WO2012002364A1

WO2012002364A1 - Electrode active material, method for producing same, and nonaqueous electrolyte secondary battery comprising same

Info

Publication number: WO2012002364A1
Application number: PCT/JP2011/064762
Authority: WO
Inventors: 徹川合
Original assignee: 株式会社村田製作所
Priority date: 2010-06-30
Filing date: 2011-06-28
Publication date: 2012-01-05
Also published as: JPWO2012002364A1

Abstract

Disclosed are: an electrode active material which contains lithium titanate having a spinel structure as a main component and is capable of improving charge/discharge characteristics of a nonaqueous electrolyte secondary battery; a method for producing the electrode active material; and a nonaqueous electrolyte secondary battery which comprises the electrode active material. The electrode active material contains lithium titanate having a spinel structure and a barium compound, and the molar ratio of lithium to titanium is less than 0.80.

Description

Electrode active material, method for producing the same, and nonaqueous electrolyte secondary battery equipped with the same

The present invention generally relates to an electrode active material, a method for producing the same, and a non-aqueous electrolyte secondary battery including the same, and more specifically, an electrode active material containing a lithium titanium composite oxide having a spinel structure as a main component. The present invention relates to a substance, a manufacturing method thereof, and a nonaqueous electrolyte secondary battery including the same.

With the expansion of the market for portable electronic devices such as mobile phones, notebook computers, and digital cameras, secondary batteries with high energy density and long life are expected as cordless power sources for these electronic devices. In response to such demands, secondary batteries have been developed that use an alkali metal ion such as lithium ion as a charge carrier and use an electrochemical reaction associated with the charge exchange. Among them, lithium ion secondary batteries having a large energy density are widely used.

In the above lithium ion secondary battery, a lithium-containing transition metal oxide such as lithium cobaltate or lithium manganate is used as the positive electrode active material. In addition, a carbon material capable of inserting and extracting lithium ions is used as the negative electrode active material. Among carbon materials, graphite such as natural graphite and artificial graphite has a discharge voltage as low as 0.2 V with respect to lithium metal, and when graphite is used as a negative electrode active material, a battery having a discharge voltage of 3.6 V is possible. Become. However, when a carbon material is used for the negative electrode, if a short circuit occurs inside the battery, lithium ions may flow from the negative electrode to the positive electrode at once, and the temperature may increase rapidly.

Therefore, lithium-titanium composite oxides such as lithium titanate, in which current does not flow suddenly even if a short circuit occurs inside the battery, are attracting attention. Lithium titanium composite oxide is a material that can occlude and release lithium ions without changing the structure and size of the crystal lattice, and is a promising electrode active material for highly reliable nonaqueous electrolyte secondary batteries.

For example, in International Publication No. 2006/106700 (hereinafter referred to as Patent Document 1), in order to obtain a lithium ion battery excellent in high rate charge / discharge characteristics, a composition formula in which a part of the lithium titanate element is substituted with Al. : Li [Li _{(1-x) / 3} Al _x Ti _{(5-2x) / 3} ] O ₄ (0 <x <1) is proposed as an electrode active material for a lithium ion battery. A lithium ion battery used as a negative electrode active material is disclosed.

In Japanese Patent No. 3502118 (hereinafter referred to as Patent Document 2), the negative electrode is represented by the general formula Li _x Ti _y O ₄ (0.8 ≦ x ≦ 1.4, 1.6 ≦ y ≦ 2.2). A lithium secondary battery made of lithium titanate is disclosed.

Further, US Pat. No. 7,390,594 (hereinafter referred to as Patent Document 3) discloses a compound represented by the general formula MLi ₂ Ti ₆ O ₁₄ (M is Ba or Sr) as a negative electrode material for a non-aqueous lithium ion battery. Has been.

International Publication No. 2006/106700 Japanese Patent No. 3502118 US Pat. No. 7,390,594

However, as described in the Examples of Patent Document 1, when a lithium titanium composite oxide having an Al substitution amount x (molar ratio) exceeding 0.1 is used as a negative electrode active material of a nonaqueous electrolyte secondary battery. There is a problem that the charge / discharge capacity per unit weight of the electrode active material decreases.

According to the knowledge of the present inventor, when lithium titanate described in Patent Document 2 is used as a negative electrode active material of a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery has good cycle characteristics. There is a problem that the rapid charge / discharge characteristics are low. Further, according to the knowledge of the present inventor, when the compound described in Patent Document 3 is used for the negative electrode active material of a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery is only inferior in cycle characteristics. However, there is a problem that the charge / discharge capacity obtained at the time of rapid charge / discharge is small.

Accordingly, an object of the present invention is to provide an electrode active material containing spinel type lithium titanate as a main component and capable of improving the charge / discharge characteristics of a nonaqueous electrolyte secondary battery, a method for producing the same, and the It is providing the nonaqueous electrolyte secondary battery provided with.

Another object of the present invention is to provide an electrode active material capable of improving the charge / discharge capacity at the time of rapid charge / discharge while having at least good cycle characteristics of the nonaqueous electrolyte secondary battery, and a method for producing the same, and A non-aqueous electrolyte secondary battery including the same is provided.

