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

Abstract

A positive electrode active material for a nonaqueous electrolyte secondary battery containing a lithium transition metal composite oxide represented by the general formula LiaNibCocMn1–b–c–dM1dO2 (I) (where 0.8 ≤ a ≤ 1.2, 0.3 ≤ b ≤ 0.95, 0.001 ≤ c ≤ 0.1, and 0 ≤ d ≤ 0.1), said positive electrode active material for a nonaqueous electrolyte secondary battery being characterized in that the surfaces of secondary particles have a cobalt-containing composite oxide represented by the general formula LixCoyM2zO2 (II) (where 0.8 ≤ x ≤ 1.1, 0.9 ≤ y ≤ 1.0, and 0 ≤ z ≤ 0.03), and the average oxidation state of cobalt in all of the lithium transition metal composite oxide particles is greater than 2.0 and less than 3.0.

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 using the positive electrode active material in a positive electrode.

[0002] In non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, the positive electrode active material has a significant impact on battery performance, such as input / output characteristics, capacity, and durability, and therefore much research has been conducted on the positive electrode active material. Lithium transition metal composite oxides containing transition metal elements such as Ni and Mn are typically used as positive electrode active materials. The types and amounts of elements contained in the lithium transition metal composite oxide, as well as the crystalline structure of the composite oxide, significantly affect battery performance, and even slight changes in these physical properties can prevent the desired performance from being achieved. For example, Patent Document 1 discloses a positive electrode active material containing Ni, Mn, and Co, with the aim of increasing the capacity of non-aqueous electrolyte secondary batteries, in which the oxidation number of Co on the particle surface is smaller than the average oxidation number of Co throughout the particles.

[0003] Patent No. 5325888

[0004] In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been used as power sources for driving vehicles, and there is a demand for even higher capacity. Conventional positive electrode active materials containing Ni and Mn, including those described in Patent Document 1, still have much room for improvement in terms of increasing capacity.

[0005] The positive electrode active material for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure is a compound represented by the general formula (I): ａ Ni ｂ Co ｃ Mn １－ｂ－ｃ－ｄ M1 ｄ O ２(wherein 0.8≦a≦1.2, 0.3≦b≦0.95, 0.001≦c≦0.1, 0≦d≦0.1, and M1 is at least one element selected from the group consisting of F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V), the lithium transition metal composite oxide includes secondary particles formed by aggregation of primary particles, and a compound represented by the general formula (II) Li ｘ Co ｙ M2 ｚ O ２ (wherein 0.8≦x≦1.1, 0.97≦y≦1.0, 0≦z≦0.03, and M2 is at least one element selected from the group consisting of Ni, Mn, F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V), and the average oxidation number of Co in the entire lithium transition metal composite oxide particles is greater than 2.0 and less than 3.0.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by including a positive electrode containing the above-described positive electrode active material, a negative electrode, and a non-aqueous electrolyte.

[0007] According to the positive electrode active material for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, it is possible to achieve a high capacity non-aqueous electrolyte secondary battery.

[0008] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, taken along an axial direction thereof; 2 is a diagram showing an X-ray diffraction pattern of a lithium transition metal composite oxide according to an example;

[0009] Hereinafter, with reference to the drawings, an example of an embodiment of a positive electrode active material according to the present disclosure and a nonaqueous electrolyte secondary battery using the positive electrode active material will be described in detail. Note that configurations obtained by selectively combining the respective components of the multiple embodiments and modifications described below are included within the scope of the present disclosure.

[0010] In the following, a cylindrical battery in which a wound electrode assembly is housed in a cylindrical, bottomed exterior body is exemplified as a nonaqueous electrolyte secondary battery; however, the battery exterior body is not limited to a cylindrical exterior body. The nonaqueous electrolyte secondary battery according to the present disclosure may be, for example, a prismatic battery with a prismatic exterior body, a coin-type battery with a coin-type exterior body, or a pouch-type battery with an exterior body made of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode assembly is not limited to a wound type, but may also be a stacked type electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween. Furthermore, the design of the nonaqueous electrolyte secondary battery according to the present disclosure is not limited to the design of the exemplified nonaqueous electrolyte secondary battery, and known nonaqueous electrolyte secondary battery designs may also be applied.

[0011] FIG. 1 is an axial cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte, and an exterior body 16 that accommodates the electrode assembly 14 and the nonaqueous 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 that is open 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."

