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

Abstract

The present invention provides a positive electrode active material for nonaqueous electrolyte secondary batteries, the positive electrode active material being capable of improving the initial efficiency. This positive electrode active material for nonaqueous electrolyte secondary batteries, which is contained in a nonaqueous electrolyte secondary battery, comprises a lithium transition metal composite oxide and a sulfonic acid compound that is present on the surface of the lithium transition metal composite oxide. The lithium transition metal composite oxide is a secondary particle that has a layered structure and contains 75% by mole or more of Ni with respect to the total number of moles of metal elements excluding Li. In the element concentration distribution of a cross-section of the secondary particle as determined using time-of-flight secondary ion mass spectrometry, the Gini coefficient on the secondary particle surface of SO3- is 0.7 or less. (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] In recent years, the applications of non-aqueous electrolyte secondary batteries have expanded to include power sources for electric vehicles and power storage devices for utilizing natural energy. The characteristics required of the positive electrode active material used in non-aqueous electrolyte secondary batteries also vary depending on the application. For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery that uses, as a positive electrode active material, a lithium transition metal composite oxide having a low-solubility Li salt scattered on its surface, with the aim of reducing reaction resistance during storage at high temperatures.

[0003] Japanese Patent Application Laid-Open No. 2019-169286

[0004] In non-aqueous electrolyte secondary batteries, improving the initial charge / discharge efficiency is an important issue. The technology described in Patent Document 1 does not consider improving the initial efficiency, and there is still room for improvement.

[0005] An object of the present disclosure is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that enables improvement in initial efficiency.

[0006] A positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a lithium transition metal composite oxide and a sulfonic acid compound present on the surface of the lithium transition metal composite oxide, the lithium transition metal composite oxide being secondary particles having a layered structure and containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and the positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a lithium transition metal composite oxide and a sulfonic acid compound present on the surface of the lithium transition metal composite oxide. The lithium transition metal composite oxide has a layered structure and is a secondary particle containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and the element concentration distribution of the cross section of the secondary particle obtained by time-of-flight secondary ion mass spectrometry shows that the positive electrode active material ３－ The Gini coefficient of the secondary particle surface is 0.7 or less. (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 positive electrode active material for a non-aqueous electrolyte secondary battery according to another embodiment of the present disclosure includes a lithium transition metal composite oxide and a sulfonic acid compound present on a surface of the lithium transition metal composite oxide, the lithium transition metal composite oxide being secondary particles having a layered structure and containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and the positive electrode active material for a non-aqueous electrolyte secondary battery according to another embodiment of the present disclosure includes a lithium transition metal composite oxide and a sulfonic acid compound present on a surface of the lithium transition metal composite oxide. The lithium transition metal composite oxide has a layered structure and is a secondary particle containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and the positive electrode active material for a non-aqueous electrolyte secondary battery according to another embodiment of the present disclosure includes a lithium transition metal composite oxide and a sulfonic acid compound present on a surface of the lithium transition metal composite oxide. ３－ The Gini coefficient inside the secondary particles is 0.6 or less. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0008] A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes a positive electrode containing the above-described positive electrode active material, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode contains S.

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

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

[0011] As described above, improving the initial efficiency of non-aqueous electrolyte secondary batteries is an important issue. The present inventors have made a sulfonic acid compound present on the particle surface of a predetermined lithium transition metal oxide, and have found that the sulfonic acid compound has a SO ３－ By dispersing the sulfonic acid compound uniformly until the Gini coefficient of the depth mapping intensity ratio distribution is 0.7 or less, the protective effect of the coating containing the sulfonic acid compound is significantly exhibited, and Li ＋ The inventors have found that this facilitates the insertion / desorption of the ions, thereby improving the initial efficiency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0012] An example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail below. In the following description, specific numerical values, materials, and designs may be used as examples. However, other numerical values, materials, and designs may be used as long as the effects of the present disclosure are obtained. A cylindrical battery in which a wound electrode assembly is housed in a cylindrical exterior body will be exemplified below. 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, rectangular or coin-shaped, or may be a battery case made of a laminate sheet including a metal layer and a resin layer.

[0013] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. As shown in FIG. 1 , the secondary battery 10 includes a wound electrode assembly 14, an electrolyte, and an exterior body 16 that accommodates the electrode assembly 14 and the electrolyte. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The exterior body 16 is a cylindrical metal container with a bottom and an opening on one axial side, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the battery will be referred to as the top, and the bottom side of the exterior body 16 will be referred to as the bottom.

