly. The electrode assembly and the above-mentioned non-aqueous electrolyte were then inserted into an aluminum coin-shaped outer casing and sealed by crimping with a press to prepare a test cell. Test cells for other Examples and Comparative Examples were prepared in the same manner.

[0071] [Evaluation of gas generation amount] The test cell was charged at a constant current of 0.2 C in a temperature environment of 25 ° C until the cell voltage reached 4.3 V (vs. Li), and then charged at a constant voltage of 4.3 V (vs. Li) until the current value reached 0.02 C. After 20 minutes, the cell voltage was discharged at a constant current of 0.2 C to 2.5 V (vs. Li), and the battery volume (V0) was calculated by Archimedes' method. Thereafter, the cell was again charged at a constant current of 0.2 C in a temperature environment of 25 ° C until the cell voltage reached 4.3 V (vs. Li), and then charged at a constant voltage of 4.3 V (vs. Li) until the current value reached 0.02 C. After leaving the cell for 3 days under conditions of a temperature of 80 ± 2 ° C, the cell voltage was discharged at a constant current of 0.2 C to 2.5 V (vs. Li) in a temperature environment of 25 ° C. Thereafter, the volume of the battery (V1) was calculated by Archimedes' method in the same manner as for V0, and the amount of gas generated was calculated as follows: ΔV (mL) = V1 (mL) - V0 (mL). The smaller the amount of gas generated, the better the high-temperature storage characteristics.

[0072] [Evaluation of Initial Charge Capacity] The test cell was charged at a constant current of 0.2 C in a temperature environment of 25° C. until the cell voltage reached 4.3 V (vs. Li), then charged at a constant voltage of 4.3 V (vs. Li) until the current value reached 0.02 C, and further discharged at a constant current of 0.2 C until the cell voltage reached 2.5 V (vs. Li). The charge capacity at this time was defined as the initial charge capacity.

[0073] Example 2 A test cell was prepared and evaluated in the same manner as in Example 1, except that in preparing the second lithium nickel oxide particles, the amount of lithium methanesulfonate added was 1 mass % relative to the mass of the lithium nickel oxide particles.

[0074] Example 3 A test cell was prepared and evaluated in the same manner as in Example 1, except that in the preparation of the first lithium nickel oxide particles, the amount of lithium methanesulfonate added was 0.3 mass % relative to the mass of the lithium nickel oxide particles.

[0075] Example 4 A test cell was produced and evaluated in the same manner as in Example 1, except that the addition step was not carried out in the production of the first lithium nickel oxide particles.

[0076] Example 5 In the preparation of the first lithium nickel oxide particles, the addition step was not carried out, and boric acid H ３ BO ３ A test cell was prepared in the same manner as in Example 1, except that 0.5 mass % of the compound was added and the mixture was heat-treated at 300° C. for 10 hours in an oxygen atmosphere, and then the test cell was evaluated.

[0077] Example 6 In the preparation of the first lithium nickel oxide particles, boric acid H ３ BO ３ A test cell was prepared in the same manner as in Example 1, except that 0.3 mass % of was added and heat treatment was carried out at 300° C. for 10 hours in an oxygen atmosphere, and evaluation was carried out.

[0078] Example 7 In the preparation of the second lithium nickel oxide particles, the composition of the lithium nickel oxide particles was changed to LiNi ０．８０ Co ０．１０ Mn ０．１０ O ２ A test cell was prepared and evaluated in the same manner as in Example 1, except for the above change.

[0079] Comparative Example 1 A test cell was produced and evaluated in the same manner as in Example 1, except that the addition step was not carried out in the production of the first lithium nickel oxide particles and the second lithium nickel oxide particles.

[0080] Comparative Example 2 A test cell was prepared and evaluated in the same manner as in Example 1, except that in the preparation of the first lithium nickel oxide particles, the amount of lithium methanesulfonate added relative to the mass of the lithium nickel oxide particles was 0.5% by mass, and in the preparation of the second lithium nickel oxide particles, the amount of lithium methanesulfonate added relative to the mass of the lithium nickel oxide particles was 0.1% by mass, where Y / X was 0.2.

[0081] <Comparative Example 3> A test cell was prepared and evaluated in the same manner as in Example 1, except that in the preparation of the first lithium nickel oxide particles, the amount of lithium methanesulfonate added was 0.5 mass% relative to the mass of the lithium nickel oxide particles.

