Positive electrode active material for lithium-ion secondary batteries, manufacturing method for the same, and lithium-ion secondary battery using the same

Abstract

To provide a positive electrode active material for a lithium-ion secondary battery containing LiMnTi oxide, a manufacturing method for the same, and a lithium-ion secondary battery using the same, which are highly productive and capable of industrial mass production.SOLUTION: The manufacturing method for a positive electrode active material for a lithium-ion secondary battery includes hydrothermally treating a specific NaMnTi-containing oxide having a tunnel structure Pbam in a lithium nitrate aqueous solution to generate a LiMnTi-containing oxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to 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. [Background technology]

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. LiMnTi-containing oxides, which are oxides containing lithium, manganese, and titanium and have a tunnel structure belonging to the space group Pbam (hereinafter referred to as the tunnel structure Pbam), have been investigated as positive electrode active materials for lithium-ion secondary batteries. A known method for producing LiMnTi-containing oxides having the tunnel structure Pbam is to replace Na in NaMnTi-containing oxides having the tunnel structure Pbam with Li. Known methods for replacing Na with Li include a molten salt method using a molten lithium salt as a lithium source and a solution method using a lithium compound solution as a lithium source (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-263583 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-268127 Summary of the Invention [Problem to be solved by the invention]

[0004] In secondary battery technology, resource sustainability is one of the challenges. LiMnTi-containing oxides are attracting attention from the perspective of resource sustainability because they do not contain rare metals such as cobalt and nickel, which are used as raw materials for manufacturing positive electrode active materials. However, LiMnTi-containing oxides require a process to replace Na in NaMnTi-containing oxides with Li. Both the molten salt method and the solution method have low productivity, making industrial mass synthesis difficult.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery containing a LiMnTi-containing oxide that is highly productive and can be mass-produced industrially, a method for producing the same, and a lithium ion secondary battery using the same. [Means for solving the problem]

[0006] The present inventors have found that an LiMnTi-containing oxide obtained by hydrothermally treating an NaMnTi-containing oxide having a predetermined composition in a nitric acid aqueous solution has a predetermined composition and a high discharge capacity, and have completed the present invention. Accordingly, the present invention provides the following.

[0007] (1) A positive electrode active material for a lithium ion secondary battery, having a tunnel structure Pbam, and having a composition represented by the following general formula (I), in which the lattice constant of the a-axis is in the range of 9.0420 Å or more and 9.1640 Å or less, the lattice constant of the b-axis is in the range of 24.294 Å or more and 25.968 Å or less, and the lattice constant of the c-axis is in the range of 2.8820 Å or more and 2.8935 Å or less. Li a Na b Mn x Ti y M z O2(I) However, in the above general formula (I), M is at least one element selected from the group consisting of Group 2 elements and Group 13 elements, a satisfies the relationship of 0.40 ≦ a ≦ 0.50, b satisfies the relationship of 0.01 ≦ b ≦ 0.18, x, y, and z satisfy x + y + z = 1, and the relationships of 0.50 ≦ x ≦ 1.00, 0 < y ≦ 0.50, and 0 ≦ z < 0.50.

[0008] According to the positive electrode active material for a lithium ion secondary battery of (1), since it has the above composition, it can be produced using a hydrothermal treatment method that can be relatively easily implemented industrially, so it is excellent in productivity and enables industrial mass production. Further, since the lattice constants of the a-axis, b-axis, and c-axis are within the above ranges, the capacitance is increased.

[0009] The positive electrode active material for a lithium ion secondary battery according to (1), which has a diffraction peak in the range of 64.47 degrees or more and 65.57 degrees or less at a diffraction angle 2θ in the X-ray diffraction pattern measured using CuKα as the X-ray source.

[0010] According to the positive electrode active material for a lithium ion secondary battery of (2), since it has the above diffraction peak, the capacitance becomes higher.

[0011] 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 the range of 2.8835 Å or more and 2.8918 Å or less.

