JP2012028288A - Manufacturing method of electrode active material, electrode active material manufactured by manufacturing method, and nonaqueous electrolyte secondary battery including electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an electrode active material, the electrode active material manufactured by the manufacturing method, and a nonaqueous electrolyte secondary battery including the electrode active material capable of improving rapid charge properties of the nonaqueous electrolyte secondary battery.SOLUTION: The electrode active material is an electrode active material including lithium titanate in a spinel structure and is manufactured by preparing at least two kinds of titanium oxide powder different from one another in average specific surface area, mixing the titanium oxide powder and a lithium compound, and calcining the mixture.

Description

  The present invention generally relates to a method for producing an electrode active material, an electrode active material produced by the production method, and a non-aqueous electrolyte secondary battery provided with the electrode active material. The present invention relates to a method for producing an electrode active material containing a lithium titanium composite oxide, an electrode active material produced by the production method, and a nonaqueous electrolyte secondary battery provided with the electrode active material.

  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.

  Then, lithium titanium complex oxides, such as lithium titanate, which does not flow abruptly even if a short circuit occurs inside the battery, have attracted 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 No. 3502118 (hereinafter referred to as Patent Document 1), 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. Patent Document 1 discloses a method for producing a negative electrode of the above lithium secondary battery by mixing lithium hydroxide or lithium carbonate and titanium oxide and firing the mixture.

JP 2008-130560 discloses (hereinafter, referred to as Patent Document 2) _{In, Li 1 + x Ti 1-} xy M y O 2 + z (0.01 ≦ x ≦ 0.5,0 ≦ y ≦ 0.3, And −0.2 ≦ z ≦ 0.2, and M is an element selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, etc.) A negative electrode active material and a manufacturing method thereof are disclosed.

Japanese Patent No. 3502118 JP 2008-130560 A

  However, according to the knowledge of the present inventors, lithium titanate described in Patent Document 1 or lithium-titanium composite oxide described in Patent Document 2 is used as a negative electrode active material for a nonaqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery has a good cycle characteristic, but has a problem that the quick charge characteristic is low.

  Accordingly, an object of the present invention is to provide a method for producing an electrode active material capable of improving the quick charge characteristics of a nonaqueous electrolyte secondary battery, an electrode active material produced by the production method, and the electrode active material. A non-aqueous electrolyte secondary battery is provided.

  As a result of intensive studies to solve the problems of the prior art, the present inventor prepared at least two types of titanium oxide powders having different average specific surface areas as raw materials for the titanium component, and obtained titanic acid having a spinel structure. It has been found that the above object can be achieved by producing an electrode active material containing lithium. Based on this finding, the method for producing an electrode active material according to the present invention has the following characteristics.

  The method for producing an electrode active material according to the present invention is a method for producing an electrode active material containing spinel type lithium titanate, and includes the following steps.

  (A) Step of preparing at least two types of titanium oxide powders having different average specific surface areas

  (B) A mixing step of mixing at least the titanium oxide powder and the lithium compound to obtain a mixture

  (C) The step of firing the above mixture

  In the method for producing an electrode active material according to the present invention, it is preferable that the average specific surface areas of the two types of titanium oxide powders differ by 2 times or more.

Moreover, in the manufacturing method of the electrode active material of this invention, said two types of titanium oxide powders are the 1st titanium oxide powder whose average specific surface area is less than 20 m < ² > / g, and an average specific surface area are 20 m < ² > / g. It is preferable that the 2nd titanium oxide powder exceeding is included.

  The lithium compound mixed in the mixing step is preferably lithium carbonate.

  The electrode active material of the present invention is manufactured by the above manufacturing method.

  The nonaqueous electrolyte secondary battery of the present invention is provided with an electrode containing the above electrode active material.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode active material which can improve the quick charge characteristic of a nonaqueous electrolyte secondary battery can be obtained in the electrode active material containing spinel type lithium titanate.

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.