[0014] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode assembly 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and alternately stacked in the radial direction of the electrode assembly 14. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal and lateral directions. The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The electrode assembly 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the lateral direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the end faces in the lateral direction of the positive electrode 11 and the negative electrode 12 form the end faces in the axial direction of the electrode body 14 .

[0015] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom side of the exterior body 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the exterior body 16 by welding or the like, and the exterior body 16 serves as the negative electrode terminal.

[0016] A gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior body 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior body 16 by the grooved portion 22 and the open end of the exterior body 16 that is crimped to the sealing body 17.

[0017] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. 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 one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0018] The positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte that constitute the secondary battery 10 will be described in detail below, with the positive electrode 11 being particularly described below.

[0019] [Positive Electrode] The positive electrode 11 includes, for example, a positive electrode core and a positive electrode mixture layer formed on the surface of the positive electrode core. The positive electrode mixture layer is preferably formed on both sides of the positive electrode core. The positive electrode core 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 with such a metal disposed on the surface. The thickness of the positive electrode core is, for example, 10 μm to 30 μm. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode current collector. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the surface of the positive electrode current collector, drying the coating, and then rolling it to form a positive electrode mixture layer on both sides of the positive electrode current collector.

[0020] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphene, graphite, and other carbon-based materials. These may be used alone or in combination of two or more. The content of the conductive agent in the positive electrode mixture layer is, for example, 0.1% by mass or more and 10% by mass or less with respect to the total mass of the positive electrode mixture layer.

[0021] Examples of binders contained in the positive electrode mixture layer 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 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.

[0022] The positive electrode active material contained in the positive electrode mixture layer 31 includes a particulate lithium transition metal composite oxide. The lithium transition metal composite oxide particles include, for example, secondary particles formed by aggregation of primary particles. The particle size of the primary particles is, for example, 0.02 μm or more and 2 μm or less. The particle size of the primary particles is measured as the diameter of a circumscribed circle in a particle image observed with a scanning electron microscope (SEM). The average particle size of the secondary particles is, for example, 2 μm or more and 30 μm or less. Here, the average particle size refers to the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0023] The lithium transition metal composite oxide particles include, for example, single particles or secondary particles formed by agglomeration of 2 to 1,000 single particles. The average particle size of the single particles is preferably 0.5 μm to 5 μm, more preferably 0.7 μm to 4 μm. Since single particles function in the same way as secondary particles, the term "secondary particles" hereinafter includes single particles.

[0024] The lithium transition metal composite oxide has a layered structure. Examples of the layered structure of the lithium transition metal composite oxide include a layered structure belonging to the space group R-3m and a layered structure belonging to the space group C2 / m. From the viewpoints of increasing capacity and crystalline structure stability, the lithium transition metal composite oxide preferably has a layered structure belonging to the space group R-3m. The layered structure of the lithium transition metal composite oxide may include a transition metal layer, a Li layer, and an oxygen layer.

[0025] The lithium transition metal composite oxide contains 75 mol% or more of Ni relative to the total number of moles of metal elements excluding Li. This allows for a high capacity battery. The Ni content is, for example, 80 mol% or more and 98 mol% or less. The lithium transition metal composite oxide may contain, in addition to Ni, one or more elements selected from the group consisting of Co, Al, and Mn. The contents of Co, Al, and Mn in the lithium transition metal composite oxide are each, for example, 0 mol% or more and 25 mol% or less relative to the total number of moles of metal elements excluding Li. Furthermore, the total content of Co, Al, and Mn is, for example, 0 mol% or more and 25 mol% or less.

[0026] The lithium transition metal composite oxide is, for example, a compound represented by the general formula Li ａ Ni ｘ M1 ｙ M2 ｚ O ２－ｂ (wherein 0.8≦a≦1.2, 0.75≦x≦0.98, 0≦y≦0.25, 0≦z≦0.10, 0≦b≦0.05, x+y+z=1, M1 is one or more elements selected from the group consisting of Co, Al, and Mn, and M2 is one or more elements selected from the group consisting of Sr, Ca, Nb, Ti, Zr, and W). The proportion of metal elements contained in the lithium transition metal composite oxide can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0027] The lithium transition metal composite oxide is produced through a first step of synthesizing a transition metal composite hydroxide containing Ni, Co, Mn, Al, and the like by, for example, a coprecipitation method, a second step of heat-treating the composite hydroxide to obtain a transition metal composite oxide, and a third step of mixing the composite oxide with lithium hydroxide and firing the mixture.