[0012] According to the positive electrode active material for a lithium ion secondary battery of (3), since the lattice constant of the c-axis is within the above range, the capacitance becomes higher.

[0013] The positive electrode active material for a lithium ion secondary battery according to (3), wherein the lattice constant of the c-axis is in the range of 2.8850 Å or more and 2.8918 Å or less.

[0014] According to the positive electrode active material for a lithium ion secondary battery of (4), since the lattice constant of the c-axis is within the above range, the capacitance becomes even higher.

[0015] (5) In the X-ray diffraction pattern measured using CuKα as the X-ray source, the full width at half maximum of the diffraction peak within the range of 64 degrees or more and 65 degrees or less at the diffraction angle 2θ is 0.158 degrees or more and 0.186 degrees or less. The positive electrode active material for a lithium-ion secondary battery according to any one of (1) to (4).

[0016] According to the positive electrode active material for a lithium-ion secondary battery of (5), since the full width at half maximum of the above diffraction peak is within the above range and the crystallinity is high, the capacitance becomes higher.

[0017] (6) In the X-ray diffraction pattern measured using CuKα as the X-ray source, the full width at half maximum of the diffraction peak within the range of 61 degrees or more and 62 degrees or less at the diffraction angle 2θ is 0.142 degrees or more and 0.280 degrees or less. The positive electrode active material for a lithium-ion secondary battery according to any one of (1) to (5).

[0018] According to the positive electrode active material for a lithium-ion secondary battery of (6), since the full width at half maximum of the above diffraction peak is within the above range and the crystallinity is even higher, the capacitance becomes even higher.

[0019] (7) A method for producing a positive electrode active material for a lithium-ion secondary battery according to any one of (1) to (6), which has a tunnel structure Pbam and includes a step of hydrothermally treating a NaMnTi-containing oxide represented by the following general formula (II) in an aqueous lithium nitrate solution to produce a LiMnTi-containing oxide. Na c Mn x Ti y M z O2(II) However, 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 ≦ a ≦ 0.50, x, y, and z satisfy x + y + z = 1, and the relationships of 0.50 ≦ x ≦ 1.00, 0 < y ≦ 0.50, and 0 ≦ z < 0.50.

[0020] According to the method for producing a positive electrode active material for a lithium ion secondary battery of (7), the NaMnTiAl-containing oxide of the general formula (II) is hydrothermally treated in an aqueous lithium nitrate solution, so that the positive electrode active material for a secondary battery of this embodiment can be produced with high efficiency.

[0021] (8) The method for producing a 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.

[0022] According to the method for producing a positive electrode active material for a lithium ion secondary battery of (8), the above-mentioned positive electrode active material for a lithium ion secondary battery can be produced reliably.

[0023] (9) The method for producing a 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 more and 220°C or less.

[0024] According to the method for producing a positive electrode active material for a lithium ion secondary battery of (9), the above-mentioned positive electrode active material for a lithium ion secondary battery can be produced more reliably.

[0025] (10) The method for producing a 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 more and 220°C or less.

[0026] According to the method for producing a positive electrode active material for a lithium ion secondary battery of (10), a positive electrode active material for a lithium ion secondary battery having high crystallinity can be produced.

[0027] (11) The method for producing a 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.

[0028] According to the method for producing a positive electrode active material for a lithium ion secondary battery of (11), a positive electrode active material for a lithium ion secondary battery having higher crystallinity can be produced industrially advantageously.

[0029] (12) A lithium ion secondary battery comprising a positive electrode mixture layer containing the positive electrode active material for a lithium ion secondary battery according to any one of (1) to (6).