As a result of intensive studies to solve the problems of the prior art, the present inventor has mixed a barium compound into at least a lithium compound and a titanium compound as a starting material, and baked to mainly produce lithium titanate having a spinel structure. When synthesizing an electrode active material as a component, it was found that the above-mentioned one object can be achieved by making a barium compound separate from lithium titanate and limiting the ratio of lithium to titanium to a specific range. . Based on this knowledge, the electrode active material according to one aspect of the present invention has the following characteristics.

The electrode active material according to one aspect of the present invention includes a spinel-type lithium titanate and a barium compound, and the molar ratio of lithium to titanium is less than 0.80.

According to one aspect of the present invention, when the barium content is about the same amount, the charge / discharge characteristics of the nonaqueous electrolyte secondary battery are improved by limiting the molar ratio of lithium to titanium to less than 0.80. An electrode active material that can be obtained can be obtained.

The electrode active material according to one aspect of the present invention contains 0.14 mass% or more and 4.0 mass% or less of barium, and the molar ratio of lithium to titanium is more than 0.71 and less than 0.80. preferable.

Thus, by limiting the barium content and the molar ratio of lithium to titanium to a specific range, the high rate charge / discharge characteristics of the nonaqueous electrolyte secondary battery can be improved compared to the case where no barium is contained. Can be obtained.

The method for producing an electrode active material according to one aspect of the present invention includes at least a mixing step of mixing a lithium compound, a titanium compound, and a barium compound to obtain a mixture, and a firing step of firing the mixture.

In the mixing step, it is preferable to mix the lithium compound, the titanium compound, and the barium compound so that the molar ratio of lithium to titanium is less than 0.80.

Furthermore, it is preferable that the barium compound mixed in the mixing step is barium carbonate. The lithium compound mixed in the mixing step is preferably lithium carbonate. The titanium compound mixed in the mixing step is preferably titanium oxide.

A nonaqueous electrolyte secondary battery according to one aspect of the present invention uses the above electrode active material as an electrode material. Moreover, the non-aqueous electrolyte secondary battery according to one aspect of the present invention uses an electrode active material manufactured by the above manufacturing method as an electrode material.

In addition, as a result of intensive studies to solve the problems of the prior art, the present inventor has produced an electrode active material by mixing spinel type lithium titanate and Li ₂ BaTi ₆ O _14. Thus, it was found that the above-mentioned another purpose can be achieved. Based on this finding, the electrode active material according to another aspect of the present invention has the following characteristics.

An electrode active material according to another aspect of the present invention includes spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ .

In the electrode active material according to another aspect of the present invention, the mixing ratio of lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ is 99.9: 0.1 to 55.0: 45 in terms of mass ratio. It is preferable to be within a range up to 0.0.

Moreover, in the electrode active material according to another aspect of the present invention, the mixing ratio of lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ is 99.9: 0.1 to 75.0 in terms of mass ratio. : It is preferable to be within the range up to 25.0.

Furthermore, in the electrode active material according to another aspect of the present invention, the mixing ratio of lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ is 93.0: 7.0 to 87.0 in mass ratio. It is preferable to be within a range up to 13.0.

The method for producing an electrode active material according to another aspect of the present invention includes the following steps.

(A) First synthesis step of obtaining lithium titanate having a spinel structure by firing a mixture obtained by mixing a lithium compound and a titanium compound

(B) Second synthesis step for obtaining Li ₂ BaTi ₆ O ₁₄ by firing a mixture obtained by mixing a lithium compound, a titanium compound and a barium compound.

(C) Mixing step of mixing spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄

In the mixing step, the mixing ratio of the spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ is in the range of 99.9: 0.1 to 55.0: 45.0 in terms of mass ratio. Furthermore, it is preferable to mix lithium titanate having a spinel structure with Li ₂ BaTi ₆ O ₁₄ .

In the mixing step, the mixing ratio of the spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ is within the range of 99.9: 0.1 to 75.0: 25.0 in terms of mass ratio. Thus, it is preferable to mix a spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ .

Furthermore, in the above mixing step, the mixing ratio of the lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ is within the range of 93.0: 7.0 to 87.0: 13.0 in terms of mass ratio. Thus, it is preferable to mix a spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ .

Furthermore, the lithium compound is preferably lithium carbonate. The titanium compound is preferably titanium oxide. The barium compound is preferably barium carbonate.

A nonaqueous electrolyte secondary battery according to another aspect of the present invention uses the above electrode active material as an electrode material. A nonaqueous electrolyte secondary battery according to another aspect of the present invention uses an electrode active material manufactured by the above manufacturing method as an electrode material.

According to one aspect of the present invention, in an electrode active material containing spinel type lithium titanate as a main component, an electrode active material capable of improving the charge / discharge characteristics of a non-aqueous electrolyte secondary battery is obtained. Can do.

According to another aspect of the present invention, since the electrode active material includes spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ , at least the cycle characteristics of the nonaqueous electrolyte secondary battery are good. At the same time, by adjusting the mixing ratio of lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ , compared to a conventional electrode active material made only of lithium titanate having a spinel structure, Li ₂ BaTi ₆ Compared with a conventional electrode active material composed only of O ₁₄ , the charge / discharge capacity during rapid charge / discharge can be improved.

It is a figure which shows the coin-type nonaqueous electrolyte secondary battery as one embodiment of this invention, and the coin-type nonaqueous electrolyte secondary battery produced by the Example and comparative example of this invention.

