JP2012059387A - Electrode active material and method of manufacturing the same, and nonaqueous electrolyte secondary battery with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode active material which includes lithium titanate with a spinel structure as a principal component, and has superior high-rate charging characteristics and a method of manufacturing the same, and a nonaqueous electrolyte secondary battery with the same.SOLUTION: The electrode active material includes the lithium titanate with the spinel structure and a yttrium compound, and yttrium is included by 0.6 to 2.4 pts.mol for 100 pts.mol of lithium in terms of mol ratio.

Description

  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 electrode active material, and more particularly, to an electrode active material composed of a lithium-titanium composite oxide having a spinel structure and its The present invention relates to a manufacturing method 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, which do not flow abruptly even when 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 Japanese Patent Application Laid-Open No. 2001-196061 (hereinafter referred to as Patent Document 1), in order to obtain a nonaqueous electrolyte lithium secondary battery having high energy density and excellent self-discharge storage characteristics, Li _x Ti _{5 / 3-y} L _y O ₄ having a spinel structure as a component (L is one or more elements other than Ti, 4/3 ≦ x ≦ 7/3, 0 ≦ y ≦ 5/3) Oxide sintered body that can be represented by Li _m MPO ₄ (M is one or more transition metals, 0 ≦ m ≦ 2.1) having an olivine structure as the main component of the positive electrode active material It has been proposed to use

JP 2001-196061 A

  However, as described in the example of Patent Document 1, by using a lithium titanium composite oxide in which a part of Ti is substituted with B, Co, or Zn as a negative electrode active material, the energy density is high, A non-aqueous electrolyte secondary battery with excellent self-discharge and excellent storage characteristics is disclosed. However, even when a lithium titanium composite oxide in which a part of Ti is substituted with B, Co, or Zn is used as a negative electrode active material, there is a problem that high rate charging characteristics are insufficient.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electrode active material having spinel-type lithium titanate as a main component and having excellent high-rate charging characteristics, a method for manufacturing the electrode active material, and a nonaqueous electrolyte secondary battery including the electrode active material. That is.

  As a result of intensive research in order to solve the problems of the prior art, the present inventors have mixed at least a lithium compound and a titanium compound as a starting material with an yttrium compound, and calcined to obtain a spinel type lithium titanate. It has been found that the above object can be achieved by synthesizing an yttrium compound separately from lithium titanate during synthesis. Based on this knowledge, the electrode active material according to the present invention has the following characteristics.

  An electrode active material according to the present invention includes lithium titanate having a spinel structure and an yttrium compound, and in a molar ratio, yttrium is included in an amount of 0.6 mol part or more and 2.4 mol part or less with respect to 100 mol parts of lithium. It is.

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

  In the mixing step, the lithium compound, the titanium compound, and the yttrium compound are mixed so that yttrium is contained in a molar ratio of 0.6 mol part or more and 2.4 mol part or less with respect to 100 mol parts of lithium. It is preferable.

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

  The nonaqueous electrolyte secondary battery of the present invention uses the above electrode active material as an electrode material. The non-aqueous electrolyte secondary battery of the present invention uses an electrode active material produced by the above production method as an electrode material.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode active material excellent in the high rate discharge characteristic can be obtained in the electrode active material which contains the lithium titanate of a spinel type structure as a main component. Moreover, since it becomes possible to reduce a slurry viscosity at the time of the synthesis | combination of a lithium titanate, handling becomes good and productivity improves.

It is sectional drawing 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.

  The electrode active material of the present invention contains lithium titanate having a spinel structure and an yttrium compound, and yttrium is contained in a molar ratio of 0.6 mol part or more and 2.4 mol part or less with respect to 100 mol parts of lithium. It is characterized by. The electrode active material of the present invention includes an yttrium compound separately from lithium titanate, and contains yttrium in the molar ratio described above, whereby an electrode active material containing spinel type lithium titanate as a main component. It is possible to obtain an electrode active material that has a high charge capacity retention rate at the time of rapid charge and excellent in rapid charge characteristics (or high rate charge characteristics). Moreover, since it becomes possible to reduce a slurry viscosity at the time of the synthesis | combination of a lithium titanate, handling becomes good and productivity improves. When yttrium is contained at a molar ratio of less than 0.6 mole part relative to 100 mole parts of lithium, or when it exceeds 2.4 mole part, the charge capacity retention rate during rapid charging is reduced.

  The method for producing an electrode active material according to the present invention includes at least a mixing step of mixing a lithium compound, a titanium compound, and an yttrium compound to obtain a mixture, and a baking step of baking the mixture. In the mixing step, the lithium compound, the titanium compound, and the yttrium compound may be mixed so that yttrium is contained in a molar ratio of 0.6 mol part or more and 2.4 mol part or less with respect to 100 mol parts of lithium. preferable.

