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

Abstract

Provided is a positive electrode active material that enables an improvement in durability of a non-aqueous electrolyte secondary battery. This positive electrode active material included in a non-aqueous electrolyte secondary battery comprises a lithium transition metal composite oxide. The lithium transition metal composite oxide contains Ni, Ca, and Sr, and contains secondary particles that are formed by agglutination of primary particles. In an element concentration distribution of a cross-section of the lithium transition metal composite oxide as determined using time-of-flight secondary ion mass spectrometry, the ratio ISr_OUT / ISr_IN of the normalized intensity ISr_OUT of Sr in the surfaces of the secondary particles to the normalized intensity ISr_IN of Sr inside the secondary particles is greater than the ratio ICa_OUT / ICa_IN of the normalized intensity ICa_OUT of Ca in the surfaces of the secondary particles to the normalized intensity ICa_IN of Ca inside the secondary particles.

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] Previously, lithium nickel oxide (LiNiO ２ ) is known to have a high energy density, and by substituting a part of Ni with Co, Al, Mn, etc., it is possible to improve battery characteristics such as durability.

[0003] Patent Document 1 discloses a technology for improving the charge-discharge cycle characteristics and safety of a secondary battery by using a positive electrode active material in which Sr is solid-dissolved at a predetermined ratio in an NCM-based lithium transition metal composite oxide containing Ni, Co, and Mn.

[0004] Patent No. 6226430

[0005] However, lithium transition metal composite oxides with a Ni content of 70% or more are prone to side reactions with non-aqueous electrolytes, and therefore battery capacity is likely to decrease with repeated charge and discharge, which can pose a durability issue. The technology described in Patent Document 1 does not consider improving the battery characteristics using lithium transition metal composite oxides with a high Ni content, and there is still room for improvement.

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

[0007] 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, the lithium transition metal composite oxide containing Ni, Ca, and Sr, and including secondary particles formed by aggregation of primary particles, and in an element concentration distribution of a cross section of the lithium transition metal composite oxide measured by time-of-flight secondary ion mass spectrometry, a normalized intensity I of Sr inside the secondary particles is Ｓｒ＿ＩＮ Normalized intensity I of Sr on the secondary particle surface Ｓｒ＿ＯＵＴ Ratio I Ｓｒ＿ＯＵＴ / I Ｓｒ＿ＩＮ is the normalized intensity I of Ca inside the secondary particle. Ｃａ＿ＩＮ Normalized intensity I of Ca on the secondary particle surface Ｃａ＿ＯＵＴ Ratio IＣａ＿ＯＵＴ / I Ｃａ＿ＩＮ is characterized by being larger than

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

[0009] According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, the durability of the non-aqueous electrolyte secondary battery 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] In general, lithium transition metal composite oxides containing Ni as a main component are known as high-capacity positive electrode active materials. However, lithium transition metal composite oxides with a Ni content of 70% or more are prone to side reactions with non-aqueous electrolytes, which can result in poor durability.

[0012] Patent Document 1 discloses a technique for improving the charge-discharge cycle characteristics and safety of a secondary battery by using a positive electrode active material in which a predetermined ratio of Sr is dissolved in an NCM-based lithium transition metal composite oxide containing Ni, Co, and Mn. However, the inventors' investigations have revealed that even if Sr is dissolved in a lithium transition metal composite oxide having a Ni content of 70% or more, the durability of the secondary battery may not be sufficiently improved.

[0013] As a result of further intensive research, the present inventors have found that durability can be improved by having Ca and Sr present inside and on the surface of secondary particles constituting a lithium transition metal composite oxide, dispersing Sr in a relatively large amount on the surface of the secondary particles, while dispersing Ca more uniformly inside and on the surface of the secondary particles than Sr. This is thought to be because the retention of non-aqueous electrolyte is improved while side reactions are suppressed.