[0012] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and stacked alternately 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 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 lateral end faces of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode assembly 14.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] The positive electrode 11, the negative electrode 12, the separator 13, and the nonaqueous electrolyte that constitute the nonaqueous electrolyte secondary battery 10 will be described in detail below, with the positive electrode 11 being particularly described below.

[0017] The positive electrode 11 includes a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode core can be a foil of a metal such as aluminum, an aluminum alloy, stainless steel, or titanium that is stable within the potential range of the positive electrode 11, or a film having such a metal disposed on its surface.

[0018] The positive electrode mixture layer preferably contains a positive electrode active material, a conductive agent, and a binder, and is provided on both sides 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, and the binder onto the positive electrode core, drying the coating, and then compressing it to form positive electrode mixture layers on both sides of the positive electrode core.

[0019] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. One type of conductive agent may be used alone, or multiple types may be used in combination. The content of the conductive agent is not particularly limited, but is, for example, 0.1 mass% or more and 5 mass% or less with respect to the mass of the positive electrode mixture layer.

[0020] Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer; and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. One type of binder may be used alone, or multiple types may be used in combination. The content of the binder is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less relative to the mass of the positive electrode mixture layer.

[0021] The positive electrode active material includes a lithium transition metal composite oxide containing a transition metal element such as Li, Ni, Mn, or Co. The lithium transition metal composite oxide includes secondary particles formed by aggregation of primary particles. A primary particle is a single particle with no grain boundary present inside, and a secondary particle is formed by aggregation of, for example, two or more and 10,000 or less primary particles. As will be described in more detail below, the lithium transition metal composite oxide of this embodiment contains Co with different oxidation states on the surface and inside of the secondary particles.

[0022] The particle size of the primary particles constituting the secondary particles of the lithium transition metal composite oxide 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 of the lithium transition metal composite oxide 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 of the lithium transition metal composite oxide 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 preferably 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 stability of the crystal structure, the lithium transition metal composite oxide more 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 and a Li layer.

[0024] The lithium transition metal composite oxide is represented by the general formula (I) Li ａ Ni ｂ Co ｃ Mn １－ｂ－ｃ－ｄ M1 ｄ O ２(wherein 0.8≦a≦1.2, 0.3≦b≦0.95, 0.001≦c≦0.1, 0≦d≦0.1, and M1 is at least one element selected from the group consisting of F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V). In other words, Ni, Mn, and Co are essential components. The contents of the elements constituting the lithium transition metal composite oxide can be measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like.

[0025] The Li content (a) in the general formula (I) may be 0.8≦a≦1.2, preferably 0.95≦a≦1.2, and more preferably 1.05≦a≦1.15. In this case, the battery capacity can be further improved. Furthermore, the Li content (a) in the general formula (I) may be 0.8≦a≦1.15, 0.95≦a≦1.15, or 1.05≦a≦1.2.

[0026] In addition, the Ni content (b) in the general formula (I) may be 0.3≦b≦0.95, preferably 0.4≦b≦0.925, and more preferably 0.485≦b≦0.9. In this case, the battery capacity can be further improved. In addition, the Ni content (b) in the general formula (I) may be 0.3≦b≦0.925, 0.3≦b≦0.9, 0.4≦b≦0.95, 0.4≦b≦0.9, 0.485≦b≦0.95, or 0.485≦b≦0.925.

[0027] Furthermore, the Co content (c) in the general formula (I) may be 0.001≦c≦0.1, preferably 0.001≦c≦0.075, and more preferably 0.001≦c≦0.05. In this case, the effects of the present disclosure, which will be described later, are significantly exhibited. Furthermore, if the Co content (c) in the general formula (I) exceeds 0.1, the capacity of the nonaqueous electrolyte secondary battery may decrease.

[0028] In addition, the content (d) of M1 in the general formula (I) may be 0≦d≦0.1, preferably 0≦d≦0.05, and more preferably 0≦d≦0.01. That is, M1 is an optional component. When Al is contained as M1 in the lithium transition metal composite oxide, for example, the crystal structure tends to be more stabilized.

[0029] The lithium transition metal composite oxide has a general formula (II) Li ｘ Co ｙ M2 ｚ O ２ (wherein 0.8≦x≦1.1, 0.97≦y≦1.0, 0≦z≦0.03, and M2 is at least one element selected from the group consisting of Ni, Mn, F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V). From the viewpoint of further exerting the effects of the present disclosure described later, the cobalt-containing composite oxide is LiCoO ２ It is preferable that:

[0030] The presence of the cobalt-containing composite oxide can be confirmed by measuring the cross section of the secondary particle of the lithium transition metal composite oxide using SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy). ２ When LiCoO is present, as shown in FIG. 2, the diffraction angle 2θ is in the range of 37.1° or more and 37.5° or less in the X-ray diffraction pattern. ２ A peak due to the (101) plane of LiCoO appears in the diffraction angle 2θ range of 45.0° or more and 45.5° or less. ２ 2 shows the X-ray diffraction pattern of the lithium transition metal composite oxide prepared in the examples described later before charging.