[0028] In the third step, the mixture is fired at a temperature of 650°C or higher. The preferred firing temperature range is 650°C or higher and 1100°C or lower. The firing is preferably carried out in an oxygen stream. In the third step, from the viewpoint of discharge capacity, an excess of lithium source (lithium hydroxide) is used relative to the stoichiometric ratio of the target product. For example, a stoichiometric ratio of 1 to 1.1 times that of the composite oxide is preferred. Furthermore, by adjusting the firing conditions, the particle size of the primary particles can be adjusted, and single particles can also be produced. For example, the particle size of the single particles can be increased by increasing the maximum temperature.

[0029] The positive electrode active material contains, in addition to a lithium transition metal composite oxide, a sulfonic acid compound represented by the following general formula I: The sulfonic acid compound is present on the surface of the lithium transition metal composite oxide. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0030] In the element concentration distribution of the secondary particle cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry, SO ３－ The Gini coefficient of the secondary particle surface may be 0.7 or less, preferably 0.6 or less, and more preferably 0.5 or less. This improves the initial efficiency. ３－ is detected due to sulfonic acid compounds, so SO ３－ The smaller the Gini coefficient on the surface of the secondary particles, the more uniformly the sulfonic acid compound is dispersed on the surface of the secondary particles. ３－ The Gini coefficient of the secondary particle surface is, for example, 0.1 or more.

[0031] In the element concentration distribution of the secondary particle cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry, SO ３－The Gini coefficient inside the secondary particles may be 0.6 or less, preferably 0.55 or less, and more preferably 0.5 or less. This improves the initial efficiency. ３－ is detected due to sulfonic acid compounds, so SO ３－ The smaller the Gini coefficient inside the secondary particles, the more uniformly the sulfonic acid compound is dispersed inside the secondary particles. ３－ The Gini coefficient inside the secondary particle is, for example, 0.1 or more.

[0032] SO ３－ The Gini coefficient of the secondary particle surface is the SO ３－ The normalized intensity I ＳＯ３－＿ＯＵＴ When the cumulative rate is expressed in order of intensity, the area between the diagonal line and the Lorenz curve is doubled. ３－ The Gini coefficient inside the secondary particle is the SO ３－ The normalized intensity I ＳＯ３－＿ＩＮ The Gini coefficient is the value obtained by doubling the area enclosed between the diagonal line and the Lorenz curve when the cumulative rate is expressed in order of intensity. The Gini coefficient is 0 in the case of complete uniformity, and increases as the uniformity decreases. ３－ The Gini coefficient inside the secondary particle of SO ３－ The Gini coefficient of the secondary particle surface may be smaller than that of SO ３－ The Gini coefficient of the secondary particle surface may be equal to or greater than SO ３－ The Gini coefficient inside the secondary particle of SO ３－ When the Gini coefficient on the secondary particle surface is equal to or greater than this, the effect of the present invention may be significantly exhibited.

[0033] SO ３－ The normalized intensity ratio of the primary ions is obtained by measurement under the following conditions using a time-of-flight secondary ion mass spectrometer (TOF-SIMS5 manufactured by IONTOF). ３ ＋ Ion voltage: 30 kV Ion current: 0.03 pA @ 100 us Observation range: 50 μm x 50 μm Mass range: 60 us (up to 310 amu) Detection: 4 frames / scan, 150 scans

[0034] The Ni and SO obtained in the above measurements ３－ The image showing the density distribution of Ni and SO is divided into 256 × 256 pixels. ３－ Furthermore, the detection intensity of SO relative to the detection intensity of Ni is calculated. ３－ The ratio of the detected intensities of ３－ The normalized intensity I ＳＯ３－ It is calculated as follows.

[0035] The area from the surface of the secondary particle recognized from the image to the inside by 0.5 μm is defined as the surface of the secondary particle, and the pixels included in the surface of this secondary particle (hereinafter referred to as surface pixels) are determined. ＳＯ３－ The set of ＳＯ３－＿ＯＵＴ The area inside the secondary particle surface defined above is defined as the interior of the secondary particle, and the pixels included in the interior of this secondary particle (hereinafter referred to as "interior pixels") are defined. ＳＯ３－ The set of ＳＯ３－＿ＩＮ It becomes. ＳＯ３－＿ＯＵＴ and I ＳＯ３－＿ＩＮ From the above, the SO ３－ Gini coefficient of the particle size and the SO ３－ The sample for cross-section observation may be a sample in which a lithium transition metal composite oxide is embedded in a resin or the like, or may be a positive electrode mixture layer containing a lithium transition metal composite oxide.