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

[0015] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. As shown in FIG. 1 , the secondary battery 10 includes a wound electrode assembly 14, a non-aqueous electrolyte, and an exterior body 16 that accommodates the electrode assembly 14 and the non-aqueous electrolyte. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The exterior body 16 is a cylindrical metal container with a bottom and an opening on one axial side, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the battery will be referred to as the top, and the bottom side of the exterior body 16 will be referred to as the bottom.

[0016] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode assembly 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and alternately stacked in the radial direction of the electrode assembly 14. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal and lateral directions. The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The electrode assembly 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the lateral direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the end faces in the lateral direction of the positive electrode 11 and the negative electrode 12 form the end faces in the axial direction of the electrode body 14 .

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

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

[0019] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. 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.

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

[0021] The positive electrode 11 has, 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 can be made of 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 or more and 30 μm or less.

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

[0023] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphene, and carbon-based particles such as 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 is, for example, 0.1% by mass or more and 10% by mass or less with respect to the total mass of the positive electrode mixture layer.

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

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

[0026] The Ni content in the lithium transition metal composite oxide is 70 mol% or more relative to the total number of moles of metal elements excluding Li. This can improve battery capacity. The Ni content is preferably 85 mol% or more, more preferably 90 mol% or more. Furthermore, from the viewpoint of structural stabilization, the Ni content is preferably 98 mol% or less.

[0027] The content of Ca in the lithium transition metal composite oxide is preferably 0.01 mol % or more and 1 mol % or less, more preferably 0.1 mol % or more and 0.5 mol % or less, and even more preferably 0.2 mol % or more and 0.4 mol % or less, based on the total number of moles of metal elements excluding Li.

[0028] The Sr content in the lithium transition metal composite oxide is preferably 0.01 mol % or more and 1 mol % or less, more preferably 0.02 mol % or more and 0.5 mol % or less, and even more preferably 0.05 mol % or more and 0.2 mol % or less, based on the total number of moles of metal elements excluding Li.

[0029] The lithium transition metal composite oxide may further contain 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 30 mol % or less relative to the total number of moles of metal elements excluding Li. The total content of Co, Al, and Mn is, for example, 0 mol % or more and 30 mol % or less.

[0030] The lithium transition metal composite oxide may further contain one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo. The contents of Nb, Ti, Zr, W, Si, and Mo in the lithium transition metal composite oxide are each, for example, 0 mol % or more and 1 mol % or less, relative to the total number of moles of metal elements excluding Li. The total content of Nb, Ti, Zr, W, Si, and Mo is, for example, 0 mol % or more and 5 mol % or less.

[0031] The lithium transition metal composite oxide is, for example, a compound represented by the general formula Li ａ Ni ｘ M1 ｙ M2 ｚ Ca ｓ Sr ｔ O ２－ｂ (wherein 0.8≦a≦1.2, 0.70≦x≦0.98, 0≦y≦0.30, 0≦z≦0.05, 0.0001≦s≦0.01, 0.0001≦t≦0.01, 0≦b≦0.05, x+y+z+s+t=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 Nb, Ti, Zr, W, Si, and Mo.) The proportion of the metal elements contained in the lithium transition metal composite oxide can be measured, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0032] The lithium transition metal composite oxide contains secondary particles formed by aggregation of primary particles. The particle size of the primary particles is, for example, 0.02 μm or more and 2 μm or less. The particle size of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM). The average particle size of the secondary particles is, for example, 2 μm or more and 30 μm or less. Here, the average particle size refers to the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0033] Ca and Sr are present on the surface of the secondary particles and inside the secondary particles. Ca and Sr are present inside the secondary particles, for example, on the surface of the primary particles, and are not solid-solved inside the primary particles. This significantly suppresses the side reaction between the non-aqueous electrolyte and the lithium transition metal composite oxide. Ca may be present on the surface of the secondary particles and inside the secondary particles as a Ca-containing compound. Examples of the Ca-containing compound include CaO and Ca(OH). ２ , CaCO ３ Sr may be present on the surface of the secondary particles and inside the secondary particles as a compound containing Sr. Examples of the compound containing Sr include SrO and Sr(OH). ２ , SrCO ３ The presence of Ca and Sr on the surface and inside of secondary particles can be confirmed by, for example, energy dispersive X-ray spectroscopy (TEM-EDX) in addition to time-of-flight secondary ion mass spectrometry, which will be described later.