[0030] The lithium ion secondary battery (12) contains the above-mentioned positive electrode active material for lithium ion secondary batteries, and therefore has a high electric capacity per mass. [Effects of the Invention]

[0031] According to the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery containing a LiMnTi-containing oxide, which has excellent productivity and can be mass-produced industrially, a method for producing the same, and a lithium ion secondary battery using the same. [Brief explanation of the drawings]

[0032] [Figure 1] 1 shows X-ray diffraction patterns of the LiMnTi-containing oxide powders obtained in Examples 1 to 4. [Figure 2] 1 shows X-ray diffraction patterns of the LiMnTi-containing oxide powders obtained in Examples 5 to 8. [Figure 3] 1 is an X-ray diffraction pattern of the LiMnTi-containing oxide powder obtained in Comparative Example 1. [Figure 4] 1 shows X-ray diffraction patterns of the LiMnTi-containing oxide powders obtained in Examples 9 to 12 after annealing treatment. [Figure 5] 1 shows X-ray diffraction patterns of the LiMnTi-containing oxide powders obtained in Examples 13 to 16 after annealing treatment. [Figure 6] 1 shows X-ray diffraction patterns of the LiMnTi-containing oxide powders obtained in Examples 17 to 19 after annealing treatment. DETAILED DESCRIPTION OF THE INVENTION

[0033] Hereinafter, embodiments of the present invention will be described. However, the embodiments described below are merely examples of the present invention, and the present invention is not limited to the following.

[0034] The positive electrode active material for the lithium-ion secondary battery of this embodiment contains lithium (Li), manganese (Mn), and titanium (Ti), and is a LiMnTi-containing oxide having a tunnel structure Pbam. The LiMnTi-containing oxide may further contain at least one element selected from the group consisting of Group 2 elements and Group 13 elements. The LiMnTi-containing oxide is represented by the following general formula (I).

[0035] Li a Na b Mn x Ti y M z O2(I)

[0036] However, in the above general formula (I), M is at least one element selected from the group consisting of Group 2 elements and Group 13 elements, a satisfies the relationship of 0.40 ≦ a ≦ 0.50, b satisfies the relationship of 0.01 ≦ b ≦ 0.25, x, y, z satisfy x + y + z = 1, and satisfy the relationships of 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 still more preferably 0.01 ≦ b ≦ 0.03.

[0037] In the general formula (I), examples of the Group 2 element represented by M include magnesium and calcium. Examples of the Group 13 element represented by M include aluminum. These elements may be used alone or in combination of two or more.

[0038] The LiMnTi-containing oxide may have a peak in the range of 64.47 degrees or more and 65.57 degrees or less at the diffraction angle 2θ in the X-ray diffraction pattern measured using CuKα as the X-ray source. The LiMnTi-containing oxide having this diffraction peak has a higher capacitance.

[0039] The LiMnTi-containing oxide has an a-axis lattice constant in the range of 9.0420 Å to 9.1640 Å, a b-axis lattice constant in the range of 24.294 Å to 25.968 Å, and a c-axis lattice constant in the range of 2.8820 Å to 2.8935 Å. The a-axis lattice constant is preferably in the range of 9.0620 Å to 9.0930 Å. The b-axis lattice constant is preferably in the range of 4.294 Å to 24.611 Å, more preferably in the range of 24.294 Å to 24.503 Å. The c-axis lattice constant is preferably in the range of 2.8835 Å to 2.8918 Å, more preferably in the range of 2.8850 Å to 2.8918 Å. When the a-axis, b-axis, and c-axis lattice constants are in the above ranges, the LiMnTi-containing oxide has a higher electric capacitance.

[0040] In an X-ray diffraction pattern of the LiMnTi-containing oxide measured using CuKα as an X-ray source, the half-width of a diffraction peak within a diffraction angle 2θ range of 64 degrees to 65 degrees may be 0.158 degrees to 0.186 degrees. LiMnTi-containing oxides having a half-width of this diffraction peak within this range have high crystallinity and therefore have a higher electric capacity.

[0041] In an X-ray diffraction pattern measured using a CuKα X-ray source, the half-width of a diffraction peak within a diffraction angle 2θ range of 61 degrees to 62 degrees may be 0.142 degrees to 0.280 degrees. A LiMnTi-containing oxide having a half-width of this diffraction peak within this range has higher crystallinity and therefore a higher electric capacitance.