[0036] In the above general formula I, A is preferably a Group 1 element, more preferably Li. This can further reduce the DC resistance. Note that when A is a Group 1 element, n=1.

[0037] In general formula I, R is preferably an alkyl group. R is more preferably an alkyl group having 5 or less carbon atoms, further 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 atoms 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 smaller the DC resistance can be.

[0038] Examples of sulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, magnesium methanesulfonate, and lithium fluoromethanesulfonate.

[0039] The amount of the sulfonic acid compound contained in the positive electrode 11 is preferably 0.1% by mass to 1.5% by mass, more preferably 0.25% by mass to 1.0% by mass, relative to the mass of the lithium transition metal composite oxide.

[0040] The presence of the sulfonic acid compound in the positive electrode 11 can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectrum obtained by FT-IR, the positive electrode 11 exhibits 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.

[0041] In the infrared absorption spectrum obtained by FT-IR, for example, the positive electrode 11 containing lithium methanesulfonate has 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.

[0042] In the case of the positive electrode 11 containing a sulfonic acid compound other than lithium methanesulfonate, an absorption peak derived from the sulfonic acid compound can be identified, similar to the case of the positive electrode 11 containing lithium methanesulfonate. The presence of the sulfonic acid compound in the positive electrode 11 can also be confirmed by ICP, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), synchrotron XRD measurement, TOF-SIMS, or the like.

[0043] A metal compound may be present on the surface of the lithium transition metal composite oxide. 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 ３ Examples 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 SrAlO ４ , CaAlO ４ The metal compound may further contain Li, and an example thereof is lithium tungstate.

[0044] A nonmetallic compound may be present on the surface of the lithium transition metal composite oxide. The nonmetallic compound contains, for example, one or more nonmetallic 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 Examples include:

[0045] The positive electrode active material can be prepared, for example, by adding a sulfonic acid solution to a lithium transition metal composite oxide and adhering the sulfonic acid compound to the surface of the lithium transition metal composite oxide (addition step). The lithium transition metal composite oxide may be subjected to a washing step and a drying step.

[0046] In the washing step, the lithium transition metal composite oxide is washed with water and dehydrated to obtain a cake-like composition. The washing and dehydration can be performed by known methods and under known conditions. The washing and dehydration should be performed within a range that does not cause lithium to leach out of the lithium transition metal composite oxide and degrade the battery characteristics. Since the positive electrode active material according to this embodiment has been washed with water, the amount of residual alkaline components is small.

[0047] 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. Drying conditions are, for example, 150°C to 400°C for 0.5 hours to 15 hours. A heat treatment may be performed after the drying step. The heating temperature is, for example, 100°C to 450°C. The heat treatment may be performed after the crushing step described below.

[0048] The powder composition obtained in the drying step can be crushed to obtain single particles. A jet mill or the like can be used for crushing. Crushing using a jet mill can be performed using, for example, a PJM-80 (manufactured by Nippon Pneumatic Co., Ltd.) under the following conditions: Compressed air consumption: 0.5 Nm ３ / min Supply gas pressure: 0.53 MPa Processing capacity: 2000 g / hour

[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 surface of the lithium transition metal composite oxide. 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 to 1% by mass, and more preferably 0.3% by mass to 0.8% by mass, relative to the mass of the lithium transition metal composite oxide. The concentrations of the sulfonic acid solution and the sulfonic acid compound solution are, for example, 0.5% by mass to 40% by mass. 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] By adding at least one of a sulfonic acid compound and a sulfonic acid solution to a cake-like composition or a powder-like composition and then mixing, the dispersibility of the sulfonic acid compound on the surface and inside of the lithium transition metal composite oxide is improved. ３－This mixing may be carried out using a mixer at a rotation speed of 10 rpm to 100 rpm for 0.1 to 60 minutes.

[0051] 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 the lithium transition metal composite oxide 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 Examples of rare earth raw materials include oxides, hydroxides, and carbonates 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 ９As the W raw material, a solution containing W may be used. As the Al raw material, Al ２ O ３、 Al(OH) ３、 Al ２ (SO ４ ) ３ The P raw material may be Al derived from a lithium transition metal composite 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 These compounds may be pulverized to appropriately change the particle size, or the water content of the hydrates may be adjusted before use.