  As one embodiment of the present invention, examples of the lithium compound include lithium oxide, carbonate, inorganic acid salt, organic acid salt and chloride. Specific examples include lithium hydroxide and lithium carbonate. In particular, it is preferable to use lithium carbonate as the lithium compound.

  Moreover, as said titanium compound, the oxide, carbonate, inorganic acid salt, organic acid salt, chloride, etc. of titanium are mentioned. In particular, it is preferable to use titanium oxide as the titanium compound.

  Furthermore, examples of the yttrium compound include yttrium oxides, carbonates, inorganic acid salts, organic acid salts, and chlorides. Specific examples include yttrium carbonate and yttrium oxide. In particular, it is preferable to use yttrium oxide as the yttrium 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 a nonaqueous electrolyte secondary battery when the electrode active material of the present invention is used as a negative electrode active material will be described in detail below.

  First, a negative electrode is formed. For example, a negative electrode active material is mixed with a conductive additive 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 applied onto 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 additive 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 applied onto 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 carboxymethyl cellulose can be used.

  Further, the organic solvent is not particularly limited, and examples thereof include basic solvents such as dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, acetonitrile, tetrahydrofuran, Nonaqueous solvents such as 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, an electrolyte 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. Here, as the electrolyte salt, for example, 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 Acrylic nitrile polymers such as lauric acid copolymer and acrylonitrile-vinyl acetate copolymer, polyethylene oxide, ethylene oxide-propylene oxide copolymer, and polymers of these acrylates and methacrylates. be able to. 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. However, the battery shape is not particularly limited, and can be applied to a cylindrical type, a square type, a sheet type, and the like. Also, the exterior method is not particularly limited, and a metal case, mold resin, 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 the present invention can also be applied to the positive electrode.

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

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

  Examples 1 to 4 and Comparative Example 1 of coin type nonaqueous electrolyte secondary batteries using spinel type lithium titanate applied to an electrode active material will be described below.

  (Synthesis of electrode active material)

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

First, lithium carbonate (Li ₂ CO ₃ ), titanium oxide (TiO ₂ ), and yttrium oxide (Y ₂ O ₃ ), which are raw materials, are shown in Examples 1 to 4 and Comparative Example 1 having mass ratios below. The slurry was weighed so as to have a ratio and wet-mixed using water as a solvent for 20 hours to obtain a slurry. In this case, the total mass of Li ₂ CO ₃ and TiO ₂ was 100 g, and the mass of water was 200 g. The slurry thus obtained was spray-dried and then fired in the atmosphere at a temperature of 850 ° C. for 1 hour to prepare each electrode active material.

  A small amount of each of the obtained slurry of Examples 1 to 4 and Comparative Example 1 was collected, and the viscosity of the slurry was measured. In the viscosity measurement, a TVB type viscometer manufactured by Toki Sangyo Co., Ltd. was used as the viscometer, and the rotor No. The rotation speed was set to 60 rpm at M3. The results of measuring the viscosity of the slurry are shown in Table 1 below.

  Example 1

Li ₂ CO ₃ : TiO ₂ : Y ₂ O ₃ = 0.37: 0.92: 0.0022 (molar ratio) (in this case, the electrode active material is Li ₄ Ti ₅ O ₁₂ and Y ₂ O having a spinel structure) _3), and in terms of molar ratio, Y is included in an amount of 0.6 mol part (Y addition amount) with respect to Li: 100 mol part.)

  (Example 2)

Li ₂ CO ₃ : TiO ₂ : Y ₂ O ₃ = 0.37: 0.92: 0.0044 (molar ratio) (in this case, the electrode active material is Li ₄ Ti ₅ O ₁₂ and Y ₂ O having a spinel structure) _3), and in terms of molar ratio, Y is included in an amount of 1.2 mol parts (Y addition amount) with respect to Li: 100 mol parts.

  (Example 3)

Li ₂ CO ₃ : TiO ₂ : Y ₂ O ₃ = 0.37: 0.92: 0.066 (molar ratio) (in this case, the electrode active material is Li ₄ Ti ₅ O ₁₂ and Y ₂ O having a spinel structure) _3), and in a molar ratio, Li is included in an amount of 1.8 mol parts (Y addition amount) with respect to 100 mol parts.)

  Example 4

Li ₂ CO ₃ : TiO ₂ : Y ₂ O ₃ = 0.37: 0.92: 0.0088 (molar ratio) (in this case, the electrode active material is Li ₄ Ti ₅ O ₁₂ and Y ₂ O having a spinel structure) _3), and 2.4 mole parts (Y addition amount) of Y with respect to 100 mole parts of Li: in a molar ratio.