An electrode active material according to one aspect of the present invention includes a lithium titanate having a spinel structure and a barium compound, and a molar ratio of lithium to titanium is less than 0.80. The electrode active material according to one aspect of the present invention includes a barium compound separately from lithium titanate, and limits the molar ratio of lithium to titanium within the above range, whereby spinel-type titanate. In an electrode active material containing lithium as a main component, when the barium content is about the same amount, the charge / discharge capacity per unit weight of the electrode active material can be improved, and the electrode active material having excellent charge / discharge characteristics Can be obtained.

The electrode active material according to one aspect of the present invention contains barium in an amount of 0.14% by mass to 4.0% by mass, and the molar ratio of lithium to titanium is more than 0.71 and less than 0.80. Can suppress the generation of a heterogeneous phase such as Li ₂ TiO _3, so that the charge / discharge capacity per unit weight of the electrode active material at the time of high rate charge / discharge can be improved as compared with the case where no barium is contained. Thus, an electrode active material having excellent rapid charge / discharge characteristics can be obtained. Moreover, the electrode active material according to one aspect of the present invention contains 0.5% to 3.5% by weight of barium, and the molar ratio of lithium to titanium is 0.73 to 0.79. Is preferred. In this case, an electrode active material superior in rapid charge / discharge characteristics can be obtained. Furthermore, the electrode active material according to one aspect of the present invention contains 1.0% by mass to 3.0% by mass of barium, and the molar ratio of lithium to titanium is 0.74 to 0.78. Is preferred. In this case, an electrode active material having further excellent rapid charge / discharge characteristics can be obtained.

Note that examples of the spinel-type lithium titanate contained in the electrode active material according to one aspect of the present invention include Li ₄ Ti ₅ O ₁₂ . Lithium titanate may contain elements other than lithium, titanium, and oxygen. In the electrode active material according to one aspect of the present invention, the barium compound present separately from lithium titanate may be a compound that acts as an electrode active material, or may be a compound that does not act as an electrode active material. is there. Moreover, a part of barium may be contained as a compound substituted in spinel type lithium titanate.

The method for producing an electrode active material according to one aspect of the present invention includes at least a mixing step of mixing a lithium compound, a titanium compound, and a barium compound to obtain a mixture, and a baking step of baking the mixture. It is characterized by. In the mixing step, it is preferable to mix the lithium compound, the titanium compound, and the barium compound so that the molar ratio of lithium to titanium is less than 0.80. The barium compound is preferably barium carbonate. The lithium compound is preferably lithium carbonate. The titanium compound is preferably titanium oxide.

An electrode active material according to another aspect of the present invention is characterized by containing spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ . Due to this feature, the electrode active material according to another aspect of the present invention has at least good cycle characteristics of the nonaqueous electrolyte secondary battery, and has a spinel type lithium titanate, Li ₂ BaTi ₆ O ₁₄ and Compared with the conventional electrode active material consisting only of spinel type lithium titanate and by adjusting the mixing ratio, rapid charge / discharge compared with the conventional electrode active material consisting only of Li ₂ BaTi ₆ O ₁₄ The charge / discharge capacity at the time can be improved.

In the electrode active material according to another aspect of the present invention, the mixing ratio of lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ is 99.9: 0.1 to 55.0: 45 in terms of mass ratio. It is preferable to be within a range up to 0.0. When lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ are mixed within the above mass ratio range, at least the cycle characteristics of the nonaqueous electrolyte secondary battery are good, and rapid charge / discharge The charge / discharge capacity at the time can be improved.

Moreover, in the electrode active material according to another aspect of the present invention, the mixing ratio of lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ is 99.9: 0.1 to 75.0 in terms of mass ratio. : More preferably, it is within the range of up to 25.0. In this case, at least the cycle characteristics of the nonaqueous electrolyte secondary battery are good, and the charge / discharge capacity during rapid charge / discharge can be further improved.

Furthermore, in the electrode active material according to another aspect of the present invention, the mixing ratio of lithium titanate having a spinel structure and Li ₂ BaTi ₆ O ₁₄ is 93.0: 7.0 to 87.0 in mass ratio. More preferably, it is within the range of up to 13.0. In this case, at least the cycle characteristics of the nonaqueous electrolyte secondary battery are good, and the charge / discharge capacity during rapid charge / discharge can be further improved.

An example of the spinel-type lithium titanate contained in the electrode active material according to another aspect of the present invention includes Li ₄ Ti ₅ O ₁₂ . Lithium titanate may contain elements other than lithium, titanium, and oxygen. In addition, elements other than lithium, titanium, and oxygen may be included in a substituted form in lithium titanate having a spinel structure.

In the method for producing an electrode active material according to another aspect of the present invention, a lithium titanate having a spinel structure is obtained by firing a mixture obtained by mixing a lithium compound and a titanium compound. On the other hand, by firing a mixture obtained by mixing the lithium compound and the titanium compound and the barium compound to obtain a Li ₂ BaTi ₆ O _14. The obtained spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ are mixed. In the mixing step, the mixing ratio of the spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ is in the range of 99.9: 0.1 to 55.0: 45.0 in terms of mass ratio. Furthermore, it is preferable to mix lithium titanate having a spinel structure with Li ₂ BaTi ₆ O ₁₄ . The mixing ratio is more preferably in the range of 99.9: 0.1 to 75.0: 25.0 by mass ratio. Furthermore, the mixing ratio is more preferably in the range of 93.0: 7.0 to 87.0: 13.0 by mass ratio.