[0052] The positive electrode mixture layer may contain other positive electrode active materials in addition to the positive electrode active material of the present embodiment, such as a positive electrode active material containing a lithium transition metal composite oxide with an Ni content of less than 75 mol %, or a positive electrode active material in which no sulfonic acid compound is present on the surface of the lithium transition metal composite oxide.

[0053] [Negative Electrode] The negative electrode 12 may have, for example, a negative electrode core and a negative electrode mixture layer formed on the surface of the negative electrode core, or a metal Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode core, and lithium metal may be deposited on the surface of the negative electrode core upon charging. When the negative electrode 12 has a negative electrode mixture layer, the negative electrode mixture layer is preferably formed on both sides of the negative electrode core. The negative electrode core may be a foil of a metal stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with such a metal disposed on the surface. The thickness of the negative electrode core is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode core. 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 a negative electrode core, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0054] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly absorb and release lithium ions, and generally, carbon materials such as graphite are used. Graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, metals that alloy with Li, such as Si and Sn, metal compounds containing Si, Sn, and lithium-titanium composite oxides may also be used as the negative electrode active material. Furthermore, those provided with a carbon coating may also be used. For example, SiO ｘ (0.5≦x≦1.6) or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2) may be used in combination with graphite.

[0055] Examples of binders contained in the negative electrode mixture layer include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0056] The negative electrode 12 preferably contains S. This further improves the initial efficiency. For example, by subjecting the secondary battery 10 to an aging treatment, a portion of the S contained in the positive electrode 11 can be transferred to the negative electrode 12. The S content in the negative electrode 12 is, for example, 10 ppm by mass or more and 1000 ppm by mass or less, relative to the total mass of the negative electrode active material. The S content in the negative electrode 12 can be measured, for example, using an inductively coupled plasma (ICP) atomic emission spectrometer (ICP-AES). The aging treatment can be performed, for example, by charging the battery at a constant current of 0.1 C or more and 0.5 C or less for 10 minutes to 60 minutes, and then storing the battery in a temperature environment of 40°C to 80°C for 10 hours to 20 hours.

[0057] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0058] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0059] [Non-aqueous electrolyte] The non-aqueous electrolyte has, for example, lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0060] 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).

[0061] 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).

[0062] 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.

[0063] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less, per 1 L of the non-aqueous solvent.

[0064] 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.

[0065] 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.

[0066] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0067] 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.

[0068] 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.

[0069] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the following examples.

[0070] <Example 1-1> [Preparation of Positive Electrode Active Material] Nickel-cobalt-aluminum composite hydroxide ([Ni ０．９０ Co ０．０５ Al ０．０５ ] (OH) ２) was calcined at 500°C for 8 hours to synthesize a composite oxide containing Ni, Co, and Al. The composite oxide was mixed with LiOH in a molar ratio of 1:1.02, and the mixture was calcined at 800°C for 3 hours in an oxygen stream to obtain a lithium transition metal composite oxide. The lithium transition metal composite oxide was in the form of secondary particles formed by aggregation of primary particles.

[0071] Water was added to the lithium transition metal composite oxide to a slurry concentration of 1500 g / L, stirred for 15 minutes, and filtered to obtain a cake-like composition (washing step). Powdered lithium methanesulfonate was added to this cake-like composition, and the mixture was mixed for 10 minutes at 25 rpm using a mixer (T.K. Hibismix, manufactured by Primix Corporation) (addition step). The amount of lithium methanesulfonate added was 0.5 mass% relative to the total mass of the lithium transition metal composite oxide. After the addition step, a drying step was performed under vacuum at 180°C for 2 hours to obtain the positive electrode active material of Example 1. Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of lithium methanesulfonate on the surface of the positive electrode active material. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was used to measure the element concentration distribution in the cross section of the positive electrode active material, revealing that SO ３－ The Gini coefficients on the surface and inside of the secondary particles were 0.39 and 0.52, respectively. Furthermore, the positive electrode active material was measured using an inductively coupled plasma (ICP) atomic emission spectrometer (ICP-AES). As a result, the elements other than Li and O were confirmed to be present, as shown in Table 1 below.

[0072] [Preparation of Positive Electrode] 92 parts by mass of the above positive electrode active material, 5 parts by mass of acetylene black (AB), and 3 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode core made of aluminum foil, and after drying the coating, the coating was rolled with a rolling roller and cut to a predetermined electrode size to prepare a positive electrode. In addition, an exposed portion in which the surface of the positive electrode core was exposed was provided in a part of the positive electrode.