[0042] The positive electrode active material for a lithium ion secondary battery of this embodiment can be produced by a method including a step of hydrothermally treating a NaMnTi-containing oxide having a tunnel structure Pbam in a lithium nitrate aqueous solution to produce a LiMnTi-containing oxide. The NaMnTiAl-containing oxide can be an oxide represented by the following general formula (II):

[0043] Na c Mn x Tiy M z O2(II)

[0044] However, 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 ≦ a ≦ 0.50, x, y, and z satisfy x + y + z = 1, 0.50 ≦ x ≦ 1.00, 0 < y ≦ 0.50, and 0 ≦ z < 0.50.

[0045] The nitric acid concentration of the lithium nitrate aqueous solution is, for example, 100 g / L or more. The lithium nitrate aqueous solution may be a saturated aqueous solution. The amount of NaMnTi-containing oxide in the lithium nitrate aqueous solution is, for example, an amount such that when the molar amount of the NaMnTi-containing oxide is 1 mol, the amount of Li is 10 to 50 mol.

[0046] The treatment temperature of the hydrothermal treatment is, for example, within 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. When the treatment temperature is within the above range, the above-mentioned positive electrode active material for a lithium ion secondary battery can be reliably produced. In particular, when the treatment temperature is 190°C or higher, a LiMnTi-containing oxide with high crystallinity can be produced. The treatment time of the hydrothermal treatment varies depending on conditions such as the Li concentration of the lithium nitrate aqueous solution, the concentration of the NaMnTi-containing oxide in the lithium nitrate aqueous solution, and the capacity of the reaction vessel, but is, for example, within the range of 1 to 30 hours.

[0047] The LiMnTi-containing oxide produced by the hydrothermal treatment may be washed and dried. The washing may be performed by water washing. By washing the LiMnTiAl-containing oxide with water, Na substituted with Li and unreacted lithium nitrate are removed. The drying method is not particularly limited, and various methods used as drying methods for inorganic substances such as a heat drying method, a vacuum drying method, and a spray drying method can be used.

[0048] The positive electrode active material for a lithium ion secondary battery according to the present embodiment can be used as the positive electrode active material for a lithium ion secondary battery. The lithium ion secondary battery includes, for example, a positive electrode, a negative electrode, an electrolyte, a separator disposed between the positive electrode and the negative electrode, and an exterior body that houses these components. A solid electrolyte may be used instead of the electrolyte.

[0049] The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. The positive electrode active material layer includes the positive electrode active material for lithium ion secondary batteries of this embodiment. The positive electrode active material layer may include a conductive additive and a binder. Because the positive electrode active material for secondary batteries of this embodiment is chemically stable, the conductive additive and binder are not particularly limited, and known conductive additives and binders used in positive electrode active material layers of lithium ion secondary batteries can be used. In addition, the positive electrode current collector is not particularly limited, and known conductive additives and binders used in positive electrode current collectors of lithium ion secondary batteries, such as aluminum foil, can be used.

[0050] The negative electrode may be a laminate including a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. Examples of the negative electrode active material include metallic lithium, a material capable of absorbing and desorbing lithium, and a metal or semimetal that forms an alloy with lithium. Examples of materials capable of absorbing and desorbing lithium include 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. Examples of metals or semimetals that form an alloy with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. When the negative electrode active material is in powder form, the negative electrode active material layer may contain a conductive additive and a binder. There are no particular limitations on the conductive additive and binder, and known conductive additives and binders used in negative electrode active material layers of lithium-ion secondary batteries can be used. The negative electrode current collector is not particularly limited, and any known negative electrode current collector used in lithium ion secondary batteries, such as copper foil, can be used.