  The electrode active material of the present invention is an electrode active material containing spinel type lithium titanate, and at least two types of titanium oxide powders having different average specific surface areas are prepared, and the titanium oxide powder and the lithium compound are prepared. It is characterized by being produced by mixing and firing the mixture. With this feature, the electrode active material of the present invention can improve the quick charge characteristics (or high rate charge characteristics).

  In the electrode active material of the present invention, it is preferable that the average specific surface areas of the two types of titanium oxide powders differ by 2 times or more. In this case, quick charge characteristics can be further improved.

In the electrode active material of the present invention, the two types of titanium oxide powders include a first titanium oxide powder having an average specific surface area of less than 20 m ² / g and a ^second titanium oxide powder having an average specific surface area of more than 20 m ² / g. The titanium oxide powder is preferably included. In this case, quick charge characteristics can be further improved.

Note that examples of the spinel-type lithium titanate contained in the electrode active material of the present invention include Li ₄ Ti ₅ O ₁₂ . Lithium titanate may contain elements other than lithium, titanium, and oxygen. In addition, an element other than lithium, titanium, and oxygen may be included as a substituted compound in lithium titanate having a spinel structure.

  The crystal structure of the above-mentioned spinel type lithium titanate is stable. For this reason, the crystal structure is unlikely to collapse due to insertion and extraction of lithium accompanying charging and discharging. Thereby, by providing the electrode containing the electrode active material of the present invention, it is possible to obtain a nonaqueous electrolyte secondary battery with good cycle characteristics.

In the method for producing an electrode active material of the present invention, first, at least two types of titanium oxide powders having different average specific surface areas are prepared. Then, at least the titanium oxide powder and the lithium compound are mixed to obtain a mixture. An electrode active material is produced by baking this mixture. It is preferable that the average specific surface areas of the two types of titanium oxide powders differ by 2 times or more. The two types of titanium oxide powders include a first titanium oxide powder having an average specific surface area of less than 20 m ² / g and a ^second titanium oxide powder having an average specific surface area of more than 20 m ² / g. Is preferred.

  As one embodiment of the present invention, examples of the lithium compound mixed in the mixing step include lithium oxides, carbonates, inorganic acid salts, organic acid salts, and chlorides. Specifically, lithium hydroxide, lithium carbonate, etc. are mentioned. In particular, it is preferable to use lithium carbonate as the lithium 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 and productivity 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 coated on the electrode current collector by an arbitrary coating method. Then, 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 coated on the electrode current collector by an arbitrary coating method. And drying to form a positive electrode.

  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-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 addition amount thereof 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 for 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-acrylic Examples include acrylic acid polymers such as formic 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, sulfide glass represented by Li ₂ S-SiS ₂ system oxide having a perovskite structure, NASICON structure An inorganic solid electrolyte such as an oxide containing

  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. 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 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.

  Hereinafter, Examples 1 to 3 and Comparative Examples 1 to 3 of a coin-type nonaqueous electrolyte secondary battery using an electrode active material containing spinel type lithium titanate as a main component and using the electrode active material will be described.

  (Production of electrode active material)

An electrode active material containing spinel type lithium titanate (Li ₄ Ti ₅ O ₁₂ ) as a main component was produced by the following method.

First, two types of titanium oxide (TiO ₂ ) powders having different average specific surface areas were prepared as raw materials for the titanium component of lithium titanate. Specifically, a first titanium oxide powder having an average specific surface area of 10.8 m ² / g and a second titanium oxide powder having an average specific surface area of 31.7 m ² / g were prepared. Here, the BET method was adopted as a method for measuring the average specific surface area.

Next, two types of titanium oxide powders having different average specific surface areas and lithium carbonate (Li ₂ CO ₃ ) powders mixed at a predetermined ratio are respectively mixed in molar ratios of lithium (Li) and titanium (Ti). Was weighed so as to be 4.05: 5, 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. A dry powder obtained by spray drying this slurry was fired in the air to prepare an electrode active material containing Li ₄ Ti ₅ O ₁₂ as a main component.