In the method for producing an electrode active material of the present invention, examples of the lithium compound include lithium oxides, carbonates, inorganic acid salts, organic acid salts, and chlorides. And lithium carbonate. In particular, it is preferable to use lithium carbonate as the lithium compound.

In addition, examples of the titanium compound include titanium oxides, carbonates, inorganic acid salts, organic acid salts, and chlorides. In particular, it is preferable to use titanium oxide as the titanium compound.

Furthermore, examples of the barium compound include barium oxides, carbonates, inorganic acid salts, organic acid salts, and chlorides. Specific examples include barium carbonate and barium oxide. In particular, it is preferable to use barium carbonate as the barium compound.

The mixing method, mixing conditions in the mixing step, and the baking method and baking conditions in the baking step can be arbitrarily set in consideration of the required characteristics, productivity, and the like of the nonaqueous electrolyte secondary battery.

Next, an example of a method for producing the nonaqueous electrolyte secondary battery of the present invention will be described in detail below.

First, a negative electrode is formed. For example, a negative electrode active material is mixed with a conductive agent and a binder, an organic solvent or water is added to form a negative electrode active material slurry, and this negative electrode active material slurry is coated on the electrode current collector by an arbitrary coating method. The negative electrode is formed by drying.

Next, a positive electrode is formed. For example, a positive electrode active material is mixed with a conductive agent and a binder, an organic solvent or water is added to form a positive electrode active material slurry, and this positive electrode active material slurry is coated on the electrode current collector by an arbitrary coating method. The positive electrode is formed by drying.

In the present invention, the positive electrode active material is not particularly limited, and a lithium transition metal composite containing lithium compounds such as lithium cobaltate, lithium manganate, and lithium nickelate, and optionally aluminum in addition to manganese and nickel. An oxide or the like can be used.

In the present invention, the binder is not particularly limited, and various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, and carboxymethylcellulose can be used.

Further, the organic solvent is not particularly limited, and examples thereof include basic solvents such as dimethyl sulfoxide, dimethylformamide, N-methyl-2-pyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, acetonitrile. Nonaqueous solvents such as tetrahydrofuran, nitrobenzene, and acetone, and protic solvents such as methanol and ethanol can be used. Moreover, the kind of organic solvent, the compounding ratio of the organic compound and the organic solvent, the kind of additive and the amount of the additive, and the like can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery.

Next, as shown in FIG. 1, the positive electrode 14 obtained above is impregnated into the electrolyte, so that the positive electrode 14 is infiltrated with the electrolyte, and then the positive electrode current collector at the center of the bottom of the case 11 that also serves as the positive electrode terminal. The positive electrode 14 is placed on the top. Thereafter, the separator 16 impregnated with the electrolyte is laminated on the positive electrode 14, the negative electrode 15 and the current collector plate 17 are sequentially laminated, and the electrolyte is injected into the internal space. Then, a metal spring member 18 is placed on the current collector plate 17, and a gasket 13 is arranged on the periphery, and a sealing plate 12 that also serves as a negative electrode terminal is fixed to the case 11 with a caulking machine or the like to seal the exterior. By doing so, the coin-type non-aqueous electrolyte secondary battery 1 is manufactured.

The electrolyte is interposed between the positive electrode 14 and the negative electrode 15 which is a counter electrode, and transports charge carriers between the two electrodes. As such an electrolyte, one having an ionic conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at room temperature can be used. For example, an electrolytic solution in which an electrolyte salt is dissolved in an organic solvent can be used. Examples of the electrolyte salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, Li (C ₂ F ₅ SO ₂ ) ₃ C, or the like can be used.

As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc. are used. be able to.

Moreover, you may use a solid electrolyte for electrolyte. Examples of the polymer compound used in the solid electrolyte include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-monofluoroethylene copolymer, and fluoride. Vinylidene fluoride polymers such as vinylidene-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and acrylonitrile-methyl methacrylate copolymer Polymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-ethyl methacrylate copolymer, acrylonitrile-ethyl acrylate copolymer, acrylonitrile-methacrylic acid copolymer, acrylonitrile-a Examples include acrylonitrile-based polymers such as lauric acid copolymers and acrylonitrile-vinyl acetate copolymers, as well as polyethylene oxide, ethylene oxide-propylene oxide copolymers, and polymers of these acrylates and methacrylates. Can do. Moreover, you may use what made these polymer compounds contain electrolyte solution and made it gelatinous as electrolyte. Alternatively, only a polymer compound containing an electrolyte salt may be used as an electrolyte as it is. Incidentally, as an _{_{electrolyte, Li 2 S-P 2 S}} 5 _{_{based, Li 2 S-B 2 S}} 3 type, may be used an inorganic solid electrolyte such as sulfide glass represented by Li _₂ S-SiS ₂ system.

In the above embodiment, the coin-type secondary battery has been described, but it is needless to say that the battery shape is not particularly limited, and can be applied to a cylindrical type, a square type, a sheet type, and the like. Further, the exterior method is not particularly limited, and a metal case, a mold resin, an aluminum laminate film, or the like may be used.