[0031] The X-ray diffraction pattern of the lithium transition metal composite oxide was obtained using a desktop X-ray diffractometer (manufactured by Rigaku Corporation, trade name "MiniFlex600"). Diffracted X-rays were detected with a high-speed one-dimensional detector (D / teX Ultra 2). The measurement conditions using the X-ray diffractometer were as follows: X-ray source: CuKα ray; Tube voltage: 40 kV; Tube current: 15 mA; Divergence slit (DS): 0.625°; Scattering slit (SS): 13 mm (open); Receiving slit (RS): 8 mm; Scan axis: 2θ / θ; Scan method: Continuous; 2θ scan range: 10-80°; Scan speed: 10° / min; Step width: 0.02°

[0032] The cobalt-containing composite oxide is present, for example, in the form of particles or layers on the surface of the secondary particles. The cobalt-containing composite oxide is preferably present so as to cover substantially the entire surface of the secondary particles. When the cobalt-containing composite oxide covers the surface of the secondary particles in the form of a layer, the thickness of the layer formed by the cobalt-containing composite oxide is, for example, 0.3 μm or more and 3 μm or less, and preferably 0.5 μm or more and 2.5 μm or less. Furthermore, a portion of the cobalt-containing composite oxide may be present inside the secondary particles.

[0033] The lithium transition metal composite oxide contains Co both inside and on the surface of the secondary particles. As a result of studies by the present inventors, it has been found that when the composition of the lithium transition metal composite oxide satisfies the above general formula (I) and a cobalt-containing composite oxide represented by the above general formula (II) is present on the surface of the secondary particles, a high capacity nonaqueous electrolyte secondary battery can be achieved by setting the average oxidation number of Co throughout the lithium transition metal composite oxide particles to greater than 2.0 and less than 3.0. Theoretically, the oxidation number of Co contained in the cobalt-containing composite oxide represented by general formula (II) is 2.8 or greater. Therefore, when the lithium transition metal composite oxide satisfies the above relationship, the oxidation number of Co contained in the cobalt-containing composite oxide present on the surface of the secondary particles is likely to be higher than the oxidation number of Co present inside the secondary particles. That is, trivalent or higher Co is present in large amounts on the surface of the secondary particles, and divalent Co is present inside the secondary particles.

[0034] Although the detailed mechanism for achieving high capacity is unclear, divalent Co has superior electronic conductivity compared to trivalent Co. Therefore, the presence of divalent Co inside the secondary particles reduces the resistance of the lithium transition metal composite oxide, enabling high-capacity non-aqueous electrolyte secondary batteries. Furthermore, trivalent Co is less likely to undergo side reactions with the non-aqueous electrolyte than divalent Co. Therefore, the presence of a large amount of trivalent Co on the surface of the secondary particles suppresses side reactions between the lithium transition metal composite oxide and the non-aqueous electrolyte, thereby preventing the transition metal from leaching from the lithium transition metal composite oxide and the products generated by the side reactions from depositing on the surface of the lithium transition metal composite oxide. As a result, high-capacity non-aqueous electrolyte secondary batteries can be achieved. In other words, if the oxidation numbers of Co present inside and on the surface of the secondary particles are the same, or if the oxidation number of Co present on the surface of the secondary particles is smaller than the oxidation number of Co present inside the secondary particles, the above-mentioned high-capacity non-aqueous electrolyte secondary batteries cannot be achieved.

[0035] The average oxidation number of Co throughout the lithium transition metal composite oxide particles may be greater than 2.0 and less than 3.0, preferably greater than 2.0 and less than 2.9, and more preferably greater than 2.0 and less than 2.8. In this case, more divalent Co is present inside the secondary particles, thereby enabling a higher capacity nonaqueous electrolyte secondary battery. Furthermore, the average oxidation number of Co throughout the lithium transition metal composite oxide particles may be greater than 2.1 and less than 3.0, greater than 2.2 and less than 3.0, greater than 2.3 and less than 3.0, or greater than 2.4 and less than 3.0.