[0051] The electrolytic solution contains an organic solvent and an electrolyte. Examples of the organic solvent that can be used include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers, aromatic ethers, sulfones, cyclic esters, chain carboxylic acid esters, and nitriles. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane. Examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, and diethyl ether. Examples of hydrofluoroethers include 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, and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane. Examples of aromatic ethers include anisole. Examples of sulfones include sulfolane and methylsulfolane. Examples of cyclic esters include γ-butyrolactone. Examples of chain carboxylic acid esters include acetate esters, butyrate esters, and propionate esters. Examples of nitriles include acetonitrile and propionitrile. The organic solvents may be used alone or in combination of two or more.

[0052] The electrolyte is a source of lithium ions, which are a charge transfer medium, and contains a lithium salt. Examples of lithium salts include LiPF, LiBF, LiClO, LiAsF, LiCFSO, LiC(CFSO), LiN(CFSO) (LiTFSI), LiN(FSO) (LiFSI), and LiBCO. The lithium salts may be used alone or in combination.

[0053] As the solid electrolyte, for example, a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, a halide solid electrolyte, or the like can be used. Examples of sulfide solid electrolytes include Li2S-P2S5 and Li2S-P2S5-LiI. Examples of oxide solid electrolytes include NASICON-type oxides, garnet-type oxides, and perovskite-type oxides. Examples of NASICON-type oxides include oxides containing Li, Al, Ti, P, and O (e.g., Li 1.5 Al 0.5 Ti 1.5 Examples of garnet-type oxides include oxides containing Li, La, Zr, and O (e.g., LiLaZrO 12 Examples of perovskite oxides include oxides containing Li, La, Ti, and O (for example, LiLaTiO3).

[0054] The separator is not particularly limited, and may be, for example, a porous sheet or a nonwoven fabric sheet. Examples of materials for the porous sheet include polyolefins such as polyethylene and polypropylene, aramid, polyimide, and fluororesin. Examples of materials for the nonwoven fabric sheet include glass fiber and cellulose fiber.

[0055] The exterior body is not particularly limited, and known exterior bodies used in lithium ion secondary batteries, such as a metal container or a container made of laminated film, can be used.

[0056] The positive electrode active material for a lithium ion secondary battery according to this embodiment has the composition of the general formula (I) above, and can be produced using a hydrothermal treatment method that is relatively easy to carry out industrially, resulting in excellent productivity and enabling industrial mass production.

[0057] According to the method for producing a positive electrode active material for a lithium ion secondary battery of the present embodiment, the NaMnTiAl-containing oxide of the general formula (II) is hydrothermally treated in an aqueous lithium nitrate solution, so that the positive electrode active material for a secondary battery of the present embodiment can be produced with high efficiency.

[0058] The lithium ion secondary battery of this embodiment has high productivity because it contains the positive electrode active material for lithium ion secondary batteries of this embodiment. [Example]

[0059] [Example 1] (Preparation of NaMnTi-containing oxide powder) Na2CO3, Mn2O3, and TiO2 were weighed out so that the molar amount of Na (Na / (Mn + Ti)) was 0.5 mol, the molar amount of Ti (Ti / (Mn + Ti)) was 0.50 mol, and the total mass was 1.0 g, assuming the total molar amount of Mn and Ti was 1 mol. The weighed Na2CO3, Mn2O3, and TiO2 were mixed using a mortar and pestle. The resulting raw material mixture was placed in an alumina crucible and fired in air at 1000°C for 12 hours. After firing, the fired product was pulverized using a mortar and pestle. Measurement of the X-ray diffraction pattern of the fired powder confirmed that the fired powder was an NaMnTi oxide powder with a tunnel structure.

[0060] (Preparation of LiMnTi-containing oxide powder) A LiNO3 solution was prepared by adding 25.00 g of LiNO3 and 50 mL of water to a hydrothermal reaction vessel and stirring the mixture to dissolve the LiNO3 in water. Next, 1.0 g of the NaMnTi oxide powder obtained above was added to the LiNO3 solution and stirred to obtain a dispersion of the NaMnTi oxide powder in the LiNO3 solution. The hydrothermal reaction vessel was then sealed and placed in a thermostatic chamber. The NaMnTi oxide powder was hydrothermally treated by heating the vessel in air at 80°C for 24 hours. After heating, the hydrothermally treated powder (LiMnTi-containing oxide powder) was recovered from the hydrothermal reaction vessel. The recovered LiMnTi-containing oxide powder was washed with water and then centrifuged three times to remove moisture. The dehydrated LiMnTi-containing oxide powder was placed in a petri dish and vacuum-dried at 100°C for 6 hours. The dried LiMnTi-containing oxide powder was pulverized using a mortar and pestle.