In the above embodiment, the electrode active material of the present invention is used for the negative electrode, but it can also be applied to the positive electrode.

Furthermore, in the above embodiment, the case where the electrode active material is used for a non-aqueous electrolyte secondary battery has been described, but it can also be used for a primary battery.

Next, specific examples of the present invention will be described. In addition, the Example shown below is an example and this invention is not limited to the following Example.

[Example A]

Hereinafter, Examples 1 to 8 and Comparative Examples 1 to 6 of a coin-type nonaqueous electrolyte secondary battery using an electrode active material mainly composed of lithium titanate having a spinel structure will be described.

(Synthesis of electrode active material)

An electrode active material mainly composed of lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure was prepared by the following method.

First, the raw materials lithium carbonate (Li ₂ CO ₃ ), titanium oxide (TiO ₂ ), and barium carbonate (BaCO ₃ ) have the following molar ratios of lithium (Li), titanium (Ti), and barium (Ba): The slurry was weighed so as to have the ratios shown in Examples 1 to 8 and Comparative Examples 1 to 6 and mixed in a wet manner using water as a solvent by a ball mill using alumina balls having a diameter of 5 mm. It was. After the slurry thus obtained was spray-dried, the dried powder was fired in the atmosphere at a temperature of 850 ° C. for 1 hour to prepare each electrode active material.

(Example 1)

Li: Ti: Ba = 4.01: 5.03: 0.005 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 0.143% by mass.

(Example 2)

Li: Ti: Ba = 4.02: 5.06: 0.01 (in this case, the electrode active material includes lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. The Ba content by ICP analysis in the obtained electrode active material was 0.291% by mass.

(Example 3)

Li: Ti: Ba = 4.1: 5.3: 0.05 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. The Ba content by ICP analysis in the obtained electrode active material was 1.37% by mass.

(Example 4)

Li: Ti: Ba = 4.2: 5.6: 0.10 (in this case, the electrode active material includes lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 2.57% by mass.

(Example 5)

Li: Ti: Ba = 4.24: 5.72: 0.12 (in this case, the electrode active material includes lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 3% by mass.

(Example 6)

Li: Ti: Ba = 4.28: 5.84: 0.14 (in this case, the electrode active material includes lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 3.5% by mass.

(Example 7)

Li: Ti: Ba = 4.32: 5.96: 0.16 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 4% by mass.

(Example 8)

Li: Ti: Ba = 4.4: 6.2: 0.20 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 4.58% by mass.

(Comparative example 1)

Li: Ti: Ba = 4.0: 5.0: 0 (in this case, the electrode active material contains only spinel-type lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and the molar ratio of lithium to titanium (Li / Ti ratio) becomes 0.80.) Ba was not detected by ICP analysis in the obtained electrode active material.

(Comparative example 2)

Li: Ti: Ba = 4.0: 5.0: 0.005 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. The Ba content by ICP analysis in the obtained electrode active material was 0.144% by mass.

(Comparative example 3)

Li: Ti: Ba = 4.0: 5.0: 0.01 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. The Ba content by ICP analysis in the obtained electrode active material was 0.294% by mass.

(Comparative example 4)

Li: Ti: Ba = 4.0: 5.0: 0.05 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 1.44% by mass.

(Comparative example 5)

Li: Ti: Ba = 4.0: 5.0: 0.10 (in this case, the electrode active material contains lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. In the obtained electrode active material, the Ba content by ICP analysis was 2.85% by mass.

(Comparative Example 6)

Li: Ti: Ba = 4.0: 5.0: 0.20 (in this case, the electrode active material includes lithium titanate (Li ₄ Ti ₅ O ₁₂ ) having a spinel structure and a barium compound, and lithium with respect to titanium. The Ba content by ICP analysis in the obtained electrode active material was 5.52% by mass.

A coin-type non-aqueous electrolyte secondary battery as shown in FIG. 1 was produced using the obtained electrode active materials.

As shown in FIG. 1, a coin-type nonaqueous electrolyte secondary battery 1 includes a case 11 that also serves as a positive electrode terminal, a sealing plate 12 that also serves as a negative electrode terminal, and a gasket 13 that insulates the case 11 and the sealing plate 12. The positive electrode 14, the negative electrode 15, the separator 16 interposed between the positive electrode 14 and the negative electrode 15, the current collector plate 17 disposed on the negative electrode 15, and between the current collector plate 17 and the sealing plate 12. It is comprised from the arrange | positioned spring member 18, and the inside of case 11 is filled with electrolyte solution.

A positive electrode 14 of the coin-type non-aqueous electrolyte secondary battery 1 shown in FIG. 1 is produced using each of the electrode active materials produced above, and the non-aqueous materials of Examples 1 to 8 and Comparative Examples 1 to 6 are produced. The effect as an electrode active material for electrolyte secondary batteries was verified.