[0036] The average oxidation number of Co throughout the lithium transition metal composite oxide particles can be determined by measuring the XANES (X-ray absorption near edge structure) spectrum of the lithium transition metal composite oxide using a transmission method through XAFS (X-ray absorption fine structure) analysis. Specifically, reference samples containing divalent and trivalent Co are prepared. The K-absorption edge energy is then calculated from the XANES spectrum of the lithium transition metal composite oxide and the XANES spectrum of the reference sample using an integration method using analysis software (product name: Athena), and compared to calculate the average oxidation number of Co throughout the lithium transition metal composite oxide particles. Note that the average oxidation number of Co throughout the lithium transition metal composite oxide particles refers to the average oxidation number of Co throughout the lithium transition metal composite oxide particles in an uncharged state.

[0037] The presence of divalent Co inside the secondary particles can also be confirmed by X-ray diffraction patterns. The atomic radius of divalent Co is larger than that of trivalent Co. Therefore, when divalent Co is contained inside the secondary particles, the lattice constant (e.g., a-axis length) of the crystal structure is larger than when only trivalent or higher valent Co is contained inside the secondary particles or when no Co is contained inside the secondary particles. Therefore, the presence of divalent Co inside the secondary particles can be confirmed by calculating the lattice constant of the lithium transition metal composite oxide using the X-ray diffraction pattern and comparing the calculated lattice constant with the lattice constant when only trivalent or higher valent Co is contained inside the secondary particles or the lattice constant when no Co is contained inside the secondary particles.

[0038] As described above, in the lithium transition metal composite oxide of this embodiment, the oxidation number of Co contained in the cobalt-containing composite oxide present on the surface of the secondary particles is higher than the oxidation number of Co present inside the secondary particles. Therefore, the oxidation number of Co contained in the cobalt-containing composite oxide present on the surface of the secondary particles is higher than the average oxidation number of Co throughout the lithium transition metal composite oxide particles. Here, the oxidation number of Co contained in the cobalt-containing composite oxide present on the surface of the secondary particles can be determined by measuring the XANES (X-ray absorption near edge structure) spectrum of the lithium transition metal composite oxide using an electron yield method through XAFS (X-ray absorption fine structure) analysis.

[0039] The average oxidation number of Ni throughout the lithium transition metal composite oxide particles is preferably 2.8 or more and 3.8 or less. In this case, the electronic conductivity of the lithium transition metal composite oxide is improved, making it easier to achieve high capacity non-aqueous electrolyte secondary batteries. The average oxidation number of Ni throughout the lithium transition metal composite oxide particles can be determined, as with the average oxidation number of Co, by measuring the XANES (X-ray absorption near edge structure) spectrum of the lithium transition metal composite oxide using a transmission method through XAFS (X-ray absorption fine structure) analysis.

[0040] The positive electrode active material may contain a positive electrode active material other than the lithium transition metal composite oxide described above, as long as the object of the present disclosure is not impaired. Multiple types of positive electrode active materials may be used in the nonaqueous electrolyte secondary battery 10, depending on, for example, the required battery performance. The mass ratio of the lithium transition metal composite oxide described above to the total mass of the positive electrode active material is, for example, 80 mass % or more, and may even be 90 mass % or more.

[0041] A lithium transition metal composite oxide, which is an example of an embodiment, can be produced by the following method. Note that the production method described here is just an example, and the method for producing a lithium transition metal composite oxide is not limited to this method. The production method for a lithium transition metal composite oxide includes, for example, a lithium transition metal composite oxide synthesis step, a washing step, a drying step, and a heat treatment step.

[0042] In the synthesis process of the lithium transition metal composite oxide, a metal hydroxide containing metals such as Ni and Mn is mixed with a Li compound, and the mixture is fired. ２ CO ３ , LiOH, Li ２ O ２ , Li ２ O, LiNO ３ , LiNO ２ , Li ２ SO ４ , LiOH·H ２ Examples of the lithium ion include O, LiH, and LiF.

[0043] The metal hydroxide can be obtained, for example, by adding an alkaline solution such as sodium hydroxide dropwise to a stirred solution of a metal salt such as Ni or Mn, adjusting the pH to the alkaline side (e.g., 8.5 or more and 12.5 or less), and then causing precipitation (coprecipitation). Note that, instead of the metal hydroxide, a metal oxide obtained by heat-treating the metal hydroxide may be used.

[0044] The metal hydroxide and the Li compound are mixed, for example, in a molar ratio of metal elements excluding Li to Li of 1:0.98 to 1:1.05. When mixing the metal hydroxide and the Li compound, a compound containing M1 (at least one element selected from the group consisting of F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V) may be added. The above compound is, for example, an oxide, hydroxide, chloride, carbonate, sulfate, or phosphate, and may be a composite compound containing another metal element such as Li.