[0034] In the element concentration distribution of the cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry (TOF-SIMS), the normalized intensity I of Sr inside the secondary particle Ｓｒ＿ＩＮ Normalized intensity I of Sr on the secondary particle surface relative to Ｓｒ＿ＯＵＴ Ratio I Ｓｒ＿ＯＵＴ / I Ｓｒ＿ＩＮ is the normalized intensity I of Ca inside the secondary particle. Ｃａ＿ＩＮNormalized intensity I of Ca on the secondary particle surface Ｃａ＿ＯＵＴ Ratio I Ｃａ＿ＯＵＴ / I Ｃａ＿ＩＮ is greater than (hereinafter, I Ｃａ＿ＯＵＴ / I Ｃａ＿ＩＮ is called the normalized intensity ratio of Ca, and I Ｓｒ＿ＯＵＴ / I Ｓｒ＿ＩＮ (This is referred to as the normalized intensity ratio of Sr.) This improves the durability of the secondary battery. This is presumably because the primary particle surfaces, including the secondary particle surfaces, are appropriately protected on the secondary particle surfaces and inside the secondary particles.

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

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

[0037] The area from the surface of the secondary particle recognized from the image to the inside by 0.5 μm is defined as the surface of the secondary particle, and the pixels included in the surface of this secondary particle (hereinafter referred to as surface pixels) are determined. Ｃａ The set of Ｃａ＿ＯＵＴ and I corresponding to each surface pixel Ｓｒ The set of Ｓｒ＿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. Ｃａ The set of Ｃａ＿ＩＮand I corresponding to each surface pixel Ｓｒ The set of Ｓｒ＿ＩＮ From the normalized intensities of Ca and Sr on the surface and inside of the secondary particles thus obtained, the normalized intensity ratio of Ca (I Ｃａ＿ＯＵＴ / I Ｃａ＿ＩＮ ) and the normalized intensity ratio of Sr (I Ｓｒ＿ＯＵＴ / I Ｓｒ＿ＩＮ 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.

[0038] The normalized intensity ratio of Ca is preferably 1 or more. The normalized intensity ratio of Ca is, for example, 1 or more and 5 or less. The normalized intensity ratio of Sr is preferably 5 or more. The normalized intensity ratio of Sr is, for example, 5 or more and 10 or less. The ratio of the normalized intensity of Sr to the normalized intensity of Ca (normalized intensity of Sr / normalized intensity of Ca) is, for example, 1.5 or more and 5 or less.

[0039] A metal compound containing a metal element such as W, Zr, Al, or a rare earth element may be present on the surface of the lithium transition metal composite oxide. Examples of the W-containing compound 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 compounds may contain these metal elements together with Ca or Sr, and examples thereof include SrAlO ４ , CaAlO ４ The metal compound may further contain Li, and an example thereof is lithium tungstate.

[0040] 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:

[0041] The pore volume of the lithium transition metal composite oxide is, for example, 0.1 mL / g to 0.5 mL / g, and can be measured by mercury intrusion porosimetry using a mercury porosimeter (e.g., Autopore IV9510 manufactured by MicroMetitex).

[0042] The lithium transition metal composite oxide may have a layered structure. Examples of the layered structure of the lithium transition metal composite oxide include a layered structure belonging to the space group R-3m and a layered structure belonging to the space group C2 / m. From the viewpoints of increasing capacity and stability of the crystal structure, 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.

[0043] The positive electrode active material preferably contains a sulfonic acid compound present on the surface of the lithium transition metal composite oxide. The sulfonic acid compound is represented, for example, by General Formula I. By having the sulfonic acid compound present on the surface of the lithium transition metal composite oxide, the coating containing the sulfonic acid compound can prevent Li ＋ This facilitates insertion / detachment of the conductive layer, thereby reducing the direct current resistance (DCIR). (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

[0044] 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.

[0045] 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.

