Positive electrode active material for lithium ion secondary battery, method for producing same, and lithium ion secondary battery using same

Abstract

The problem to be solved by the present invention is to provide: a positive electrode active material for lithium ion secondary batteries, which contains a LiMnTi-containing oxide, and which has excellent productivity and can be industrially mass-produced; a method for producing the positive electrode active material; and a lithium ion secondary battery which uses the positive electrode active material for lithium ion secondary batteries. In order to solve the problem, this method for producing a positive electrode active material for a lithium ion secondary battery comprises a step for generating a LiMnTi-containing oxide by subjecting a specific NaMnTi-containing oxide having a tunnel structure Pbam to hydrothermal treatment in an aqueous lithium nitrate solution.

Description

TECHNICAL FIELD

[0001] The present application relates to a positive electrode active material for a lithium ion secondary battery, a manufacturing method thereof, and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery. BACKGROUND

[0002] In recent years, in order to enable more people to obtain affordable, reliable, sustainable, and advanced energy, research and development related to secondary batteries that contribute to the efficiency of energy are being conducted. As a positive electrode active material for a lithium ion secondary battery, a LiMnTi-containing oxide that is an oxide containing lithium, manganese, and titanium and has a tunnel structure belonging to space group Pbam (hereinafter, referred to as tunnel structure Pbam) is investigated. As a manufacturing method of the LiMnTi-containing oxide having the tunnel structure Pbam, a method of substituting Na of a NaMnTi-containing oxide having the tunnel structure Pbam with Li is known. As the method of substituting Na with Li, a molten salt method of using a molten salt of a lithium salt as a lithium source and a solution method of using a lithium compound solution as a lithium source are known (refer to Patent Documents 1 and 2).

[0003] [Prior Art Documents]

[0004] (Patent Documents)

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-263583

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-268127 SUMMARY

[0007] [Problems to be Solved by the Invention]

[0008] Also, in the technology related to secondary batteries, one of the problems to be solved is the sustainability of resources. The LiMnTi-containing oxide is attracting attention from the viewpoint of the sustainability of resources because it does not contain a rare metal such as cobalt or nickel used as a raw material for manufacturing a positive electrode active material. However, the LiMnTi-containing oxide requires a process of substituting Na of a NaMnTi-containing oxide with Li, and both the molten salt method and the solution method are low in productivity and are difficult to synthesize in large quantities in industry.

[0009] The present application was made in view of the above-described problems, and aims to provide a positive electrode active material for a lithium ion secondary battery, a manufacturing method thereof, and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery, which are excellent in productivity and can be produced in large quantities in industry, and which include a LiMnTi-containing oxide.

[0010] [Technical Means to Solve the Problems]

[0011] The present inventors have found that a LiMnTi-containing oxide obtained by subjecting a NaMnTi-containing oxide having a prescribed composition to hydrothermal treatment in an aqueous nitric acid solution has a prescribed composition and has a high discharge capacity, thereby completing the present invention. Thus, the present invention provides the following solutions.

[0012] (1) A positive electrode active material for a lithium ion secondary battery, having a tunnel structure Pbam, a composition represented by the following general formula (I), a lattice constant of an a-axis in a range of 9.0420 A or more and 9.1640 A or less, a lattice constant of a b-axis in a range of 24.294 A or more and 25.968 A or less, and a lattice constant of a c-axis in a range of 2.8820 A or more and 2.8935 A or less;

[0013] Li a Na b Mn x Ti y M z O2(I)

[0014] wherein in the above general formula (I), M is at least one element selected from the group consisting of a second group element and a thirteenth group element, a satisfies the relation of 0.40 ≦ a ≦ 0.50, b satisfies the relation of 0.01 ≦ b ≦ 0.18, x, y, z satisfy the relations of x + y + z = 1 and 0.50 ≦ x ≦ 1.00, 0 < y ≦ 0.50, and 0 ≦ z < 0.50.

[0015] The positive electrode active material for a lithium ion secondary battery according to (1) can be produced using a hydrothermal treatment method which can be relatively easily implemented industrially, and is therefore excellent in productivity and can be mass-produced industrially. In addition, since the lattice constants of the a-axis, the b-axis, and the c-axis are in the above ranges, the capacity is high.