[0045] The mixture of metal hydroxide and Li compound or the like is fired, for example, in an oxygen atmosphere (under a gas flow with an oxygen concentration of 80% or more). The firing process may be multi-stage firing. An example of multi-stage firing is a heating rate of 1.0°C / min or more and 5.5°C / min or less in the temperature range of 450°C or more and 680°C or less, and a maximum temperature of 750°C or more and 1100°C or less. The heating rate from 680°C to the maximum temperature may be 0.1°C / min or more and 3.5°C / min or less. The holding time at the maximum temperature may be 1 hour or more and 30 hours or less.

[0046] In the washing step, the fired product obtained in the synthesis step is washed with an aqueous solution containing Co and then dehydrated. ２ CO ３ , LiOH, LiOH・H ２ Li compounds such as O remain, and these Li compounds dissolve in the aqueous solution during washing. Therefore, by washing with a Co-containing aqueous solution, the dissolved Li compounds react with Co, forming compounds containing Li and Co on the surfaces of the secondary particles. Generally, Li compounds are alkaline. Therefore, from the viewpoint of easily forming Li and Co-containing compounds on the surfaces of the secondary particles, it is preferable that the Co-containing aqueous solution is acidic. Examples of Co-containing aqueous solutions include a cobalt nitrate aqueous solution and a cobalt sulfate aqueous solution, and among these, a cobalt nitrate aqueous solution is preferred. The Co content in the lithium transition metal composite oxide can be adjusted by adjusting the Co content in the aqueous solution. Furthermore, dehydration in the washing step can be performed using known methods and conditions.

[0047] In the washing step, the method for forming a compound containing Li and Co on the surface of the secondary particles is not limited to this. For example, a method for forming a compound containing Li and Co on the surface of the secondary particles by washing with water or by adding cobalt oxide (CoO, Co ３ O ４ ), cobalt sulfate (CoSO ４ By adding a Co-containing compound such as Li, Co, etc., a compound containing Li and Co may be formed on the surface of the secondary particles.

[0048] In the drying step, the composition obtained in the washing step is dried to obtain a powdery composition. The drying step may be performed, for example, under a vacuum atmosphere. For example, the drying temperature is 150° C. or higher and 400° C. or lower, and the drying time is 0.5 hours or higher and 15 hours or lower.

[0049] In the heat treatment step, the composition obtained in the drying step is heat-treated to produce a lithium transition metal composite oxide. By heat-treating the composition obtained in the drying step, a cobalt-containing composite oxide can be formed on the surface of the secondary particles. In addition, by heat-treating the composition obtained in the drying step, a portion of Co is solid-dissolved inside the secondary particles. In this case, by adjusting the heat treatment temperature in the heat treatment step, divalent Co is solid-dissolved inside the secondary particles, and the average oxidation number of Co throughout the lithium transition metal composite oxide particles is greater than 2.0 and less than 3.0.

[0050] The heat treatment temperature in the heat treatment step is preferably 400°C or higher and 800°C or lower, and more preferably 500°C or higher and 700°C or lower. In this case, a high-quality cobalt-containing composite oxide can be attached to the surface of the secondary particles. In other words, if the heat treatment temperature is lower than 400°C or higher than 800°C, a sufficient amount of cobalt-containing composite oxide may not be formed on the surface of the secondary particles. Furthermore, if the heat treatment temperature is lower than 400°C or higher than 800°C, divalent Co may not be solid-solved inside the secondary particles.

[0051] The atmosphere in the heat treatment step is not particularly limited and may be, for example, an air atmosphere, an oxygen atmosphere, a decarbonation atmosphere, etc. The treatment time in the heat treatment step is preferably 0.25 hours or more and 5 hours or less, from the viewpoint of forming a cobalt-containing composite oxide on the surfaces of the secondary particles.

[0052] [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.

[0053] 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.

[0054] 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.

[0055] [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.

[0056] 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.

[0057] [Non-aqueous electrolyte] The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0058] 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).

[0059] 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).

[0060] 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 ethyl 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, 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0065] 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.

[0066] 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.

[0067] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0068] Example 1 Preparation of Positive Electrode Active Material Ni Obtained by Coprecipitation Method ０．８２ Mn ０．１８ (OH) ２The powder was calcined in air at 400°C for 4 hours to obtain a metal oxide containing Ni and Mn. Next, lithium hydroxide monohydrate (LiOH·H) was added to the powder so that the molar ratio of Li to the total amount of Ni and Mn was 1:1.09. ２ Then, this mixture was heated from room temperature to 650°C at a heating rate of 2.0°C / min in an oxygen stream having an oxygen concentration of 95%, and then heated from 650°C to 770°C at a heating rate of 0.5°C / min and maintained at this temperature (synthesis step).