[0046] Examples of sulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium propanesulfonate, sodium methanesulfonate, magnesium methanesulfonate, and lithium fluoromethanesulfonate.

[0047] The amount of the sulfonic acid compound present on the surface of the lithium transition metal composite oxide is preferably 0.1 mass % or more and 2 mass % or less, and more preferably 0.25 mass % or more and 1.0 mass % or less, relative to the mass of the lithium transition metal composite oxide.

[0048] The presence of the sulfonic acid compound on the surface of the lithium transition metal composite oxide can be confirmed by Fourier transform infrared spectroscopy (FT-IR). In the infrared absorption spectrum obtained by FT-IR, the lithium transition metal composite oxide 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.

[0049] In the infrared absorption spectrum obtained by FT-IR, for example, a lithium transition metal composite oxide 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.

[0050] In lithium transition metal composite oxides having a sulfonic acid compound other than lithium methanesulfonate present on the surface, absorption peaks derived from the sulfonic acid compound can be identified, similar to lithium transition metal composite oxides having lithium methanesulfonate present on the surface. The presence of the sulfonic acid compound on the surface of the lithium transition metal composite oxide can also be confirmed by ICP, atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), synchrotron XRD measurement, TOF-SIMS, etc.

[0051] The positive electrode mixture layer may contain, in addition to the positive electrode active material of the present embodiment, other positive electrode active materials, such as lithium transition metal composite oxides containing Ni, Ca, and Sr, in which the normalized intensities of Ca and Sr do not satisfy the above relationship.

[0052] Next, an example of a method for manufacturing the positive electrode active material according to this embodiment will be described. Note that the manufacturing method described here is just an example, and the method for manufacturing the positive electrode active material is not limited to this method.

[0053] The process for producing a positive electrode active material includes a synthesis step of obtaining a lithium transition metal composite oxide, a washing step of washing the lithium transition metal composite oxide obtained in the synthesis step with water and dehydrating it to obtain a cake-like composition, an addition step of adding at least one of a sulfonic acid compound and a sulfonic acid solution to the cake-like composition, and a drying step of drying the cake-like composition to obtain a powder-like composition.The synthesis step also includes a mixing step of mixing a metal oxide, a Li raw material, a Ca raw material, a Sr raw material, etc. to obtain a mixture, and a calcination step of calcining the mixture to obtain a lithium transition metal composite oxide.

[0054] In the mixing step, a mixture is obtained by mixing a metal oxide, a Li raw material, a Ca raw material, and a Sr raw material. The metal oxide can be produced by dropping an alkaline solution such as sodium hydroxide into a solution of a metal salt containing Ni, Co, Al, Mn, etc. while stirring it, adjusting the pH to the alkaline side (e.g., 8.5 to 12.5), thereby precipitating (co-precipitating) a composite hydroxide, and then heat-treating the metal hydroxide. The firing temperature is not particularly limited, but is, for example, in the range of 250°C to 600°C. The Li raw material can be, for example, Li ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２ O, LiH, LiF, etc. Ca raw material is Ca(OH) ２ , CaHPO ４ , Ca(H ２ P.O. ４ ) ２ , Ca ３ (P.O. ４ ) ２ , CaO, CaCO ３ , CaSO ４ , Ca(NO ３ ) ２、 CaCl ２ , CaAlO ４ The Sr raw material is Sr(OH) ２ , SrHPO ４ , Sr(H ２ P.O. ４ ) ２ , Sr ３ (P.O. ４ ) ２ , SrO, SrCO ３ , SrSO ４ , Sr(NO ３ ) ２、 SrCl ２ , SrAlO ４By adjusting the average particle diameter (D50) of the Ca raw material and the Sr raw material, it is possible to disperse Sr relatively more on the surface of the secondary particles, while dispersing Ca more uniformly inside and on the surface of the secondary particles than Sr, so that the effect of adding Ca and Sr becomes more pronounced. Furthermore, during mixing, an M2 raw material for adding M2, which is one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo, may be mixed. As the M2 raw material, Nb ２ O ５ , TiO ２ , ZrO ２ , W.O. ３ etc.