[0061] [Examples 2 to 8] LiMnTi-containing oxide powders were produced in the same manner as in Example 1, except that the hydrothermal treatment temperature was 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.

[0062] [Comparative Example 1] A LiMnTi-containing oxide powder was produced in the same manner as in Example 1, except that Na in the NaMnTi-containing oxide powder was replaced with Li using a molten salt method. The replacement conditions were as follows: The molten salt used was a molten salt containing lithium nitrate and lithium chloride in a molar ratio of 88:12. The ratio of the molten salt to the NaMnTi-containing oxide powder was 20:1 in terms of the molar ratio of Li to Na. The replacement time was 10 hours.

[0063] [evaluation] The LiMnTi-containing oxide powders obtained in Examples 1 to 8 and Comparative Example 1 were evaluated for chemical composition, X-ray diffraction pattern, lattice constant, full width at half maximum (FWHM), and charge / discharge characteristics by the following methods.

[0064] (chemical composition) The sample was dissolved in acid. The contents of Li, Na, Mn, Ti, and Al in the resulting solution were measured using an ICP emission spectrometer. The resulting contents of Li, Na, Mn, Ti, and Al were converted to molar amounts, with the total amount of Mn, Ti, and Al being 1 mole. The results, along with the hydrothermal treatment temperature, are shown in Table 1 below.

[0065] (X-ray diffraction pattern) The X-ray diffraction pattern was measured under the following conditions, and the results are shown in Figures 1 to 3.

[0066] Measurement equipment: RINT-2550V, manufactured by Rigaku Corporation X-ray source:CuKα X-ray output: 40kV, 200mA Measurement conditions: 1.0 s, 0.03 deg intervals

[0067] (lattice constant) The lattice constants of the a-axis, b-axis, and c-axis were measured using the X-ray diffraction pattern. The lattice constants were calculated by the least squares method using the indices of the diffraction peaks due to the tunnel structure Pbam extracted from the X-ray diffraction pattern and their interplanar spacings. The results are shown in Table 2 below.

[0068] (FWHM) From the X-ray diffraction pattern, diffraction peaks within the diffraction angle 2θ range of 61 degrees to 62 degrees (diffraction peaks at 61-62 degrees) and diffraction peaks within the diffraction angle 2θ range of 64 degrees to 65 degrees (diffraction peaks at 64-65 degrees) were extracted. The full width at half maximum (FWHM) of the extracted peaks was measured. The results are shown in Table 2 below.

[0069] (Charge / discharge characteristics) 5 mg of sample was mixed with 5 mg of acetylene black as a conductive material and 1 mg of PTFE as a binder. The resulting mixture was formed into a sheet and pressed onto an Al mesh to form the working electrode, and a lithium foil counter electrode. The working electrode and counter electrode were immersed in an electrolyte solution of LiPF6 dissolved in an EC+DMC solvent to prepare a two-electrode cell.

[0070] A charge-discharge test was conducted using a two-electrode cell. The conditions for the charge-discharge test 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 elapsed). The charge-discharge test was conducted in an environment of 25°C. The initial (first cycle) discharge capacity is shown in Table 2 below.