[0073] [Preparation of Negative Electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and lithium methanesulfonate were mixed in an aqueous solution at a solids mass ratio of 100:1:1:0.08 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, and after drying the coating, the coating was rolled with a rolling roller and cut to a predetermined electrode size to prepare a negative electrode. Note that an exposed portion was provided in part of the negative electrode, exposing the surface of the negative electrode core. The sulfur content of the negative electrode was measured using an inductively coupled plasma (ICP) atomic emission spectrometer (ICP-AES), and was found to be 250 ppm by mass relative to the total mass of the negative electrode active material.

[0074] [Preparation of non-aqueous electrolyte] A mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4 was added to a non-aqueous electrolyte solution containing lithium hexafluorophosphate (LiPF ６ ) was dissolved in the solution to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0075] [Preparation of Test Cell] A positive electrode lead was attached to the exposed portion of the positive electrode, and a negative electrode lead was attached to the exposed portion of the negative electrode. The positive and negative electrodes were spirally wound with a polyolefin separator interposed therebetween, and then pressed radially to prepare a flat wound electrode assembly. This electrode assembly was housed in an exterior body made of an aluminum laminate sheet, and the nonaqueous electrolyte was poured into it. The opening of the exterior body was then sealed to obtain a test cell.

[0076] [Evaluation of Initial Efficiency] The test cell was charged at a constant current of 0.2 C in a temperature environment of 25°C until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 C. After leaving the cell to stand for 1 hour, constant current discharge was performed at a constant current of 0.2 C until the battery voltage reached 2.5 V. The initial efficiency was calculated from the charge capacity and discharge capacity measured in the above charge / discharge tests using the following formula: Initial efficiency = Discharge capacity / Charge capacity

[0077] Example 1-2 A test cell was produced and evaluated in the same manner as in Example 1-1, except that in the preparation of the positive electrode active material, the mixing time of the cake-like composition and the powdery lithium methanesulfonate was changed to 3 minutes.

[0078] Examples 1-3 to 1-6 Test cells were prepared and evaluated in the same manner as in Example 1-1, except that in preparing the positive electrode active material, a lithium methanesulfonate solution prepared by dissolving lithium methanesulfonate in pure water was added instead of powdered lithium methanesulfonate, and the amount of lithium methanesulfonate added and the mixing time of the cake-like composition and powdered lithium methanesulfonate were changed as shown in Table 1. Fourier transform infrared spectroscopy (FT-IR) confirmed that lithium methanesulfonate was present on the surface of each positive electrode active material.

[0079] Example 1-7 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that in the addition step of preparing the positive electrode active material, a solution containing methanesulfonic acid and LiOH (hereinafter, methanesulfonic acid + LiOH solution) was added, in which methanesulfonic acid and LiOH were dissolved in pure water at a molar ratio of 1:1, instead of powdered lithium methanesulfonate, and the amount of lithium methanesulfonate added relative to the total mass of the lithium transition metal composite oxide was 0.5% by mass. Note that the concentration of the added methanesulfonic acid + LiOH solution was 10% by mass, and the methanesulfonic acid + LiOH solution was added so that the amount of lithium methanesulfonate added was as described above. The presence of lithium methanesulfonate on the surface of the positive electrode active material was confirmed by Fourier transform infrared spectroscopy (FT-IR).

[0080] Example 1-8 A test cell was prepared and evaluated in the same manner as in Example 1-2, except that in the addition step of preparing the positive electrode active material, a solution containing methanesulfonic acid and LiOH (hereinafter, methanesulfonic acid + LiOH solution) was added, in which methanesulfonic acid and LiOH were dissolved in pure water at a molar ratio of 1:1, instead of powdered lithium methanesulfonate, and the amount of lithium methanesulfonate added relative to the total mass of the lithium transition metal composite oxide was 0.5% by mass. Note that the concentration of the added methanesulfonic acid + LiOH solution was 10% by mass, and the methanesulfonic acid + LiOH solution was added so that the amount of lithium methanesulfonate added was as described above. The presence of lithium methanesulfonate on the surface of the positive electrode active material was confirmed by Fourier transform infrared spectroscopy (FT-IR).