[0069] Next, a cobalt nitrate aqueous solution was added to the obtained fired product so that the molar ratio of Co to the total amount of Ni and Mn was 99:1, and the mixture was stirred for 10 minutes, filtered, and dehydrated (washing step). The composition obtained in the washing step was then dried in a vacuum atmosphere at 180°C for 2 hours (drying step). The composition obtained in the drying step was then heated from room temperature to 600°C at a heating rate of 2.0°C / min in an oxygen stream with an oxygen concentration of 95%, and then maintained at 600°C for 0.25 hours to obtain a lithium transition metal composite oxide (heat treatment step).

[0070] When the cross section of the obtained lithium transition metal composite oxide particle was measured using SEM-EDX, it was confirmed that a cobalt-containing composite oxide was formed so as to cover the entire surface of the secondary particle. Furthermore, the X-ray diffraction pattern of the obtained lithium transition metal composite oxide is shown in FIG. 2. As shown in FIG. 2, in the X-ray diffraction pattern, LiCoO was observed in the range of the diffraction angle 2θ of 37.1° or more and 37.5° or less. ２ A peak due to the (101) plane of LiCoO appears in the diffraction angle 2θ range of 45.0° or more and 45.5° or less. ２ Therefore, it is believed that LiCoO exists on the surface of the secondary particles as a cobalt-containing composite oxide. ２ is presumed to be formed.

[0071] The average oxidation number of Co in the entire particles of the obtained lithium transition metal composite oxide was measured by the above-mentioned method and was found to be 2.74. The a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and was found to be 2.8770 Å. This is longer than the a-axis length (2.8765 Å) of Comparative Example 1 described below. From the above results, it can be seen that the produced lithium transition metal composite oxide has divalent Co present inside the secondary particles and cobalt-containing composite oxide (LiCoO ２ It can be said that the oxidation number of Co contained in the secondary particles is larger than the oxidation number of Co present inside the secondary particles.

[0072] [Preparation of Positive Electrode] The above positive electrode active material, acetylene black (AB), and polyvinylidene fluoride were mixed in a mass ratio of 92:5:3, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to a positive electrode core made of aluminum foil, the coating was dried and compressed, and then the positive electrode core was cut to a predetermined electrode size to obtain a positive electrode in which a positive electrode mixture layer was disposed on both sides of the positive electrode core. In addition, an exposed portion in which the surface of the positive electrode core was exposed was provided in a part of the positive electrode.

[0073] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:5:75. Lithium hexafluorophosphate (LiPF ６ ) was dissolved in the solution to a concentration of 1.35 mol / L to prepare a non-aqueous electrolyte.

[0074] [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 lithium metal foil serving as the negative electrode. The positive electrode and the negative electrode were spirally wound with a polyolefin separator interposed therebetween to prepare a 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.

[0075] [Evaluation of Discharge Capacity] The prepared test cell was charged to 4.5 V (vs. Li metal) at a constant current of 0.2 C in a temperature environment of 25° C., and then charged to 0.02 C at a constant voltage of 4.5 V. Thereafter, it was discharged to 2.5 V at a constant current of 0.2 C, and the discharge capacity was measured.

[0076] Example 2 A test cell was produced and evaluated in the same manner as in Example 1, except that in the washing step of producing the positive electrode active material, an aqueous cobalt nitrate solution was added to the obtained fired product so that the molar ratio of Co to the total amount of Ni and Mn was 98:2.

[0077] When the cross section of the obtained lithium transition metal composite oxide particle was measured using SEM-EDX, it was confirmed that a cobalt-containing composite oxide was formed so as to cover the entire surface of the secondary particle. In addition, as shown in Figure 2, in the X-ray diffraction pattern, LiCoO was found to be present in the range of the diffraction angle 2θ of 37.1° or more and 37.5° or less. ２ A peak due to the (101) plane of LiCoO appears in the diffraction angle 2θ range of 45.0° or more and 45.5° or less. ２ Therefore, it is believed that LiCoO exists on the surface of the secondary particles as a cobalt-containing composite oxide. ２ is presumed to be formed.