[0055] The above mixture is calcined to obtain a lithium transition metal composite oxide (calcination step). The calcination step is performed, for example, in an oxygen stream in a calcination furnace. The calcination step includes, for example, a first calcination step in which the mixture is calcined at a first temperature increase rate to a first set temperature of 300°C or higher and 600°C or lower, and a second calcination step in which the mixture is calcined from the first set temperature to a second set temperature of higher than 600°C and lower than 800°C at a second temperature increase rate. The first temperature increase rate is, for example, in the range of 10°C / min to 100°C / min, and the second temperature increase rate is, for example, in the range of 0.1°C / min to less than 10°C / min. By increasing the first temperature increase rate, Sr can be dispersed relatively more on the secondary particle surface, thereby increasing the value of the normalized intensity ratio of Sr. The normalized intensity ratio of Ca does not change as significantly as the normalized intensity ratio of Sr, even when the first temperature increase rate is increased. In each of the first and second firing steps, further subdivided temperature ranges may be set to perform multi-stage firing.

[0056] The synthesis process is not limited to the above process, and a precursor obtained by co-precipitation or mixing of a compound such as a hydroxide, oxide, or carbonate compound containing at least one of Ni, M1, or M2 (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 Nb, Ti, Zr, W, Si, and Mo) may be used instead of the metal oxide. If the precursor does not contain a compound such as M1 or M2, the compound may be added and mixed when mixing the precursor, Li raw material, Ca raw material, and Sr raw material. Furthermore, these compounds may be pulverized to appropriately change the particle shape or particle size, or may be used after adjusting the water content by including a hydrate.

[0057] In the washing step, the lithium transition metal composite oxide is washed with water and dehydrated to obtain a cake-like composition. The particulate lithium transition metal composite oxide obtained in the synthesis step can be used. By washing with water, unreacted lithium compounds added in the synthesis step and impurities other than the lithium compounds can be removed. When washing with water, for example, 300 g to 5000 g of lithium transition metal composite oxide is added to 1 L of water. The water washing may be repeated multiple times. The dehydration after washing can be performed, for example, using a filter press.

[0058] 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 in a vacuum atmosphere. The drying conditions are, for example, 150°C to 400°C and 0.5 hours to 15 hours.

[0059] 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-containing 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 or more and 2% by mass or less relative to the mass of the lithium-containing composite 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.

[0060] A metal compound containing one or more metal elements selected from the group consisting of W, Zr, Al, and rare earth elements, 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-containing composite oxide by adding the raw materials of the metal compound and the nonmetallic compound, for example, during the synthesis process, after the synthesis process, during the washing process, after the washing process, during the drying process, after the drying process, or during the addition process.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、 Al ２ (SO ４ ) ３ The P raw material may be Al derived from a lithium-containing 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 , 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.

[0061] [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.

[0062] 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.

[0063] 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.

[0064] [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.

[0065] 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.

[0066] [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.

[0067] 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).

[0068] 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).

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Example 1-1 [Preparation of Positive Electrode Active Material] [Ni ０．９２ Co ０．０４ Al ０．０４ ](OH) ２The composite hydroxide represented by the formula (1) was calcined at 500°C for 8 hours to obtain a metal oxide containing Ni, Co, and Al. Next, Ca(OH) was added to the metal oxide so that the molar ratio of Ca was 0.3 mol% and the molar ratio of Sr was 0.1 mol% relative to the total amount of Ni, Co, and Al. ２ , and Sr(OH) ２ and further, lithium hydroxide monohydrate (LiOH·H) was added so that the molar ratio of Li to the total amount of Ni, Co, Al, Ca, and Sr was 103 mol %. ２ O) to obtain a mixture. ２ The average particle size (D50) of Sr(OH) is 3 μm. ２ The D50 of the mixture was 3 μm. This mixture was fired in an oxygen stream having an oxygen concentration of 95% (flow rate of 5 L / min per 1 kg of the mixture) at a first temperature increase rate of 30° C. / min from room temperature to 450° C., and then fired at a second temperature increase rate of 3° C. / min from 450° C. to 720° C. to obtain a lithium transition metal composite oxide. This lithium transition metal composite oxide was washed with water and dried to obtain the positive electrode active material of Example 1-1.