[0082] Comparative Example 4 A test cell was prepared and evaluated in the same manner as in Example 1, except that a positive electrode active material prepared by the following procedure was used: (1) A positive electrode having an average particle size (D50) of 10 μm and a composition of LiNi ０．８５ Co ０．０５ Mn ０．１０ O ２ Lithium nickel oxide particles represented by the formula (1) were prepared. The lithium nickel oxide particles had a (D90-D10) / average particle size ratio of 1.20 and a broad particle size distribution. (2) Water was added to the above to adjust the slurry concentration to 1500 g / L, and the mixture was stirred for 15 minutes and filtered to obtain a cake-like composition (washing step). (3) Powdered lithium methanesulfonate was added to the cake-like composition (addition step). The amount of lithium methanesulfonate added was 0.5% by mass relative to the mass of the lithium nickel oxide particles. After the addition step, a drying step was performed under vacuum at 180°C for 2 hours to obtain a positive electrode active material. The presence of lithium methanesulfonate on the surface of the positive electrode active material was confirmed by Fourier transform infrared spectroscopy (FT-IR).

[0083] Example 8 A test cell was prepared and evaluated in the same manner as in Example 1, except that lithium nickel oxide particles composed of single particles were used in the preparation of the second lithium nickel oxide particles. The lithium nickel oxide particles had an average particle size (D50) of 4 μm and a composition of LiNi ０．８５ Co ０．０５ Mn ０．１０ O ２ Furthermore, the lithium nickel oxide particles have a value of (D90-D10) / average particle size of 0.88, and have a sharp particle size distribution.

[0084] Comparative Example 5 A test cell was produced and evaluated in the same manner as in Example 7, except that the addition step was not carried out in the production of the first lithium nickel oxide particles and the second lithium nickel oxide particles.

[0085] Examples 9 to 12, Comparative Examples 6 to 9 Examples 9 to 13 correspond to Examples 1 to 4, and Comparative Examples 6 to 9 correspond to Comparative Examples 1 to 4. In the preparation of the first lithium nickel oxide particles and the preparation of the second lithium nickel oxide particles, the composition of the lithium nickel oxide particles was changed to LiNi ０．５０ Co ０．２０ Mn ０．３０ O ２ Test cells were prepared and evaluated in the same manner as in the corresponding Examples or Comparative Examples, except that the addition step was changed to the addition step without performing the washing step and the addition step was performed by adding a lithium methanesulfonate solution to the lithium nickel oxide particles. The concentration of the added lithium methanesulfonate solution was 10 mass %, and the lithium methanesulfonate solution was added so that the amount of lithium methanesulfonate added was the value shown in Table 3.

[0086] Example 13 and Comparative Example 10 Example 13 corresponds to Example 8, and Comparative Example 10 corresponds to Comparative Example 5. In the preparation of the first lithium nickel oxide particles and the preparation of the second lithium nickel oxide particles, the composition of the lithium nickel oxide particles was changed to LiNi ０．５０ Co ０．２０ Mn ０．３０ O ２ Test cells were prepared and evaluated in the same manner as in the corresponding Examples or Comparative Examples, except for the above changes.

[0087] Examples 14 to 16, Comparative Examples 11 to 14 Examples 14 to 16 correspond to Examples 1 to 3, and Comparative Examples 11 to 14 correspond to Comparative Examples 1 to 4. In the preparation of the first lithium nickel oxide particles and the preparation of the second lithium nickel oxide particles, the composition of the lithium nickel oxide particles was changed to LiNi ０．９２ Co ０．０４ Mn ０．０４ O ２ Test cells were prepared and evaluated in the same manner as in the corresponding Examples or Comparative Examples, except for the above changes.

[0088] Examples 17 to 19 and Comparative Examples 15 to 18 Examples 17 to 19 correspond to Examples 1 to 3, and Comparative Examples 15 to 18 correspond to Comparative Examples 1 to 4. In the preparation of the first lithium nickel oxide particles and the preparation of the second lithium nickel oxide particles, the composition of the lithium nickel oxide particles was changed to LiNi ０．９０ Mn ０．１０ O ２ Test cells were prepared and evaluated in the same manner as in the corresponding Examples or Comparative Examples, except for the above changes.

[0089] The evaluation results of the test cells of Examples 1 to 7 and Comparative Examples 1 to 4 are shown in Table 1. The gas generation amount and initial charge capacity of the test cells of Examples 1 to 7 and Comparative Examples 2 to 4 are expressed relative to the gas generation amount and initial charge capacity of the test cell of Comparative Example 1, which are set to 100.

[0090] The evaluation results of the test cells of Example 8 and Comparative Example 5 are shown in Table 2. The gas generation amount and initial charge capacity of the test cell of Example 8 are expressed relative to the gas generation amount and initial charge capacity of the test cell of Comparative Example 5, which are set to 100.

[0091] The evaluation results of the test cells of Examples 9 to 12 and Comparative Examples 6 to 9 are shown in Table 3. The gas generation amounts and initial charge capacities of the test cells of Examples 9 to 12 and Comparative Examples 7 to 9 are expressed relative to the gas generation amount and initial charge capacity of the test cell of Comparative Example 6, which are set to 100.