[0016] (2) The positive electrode active material for a lithium ion secondary battery according to (1), wherein an X-ray diffraction pattern measured using CuKα as an X-ray source has a diffraction peak in a range of 64.47 degrees or more and 65.57 degrees or less in terms of diffraction angle 2θ.

[0017] The positive electrode active material for a lithium ion secondary battery according to (2) has the above diffraction peak, and the capacity is higher.

[0018] (3) The positive electrode active material for a lithium ion secondary battery according to (1) or (2), wherein the lattice constant of the c-axis is in a range of 2.8835 A or more and 2.8918 A or less.

[0019] The positive electrode active material for a lithium ion secondary battery according to (3) has a higher capacity because the lattice constant of the c-axis is within the above range.

[0020] (4) The positive electrode active material for a lithium ion secondary battery according to (3), wherein the lattice constant of the c-axis is within a range of 2.8850 A or more and 2.8918 A or less.

[0021] The positive electrode active material for a lithium ion secondary battery according to (4) has a higher capacity because the lattice constant of the c-axis is within the above range.

[0022] (5) The positive electrode active material for a lithium ion secondary battery according to any one of (1) to (4), wherein a half-value width of a diffraction peak within a range of 64 degrees or more and 65 degrees or less in terms of diffraction angle 2θ in an X-ray diffraction pattern measured using CuKα as an X-ray source is 0.158 degrees or more and 0.186 degrees or less.

[0023] The positive electrode active material for a lithium ion secondary battery according to (5) has a higher capacity because the half-value width of the above diffraction peak is within the above range and the crystallinity is high.

[0024] (6) The positive electrode active material for a lithium ion secondary battery according to any one of (1) to (5), wherein a half-value width of a diffraction peak within a range of 61 degrees or more and 62 degrees or less in terms of diffraction angle 2θ in an X-ray diffraction pattern measured using CuKα as an X-ray source is 0.142 degrees or more and 0.280 degrees or less.

[0025] The positive electrode active material for a lithium ion secondary battery according to (6) has a higher capacity because the half-value width of the above diffraction peak is within the above range and the crystallinity is higher.

[0026] (7) A method for manufacturing a positive electrode active material for a lithium ion secondary battery, which is the method for manufacturing the positive electrode active material for a lithium ion secondary battery according to any one of (1) to (6), comprising the step of: hydrothermally treating a NaMnTi-containing oxide having a tunnel structure Pbam and represented by the following general formula (II) in a lithium nitrate aqueous solution to produce a LiMnTi-containing oxide;

[0027] Na c Mn x Ti y M z O2(II)

[0028] In the above general formula (II), M is at least one element selected from the group consisting of a Group 2 element and a Group 13 element, c satisfies the relationship 0.40 ≤ c ≤ 0.50, and x, y, and z satisfy the relationships x + y + z = 1, 0.50 ≤ x ≤ 1.00, 0 < y ≤ 0.50, and 0 ≤ z < 0.50.

[0029] The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (7) can efficiently manufacture the positive electrode active material for a secondary battery of the present embodiment, since the NaMnTi-containing oxide of the above general formula (II) is subjected to hydrothermal treatment in a lithium nitrate aqueous solution.

[0030] (8) The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (7), wherein the treatment temperature of the hydrothermal treatment is in the range of 80°C or higher and 220°C or lower.

[0031] The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (8) can reliably manufacture the positive electrode active material for a lithium-ion secondary battery.

[0032] (9) The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (8), wherein the treatment temperature of the hydrothermal treatment is in the range of 150°C or higher and 220°C or lower.

[0033] The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (9) can more reliably manufacture the positive electrode active material for a lithium-ion secondary battery.

[0034] (10) The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (9), wherein the treatment temperature of the hydrothermal treatment is in the range of 190°C or higher and 220°C or lower.

[0035] The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (10) can manufacture a positive electrode active material for a lithium-ion secondary battery having high crystallinity.

[0036] (11) The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to any one of (7) to (10), further comprising a step of heating the LiMnTi-containing oxide at a temperature of 200°C or higher and 320°C or lower.