[0078] The positive electrode active material was measured using an inductively coupled plasma (ICP) atomic emission spectrometer (ICP-AES), and the elements other than Li and O were confirmed to be present, as shown in Table 1 below. The element concentration distribution in the cross section of the positive electrode active material was measured using time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the normalized intensity ratio of Ca (I Ｃａ＿ＯＵＴ / I Ｃａ＿ＩＮ ) is 2.6, and the normalized intensity ratio of Sr (I Ｓｒ＿ＯＵＴ / I Ｓｒ＿ＩＮ The pore volume of the positive electrode active material was 0.20 mL / g.

[0079] [Preparation of Positive Electrode] 95 parts by mass of the above positive electrode active material, 3 parts by mass of acetylene black (AB), and 2 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode 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.

[0080] [Preparation of Negative Electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, carboxymethyl cellulose sodium (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution at a solids mass ratio of 100:1:1 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode 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.

[0081] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluorophosphate (LiPF ６ ) was dissolved in the solution to a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0082] [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.

[0083] [Evaluation of durability] At an ambient temperature of 45°C, the test cell was charged at a constant current of 0.3 C to 4.3 V, and then at a constant voltage of 4.3 V to 0.02 C. It was then discharged at a constant current of 0.5 C to 2.5 V. This charge / discharge cycle was counted as one cycle, and 200 cycles were performed. The durability of the test cell was calculated using the following formula: Durability = (discharge capacity at 200th cycle / discharge capacity at 1st cycle) x 100

[0084] [Evaluation of DC Resistance] At an ambient temperature of 25°C, the test cell was charged at a constant current of 0.3 C to 4.3 V, and then at a constant voltage of 4.3 V to 0.02 C. The test cell was then left to stand for 2 hours and then discharged at a constant current of 0.5 C for 10 seconds. The open circuit voltage (OCV), the closed circuit voltage (CCV) 10 seconds after discharge, and the current value (I) 10 seconds after discharge were measured. １０ｓ The direct current resistance (DCIR) was calculated from the OCV-CCV using the following formula: DCIR = (OCV-CCV) / I １０ｓ

[0085] Example 1-2 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that in the preparation of the positive electrode active material, powdered lithium methanesulfonate was added to the lithium transition metal composite oxide after washing with water. The amount of lithium methanesulfonate added was 0.5% by mass relative to the mass of the lithium transition metal composite oxide.

[0086] <Example 1-3> In the preparation of the positive electrode active material, the Ca raw material was Ca(OH) ２ A test cell was prepared in the same manner as in Example 1-2 and evaluated.

[0087] <Example 1-4> In the preparation of the positive electrode active material, the Sr raw material was Sr(OH) ２ A test cell was prepared in the same manner as in Example 1-2 and evaluated.

[0088] Comparative Example 1-1 A test cell was prepared and evaluated in the same manner as in Example 1-1, except that in preparing the positive electrode active material, the first temperature increase rate was changed to 5° C. / min.

[0089] Comparative Example 1-2 A test cell was prepared and evaluated in the same manner as in Example 1-2, except that in preparing the positive electrode active material, the first temperature increase rate was changed to 5° C. / min.

[0090] <Comparative Example 1-3> In the preparation of the positive electrode active material, [Ni ０．９２ Co ０．０４ Al ０．０４ ](OH) ２ A composite hydroxide represented by the formula (1) was fired at 500°C for 12 hours to obtain a metal oxide containing Ni, Co, and Al. A test cell was produced in the same manner as in Example 1-2, except that the first heating rate was changed to 5°C / min, and an evaluation was performed.