  In Examples 1 to 3 and Comparative Examples 1 to 3, the mixing ratio of two types of titanium oxide powders having different average specific surface areas (SSA) was set as shown in Table 1 in terms of titanium (Ti) molar ratio. . Moreover, in Examples 1-3 and Comparative Examples 1-3, the firing conditions (firing temperature and time) of the dry powder were set as shown in Table 1.

  (Preparation of non-aqueous electrolyte secondary battery)

  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 nonaqueous electrolyte secondary battery 1 shown in FIG. 1 is produced using each of the electrode active materials produced above, and the nonaqueous materials of Examples 1 to 3 and Comparative Examples 1 to 3 are produced. The effect as an electrode active material for electrolyte 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., 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 nonaqueous 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. .

  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 for 2 hours at a constant voltage of 3.0 V, and then 5 C The battery was charged to 1.0 V at a current value of 5 C, and the charge capacity (5 C charge capacity) at a current value of 5 C was measured.

  Here, as described above, 1C is a current value at which charging or discharging ends in 1 hour, 0.2C is a current value at which charging or discharging ends in 5 hours, and 5C is charged or discharged in 12 minutes. This is the current value at which the discharge ends.

  In this verification experiment, coin-type nonaqueous electrolytes of Examples 1 to 3 and Comparative Examples 1 to 3 in which an electrode active material containing spinel-type lithium titanate as a main component was used as the electrode active material of the positive electrode 14. In the secondary battery 1, a decrease in potential due to insertion of lithium into the electrode active material of the positive electrode 14 is defined as charging, and a rise in potential due to lithium desorption from each electrode active material is defined as discharging.

  The measurement results of the battery characteristics of the coin-type nonaqueous electrolyte secondary batteries 1 of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1 as “0.2 C charge capacity”, “5 C charge capacity”, and “5 C / 0. 2C charge capacity ratio ”.

  From Table 1, in the coin-type non-aqueous electrolyte secondary battery 1 of Examples 1 to 3 using electrode active materials produced using two types of titanium oxide powders having different average specific surface areas, one type of titanium oxide powder was used. Compared with the coin-type nonaqueous electrolyte secondary battery 1 of Comparative Examples 1 to 3 using the electrode active material manufactured using the above, the 5C charge capacity is higher, and the 5C / 0.2C charge capacity ratio is It turns out that it is a high value. Therefore, it is possible to improve the charge capacity per unit weight of the electrode active material by using an electrode active material produced using two types of titanium oxide powders having different average specific surface areas, and excellent quick charge characteristics. An electrode active material can be obtained.

  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. .

  By using the electrode active material of the present invention, the quick charge characteristics of the nonaqueous electrolyte secondary battery can be improved, which is useful for the production of nonaqueous electrolyte secondary 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 (6)

A method for producing an electrode active material containing lithium titanate having a spinel structure,
Preparing at least two types of titanium oxide powders having different average specific surface areas;
At least a mixing step of mixing the titanium oxide powder and the lithium compound to obtain a mixture;
A method for producing an electrode active material, comprising the step of firing the mixture.   The method for producing an electrode active material according to claim 1, wherein the average specific surface areas of the two types of titanium oxide powders differ by 2 times or more. The two types of titanium oxide powders include a first titanium oxide powder having an average specific surface area of less than 20 m ² / g and a ^second titanium oxide powder having an average specific surface area of more than 20 m ² / g. Or the manufacturing method of the electrode active material of Claim 2.   The method for producing an electrode active material according to any one of claims 1 to 3, wherein the lithium compound to be mixed in the mixing step is lithium carbonate.   The electrode active material manufactured by the manufacturing method of any one of Claim 1- Claim 4. A nonaqueous electrolyte secondary battery comprising an electrode comprising the electrode active material according to claim 5.

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