[0037] The manufacturing method of the positive electrode active material for a lithium-ion secondary battery according to (11) can industrially advantageously manufacture a positive electrode active material for a lithium-ion secondary battery having higher crystallinity.

[0038] (12) A lithium ion secondary battery provided with a positive electrode mixed material layer containing the positive electrode active material for a lithium ion secondary battery according to any one of (1) to (6).

[0039] The lithium ion secondary battery according to (12) has a high capacity per unit mass due to containing the positive electrode active material for a lithium ion secondary battery described above.

[0040] (EFFECTS OF THE INVENTION)

[0041] According to the present application, it is possible to provide a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery using the same, which are excellent in productivity and can be mass-produced industrially, and which include a LiMnTi-containing oxide. BRIEF DESCRIPTION OF DRAWINGS

[0042] Fig. 1 is an X-ray diffraction pattern of the LiMnTi-containing oxide powder obtained in Examples 1 to 4.

[0043] Fig. 2 is an X-ray diffraction pattern of the LiMnTi-containing oxide powder obtained in Examples 5 to 8.

[0044] Fig. 3 is an X-ray diffraction pattern of the LiMnTi-containing oxide powder obtained in Comparative Example 1.

[0045] Fig. 4 is an X-ray diffraction pattern of the LiMnTi-containing oxide powder after annealing treatment obtained in Examples 9 to 12.

[0046] Fig. 5 is an X-ray diffraction pattern of the LiMnTi-containing oxide powder after annealing treatment obtained in Examples 13 to 16.

[0047] Fig. 6 is an X-ray diffraction pattern of the LiMnTi-containing oxide powder after annealing treatment obtained in Examples 17 to 19. DETAILED DESCRIPTION

[0048] Hereinafter, an embodiment of the present application will be described. Among them, the following embodiment is an example of the present application, and the present application is not limited to the following.

[0049] The positive electrode active material for a lithium-ion secondary battery of the present embodiment is a LiMnTi-containing oxide containing lithium (Li), manganese (Mn), and titanium (Ti) and having a tunnel structure Pbam. The LiMnTi-containing oxide can also contain at least one element selected from the group consisting of a second group element and a thirteenth group element. The LiMnTi-containing oxide is represented by the following general formula (I).

[0050] Li a Na b Mn x Ti y M z O2(I)

[0051] In the above general formula (I), M is at least one element selected from the group consisting of a second group element and a thirteenth group element, a satisfies the relationship 0.40 ≦ a ≦ 0.50, b satisfies the relationship 0.01 ≦ b ≦ 0.25, x, y, z satisfy the relationships x + y + z = 1 and 0.50 ≦ x ≦ 1.00, 0 < y ≦ 0.50, and 0 ≦ z < 0.50. b is preferably 0.01 ≦ b ≦ 0.20, more preferably 0.01 ≦ b ≦ 0.10, and further preferably 0.01 ≦ b ≦ 0.03.

[0052] In the general formula (I), as the second group element represented by M, magnesium and calcium can be exemplified. As the thirteenth group element represented by M, aluminum can be exemplified. These elements can be used singly or in combination of two or more.

[0053] The LiMnTi-containing oxide can also have a peak in the range of 64.47 degrees or more and 65.57 degrees or less in terms of diffraction angle 2θ in an X-ray diffraction pattern measured using CuKα as an X-ray source. The LiMnTi-containing oxide having this diffraction peak has a higher capacity.

[0054] In the LiMnTi-containing oxide, the lattice constant of the a-axis is in the range of 9.0420 A or more and 9.1640 A or less, the lattice constant of the b-axis is in the range of 24.294 A or more and 25.968 A or less, and the lattice constant of the c-axis is in the range of 2.8820 A or more and 2.8935 A or less. The lattice constant of the a-axis is preferably in the range of 9.0620 A or more and 9.0930 A or less. The lattice constant of the b-axis is preferably in the range of 24.294 A or more and 24.611 A or less, more preferably in the range of 24.294 A or more and 24.503 A or less. The lattice constant of the c-axis is preferably in the range of 2.8835 A or more and 2.8918 A or less, more preferably in the range of 2.8850 A or more and 2.8918 A or less. If the lattice constants of the a-axis, the b-axis, and the c-axis are in the above ranges, the capacity of the LiMnTi-containing oxide becomes higher.