[0091] Example 2-1 In the preparation of a positive electrode active material, [Ni ０．９０ Co ０．０５ Mn ０．０５ ](OH) ２ The composite hydroxide represented by the formula (I) was used, and the Ca raw material was Ca(OH) ２ The Sr raw material was changed to Sr(OH) with a D50 of 1 μm. ２ A test cell was produced in the same manner as in Example 1-1 except for the above change, and evaluation was carried out.

[0092] <Examples 2-2 to 2-5> In the preparation of the positive electrode active material, WO was prepared so that the molar ratio of W, Nb, Ti, or Zr to the total amount of Ni, Co, and Mn was the value shown in Table 2. ３ , Nb ２ O ５ , TiO ２ , or ZrO ２ A test cell was prepared and evaluated in the same manner as in Example 2-1, except that a mixture was prepared by adding lithium methanesulfonate powder to the lithium transition metal composite oxide after washing with water. The amount of lithium methanesulfonate added was 0.5% by mass relative to the mass of the lithium transition metal composite oxide.

[0093] <Comparative Example 2-1> In the preparation of the positive electrode active material, the Ca raw material was changed to Ca(OH) ２ The Sr raw material was changed to Sr(OH) with a D50 of 3 μm.２ and the first temperature rise rate was changed to 5° C. / min, and a test cell was fabricated and evaluated in the same manner as in Example 2-1.

[0094] <Comparative Examples 2-2 to 2-5> In the preparation of the positive electrode active material, WO was added so that the molar ratio of W, Nb, Ti, or Zr to the total amount of Ni, Co, and Mn was the value shown in Table 2. ３ , Nb ２ O ５ , TiO ２ , or ZrO ２ Test cells were prepared and evaluated in the same manner as in Comparative Example 2-1, except that a mixture was prepared by adding lithium methanesulfonate powder to the lithium transition metal composite oxide after washing with water in Comparative Examples 2-3 and 2-4. The amount of lithium methanesulfonate added was 0.5% by mass relative to the mass of the lithium transition metal composite oxide.

[0095] Example 3-1 In the preparation of a positive electrode active material, [Ni ０．９０ Mn ０．１０ ](OH) ２ The composite hydroxide represented by the formula (I) was used, and the Ca raw material was Ca(OH) ２ The Sr raw material was changed to Sr(OH) with a D50 of 1 μm. ２ A test cell was prepared in the same manner as in Example 1-2, except for the above change, and evaluation was carried out.

[0096] <Examples 3-2 to 3-5> In the preparation of the positive electrode active material, WO was prepared so that the molar ratio of W, Nb, Ti, or Zr to the total amount of Ni, Co, and Mn was the value shown in Table 3. ３ , Nb ２ O ５ , TiO ２ , or ZrO ２ A test cell was prepared in the same manner as in Example 3-1, except that the mixture was prepared by adding the above, and evaluation was carried out.

[0097] Comparative Examples 3-1 to 3-5: Test cells were prepared and evaluated in the same manner as in Example 3-1, except for the following: (1) The Ca raw material was changed to Ca(OH) with a D50 of 3 μm. ２ The Sr raw material was changed to Sr(OH) with a D50 of 3 μm. ２ (2) In Comparative Examples 3-1 and 3-2, lithium methanesulfonate was not added. (3) The first heating rate was changed to 5° C. / min.

[0098] The evaluation results of the test cells of the examples and comparative examples are shown in Tables 1 to 3. Tables 1 to 3 also show the pore volume of the positive electrode active material. In Table 1, the durability and DC resistance of the test cells other than Comparative Example 1-1 are expressed relative to the durability and DC resistance of the test cell of Comparative Example 1-1, each set to 100. In Table 2, the durability and DC resistance of the test cells other than Comparative Example 2-4 are expressed relative to the durability and DC resistance of the test cell of Comparative Example 2-4, each set to 100. In Table 3, the durability and DC resistance of the test cells other than Comparative Example 3-5 are expressed relative to the durability and DC resistance of the test cell of Comparative Example 3-5, each set to 100.