[0071] [Table 1]

[0072] [Table 2]

[0073] The X-ray diffraction patterns shown in Figures 2 to 4 confirm that the LiMnTi-containing oxide powders obtained in Examples 1 to 8 all had a tunnel structure Pbam. The results in Table 1 show that the Li content of the LiMnTi-containing oxide powder increases as the hydrothermal treatment temperature increases, that is, as the heat treatment temperature increases, the substitution of Na with Li becomes more likely. The results in Table 2 also show that as the hydrothermal treatment temperature increases, the lattice constants of the a-axis and b-axis decrease, the c-axis increases, and the half-width tends to decrease. Furthermore, it can be seen that the LiMnTi-containing oxide powders obtained in Examples 1 to 8 are all capable of absorbing and releasing Li, and that the discharge capacity increases as the hydrothermal treatment temperature increases.

[0074] [Example 9] (Annealing treatment of LiMnTi-containing oxide powder) The LiMnTi-containing oxide powder obtained in Example 1 was placed in an alumina crucible and annealed in air at an annealing temperature of 270°C for 12 hours. After annealing, the annealed product was pulverized using a mortar and pestle.

[0075] [Examples 10 to 19] Annealing was carried out in the same manner as in Example 9, except that the LiMnTi-containing oxide powder shown in Table 3 below was used and the annealing temperature was set to the temperature shown in Table 3 below.

[0076] [evaluation] The X-ray diffraction patterns, lattice constants, full width at half maximum (FWHM), and charge / discharge characteristics of the LiMnTi-containing oxide powders obtained in Examples 1 to 8 were evaluated by the above-mentioned methods. The X-ray diffraction patterns are shown in Tables 4 to 8. The lattice constants, full width at half maximum (FWHM), and discharge capacities are shown in Table 3 below.

[0077] [Table 3]

[0078] The results in Table 3 show that the discharge capacity of the LiMnTi-containing oxide powder after annealing tends to improve as the treatment temperature increases when the NaMnTi-containing oxide powder is hydrothermally treated to produce the LiMnTi-containing oxide powder. Therefore, the results of this example confirm that the hydrothermal treatment and annealing treatment make it possible to obtain a LiMnTi-containing oxide powder with a high electrical capacity.

Claims

1. A positive electrode active material for a lithium ion secondary battery, having a tunnel structure Pbam, and a composition represented by the following general formula (I), wherein the lattice constant of the a-axis is in the range of 9.0420 Å or more and 9.1640 Å or less, the lattice constant of the b-axis is in the range of 24.294 Å or more and 25.968 Å or less, and the lattice constant of the c-axis is in the range of 2.8820 Å or more and 2.8935 Å or less: Li ａ No ｂ Mn ｘ Today ｙ M ｚ O ２ (I) In the above general formula (I), M is at least one element selected from the group consisting of Group 2 elements and Group 13 elements, a satisfies the relationship 0.40≦a≦0.50, b satisfies the relationship 0.01≦b≦0.25, and x, y, and z satisfy the relationship x+y+z=1, and satisfy the relationships 0.50≦x≦1.00, 0<y≦0.50, and 0≦z<0.

50.

2. 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the positive electrode active material 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 in an X-ray diffraction pattern measured using CuKα as an X-ray source.

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

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

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

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

7. 3. A method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: a step of hydrothermally treating an NaMnTi-containing oxide having a tunnel structure Pbam and represented by the following general formula (II) in an aqueous lithium nitrate solution to produce a LiMnTi-containing oxide: Na ｃ Mn ｘ Ti ｙ M ｚ O ２ (II) 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 0.40≦a≦0.50, and x, y, and z satisfy the relationship x+y+z=1, 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 6, wherein the treatment temperature of the hydrothermal treatment is in the range of 80°C or higher and 220°C or lower.

9. 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 hydrothermal treatment is in the range of 150°C or higher and 220°C or lower.

10. 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 hydrothermal treatment is in the range of 190°C or higher and 220°C or lower.

11. 8. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 7, further comprising the step of heating the LiMnTi-containing oxide at a temperature of 200°C or higher and 320°C or lower.

12. A lithium ion secondary battery comprising a positive electrode mixture layer containing the positive electrode active material for lithium ion secondary batteries according to claim 1 or 2.

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