Specifically, the electrode active material, acetylene black, and polyvinylidene fluoride prepared above were weighed so as to have a mass ratio of 88: 6: 6 and mixed to prepare an electrode mixture. This electrode mixture was dispersed in a solvent (N-methyl-2-pyrrolidone) to prepare an electrode slurry. This electrode slurry was applied on the surface of an aluminum foil having a thickness of 20 μm at a coating amount of 6 mg / cm ² , dried at a temperature of 140 ° C., pressed at a pressure of 1 ton / cm ² , and then circular with a diameter of 12 mm. An electrode sheet was produced by punching into a plate. This electrode sheet was used as the positive electrode 14 of the coin-type nonaqueous electrolyte secondary battery 1 shown in FIG. As the negative electrode 15, a disk made of a metal lithium foil having a diameter of 15.5 mm was used. A current collector plate 17 was bonded to the negative electrode 15. As the separator 16, a disk-like polyethylene porous film having a diameter of 16 mm was used. As the electrolytic solution, a solution in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 and lithium hexafluorophosphate (LiPF ₆ ) was mixed so as to be 1 mol was used. In this way, a coin-type non-aqueous electrolyte secondary battery 1 having a diameter of 20 mm and a thickness of 3.2 mm was produced.

The charge / discharge characteristics were evaluated using the coin-type non-aqueous electrolyte secondary battery 1 produced as described above. After charging and discharging for 3 cycles in a constant temperature bath at 25 ° C. with a current value of 0.2 C and a voltage range of 1.0 to 3.0 V, assuming that the current value at which charging or discharging ends in 1 hour is 1 C. The battery was discharged for 2 hours at a constant voltage of 3.0 V, charged to 1.0 V at a current value of 0.2 C, and the charge capacity (0.2 C charge capacity) at a current value of 0.2 C was measured. . Then, after charging for 2 hours at a constant voltage of 1.0 V, discharging is performed to a voltage of 3.0 V at a current value of 0.2 C, and a discharge capacity at a current value of 0.2 C (0.2 C discharge capacity) Was measured.

In addition, after charging and discharging for 3 cycles at a current value of 0.2 C and a voltage range of 1.0 to 3.0 V in a constant temperature bath at 25 ° C., the battery was discharged at a constant voltage of 3.0 V for 2 hours, and then 10 C The battery was charged to 1.0 V at a current value of 10 C, and the charge capacity (10 C charge capacity) at a current value of 10 C was measured. In addition, after 10 minutes have elapsed after charging, after charging to 1.0 V at a current value of 0.2 C, charging was performed for 2 hours at a constant voltage of 1.0 V, and then 3.0 V at a current value of 10 C. Then, the battery was discharged to a voltage of 10 C, and the discharge capacity (10 C discharge capacity) at a current value of 10 C was measured.

In this verification experiment, it was confirmed that the potential dropped due to the insertion of lithium into each electrode active material of Examples 1 to 8 and Comparative Examples 1 to 6 used as the electrode active material of the positive electrode 14. An increase in potential due to lithium desorption from is defined as discharge.

The measurement results of the battery characteristics of the coin-type nonaqueous electrolyte secondary battery 1 using the electrode active materials of Examples 1 to 8 and Comparative Examples 1 to 6 are shown in Table 1, “0.2 C charge capacity”, “0.2 C It is shown as “discharge capacity”, “10C charge capacity” and “10C discharge capacity”.

From Table 1, in each of Examples 1 to 8, the Li / Ti ratio was made smaller than 0.80, so that it was 0 as compared with any of Comparative Examples 1 to 6 in which the Ba content was about the same amount. .2C charge capacity, 0.2C discharge capacity, 10C charge capacity, and 10C discharge capacity are high values, and the charge / discharge capacity per unit weight of the electrode active material can be improved, and the electrode has excellent charge / discharge characteristics. It can be seen that an active material can be obtained. In Examples 1 to 7, the Ba content is 0.14% by mass or more and 4.0% by mass or less, and the Li / Ti ratio is greater than 0.71 and less than 0.80, so that Ba is not included. Compared to the above, the 10C charge capacity and 10C discharge capacity are high values, and it is possible to improve the charge / discharge capacity per unit weight of the electrode active material during high rate charge / discharge, and the electrode has excellent rapid charge / discharge characteristics It can be seen that an active material can be obtained.

[Example B]

Hereinafter, an electrode active material containing spinel type lithium titanate and Li ₂ BaTi ₆ O ₁₄ was prepared, and coin-type non-aqueous electrolyte secondary batteries using the same were used as Examples 11 to 18 and Comparative Examples 11 to 12. Will be described.

(Synthesis of lithium titanate)

The spinel type lithium titanate (Li ₄ Ti ₅ O ₁₂ ) was synthesized by the following method.

The raw materials lithium carbonate (Li ₂ CO ₃ ) and titanium oxide (TiO ₂ ) were weighed so that the molar ratio of lithium (Li) and titanium (Ti) was 4: 5, respectively, and alumina having a diameter of 5 mm. By a ball mill using balls, water was used as a solvent and mixed in a wet manner to obtain a slurry. The dried powder obtained by spray drying this slurry was put in a sheath containing alumina as a main component and fired in the atmosphere at a temperature of 850 ° C. for 1 hour to produce Li ₄ Ti ₅ O ₁₂ .

(Synthesis of Li ₂ BaTi ₆ O ₁₄ )

Li ₂ BaTi ₆ O ₁₄ was synthesized by the following method.

