Positive electrode active material for lithium-ion secondary battery, 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, which can be manufactured using metal elements that are industrially readily obtainable and has a small atomic weight, and which has a high specific capacity, a manufacturing method for the same, and a lithium-ion secondary battery using the same.SOLUTION: The positive electrode active material for a lithium-ion secondary battery is represented by the following general formula (I): LiaMnxTiyAlzO2(I). In the above general formula (I), a satisfies the relationship 0.40≤a≤0.50, and x, y, z satisfy the relationships 0.48≤x≤0.58, 0.31≤y≤0.50, 0.01≤z≤0.12, and x+y+z=1.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 has been conducted on secondary batteries that contribute to energy efficiency in order 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, have been studied as positive electrode active materials for lithium-ion secondary batteries (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, improving the electrical capacity per mass is one of the challenges. This is particularly important for secondary batteries used as power sources for driving the motors of electric vehicles and hybrid electric vehicles. Therefore, further improvements in the electrical capacity per mass of LiMnTi-containing oxides with tunnel structures are also desired. Adding metal elements to LiMnTi-containing oxides is one way to improve their electrical capacity. However, from the perspective of resource sustainability, it is desirable for the metal elements to be easily available industrially and have small atomic weights.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a positive electrode active material for a lithium ion secondary battery that can be produced using a metal element that is easily available industrially and has a small atomic weight, and that has a high electric capacity per mass, 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 adding Al to an LiMnTi-containing oxide is effective in solving the above problems, and have completed the present invention. Therefore, the present invention provides the following.

[0007] (1) A positive electrode active material for a lithium ion secondary battery represented by the following general formula (I): Li a Mn x Ti y Al z O2(I) In the above general formula (I), a satisfies the relationship 0.40≦a≦0.50, and x, y, and z satisfy the relationships 0.48≦x≦0.58, 0.31≦y≦0.50, and 0.01≦z≦0.12, where x+y+z=1.

[0008] The positive electrode active material for a lithium-ion secondary battery (1) contains Li, Mn, Ti, and Al within the above-mentioned ranges, and therefore has a high electrical capacity per mass. Furthermore, Li, Mn, Ti, and Al are easily available industrially and have a high resource sustainability. In particular, Al is more easily available industrially than Mn and Ti, is inexpensive, and has a small atomic weight.

[0009] (2) The positive electrode active material for a lithium ion secondary battery according to (1), wherein x satisfies the relationship 0.48≦x≦0.58, y satisfies the relationship 0.37≦y≦0.50, and z satisfies the relationship z0.01≦z≦0.06.

[0010] According to the positive electrode active material for a lithium ion secondary battery of (2), since Li, Mn, Ti and Al are contained within the above ranges, the electric capacity per mass becomes higher.

[0011] (3) The positive electrode active material for a lithium ion secondary battery according to (1) or (2), which has a tunnel structure Pbam.

[0012] The positive electrode active material for a lithium ion secondary battery of (3) has a tunnel structure Pbam, and therefore has a higher electric capacity per mass.

[0013] (4) The positive electrode active material for a lithium ion secondary battery according to (3), which is a single phase having the tunnel structure Pbam.

[0014] According to the positive electrode active material for lithium ion secondary batteries (4), since it is a single phase of the tunnel structure Pbam, the electric capacity per mass is further increased.

[0015] (5) The positive electrode active material for a lithium ion secondary battery according to any one of (1) to (4), wherein an X-ray diffraction pattern measured using a CuKα X-ray source shows two diffraction peaks within a diffraction angle 2θ range of 19.5 degrees or more and 21.0 degrees or less, and the ratio of the maximum diffraction intensity of the diffraction peak on the higher angle side to the maximum diffraction intensity of the diffraction peak on the lower angle side of the two diffraction peaks is within a range of 1.00 or more and 1.50 or less.

[0016] According to the positive electrode active material for a lithium ion secondary battery of (5), the maximum diffraction intensities of the two diffraction peaks satisfy the above-mentioned relationship within the range of the diffraction angle 2θ of 19.5 degrees or more and 21.0 degrees or less, and therefore the electrical capacity per mass is higher.

[0017] (6) The positive electrode active material for a lithium ion secondary battery according to any one of (1) to (5), wherein the content of Na relative to the total content of Mn, Ti, and Al is 4 mol % or less.

[0018] According to the positive electrode active material for a lithium ion secondary battery of (6), the Na content is as small as the amount described above, so that a decrease in electrical capacity due to the inclusion of Na can be suppressed.