[0078] The a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and was found to be 2.8782 Å. This is longer than the a-axis length (2.8765 Å) of Comparative Example 1 described later. From the above results, it can be seen that the lithium transition metal composite oxide produced has divalent Co present inside the secondary particles and cobalt-containing composite oxide (LiCoO ２ It can be said that the oxidation number of Co contained in the secondary particles is larger than the oxidation number of Co present inside the secondary particles.

[0079] Example 3 A test cell was produced and evaluated in the same manner as in Example 1, except that in the cleaning step of producing the positive electrode active material, an aqueous cobalt nitrate solution was added to the obtained fired product so that the molar ratio of Co to the total amount of Ni and Mn was 97:3.

[0080] When the cross section of the obtained lithium transition metal composite oxide particle was measured using SEM-EDX, it was confirmed that a cobalt-containing composite oxide was formed so as to cover the entire surface of the secondary particle. In addition, as shown in Figure 2, in the X-ray diffraction pattern, LiCoO was found to be present in the range of the diffraction angle 2θ of 37.1° or more and 37.5° or less. ２ A peak due to the (101) plane of LiCoO appears in the diffraction angle 2θ range of 45.0° or more and 45.5° or less. ２ Therefore, it is believed that LiCoO exists on the surface of the secondary particles as a cobalt-containing composite oxide. ２ is presumed to be formed.

[0081] The a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and was found to be 2.8792 Å. This is larger than the a-axis length (2.8765 Å) of Comparative Example 1 described later. From the above results, it can be seen that the lithium transition metal composite oxide produced has divalent Co present inside the secondary particles and cobalt-containing composite oxide (LiCoO ２ It can be said that the oxidation number of Co contained in the secondary particles is larger than the oxidation number of Co present inside the secondary particles.

[0082] Comparative Example 1 A test cell was produced and evaluated in the same manner as in Example 1, except that the cleaning step, drying step, and heat treatment step were not performed in the production of the positive electrode active material. That is, the lithium transition metal composite oxide of Comparative Example 1 did not contain Co. The a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and was found to be 2.8765 Å.

[0083] Table 1 shows the discharge capacities of the test cells of Examples 1 to 3 and Comparative Example 1. Table 1 also shows the molar ratios of Ni, Co, and Mn, the average oxidation number of Co, and the a-axis length of each lithium transition metal composite oxide. The discharge capacities of the test cells of Examples 1 to 3 and Comparative Example 1 shown in Table 1 are expressed relative to the discharge capacity of the test cell of Comparative Example 1, which is set at 100. A larger value of discharge capacity indicates a higher capacity.

[0084]

[0085] As shown in Table 1, the test cells of Examples 1 to 3 have increased discharge capacities compared to the test cell of Comparative Example 1. Therefore, it is believed that the cobalt-containing composite oxide (LiCoO ２ It can be said that a high capacity can be realized by making the average oxidation number of Co in the entire particles of the lithium transition metal composite oxide greater than 2.0 and less than 3.0 while making the lithium transition metal composite oxide have the above-mentioned Co.

[0086] Example 4 In the synthesis process of the positive electrode active material, Ni ０．８２ Mn ０．１８ (OH) ２ Instead of powder, Ni ０．７０ Mn ０．３０ (OH) ２ A test cell was prepared and evaluated in the same manner as in Example 1, except that powder was used.

[0087] The a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and was found to be 2.8850 Å. This is larger than the a-axis length (2.8840 Å) of Comparative Example 2 described later. From the above results, it can be seen that the lithium transition metal composite oxide produced has divalent Co present inside the secondary particles and cobalt-containing composite oxide (LiCoO ２ It can be said that the oxidation number of Co contained in the secondary particles is larger than the oxidation number of Co present inside the secondary particles.

[0088] Comparative Example 2 A test cell was prepared and evaluated in the same manner as in Example 4, except that the cleaning step, drying step, and heat treatment step were not performed in the preparation of the positive electrode active material. In other words, the lithium transition metal composite oxide of Comparative Example 2 did not contain Co. The a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and was found to be 2.8840 Å.

[0089] Example 5 In the synthesis process of the positive electrode active material, Ni ０．８２ Mn ０．１８ (OH) ２ Instead of powder, Ni ０．５０ Mn ０．５０ (OH) ２ A test cell was prepared and evaluated in the same manner as in Example 1, except that powder was used.

[0090] Furthermore, the a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and found to be 2.8881 Å. This is longer than the a-axis length (2.8853 Å) of Comparative Example 3 described below. From the above results, it can be seen that the lithium transition metal composite oxide produced has divalent Co present inside the secondary particles and cobalt-containing composite oxide (LiCoO ２ It can be said that the oxidation number of Co contained in the secondary particles is larger than the oxidation number of Co present inside the secondary particles.