[0055] In the X-ray diffraction pattern of the LiMnTi-containing oxide measured using CuKα as an X-ray source, the half-value width of the diffraction peak in the range of 64 degrees or more and 65 degrees or less in terms of diffraction angle 2θ can also be 0.158 degrees or more and 0.186 degrees or less. The LiMnTi-containing oxide in which the half-value width of this diffraction peak is in this range has high crystallinity, and thus the capacity becomes higher.

[0056] In the X-ray diffraction pattern of the LiMnTi-containing oxide measured using CuKα as an X-ray source, the half-value width of the diffraction peak in the range of 61 degrees or more and 62 degrees or less in terms of diffraction angle 2θ can also be 0.142 degrees or more and 0.280 degrees or less. The LiMnTi-containing oxide in which the half-value width of this diffraction peak is in this range has higher crystallinity, and thus the capacity becomes higher.

[0057] The positive electrode active material for lithium-ion secondary batteries of the present embodiment can be produced, for example, by a method including a step of hydrothermally treating a NaMnTi-containing oxide having a tunnel structure Pbam in an aqueous lithium nitrate solution to produce a LiMnTi-containing oxide. The NaMnTi-containing oxide can be an oxide represented by the following general formula (II).

[0058] Na c Mn x Ti y M z O2(II)

[0059] In the above general formula (II), M is at least one element selected from the group consisting of Group 2 elements and Group 13 elements, c satisfies the relationship of 0.40 ≤ c ≤ 0.50, and x, y, and z satisfy the relationships of x + y + z = 1, 0.50 ≤ x ≤ 1.00, 0 < y ≤ 0.50, and 0 ≤ z < 0.50.

[0060] The nitric acid concentration of the aqueous lithium nitrate solution is, for example, 100 g / L or more. The aqueous lithium nitrate solution can also be a saturated aqueous solution. The amount of the NaMnTi-containing oxide in the aqueous lithium nitrate solution is, for example, an amount in which, when the molar amount of the NaMnTi-containing oxide is taken as 1 mole, the amount of Li is 10 to 50 moles.

[0061] The treatment temperature of the hydrothermal treatment is, for example, in the range of 80°C or higher and 220°C or lower, preferably 110°C or higher, more preferably 150°C or higher, and particularly preferably 190°C or higher. By setting the treatment temperature in the above range, the above positive electrode active material for a lithium ion secondary battery can be reliably produced. In particular, if the treatment temperature is 190°C or higher, a LiMnTi-containing oxide having high crystallinity can be produced. The treatment time of the hydrothermal treatment varies depending on the Li concentration of the aqueous lithium nitrate solution, the concentration of the NaMnTi-containing oxide in the aqueous lithium nitrate solution, the capacity of the reaction vessel, and the like, and is, for example, in the range of 1 to 30 hours.

[0062] The LiMnTi-containing oxide produced by the hydrothermal treatment can also be washed and dried. The washing can also be performed by water washing. By water washing the LiMnTi-containing oxide, Na displaced by Li and unreacted lithium nitrate are removed. The drying method is not particularly limited, and various methods that can be used as drying methods for inorganic substances, such as a heating drying method, a vacuum drying method, a spray drying method, and the like, can be used.

[0063] The positive electrode active material for a lithium ion secondary battery according to the present embodiment can be used as a positive electrode active material for a lithium ion secondary battery. The lithium ion secondary battery has, for example, a positive electrode, a negative electrode, an electrolyte, a separator disposed between the positive electrode and the negative electrode, and a case that accommodates them. A solid electrolyte can also be used instead of the electrolyte.

[0064] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on a surface of the positive electrode current collector. The positive electrode active material layer contains the positive electrode active material for lithium-ion secondary batteries according to the present embodiment. The positive electrode active material layer can also contain a conductive aid and a binder. Since the positive electrode active material for secondary batteries according to the present embodiment is chemically stable, the conductive aid and the binder are not particularly limited, and known conductive aids and binders used in the positive electrode active material layer of lithium-ion secondary batteries can be used. In addition, the positive electrode current collector is not particularly limited, and known positive electrode current collectors used in the positive electrode current collector of lithium-ion secondary batteries, such as an aluminum foil, can be used.