[0099]

[0100]

[0101]

[0102] In Tables 1 to 3, the test cells of the examples have improved durability compared to the test cells of the comparative examples. Ｓｒ＿ＯＵＴ / I Ｓｒ＿ＩＮ ) is the normalized intensity ratio of Ca (I Ｃａ＿ＯＵＴ / I Ｃａ＿ＩＮ ) in the positive electrode active material improves durability. Furthermore, by including a sulfonic acid compound on the surface of the lithium transition metal composite oxide in the positive electrode active material, DC resistance can be reduced.

[0103] 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, wherein the lithium transition metal composite oxide contains Ni, Ca, and Sr and comprises secondary particles formed by aggregation of primary particles, and wherein an element concentration distribution of a cross section of the lithium transition metal composite oxide obtained by time-of-flight secondary ion mass spectrometry reveals that the normalized intensity I of Sr inside the secondary particles is Ｓｒ＿ＩＮ Normalized intensity I of Sr on the secondary particle surface relative to Ｓｒ＿ＯＵＴ Ratio I Ｓｒ＿ＯＵＴ / I Ｓｒ＿ＩＮ is the normalized intensity I of Ca inside the secondary particle Ｃａ＿ＩＮ The normalized intensity I of Ca on the secondary particle surface relative to Ｃａ＿ＯＵＴ Ratio I Ｃａ＿ＯＵＴ / I Ｃａ＿ＩＮ A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the Ni content in the lithium transition metal composite oxide is 70 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the Ni content in the lithium transition metal composite oxide is 70 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the lithium transition metal composite oxide further contains one or more elements selected from the group consisting of Co, Al, and Mn. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the lithium transition metal composite oxide further contains one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the Ni content in the lithium transition metal composite oxide is 70 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the I ... Ｃａ＿ＯＵＴ / I Ｃａ＿ＩＮ is at least 1. Configuration 6: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the pore volume of the lithium transition metal composite oxide is at least 0.1 mL / g and at most 0.5 mL / g. Configuration 7: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, comprising a sulfonic acid compound present on a surface of the lithium transition metal composite oxide, the sulfonic acid compound being represented by general formula I. (wherein A is a Group 1 element or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.) Configuration 8: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 7, wherein A is a Group 1 element. Configuration 9: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 7, wherein A is Li. Configuration 10: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 7 to 9, wherein R is an alkyl group. Configuration 11: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 7 to 9, wherein R is a methyl group. Configuration 12: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 7 to 11, 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 2 mass % or less, based on the mass of the lithium transition metal composite oxide. Configuration 13: 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 12, a negative electrode, and a non-aqueous electrolyte.

[0104] 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, the lithium transition metal composite oxide contains Ni, Ca, and Sr, and includes secondary particles formed by aggregation of primary particles; In the element concentration distribution of the cross section of the lithium transition metal composite oxide using time-of-flight secondary ion mass spectrometry, a ratio ISc_OUT / ISr_IN of a normalized intensity of Sr on the surface of the secondary particles to a normalized intensity of Sr inside the secondary particles, ISc_OUT, is greater than a ratio ICa_OUT / ICa_IN of a normalized intensity of Ca on the surface of the secondary particles to a normalized intensity of Ca inside the secondary particles, ICa_IN.

2. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a Ni content of 70 mol % or more relative to the total number of moles of metal elements excluding Li in the lithium transition metal composite oxide.

3. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide further contains one or more elements selected from the group consisting of Co, Al, and Mn.

4. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide further contains one or more elements selected from the group consisting of Nb, Ti, Zr, W, Si, and Mo.

5. 2 . The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the ratio ICa_OUT / ICa_IN is 1 or more.

6. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a pore volume of 0.1 mL / g or more and 0.5 mL / g or less.

7. a sulfonic acid compound present on the surface of the lithium transition metal composite oxide, 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the sulfonic acid compound is represented by general formula I. 【Chemistry 1】 (In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2.)

8. 8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein A is a Group 1 element.

9. 8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein A is Li.

10. 8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein R is an alkyl group.

11. 8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 7, wherein R is a methyl group.

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

13. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 12, a negative electrode, and a non-aqueous electrolyte.

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