[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), comprising substituting at least a portion of sodium in an NaMnTiAl-containing oxide having a tunnel structure and represented by the following general formula (II) with lithium: Na b Mn x Ti y Al z O2(II) In the above general formula (II), b satisfies the relationship 0.40≦b≦0.50, and x, y, and z satisfy the relationships 0.48≦x≦0.58, 0.31≦y≦0.50, and 0.01≦z≦0.12, where x+y+z=1.

[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 used as a raw material, so that the positive electrode active material for a lithium ion secondary battery can be produced with high efficiency.

[0021] (8) A lithium ion secondary battery comprising a positive electrode mixture layer containing the positive electrode active material for lithium ion secondary batteries according to any one of (1) to (6).

[0022] According to the lithium ion secondary battery of (8), since the above-mentioned positive electrode active material for lithium ion secondary batteries is contained, the electric capacity per mass is high. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery that can be produced using a metal element that is easily available industrially and has a small atomic weight, and that has a high electric capacity per mass, a method for producing the same, and a lithium ion secondary battery using the same. [Brief explanation of the drawings]

[0024] [Figure 1] 1 shows X-ray diffraction patterns of the LiMnTiAl-containing oxide powders obtained in Examples 1 to 3 and Comparative Example 1. [Figure 2] 1 shows X-ray diffraction patterns of the LiMnTiAl-containing oxide powders obtained in Examples 4 to 6 and Comparative Example 2. [Figure 3] 1 shows X-ray diffraction patterns of the LiMnTiAl-containing oxide powders obtained in Comparative Examples 3 to 6. [Figure 4] 1 shows an X-ray diffraction pattern of the LiMnTiAl-containing oxide powder obtained in Example 5 and an X-ray diffraction pattern of the NaMnTiAl-containing oxide powder used in the production thereof. [Figure 5] 1 is a graph showing initial discharge curves of two-electrode cells using the LiMnTiAl-containing oxide powders obtained in Examples 1 to 3 and Comparative Example 1. [Figure 6] 1 is a graph showing initial discharge curves of two-electrode cells using the LiMnTiAl-containing oxide powders obtained in Examples 4 to 6 and Comparative Example 2. [Figure 7] 1 is a graph showing the initial discharge curves of two-electrode cells using the LiMnTiAl-containing oxide powders obtained in Comparative Examples 3 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0025] 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.

[0026] The positive electrode active material for a lithium ion secondary battery of this embodiment is a LiMnTiAl-containing oxide containing lithium (Li), manganese (Mn), titanium (Ti), and aluminum (Al). The positive electrode active material for a lithium ion secondary battery is represented by the following general formula (I):

[0027] Li a Mn x Ti y Alz O2(I)

[0028] In general formula (I), a satisfies the relationship 0.40≦a≦0.50, and x, y, and z satisfy the relationships 0.48≦x≦0.58, 0.31≦y≦0.50, and 0.01≦z≦0.12, where x+y+z=1.

[0029] In general formula (I), x, y, and z more preferably satisfy the relationships 0.48≦x≦0.58, 0.37≦y≦0.50, and z0.01≦z≦0.06, even more preferably satisfy the relationships 0.54≦x≦0.58, 0.37≦y≦0.44, and 0.01≦z≦0.06, and most preferably satisfy the relationships 0.54≦x≦0.58, 0.37≦y≦0.41, and 0.04≦z≦0.06. By containing Li, Mn, Ti, and Al within the above ranges, the electric capacity per mass of the LiMnTiAl-containing oxide becomes higher.

[0030] The LiMnTiAl-containing oxide preferably has a tunnel structure Pbam. By having the tunnel structure Pbam, the electric capacity per mass of the LiMnTiAl-containing oxide becomes higher. The LiMnTiAl-containing oxide is more preferably a single phase having the tunnel structure Pbam. When the LiMnTiAl-containing oxide has a single phase of the tunnel structure Pbam, the electric capacity per mass of the LiMnTiAl-containing oxide becomes even higher. The fact that the LiMnTiAl-containing oxide has a single phase having the tunnel structure Pbam can be confirmed, for example, from the X-ray diffraction pattern of the LiMnTiAl-containing oxide.