The raw materials lithium carbonate (Li ₂ CO ₃ ), titanium oxide (TiO ₂ ) and barium carbonate (BaCO ₃ ) are in a molar ratio of 2: 6 for lithium (Li), titanium (Ti) and barium (Ba), respectively. Was weighed to 1 and mixed with a ball mill using alumina balls having a diameter of 5 mm in a wet manner using water as a solvent to obtain a slurry. The dried powder obtained by spray drying this slurry was put in a sheath containing alumina as a main component and fired in the atmosphere at a temperature of 850 ° C. for 1 hour to prepare Li ₂ BaTi ₆ O ₁₄ .

(mixture)

As the mixing ratio of the obtained Li ₄ Ti ₅ O ₁₂ and Li ₂ BaTi ₆ O ₁₄ is the ratio shown in Table 2 below at a mass ratio, Li ₄ Ti ₅ O ₁₂ and Li ₂ BaTi ₆ O ₁₄ Were mixed to prepare electrode active materials of Examples 11 to 18 and Comparative Examples 11 to 12.

A positive electrode 14 of the coin-type non-aqueous electrolyte secondary battery 1 shown in FIG. 1 is produced using each of the electrode active materials produced above, and the non-aqueous materials of Examples 11 to 18 and Comparative Examples 11 to 12 are produced. The effect as an electrode active material for electrolyte secondary batteries was verified.

Specifically, the electrode active material, acetylene black, and polyvinylidene fluoride prepared above were weighed so as to have a mass ratio of 88: 6: 6 and mixed to prepare an electrode mixture. This electrode mixture was dispersed in a solvent (N-methyl-2-pyrrolidone) to prepare an electrode slurry. This electrode slurry was applied on the surface of an aluminum foil having a thickness of 20 μm at a coating amount of 6 mg / cm ² , dried at a temperature of 140 ° C., pressed at a pressure of 1 ton / cm ² , and then circular with a diameter of 12 mm. An electrode sheet was produced by punching into a plate. This electrode sheet was used as the positive electrode 14 of the coin-type nonaqueous electrolyte secondary battery 1 shown in FIG. As the negative electrode 15, a disk made of a metal lithium foil having a diameter of 15.5 mm was used. A current collector plate 17 was bonded to the negative electrode 15. As the separator 16, a disk-like polyethylene porous film having a diameter of 16 mm was used. As the electrolytic solution, a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 and 1 mole of lithium hexafluorophosphate (LiPF ₆ ) was mixed per liter of the solvent was used. In this way, a coin-type non-aqueous electrolyte secondary battery 1 having a diameter of 20 mm and a thickness of 3.2 mm was produced.

The charge / discharge characteristics were evaluated using the coin-type non-aqueous electrolyte secondary battery 1 produced as described above. After charging and discharging for 3 cycles in a constant temperature bath at 25 ° C. with a current value of 0.2 C and a voltage range of 0.5 to 3.0 V, assuming that the current value at which charging or discharging ends in 1 hour is 1 C. The battery was discharged at a constant voltage of 3.0 V for 2 hours and then charged to 0.5 V at a current value of 10 C, and the charge capacity (10 C charge capacity) at a current value of 10 C was measured. In addition, after 10 minutes have elapsed after charging, the battery is charged to 0.5 V with a current value of 0.2 C, charged for 2 hours with a constant voltage of 0.5 V, and then 3.0 V with a current value of 10 C. Then, the battery was discharged to a voltage of 10 C, and the discharge capacity (10 C discharge capacity) at a current value of 10 C was measured.

In addition, cycle characteristics were evaluated using the produced coin-type non-aqueous electrolyte secondary battery 1. Specifically, assuming that the current value at which charging or discharging ends in 1 hour is 1 C, charging and discharging is performed 100 cycles in a constant temperature bath at 25 ° C. with a current value of 1 C and a voltage range of 0.5 to 3.0 V. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle was calculated as the capacity retention rate after 100 cycles, and the cycle characteristics were evaluated.

Note that in this verification experiment, charging was carried out to show that the potential dropped due to insertion of lithium into each electrode active material of Examples 11 to 18 and Comparative Examples 11 to 12 used as the electrode active material of the positive electrode 14, and each electrode active material An increase in potential due to lithium desorption from is defined as discharge.

The measurement results of the battery characteristics of the coin-type nonaqueous electrolyte secondary battery 1 using the electrode active materials of Examples 11 to 18 and Comparative Examples 11 to 12 are shown in Table 2 as “10C charge capacity”, “10C discharge capacity” and “ It is shown as “capacity maintenance rate after 100 cycles”.

From Table 2, in Examples 11 to 18, when an electrode active material consisting only of Li ₄ Ti ₅ O ₁₂ (Comparative Example 11) or an electrode active material consisting only of Li ₂ BaTi ₆ O ₁₄ (Comparative Example 12) is used. In comparison, it can be seen that the capacity retention rate after at least 100 cycles is equivalent or higher. In particular, as in Examples 11 to 16, the mixing ratio of Li ₄ Ti ₅ O ₁₂ and Li ₂ BaTi ₆ O ₁₄ ranges from 99.9: 0.1 to 75.0: 25.0 in terms of mass ratio. The capacity retention rate after at least 100 cycles is good by limiting to the inside, and compared with the case of using an electrode active material (Comparative Example 11) made only of Li ₄ Ti ₅ O ₁₂ , Li ₂ BaTi ₆ in comparison with the case of using the O ₁₄ consists of only the electrode active material (Comparative example 12), as charge-discharge capacity at the time of rapid charging and discharging, it is understood that it is possible to improve the 10C charge capacity and 10C discharge capacity. Further, as in Examples 14 to 15, the mixing ratio of Li ₄ Ti ₅ O ₁₂ and Li ₂ BaTi ₆ O ₁₄ ranges from 93.0: 7.0 to 87.0: 13.0 in terms of mass ratio. The capacity retention rate after at least 100 cycles is good by limiting to the inside, and compared with the case of using an electrode active material (Comparative Example 11) made only of Li ₄ Ti ₅ O ₁₂ , Li ₂ BaTi ₆ in comparison with the case of using the O ₁₄ consists of only the electrode active material (Comparative example 12), as charge-discharge capacity at the time of rapid charging and discharging, it is understood that it is possible to further improve the 10C charge capacity and 10C discharge capacity.