[0081] Example 1-9: A test cell was prepared in the same manner as in Example 1-3, and then subjected to the aging treatment described below while evaluating the initial efficiency. After the evaluation, 250 ppm of S was detected in the negative electrode contained in the test cell relative to the total mass of the negative electrode active material. [Evaluation of Initial Efficiency During Aging Treatment] The test cell was charged at 0.2 C for 30 minutes in a 25°C environment and then stored in a 60°C environment for 15 hours. Thereafter, the test cell was again charged at a constant current of 0.2 C in a 25°C environment until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 C. After allowing to stand for 1 hour, constant-current discharge was performed at a constant current of 0.2 C until the battery voltage reached 2.5 V. The initial efficiency was calculated from the charge capacity and discharge capacity measured in the above charge / discharge tests using the following formula: The charge capacity is the sum of the charge capacity when charged at 0.2 C for 30 minutes, the charge capacity when charged at 0.2 C to 4.2 V, and the charge capacity when charged at 4.2 V to 0.02 C. Initial efficiency = discharge capacity / charge capacity

[0082] Example 1-10 A test cell was prepared in the same manner as in Example 1-4, and then subjected to an aging treatment in the same manner as in Example 1-9, while evaluating the initial efficiency. After the evaluation, 400 ppm of S was detected in the negative electrode contained in the test cell relative to the total mass of the negative electrode active material.

[0083] Comparative Example 1-1 A test cell was prepared in the same manner as in Example 1-1, except that the cake-like composition and powdered lithium methanesulfonate were not mixed in the preparation of the positive electrode active material, and then the initial efficiency was evaluated while performing an aging treatment in the same manner as in Example 1-9. After the evaluation, 400 ppm of S was detected in the negative electrode contained in the test cell relative to the total mass of the negative electrode active material.

[0084] Comparative Example 1-2 A test cell was produced and evaluated in the same manner as in Example 1-1, except that the cake-like composition and powdered lithium methanesulfonate were not mixed in the production of the positive electrode active material.

[0085] Example 2-1 [Preparation of Positive Electrode Active Material] A nickel-manganese composite hydroxide ([Ni ０．８０ Mn ０．２０ ] (OH) ２ ) was calcined at 500°C for 8 hours to synthesize a composite oxide containing Ni and Mn. The composite oxide was mixed with LiOH in a molar ratio of 1:1.02, and the mixture was calcined at 900°C for 10 hours in an oxygen stream to obtain a lithium transition metal composite oxide. The lithium transition metal composite oxide was in the form of single particles.

[0086] Water was added to the lithium transition metal composite oxide to a slurry concentration of 1500 g / L, stirred for 15 minutes, and filtered to obtain a cake-like composition (washing step). A lithium methanesulfonate solution prepared by dissolving lithium methanesulfonate in pure water was added to this cake-like composition, and the mixture was mixed for 10 minutes at 25 rpm using a mixer (T.K. Hibismix, manufactured by Primix Corporation) (addition step). The amount of lithium methanesulfonate solution added was 0.25 mass% relative to the total mass of the lithium transition metal composite oxide. After the addition step, a drying step was performed under vacuum at 180°C for 2 hours to obtain the positive electrode active material of Example 2-1. Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of lithium methanesulfonate on the surface of the positive electrode active material. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) was used to measure the element concentration distribution in the cross section of the positive electrode active material, revealing that SO ３－The Gini coefficient on the surface of the positive electrode active material was 0.39. Furthermore, the positive electrode active material was measured using an ICP atomic emission spectrometer (ICP-AES), and the elements other than Li and O were confirmed to be present, as shown in Table 2.

[0087] A test cell was prepared using the positive electrode active material of Example 2-1 in the same manner as in Example 1-1, and evaluation was carried out.

[0088] Examples 2-2 to 2-4 Test cells were prepared and evaluated in the same manner as in Example 2-1, except that in preparing the positive electrode active materials, the amount of lithium methanesulfonate solution added and the mixing time of the cake-like composition and the lithium methanesulfonate solution were changed as shown in Table 1. Fourier transform infrared spectroscopy (FT-IR) confirmed that lithium methanesulfonate was present on the surface of each of the positive electrode active materials.

[0089] Comparative Example 2-1 A test cell was produced and evaluated in the same manner as in Example 2-1, except that in the addition step of producing a positive electrode active material, powdery lithium methanesulfonate was added instead of a lithium methanesulfonate solution in which lithium methanesulfonate was dissolved in pure water, and that the cake-like composition and powdery lithium methanesulfonate were not mixed.