[0031] The LiMnTiAl-containing oxide may have two diffraction peaks within a diffraction angle 2θ range of 19.5 degrees to 21.0 degrees. The ratio of the maximum diffraction intensity (A) of the diffraction peak at the lower angle of the two diffraction peaks to the maximum diffraction intensity (B) of the diffraction peak at the higher angle (peak intensity ratio B / A) may be, for example, within a range of 1.00 to 1.50. The peak intensity ratio B / A is more preferably within a range of 1.00 to 1.40, even more preferably within a range of 1.00 to 1.25, and most preferably within a range of 1.10 to 1.25. When the maximum diffraction intensities of the two diffraction peaks within a diffraction angle 2θ range of 19.5 degrees to 21.0 degrees satisfy the above relationship, the electric capacity per mass of the LiMnTiAl-containing oxide is increased.

[0032] The positive electrode active material for a lithium ion secondary battery of this embodiment can be produced, for example, by a method in which at least a portion of Na in an NaMnTiAl-containing oxide having a tunnel structure is replaced with Li.

[0033] The NaMnTiAl-containing oxide may be an oxide represented by the following general formula (II).

[0034] Na b Mn x Ti y Al z O2(II)

[0035] In the above general formula (II), b satisfies the relationship 0.40≦b≦0.50, and x, y, and z satisfy the relationships 0.48≦x≦0.58, 0.31≦y≦0.50, and 0.01≦z≦0.12, where x+y+z=1. The preferred ranges of x, y, and z are the same as those in the case of the above LaMnTiAl-containing oxide.

[0036] The NaMnTiAl-containing oxide can be produced by mixing a sodium source, a manganese source, a titanium source, and an aluminum source to obtain a raw material mixture, and then calcining the obtained raw material mixture. There are no particular limitations on the sodium source, manganese source, and titanium source, and various compounds such as oxides, carbonates, hydroxides, and chlorides can be used. The raw material mixture can be calcined, for example, in air at a calcination temperature of 900 to 1200°C. The calcination time varies depending on conditions such as the composition of the raw material mixture and the calcination temperature, but is, for example, within the range of 1 to 30 hours.

[0037] As a method for substituting Li for Na in the NaMnTiAl-containing oxide, for example, a molten salt method using a molten lithium salt as a lithium source, or a solution method using a lithium compound solution as a lithium source can be used.

[0038] In the molten salt method, for example, an NaMnTiAl-containing oxide and a lithium salt are mixed, and the resulting mixture is heated to generate a molten lithium salt. In the generated molten lithium salt, Na in the NaMnTiAl-containing oxide is substituted with Li. Examples of lithium salts used in the molten salt method include low-melting-point lithium salts such as lithium nitrate and lithium halides (lithium chloride, lithium bromide, and lithium iodide). The mixing ratio of the NaMnTiAl-containing oxide and the lithium salt, expressed as the molar ratio of lithium in the lithium salt to sodium in the NaMnTiAl-containing oxide (Li / Na ratio), is in the range of 2 to 40, preferably 10 to 30. The heating temperature in the molten salt method is equal to or higher than the melting point of the lithium salt. The heating temperature is preferably 330°C or lower.

[0039] In the solution method, for example, an NaMnTiAl-containing oxide is mixed with a lithium compound solution, and the resulting mixture is heated to replace Na in the NaMnTiAl-containing oxide with Li in the mixture. Water or an organic solvent can be used as the solvent for the lithium compound solution. Examples of organic solvents that can be used include higher alcohols such as hexanol and ethoxyethanol, ethers such as diethylene glycol monoethyl ether, and organic solvents with a boiling point of 140°C or higher. Examples of lithium compounds used in the solution method include soluble lithium compounds such as lithium carbonate, lithium acetate, lithium nitrate, lithium oxalate, lithium halide, lithium hydroxide, and butyllithium. The lithium concentration in the lithium compound solution is, for example, in the range of 3 to 10 mol%, preferably in the range of 4 to 6 mol%. The heating temperature in the molten salt method is below the boiling point of the lithium salt solution. The heating temperature is, for example, 100°C or higher, preferably 140°C or higher. The concentration of the NaMnTiAl-containing oxide in the mixture is, for example, in the range of 1 to 20 mass%.

[0040] Substitution of Na in the NaMnTiAl-containing oxide with Li produces a LiMnTiAl-containing oxide. The resulting LiMnTiAl-containing oxide may be washed and dried. Washing may be performed by water washing. By washing the LiMnTiAl-containing oxide with water, Na that has substituted for Li and unreacted lithium sources are removed. There are no particular limitations on the drying method, and various methods used as drying methods for inorganic materials, such as heat drying, vacuum drying, and spray drying, can be used.