[0065] As the negative electrode, a laminate including a negative electrode current collector and a negative electrode active material layer formed on a surface of the negative electrode current collector can be used. The negative electrode active material layer contains a negative electrode active material. As the negative electrode active material, metal lithium, a substance capable of occluding and releasing lithium, a metal or semimetal that forms an alloy with lithium, or the like can be used. As examples of the substance capable of occluding and releasing lithium, lithium transition metal oxides such as lithium titanate, transition metal oxides such as TiO2, Nb2O3, and WO3, SiO, metal sulfides, metal nitrides, and carbon materials such as artificial graphite, natural graphite, graphite, soft carbon, and hard carbon can be listed. As examples of the metal or semimetal that forms an alloy with lithium, Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, Zn, and the like can be listed. In the case where the negative electrode active material is in a powder form, the negative electrode active material layer can also contain a conductive aid and a binder. The conductive aid and the binder are not particularly limited, and known conductive aids and binders used in the negative electrode active material layer of lithium-ion secondary batteries can be used. In addition, the negative electrode current collector is not particularly limited, and known negative electrode current collectors used in the negative electrode current collector of lithium-ion secondary batteries, such as a copper foil, can be used.

[0066] The electrolytic solution contains an organic solvent and an electrolyte. As the organic solvent, for example, a cyclic carbonate, a chain carbonate, a cyclic ether, a chain ether, a hydrofluoro ether, an aromatic ether, a sulfone, a cyclic ester, a chain carboxylate, a nitrile can be used. As examples of the cyclic carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate and the like can be listed. As examples of the chain carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and the like can be listed. As examples of the cyclic ether, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl 1,3-dioxolane and the like can be listed. As examples of the chain ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, diethyl ether and the like can be listed. As examples of the hydrofluoro ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and the like can be listed. As examples of the aromatic ether, anisole can be listed. As examples of the sulfone, sulfolane, methylsulfolane and the like can be listed. As examples of the cyclic ester, γ-butyrolactone and the like can be listed. As examples of the chain carboxylate, acetate, butyrate, propionate and the like can be listed. As examples of the nitrile, acetonitrile, propionitrile and the like can be listed. The organic solvent can be used singly or in combination of two or more.

[0067] The electrolyte is a charge moving medium, that is, a supply source of lithium ions, and contains a lithium salt. As examples of the lithium salt, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(CF3SO2)2 (LiTFSI), LiN(FSO2)2 (LiFSI), LiBC4O8 and the like can be listed. The lithium salt can be used singly or in combination of two or more.

[0068] As the solid electrolyte, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, a halide solid electrolyte and the like can be used.

[0069] As examples of the sulfide solid electrolyte, Li2S-P2S5, Li2S-P2S5-LiI and the like can be listed. As examples of the oxide solid electrolyte, a sodium superionic conductor (NASICON) type oxide, a garnet type oxide, a perovskite type oxide and the like can be listed. As examples of the NASICON type oxide, an oxide containing Li, Al, Ti, P and O (for example, Li1+xAlxTi2-x(PO4)3 (0≤x≤2)) can be listed. As examples of the garnet type oxide, an oxide containing Li, La, Zr, Ga and O (for example, Li7La3Zr2Ga3O12) can be listed. As examples of the perovskite type oxide, an oxide containing Li, Ge, O and the like (for example, Li10GeP2O8) can be listed. 1.5 Al 0.5 Ti 1.5(PO4)3). As an example of the garnet-type oxide, an oxide containing Li, La, Zr, and O (e.g., Li7La3Zr2O 12 As an example of the perovskite-type oxide, an oxide containing Li, La, Ti, and O (e.g., LiLaTiO3) can be given.

[0070] The separator is not particularly limited, and for example, a porous body sheet, a nonwoven fabric sheet can be used. As an example of the material of the porous body sheet, a polyolefin such as polyethylene, polypropylene, an aromatic polyamide, a polyimide, a fluororesin, or the like can be given. As an example of the material of the nonwoven fabric sheet, a glass fiber, a cellulose fiber, or the like can be given.

[0071] The exterior body is not particularly limited, and a known exterior body used in a lithium ion secondary battery, such as a metal container, a laminated film container, or the like can be used.