[0091] Comparative Example 3 A test cell was prepared and evaluated in the same manner as in Example 5, except that the cleaning step, drying step, and heat treatment step were not performed in the preparation of the positive electrode active material. That is, the lithium transition metal composite oxide of Comparative Example 3 did not contain Co. The a-axis length of the lithium transition metal composite oxide was calculated from the X-ray diffraction pattern and was found to be 2.8853 Å.

[0092] Table 2 shows the discharge capacities of Example 4 and Comparative Example 2, and Table 3 shows the discharge capacities of Example 5 and Comparative Example 3. Tables 2 and 3 also show the molar ratios of Ni, Co, and Mn and the a-axis length of each lithium transition metal composite oxide. The discharge capacities of the test cells of Example 4 and Comparative Example 2 shown in Table 2 are expressed relative to the discharge capacity of the test cell of Comparative Example 2, which is set to 100. The discharge capacities of the test cells of Example 5 and Comparative Example 3 shown in Table 3 are expressed relative to the discharge capacity of the test cell of Comparative Example 3, which is set to 100.

[0093]

[0094]

[0095] As shown in Tables 2 and 3, the test cells of Examples 4 and 5 have increased discharge capacities compared to the test cells of Comparative Examples 2 and 3. Therefore, even when the molar ratios of Ni and Mn are different, it can be said that high capacity can be achieved by using a lithium transition metal composite oxide having the configuration of the present disclosure.

[0096] The present disclosure is further illustrated by the following embodiments: Structural 1: General formula (I) Liａ Ni ｂ Co ｃ Mn １－ｂ－ｃ－ｄ M1 ｄ O ２ (wherein 0.8≦a≦1.2, 0.3≦b≦0.95, 0.001≦c≦0.1, 0≦d≦0.1, and M1 is at least one element selected from the group consisting of F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V), the lithium transition metal composite oxide includes secondary particles formed by aggregation of primary particles, and a compound represented by the general formula (II) Li ｘ Co ｙ M2 ｚ O ２ (wherein 0.8≦x≦1.1, 0.97≦y≦1.0, 0≦z≦0.03, and M2 is at least one element selected from the group consisting of Ni, Mn, F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V), and the average oxidation number of Co in all particles of the lithium transition metal composite oxide is greater than 2.0 and less than 3.0. ２A positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein the formula is: a. Configuration 3: The positive electrode active material for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the lithium transition metal composite oxide has a layered structure. Configuration 4: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein, in General Formula (I), 1.05≦a≦1.15, 0.485≦b≦0.9, 0.001≦c≦0.05, and 0≦d≦0.01. Configuration 5: The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein divalent Co is contained inside the secondary particles. 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 average oxidation number of Ni in the entire lithium transition metal composite oxide particles is 2.8 or more and 3.8 or less. Configuration 7: 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 6, a negative electrode, and a non-aqueous electrolyte.

[0097] REFERENCE SIGNS LIST 10 nonaqueous electrolyte 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. General formula (I) Li ａ Ni ｂ Co ｃ Mn １－ｂ－ｃ－ｄ M1 ｄ O ２ (wherein 0.8≦a≦1.2, 0.3≦b≦0.95, 0.001≦c≦0.1, 0≦d≦0.1, and M1 is at least one element selected from the group consisting of F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V), the lithium transition metal composite oxide includes secondary particles formed by aggregation of primary particles, and a compound represented by the general formula (II) Li ｘ Co ｙ M2 ｚ O ２ (wherein 0.8≦x≦1.1, 0.97≦y≦1.0, 0≦z≦0.03, and M2 represents at least one element selected from the group consisting of Ni, Mn, F, W, Ca, Sr, Ti, Nb, Al, Zr, Fe, La, Mo, Si, V, Bi, B, Sb, Ta, Ce, and V), and the average oxidation number of Co in all particles of the lithium transition metal composite oxide is greater than 2.0 and less than 3.

0.

2. The cobalt-containing composite oxide is LiCoO ２ 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein 3. 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 layered structure.

4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein in said general formula (I), 1.05≦a≦1.15, 0.485≦b≦0.9, 0.001≦c≦0.05, and 0≦d≦0.

01.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein divalent Co is contained inside the secondary particles.

6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the average oxidation number of Ni throughout the entire particles of said lithium transition metal composite oxide is 2.8 or more and 3.8 or less.

7. 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 6, a negative electrode, and a non-aqueous electrolyte.

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