[0092] The evaluation results of the test cells of Example 13 and Comparative Example 10 are shown in Table 4. The gas generation amount and initial charge capacity of the test cell of Example 13 are expressed relative to the gas generation amount and initial charge capacity of the test cell of Comparative Example 10, which are set to 100.

[0093] The evaluation results of the test cells of Examples 14 to 16 and Comparative Examples 11 to 14 are shown in Table 5. The gas generation amounts and initial charge capacities of the test cells of Examples 14 to 16 and Comparative Examples 12 to 14 are expressed relative to the gas generation amount and initial charge capacity of the test cell of Comparative Example 11, which are set to 100.

[0094] The evaluation results of the test cells of Examples 17 to 19 and Comparative Examples 15 to 18 are shown in Table 6. The gas generation amounts and initial charge capacities of the test cells of Examples 17 to 19 and Comparative Examples 16 to 18 are expressed relative to the gas generation amount and initial charge capacity of the test cell of Comparative Example 15, which are set to 100.

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101] In Table 1, the test cells of the examples maintained the same initial charge capacity as Comparative Example 1, while generating less gas than Comparative Example 1. On the other hand, none of Comparative Examples 2 to 4 generated less gas than Comparative Example 1, while maintaining the same initial charge capacity as Comparative Example 1. This shows that by using first lithium-nickel oxide particles and second lithium-nickel oxide particles having a predetermined average particle size and disposing a larger amount of sulfonic acid compound in the second lithium-nickel oxide particles than in the first lithium-nickel oxide particles, it is possible to achieve both high-temperature storage characteristics and charge capacity of the battery. Furthermore, the results of Tables 2 to 6 show that similar effects can be obtained even if the compositions of the first lithium-nickel oxide particles and second lithium-nickel oxide particles are changed.

[0102] The present disclosure is further described by the following embodiments: Configuration 1: A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising first lithium nickel oxide particles having an average particle size of 8 μm or more and 30 μm or less, and second lithium nickel oxide particles having an average particle size of 6 μm or less, wherein a sulfonic acid compound represented by general formula I is present on the surfaces of the first lithium nickel oxide particles, and when the ratio of the mass of the sulfonic acid compound present on the surfaces of the first lithium nickel oxide particles to the mass of the first lithium nickel oxide particles is X mass %, and the ratio of the mass of the sulfonic acid compound present on the surfaces of the second lithium nickel oxide particles to the mass of the second lithium nickel oxide particles is Y mass %, X and Y satisfy the relationship Y > X. (wherein A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.) Configuration 2: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein A is a Group 1 element. Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein A is Li. Configuration 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein R is an alkyl group. Configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein R is a methyl group. Configuration 6: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein Y satisfies Y≦1. Configuration 7: In an infrared absorption spectrum, －１ , 1175 cm －１ , 1065 cm －１ , 785 cm －１ The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 6, wherein the positive electrode active material for a non-aqueous electrolyte secondary battery has an absorption peak at at least one position near the positive electrode active material for a non-aqueous electrolyte secondary battery. Configuration 8: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 7, wherein the first lithium nickel oxide particles and the second lithium nickel oxide particles each contain 50 mol % or more of Ni relative to the total molar amount of metal elements excluding Li. Configuration 9: A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 8, a negative electrode, and a non-aqueous electrolyte.

[0103] REFERENCE SIGNS LIST 10 Non-aqueous 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 electrode tab, 21 Negative electrode tab, 22 Grooved portion, 23 Bottom plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 31 Positive electrode mixture layer, 40 Negative electrode current collector, 41 Negative electrode mixture layer

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery comprising first lithium nickel oxide particles having an average particle size of 8 μm or more and 30 μm or less, and second lithium nickel oxide particles having an average particle size of 6 μm or less, wherein a sulfonic acid compound represented by general formula I is present on the surface of the second lithium nickel oxide particles, and when a ratio of the mass of the sulfonic acid compound present on the surface of the first lithium nickel oxide particles to the mass of the first lithium nickel oxide particles is X mass %, and a ratio of the mass of the sulfonic acid compound present on the surface of the second lithium nickel oxide particles to the mass of the second lithium nickel oxide particles is Y mass %, X and Y satisfy the relationship Y>X. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.) 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein A is a Group 1 element.

3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein A is Li.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein R is an alkyl group.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein R is a methyl group.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein Y satisfies Y≦1.

7. In the infrared absorption spectrum, 1238 cm －１ , 1175 cm －１ , 1065cm －１ , 785 cm －１ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, having an absorption peak at at least one position in the vicinity of said positive electrode active material.

8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first lithium-nickel oxide particles and the second lithium-nickel oxide particles each contain 50 mol % or more of Ni relative to the total molar amount of metal elements excluding Li.

9. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 8, a negative electrode, and a non-aqueous electrolyte.

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