[0072] The positive electrode active material for a lithium ion secondary battery according to the present embodiment, since having the composition of the above general formula (I), can be manufactured using a hydrothermal treatment method which can be relatively easily implemented industrially, and thus is excellent in productivity, and can be mass-produced industrially.

[0073] The production method of the positive electrode active material for a lithium ion secondary battery according to the present embodiment, since performing hydrothermal treatment on the above NaMnTi-containing oxide of general formula (II) in a lithium nitrate aqueous solution, can efficiently produce the positive electrode active material for a secondary battery according to the present embodiment.

[0074] The lithium ion secondary battery according to the present embodiment, since containing the positive electrode active material for a lithium ion secondary battery according to the present embodiment, is high in productivity.

[0075] [Examples]

[0076] (Example 1)

[0077] (Production of NaMnTi-containing oxide powder)

[0078] Na2CO3, Mn2O3, and TiO2 were weighed so that the total molar amount of Mn and Ti would be 1 mol, the molar amount of Na (Na / (Mn+Ti)) would be 0.5 mol, the molar amount of Ti (Ti / (Mn+Ti)) would be 0.50 mol, and the total mass would be 1.0 g. The weighed Na2CO3, Mn2O3, and TiO2 were mixed using a mortar and a pestle. The obtained raw material mixture was put into an alumina crucible, and calcination was performed in the atmosphere at a calcination temperature of 1000°C for 12 hours. After the calcination, the obtained calcinates were pulverized using a mortar and a pestle. The X-ray diffraction pattern of the obtained calcinates was measured, and it was confirmed that the obtained calcinates were NaMnTi oxide powder having a tunnel structure.

[0079] (LiMnTi oxide powder-containing production)

[0080] A LiNO3 solution was prepared by putting LiNO3 25.00 g and water 50 mL into a hydrothermal reaction vessel and stirring to dissolve the LiNO3 in the water. Then, the obtained NaMnTi oxide powder 1.0 g was put into the LiNO3 solution and stirred to obtain a dispersion in which the NaMnTi oxide powder was dispersed in the LiNO3 solution. Then, the hydrothermal reaction vessel was closed, and the closed hydrothermal reaction vessel was put into a thermostat and heated in the atmosphere at a hydrothermal treatment temperature of 80°C for 24 hours to hydrothermally treat the NaMnTi oxide powder. After the heating, the hydrothermally treated powder (LiMnTi oxide powder-containing) was recovered from the hydrothermal reaction vessel. The recovered LiMnTi oxide powder-containing was washed with water, and the water was removed by centrifugal separation three times. The LiMnTi oxide powder-containing from which the water had been removed was loaded on a shallow tray and vacuum-dried at a temperature of 100°C for 6 hours. The dried LiMnTi oxide powder-containing was pulverized using a mortar and a pestle.

[0081] (Examples 2 to 8)

[0082] The hydrothermal treatment temperature was set to 100°C in Example 2, 120°C in Example 3, 140°C in Example 4, 160°C in Example 5, 180°C in Example 6, 200°C in Example 7, and 220°C in Example 8, and the LiMnTi oxide powder-containing was produced in the same manner as in Example 1 except for the above.

[0083] (Comparative Example 1)

[0084] In addition to using the molten salt method to replace Na in the NaMnTi oxide-containing powder with Li, a LiMnTi oxide-containing powder was produced in the same manner as in Example 1. The replacement conditions were as follows. The molten salt used was a molten salt containing lithium nitrate and lithium chloride at a molar ratio of 88:12. The ratio of the molten salt to the NaMnTi oxide-containing powder was set to 20:1 in terms of the molar ratio of Li to Na. The replacement time was set to 10 hours.

[0085] [Assessment]

[0086] For the LiMnTi oxide-containing powders obtained in Examples 1 to 8 and Comparative Example 1, the chemical composition, X-ray diffraction pattern, lattice constants, half-value width FWHM, and charge / discharge characteristics were assessed by the following methods.

[0087] (Chemical Composition)

[0088] The sample was dissolved with acid. The contents of Li, Na, Mn, Ti, and Al in the obtained solution were measured using an inductively coupled plasma (ICP) emission spectrometer. The obtained contents of Li, Na, Mn, Ti, and Al were converted to molar amounts based on 1 mole of the total amount of Mn, Ti, and Al. The results thereof are shown in Table 1 below together with the hydrothermal treatment temperature.