[0041] The positive electrode active material obtained as described above may be contaminated with a trace amount of Na. The Na content of the positive electrode active material is preferably, for example, 4 mol % or less relative to the total content of Mn, Ti, and Al. If the Na content is as small as 4 mol %, it is possible to suppress a decrease in electrical capacity due to Na contamination. The Na content relative to the total content of Mn, Ti, and Al may be 1 mol % or more.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] The positive electrode active material for a lithium-ion secondary battery of this embodiment configured as described above contains Li, Mn, Ti, and Al within the above-mentioned ranges, and therefore has a high electrical capacity per mass. Furthermore, Li, Mn, Ti, and Al are easily available industrially and have a high resource sustainability. In particular, Al is more easily available industrially than Mn and Ti, is inexpensive, and has a small atomic weight. Therefore, the positive electrode active material for a lithium-ion secondary battery of this embodiment can be stably produced over a long period of time.

[0051] 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 used as a raw material, so that the positive electrode active material for a secondary battery of the present embodiment can be produced with high efficiency.

[0052] The lithium ion secondary battery of this embodiment contains the positive electrode active material for lithium ion secondary batteries of this embodiment, and therefore has a high electric capacity per mass. [Example]

[0053] [Example 1] (Preparation of NaMnTiAl-containing oxide powder) Na2CO3, Mn2O3, TiO2, and Al(OH)3 were weighed out to a total mass of 1.0 g in a molar ratio of Na:Mn:Ti:Al of 0.5:0.50:0.48:0.2. The weighed Na2CO3, Mn2O3, TiO2, and Al(OH)3 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 NaMnTiAl oxide powder with a tunnel structure.

[0054] (Preparation of LiMnTiAl-containing oxide powder) The obtained NaMnTiAl oxide and LiNO3 were weighed out in a ratio of 1.5 g and 5.4 g, respectively, and mixed using a mortar and pestle. The resulting mixture was then placed in a crucible and heated in the atmosphere at 270°C for 12 hours. After heating, the treated powder (LiMnTiAl-containing oxide powder) was recovered from the crucible. The recovered LiMnTiAl-containing oxide powder was washed with water and then centrifuged three times to remove moisture. The dehydrated LiMnTiAl-containing oxide powder was placed in a petri dish and vacuum-dried at 100°C for 6 hours. The dried LiMnTiAl-containing oxide powder was pulverized using a mortar and pestle.

[0055] [Examples 2 to 5, Comparative Examples 1 to 6] An NaMnTiAl-containing oxide powder was produced in the same manner as in Example 1, except that the blending ratio of Na:Mn:Ti:Al was set to the molar ratio shown in the following Table 1. Then, using the obtained NaMnTiAl oxide, an LiMnTiAl-containing oxide powder was obtained in the same manner as in Example 1.

[0056] [Table 1]

[0057] [evaluation] The LiMnTiAl-containing oxide powders obtained in Examples 1 to 5 and Comparative Examples 1 to 6 were evaluated for chemical composition, X-ray diffraction pattern, and charge / discharge characteristics by the following methods.

[0058] (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 atomic 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 composition formula was calculated from the resulting molar amounts of Li, Mn, Ti, and Al. The results are shown in Table 2 below.

[0059] (X-ray diffraction pattern) X-ray diffraction patterns were measured under the following conditions. Fig. 1 shows the X-ray diffraction patterns of the LiMnTiAl-containing oxide powders obtained in Examples 1 to 3 and Comparative Example 1, Fig. 2 shows the X-ray diffraction patterns of the LiMnTiAl-containing oxide powders obtained in Examples 4 to 6 and Comparative Example 2, and Fig. 3 shows the X-ray diffraction patterns of the LiMnTiAl-containing oxide powders obtained in Comparative Examples 3 to 6. Fig. 4 shows the X-ray diffraction pattern of the LiMnTiAl-containing oxide powder obtained in Example 5 and the X-ray diffraction pattern of the NaMnTiAl-containing oxide powder used in the production thereof.

[0060] Measurement equipment: SmartLab, manufactured by Rigaku Corporation X-ray source:CuKα X-ray output: 40kV, 200mA Measurement conditions: 10.0 seconds, 0.01 degree intervals

[0061] From the obtained X-ray diffraction pattern, two diffraction peaks within the range of diffraction angle 2θ of 19.5 degrees or more and 21.0 degrees or less were extracted. The peak intensity ratio B / A was calculated by taking the maximum diffraction intensity of the diffraction peak on the lower angle side of the two extracted diffraction peaks as A and the maximum diffraction intensity of the diffraction peak on the higher angle side as B. The results are shown in Table 2 below.