  (Comparative Example 1)

Li ₂ CO ₃ : TiO ₂ : Y ₂ O ₃ = 0.37: 0.92: 0.0 (molar ratio) (in this case, the electrode active material contains only Li ₄ Ti ₅ O ₁₂ having a spinel structure) become.)

  A coin-type non-aqueous electrolyte secondary battery as shown in FIG. 1 was produced using each of 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.

  The 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 electrolyte 2 of Examples 1 to 4 and Comparative Example 1 is produced. The effect as an electrode active material for secondary batteries was verified.

Specifically, the electrode active material prepared above, acetylene black, and polyvinylidene fluoride 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., and then punched into a disk having a diameter of 12 mm at a pressure of 1 ton / cm ^2. This produced an electrode sheet. 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, one obtained by dissolving 1 mol of lithium hexafluorophosphate (LiPF ₆ ) per liter of the solvent in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 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.

Charging characteristics were evaluated using the coin-type non-aqueous electrolyte secondary battery 1 produced as described above. The coin-type non-aqueous electrolyte secondary battery 1 was charged and discharged for 3 cycles in a constant temperature bath at a temperature of 25 ° C. with a current value of 0.2 mA / cm ² and a voltage range of 1.0 to 3.0 V. The charge capacity at the cycle was measured. Thereafter, similarly, the coin-type nonaqueous electrolyte secondary battery 1 was charged and discharged at a current value of 4 mA / cm ² and a voltage range of 1.0 to 3.0 V, and the charge capacity was measured. And the charge capacity maintenance factor was computed with the following formula | equation. 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 4 and Comparative Example 1 are shown in Table 2 below.

Charging capacity maintenance rate [%] = {(charging capacity at current value 4 mA / cm ² ) / (charging capacity at the third cycle at current value 0.2 mA / cm ² )} × 100

  In this verification experiment, it was charged that the potential dropped due to the insertion of lithium into each electrode active material of Examples 1 to 4 and Comparative Example 1 used as the active material of the positive electrode 14, and the lithium from each electrode active material An increase in potential due to desorption is defined as discharge.

  From Table 1, it can be seen that the viscosity of the slurry of Comparative Example 1 not containing yttrium oxide is high, and the viscosity of the slurries of Examples 1 to 4 containing yttrium oxide is low. Therefore, it can be seen that the viscosity of the slurry can be reduced by adding yttrium oxide.

From Table 2, it can be seen that in Examples 1 to 4, the charge capacity maintenance rate is higher than that of Comparative Example 1, and the high rate charging characteristics are good. Moreover, in Example 4, although the charge capacity of the 3rd cycle of electric current value 0.2mA / cm < ² > is comparatively low, it turns out that a charge capacity maintenance factor is high and a high rate charge characteristic is favorable. Therefore, when the electrode active material includes lithium titanate having a spinel structure and yttrium oxide, and yttrium is included in a molar ratio of 0.6 mol part or more and 2.4 mol part or less with respect to 100 mol parts of lithium. It can be seen that it is possible to obtain an electrode active material having a high charge capacity retention rate during rapid charging of the nonaqueous electrolyte secondary battery and excellent in high rate charging characteristics.

  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 scope of claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the scope of claims. .

  Since the electrode active material of the present invention contains a spinel-type lithium titanate as a main component and is an electrode active material having a high charge capacity retention rate at the time of quick charge of a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary Useful in the manufacture of batteries.

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 (8)

  An electrode active material comprising a spinel type lithium titanate and an yttrium compound, and containing yttrium in a molar ratio of not less than 0.6 mole parts and not more than 2.4 mole parts with respect to 100 mole parts of lithium. It is a manufacturing method of the electrode active material according to claim 1,
At least a mixing step of mixing a lithium compound, a titanium compound, and an yttrium compound to obtain a mixture;
The manufacturing method of an electrode active material provided with the baking process which bakes the said mixture.   The lithium compound, the titanium compound, and the yttrium compound are mixed so that, in the mixing step, yttrium is contained in a molar ratio of 0.6 mol part or more and 2.4 mol part or less with respect to 100 mol parts of lithium. 2. A method for producing an electrode active material according to 2.   The method for producing an electrode active material according to claim 2 or 3, wherein the yttrium compound is yttrium oxide.   The method for producing an electrode active material according to claim 2, wherein the lithium compound is lithium carbonate.   The method for producing an electrode active material according to claim 2, wherein the titanium compound is titanium oxide.   A non-aqueous electrolyte secondary battery using the electrode active material according to claim 1 as an electrode material. A nonaqueous electrolyte secondary battery using, as an electrode material, an electrode active material produced by the production method according to any one of claims 2 to 6.

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