[0089] (X-ray Diffraction Pattern)

[0090] The X-ray diffraction pattern was measured under the following conditions. The results thereof are shown in FIG. 1. Figs. 1-3 .

[0091] Measuring device: RINT-2550V, manufactured by Rigaku Corporation

[0092] X-ray source: Cu Kα

[0093] X-ray output: 40 kV, 200 mA

[0094] Measurement conditions: 1.0 s, 0.03 deg interval

[0095] (Lattice Constants)

[0096] Using the above-described X-ray diffraction pattern, the lattice constants of the a-axis, b-axis, and c-axis were measured. The lattice constants were calculated by the least squares method using the indices of the diffraction peaks and the interplanar spacings thereof derived from the tunnel structure Pbam. The results thereof are shown in Table 2 below.

[0097] (Half-Value Width FWHM)

[0098] From the X-ray diffraction pattern, a diffraction peak with a diffraction angle 2θ of 61 to 62 degrees (61-62 degree diffraction peak) and a diffraction peak with a diffraction angle 2θ of 64 to 65 degrees (64-65 degree diffraction peak) were extracted. The half-value width (FWHM) of the extracted peaks was measured. The results are shown in Table 2 below.

[0099] (Charge and discharge characteristics)

[0100] A 5 mg sample, 5 mg of acetylene black (a conductive material), and 1 mg of polytetrafluoroethylene (PTFE) (a binder) were mixed. The resulting mixture was formed into a sheet and pressed onto an Al mesh, which served as the working electrode. A lithium foil was used as the counter electrode. The working and counter electrodes were immersed in an electrolyte solution consisting of LiPF6 dissolved in an ethylene carbonate (EC) and dimethyl carbonate (DMC) solvent to create a two-electrode cell.

[0101] A charge-discharge test was conducted using a two-electrode cell. The test conditions were a current density (per sample) of 10 mA / g, a potential range of 2.0-4.8 V, and constant current / constant voltage charging (until 2 hours had passed). The test was conducted at 25°C. The initial (first cycle) discharge capacity is shown in Table 2 below.

[0102] [Table 1]

[0103]

[0104] [Table 2]

[0105]

[0106] Depend on Figs. 2-4 The X-ray diffraction patterns shown in confirm that the LiMnTi oxide powders obtained in Examples 1 to 8 all have a tunnel structure Pbam. From the results of Table 1, it can be seen that as the hydrothermal treatment temperature increases, the Li content of the LiMnTi oxide powder increases, that is, as the heat treatment temperature increases, it becomes easier for Na and Li to be replaced. In addition, from the results of Table 2, it can be seen that as the hydrothermal treatment temperature increases, the lattice constants of the a-axis and b-axis tend to decrease, the c-axis increases, and the half-value width decreases. In addition, it can be seen that the LiMnTi oxide powders obtained in Examples 1 to 8 are all capable of Li occlusion / release, and the discharge capacity increases as the hydrothermal treatment temperature increases.

[0107] (Example 9)

[0108] Annealing treatment (annealing treatment of LiMnTi-containing oxide powder)

[0109] The LiMnTi-containing oxide powder obtained in Example 1 was placed in an alumina crucible, and calcined in the atmosphere at an annealing temperature of 270°C for 12 hours to perform annealing treatment. After the annealing, the obtained calcined product was pulverized using a mortar and a pestle.

[0110] (Examples 10 to 19)

[0111] Annealing treatment was performed in the same manner as in Example 9, except that the LiMnTi-containing oxide powder of Table 3 below was used, and the annealing temperature was set to the temperature of Table 3 below.

[0112] [Evaluation]

[0113] The X-ray diffraction pattern, lattice constant, half-value width FWHM, and charge-discharge characteristics were evaluated for the LiMnTi-containing oxide powders obtained in Examples 1 to 8 by the above-described methods. The X-ray diffraction pattern is shown in FIG. 1. Figs. 4-6 The lattice constant, half-value width FWHM, and discharge capacity are shown in Table 3 below.