It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the claims.

Since the electrode active material according to one aspect of the present invention is an electrode active material that contains spinel-type lithium titanate as a main component and can improve the charge / discharge characteristics of the nonaqueous electrolyte secondary battery. It is useful for manufacturing non-aqueous electrolyte secondary batteries.

Further, by using the electrode active material according to another aspect of the present invention, it is possible to improve both the cycle characteristics of the nonaqueous electrolyte secondary battery and the charge / discharge capacity at the time of rapid charge / discharge. The electrode active material according to another aspect of is useful for the production of a non-aqueous electrolyte secondary battery.

1: coin-type non-aqueous electrolyte secondary battery, 11: case, 12: sealing plate, 13: gasket, 14: positive electrode, 15: negative electrode, 16: separator, 17: current collector plate, 18: spring member.

Claims

An electrode active material comprising a spinel type lithium titanate and a barium compound, wherein the molar ratio of lithium to titanium is less than 0.80.
The electrode active material according to claim 1, comprising 0.14% by mass or more and 4.0% by mass or less of barium, wherein the molar ratio of lithium to titanium is more than 0.71 and less than 0.80.
It is a manufacturing method of the electrode active material according to claim 1 or 2,
At least a mixing step of mixing a lithium compound, a titanium compound and a barium compound to obtain a mixture;
The manufacturing method of an electrode active material provided with the baking process which bakes the said mixture.
The method for producing an electrode active material according to claim 3, wherein in the mixing step, the lithium compound, the titanium compound, and the barium compound are mixed so that the molar ratio of lithium to titanium is less than 0.80.
The method for producing an electrode active material according to claim 3 or 4, wherein the barium compound mixed in the mixing step is barium carbonate.
The method for producing an electrode active material according to any one of claims 3 to 5, wherein the lithium compound mixed in the mixing step is lithium carbonate.
The method for producing an electrode active material according to any one of claims 3 to 6, wherein the titanium compound mixed in the mixing step is titanium oxide.
A non-aqueous electrolyte secondary battery using the electrode active material according to claim 1 or 2 as an electrode material.
A non-aqueous electrolyte secondary battery using, as an electrode material, an electrode active material produced by the production method according to any one of claims 3 to 7.
An electrode active material containing spinel type lithium titanate and Li 2 BaTi 6 O 14 .
The mixture ratio of the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 is in a range of 99.9: 0.1 to 55.0: 45.0 in mass ratio. The electrode active material as described.
The mixture ratio of the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 is in a range of 99.9: 0.1 to 75.0: 25.0 in mass ratio. The electrode active material as described.
The mixture ratio of the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 is in a range of 93.0: 7.0 to 87.0: 13.0 in mass ratio. The electrode active material as described.
A method for producing an electrode active material according to any one of claims 10 to 13,
A first synthesis step for obtaining a spinel type lithium titanate by firing a mixture obtained by mixing a lithium compound and a titanium compound;
A second synthesis step for obtaining Li 2 BaTi 6 O 14 by firing a mixture obtained by mixing a lithium compound, a titanium compound and a barium compound;
And a mixing step of mixing the lithium titanate of the spinel structure Li 2 BaTi 6 O 14, a manufacturing method of the electrode active material.
In the mixing step, the mixing ratio of the spinel type lithium titanate and the Li 2 BaTi 6 O 14 is in the range of 99.9: 0.1 to 55.0: 45.0 in terms of mass ratio. The method of manufacturing an electrode active material according to claim 14, wherein the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 are mixed.
In the mixing step, the mixing ratio of the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 is within a range of 99.9: 0.1 to 75.0: 25.0 in terms of mass ratio. The method of manufacturing an electrode active material according to claim 14, wherein the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 are mixed.
In the mixing step, the mixing ratio of the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 is in the range of 93.0: 7.0 to 87.0: 13.0 in terms of mass ratio. The method of manufacturing an electrode active material according to claim 14, wherein the lithium titanate having the spinel structure and the Li 2 BaTi 6 O 14 are mixed.
The method for producing an electrode active material according to any one of claims 14 to 17, wherein the lithium compound is lithium carbonate.
The method for producing an electrode active material according to any one of claims 14 to 18, wherein the titanium compound is titanium oxide.
The method for producing an electrode active material according to any one of claims 14 to 19, wherein the barium compound is barium carbonate.
A nonaqueous electrolyte secondary battery using the electrode active material according to any one of claims 10 to 13 as an electrode material.