[0062] (Charge / discharge characteristics) The resulting sample was used as the positive electrode active material. Acetylene black (AB) was used as a conductive agent, and polyvinylidene fluoride (PVDF) was used as a binder. A slurry was prepared by mixing the resulting material with N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 8:1:1. The resulting slurry was coated onto a 20 μm-thick aluminum foil and dried to prepare a 14 mm-diameter positive electrode. A 200 μm-thick, 16 mm-diameter lithium metal counter electrode and a 20 μm-thick, 18 mm-diameter polyethylene microporous membrane were used as the separator. A 1.2 mol / L solution of lithium hexafluorophosphate (LiPF6) dissolved in a 3:4:3 volumetric ratio mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were used as the electrolyte. A lithium-ion secondary battery (2032 coin cell) was fabricated using this solution. The battery was fabricated according to a known cell construction and assembly method.

[0063] 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 2.5-4.8 V, and constant current-constant voltage charging (until the current density reached 2 mA / g). The charge-discharge test was conducted in an environment of 25°C. The discharge curves for the first cycle are shown in Figures 5 to 7. The charge capacity, discharge capacity, charge-discharge efficiency (initial discharge capacity / initial charge capacity × 100), average discharge voltage, and energy density (initial discharge capacity × average discharge voltage) calculated from the first charge-discharge cycle are shown in Table 3 below.

[0064] [Table 2]

[0065] [Table 3]

[0066] 1 to 3, it was confirmed that the LiMnTiAl-containing oxide powder obtained in this example was a single phase having a tunnel structure Pbam. The X-ray diffraction pattern in Fig. 4 confirmed that the diffraction peak shifted to a higher angle by substituting Li for Na in the NaMnTiAl-containing oxide powder.

[0067] Comparisons of Examples 1 and 2 with Comparative Example 1 and Examples 3 to 5 with Comparative Example 2 shown in Table 3 confirm that LiMnTiAl-containing oxide powders containing Al, which is industrially readily available, inexpensive, and has a small atomic weight compared to Mn and Ti, within the scope of the present invention, have a higher discharge capacity than LiMnTi-containing oxide powders that do not contain Al. Furthermore, the results of Comparative Examples 3 to 6 reveal that LiMnTi-containing oxide powders with a Mn molar amount of 0.66 do not achieve the effect of increasing discharge capacity due to the addition of Al. In Table 3, the discharge capacity is higher than the charge capacity for all of Examples 1 to 5 and Comparative Examples 1 to 6. This indicates that the amount of Li that migrated from the counter electrode to the LiMnTiAl-containing oxide in the positive electrode during the first discharge was greater than the amount of Li that migrated from the LiMnTiAl-containing oxide in the positive electrode to the counter electrode during the first charge.

Claims

1. A positive electrode active material for a lithium ion secondary battery, represented by the following general formula (I): Li ａ Mn ｘ Three ｙ Al ｚ Oh ２ (I) In the above general formula (I), a satisfies the relationship 0.40≦a≦0.50, and x, y, and z satisfy the relationships 0.48≦x≦0.58, 0.31≦y≦0.50, and 0.01≦z≦0.12, where x+y+z=1.

2. 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein x satisfies a relationship of 0.48≦x≦0.58, y satisfies a relationship of 0.37≦y≦0.50, and z satisfies a relationship of z0.01≦z≦0.

06.

3. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, having a tunnel structure Pbam.

4. The positive electrode active material for a lithium ion secondary battery according to claim 3 , which is a single phase having the tunnel structure Pbam.

5. 3. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein an X-ray diffraction pattern measured using CuKα as an X-ray source has two diffraction peaks within a diffraction angle 2θ range of 19.5 degrees or more and 21.0 degrees or less, and a ratio of the maximum diffraction intensity of the diffraction peak on the higher angle side to the maximum diffraction intensity of the diffraction peak on the lower angle side of the two diffraction peaks is within a range of 1.00 or more and 1.50 or less.

6. 3. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the content of Na relative to the total content of Mn, Ti, and Al is 4 mol% 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 substituting lithium for at least a portion of sodium in an NaMnTiAl-containing oxide having a tunnel structure and represented by the following general formula (II): Yes ｂ Mn ｘ Three ｙ Al ｚ Oh ２ (II) In the above general formula (II), b satisfies the relationship 0.40≦b≦0.50, and x, y, and z satisfy the relationships 0.48≦x≦0.58, 0.31≦y≦0.50, and 0.01≦z≦0.12, where x+y+z=1.

8. 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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