[0114] [Table 3]

[0115]

[0116] As is clear from the results of Table 3, the discharge capacity of the LiMnTi-containing oxide powder after the annealing treatment tended to increase as the treatment temperature at which the LiMnTi-containing oxide powder was generated by performing hydrothermal treatment on the NaMnTi-containing oxide powder became higher. Thus, it was confirmed from the results of the present example that a LiMnTi-containing oxide powder having a high capacity could be obtained by performing hydrothermal treatment and annealing treatment.

Claims

1. A positive electrode active material for a lithium ion secondary battery, having a tunnel structure Pbam, the composition being represented by the following general formula (I), the lattice constant of the a-axis being in the range of 9.0420 Å or more and 9.1640 Å or less, the lattice constant of the b-axis being in the range of 24.294 Å or more and 25.968 Å or less, and the lattice constant of the c-axis being in the range of 2.8820 Å or more and 2.8935 Å or less; Li a Na b Mn x You y M z O2(I) in, In the above general formula (I), M is at least one element selected from the group consisting of Group II elements and Group XIII elements, a satisfies the relationship of 0.40 ≦ a ≦ 0.50, b satisfies the relationship of 0.01 ≦ b ≦ 0.25, and x, y, z satisfy x + y + z = 1 and 0.50 ≦ x ≦ 1.00, 0 < y ≦ 0.50, and 0 ≦ z < 0.

50.

2. The positive electrode active material for lithium ion secondary batteries according to claim 1, wherein In the X-ray diffraction pattern measured using CuKα as the X-ray source, there is a diffraction peak in the range of 64.47 degrees or more and 65.57 degrees or less in terms of the diffraction angle 2θ.

3. The positive electrode active material for lithium ion secondary batteries according to claim 1 or 2, wherein The lattice constant of the c-axis is in the range of 2.8835 Å or more and 2.8918 Å or less.

4. The positive electrode active material for lithium ion secondary batteries according to claim 1 or 2, wherein The lattice constant of the c-axis is in the range of 2.8850 Å or more and 2.8918 Å or less.

5. The positive electrode active material for lithium ion secondary batteries according to claim 1 or 2, wherein In the X-ray diffraction pattern measured using CuKα as the X-ray source, the half-value width of the diffraction peak in the range of 64 degrees or more and 65 degrees or less in terms of the diffraction angle 2θ is 0.158 degrees or more and 0.186 degrees or less.

6. The positive electrode active material for lithium ion secondary batteries according to claim 1 or 2, wherein [[ID=@6]]In the X-ray diffraction pattern measured using CuKα as the X-ray source, the half-value width of the diffraction peak in the range of 61 degrees or more and 62 degrees or less in terms of the diffraction angle 2θ is 0.142 degrees or more and 0.280 degrees or less.

7. A method for manufacturing a positive electrode active material for a lithium ion secondary battery, which is the method for manufacturing the positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, including the following steps: Hydrothermally treating a NaMnTi oxide having a tunnel structure Pbam and represented by the following general formula (II) in an aqueous lithium nitrate solution to generate a LiMnTi oxide; And c Mn x Tea y I z O2(II) in, In the above general formula (II), M is at least one element selected from the group consisting of Group II elements and Group XIII elements, c satisfies the relationship of 0.40 ≦ c ≦ 0.50, and x, y, z satisfy x + y + z = 1 and 0.50 ≦ x ≦ 1.00, 0 < y ≦ 0.50, and 0 ≦ z < 0.

50.

8. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 7, wherein: The treatment temperature of the aforementioned hydrothermal treatment is in the range of 80°C or more and 220°C or less.

9. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 8, wherein: The treatment temperature of the aforementioned hydrothermal treatment is in the range of 150°C or more and 220°C or less.

10. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 9, wherein: The treatment temperature of the aforementioned hydrothermal treatment is in the range of 190°C or more and 220°C or less.

11. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 7, wherein: It further includes the following step: heating the aforementioned LiMnTi oxide at a temperature of 200°C or more and 320°C or less.

12. A lithium ion secondary battery, including a positive electrode mixture layer, and the positive electrode mixture layer contains the positive electrode active material for a lithium ion secondary battery according to claim 1 or 2.

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