[0090] The evaluation results of the test cells of the Examples and Comparative Examples are shown in Tables 1 and 2. In Table 1, the initial efficiencies of the test cells of Examples 1-1 to 1-10 and Comparative Example 1-1 are expressed relative to the initial efficiency of the test cell of Comparative Example 1-2, which is set to 100. In Table 2, the initial efficiencies of the test cells of Examples 2-1 to 2-4 are expressed relative to the initial efficiency of the test cell of Comparative Example 2-1, which is set to 100. In Tables 1 and 2, the initial efficiencies of the test cells of Examples 2-1 to 2-4 are expressed relative to the initial efficiency of the test cell of Comparative Example 2-1, which is set to 100. ３－ The Gini coefficients on the surface and inside of the lithium transition metal composite oxide particles, as well as the amount of lithium methanesulfonate added and the mixing time are also shown. Note that no S was detected in the negative electrodes of the test cells other than those of Examples 1-9, 1-10 and Comparative Example 1-1.

[0091]

[0092]

[0093] In Tables 1 and 2, the test cells of the examples all have improved initial efficiencies compared to the corresponding test cells of the comparative examples. This tendency is particularly noticeable in the test cells that have undergone aging treatment. Therefore, when a sulfonic acid compound is present on the particle surface of a specific lithium transition metal oxide, and the sulfonic acid compound is analyzed by TOF-SIMS, the initial efficiencies of the test cells of the examples are improved. ３－ It can be seen that the initial efficiency is improved by uniformly distributing the depth mapping intensity ratio distribution until the Gini coefficient of the distribution is 0.7 or less.

[0094] 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 a lithium transition metal composite oxide and a sulfonic acid compound present on the surface of the lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has a layered structure and is a secondary particle containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and wherein an element concentration distribution in a cross section of the secondary particle obtained by time-of-flight secondary ion mass spectrometry shows that the ３－ wherein the Gini coefficient of the secondary particle surface is 0.7 or less. (wherein A is a Group 1 element or a Group 2 element, R is a hydrocarbon group, and n is 1 or 2.) Configuration 2: A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium transition metal composite oxide and a sulfonic acid compound present on the surface of the lithium transition metal composite oxide, wherein the lithium transition metal composite oxide has a layered structure and is a secondary particle containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and wherein an element concentration distribution in a cross section of the secondary particle obtained by time-of-flight secondary ion mass spectrometry shows that ３－ wherein the Gini coefficient inside the secondary particles is 0.6 or less. (wherein A is a Group 1 element or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.) Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein A is a Group 1 element. Configuration 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein A is Li. Configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein R is an alkyl group. Configuration 6: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein R is a methyl group. Configuration 7: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the amount of the sulfonic acid compound present on the surface of the lithium transition metal composite oxide is 0.1 mass % or more and 1.5 mass % or less, relative to the mass of the lithium transition metal composite oxide. Configuration 8: In an infrared absorption spectrum, －１ , 1175 cm －１ , 1065 cm －１ , 785 cm －１ 8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of configurations 1 to 7, having an absorption peak at at least one position near the positive electrode active material for a non-aqueous electrolyte secondary battery. 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, wherein the negative electrode contains S.

[0095] REFERENCE SIGNS LIST 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Exterior body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket

Claims

1. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium transition metal composite oxide and a sulfonic acid compound present on a surface of the lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is a secondary particle having a layered structure and containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and wherein an element concentration distribution in a cross section of the secondary particle obtained by time-of-flight secondary ion mass spectrometry shows that the concentration of SO ３－ The positive electrode active material for a non-aqueous electrolyte secondary battery has a Gini coefficient of 0.7 or less on the surface of the secondary particles. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.) 2. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium transition metal composite oxide and a sulfonic acid compound present on a surface of the lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is a secondary particle having a layered structure and containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, and wherein an element concentration distribution in a cross section of the secondary particle obtained by time-of-flight secondary ion mass spectrometry shows that the sulfonic acid compound is more than 75 mol % of SO ３－ a Gini coefficient inside the secondary particles of said positive electrode active material for a non-aqueous electrolyte secondary battery of 0.6 or less. (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.) 3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein A is a Group 1 element.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein A is Li.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein R is an alkyl group.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein R is a methyl group.

7. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the amount of the sulfonic acid compound present on the surface of the lithium transition metal composite oxide is 0.1 mass % or more and 1.5 mass % or less, based on the mass of the lithium transition metal composite oxide.

8. In the infrared absorption spectrum, 1238 cm －１ , 1175 cm －１ , 1065cm －１ , 785 cm －１ 3. 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.

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 claim 1 or 2, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode contains S.

Images