JP5008325B2 - Lithium battery - Google Patents

Description

  The present invention relates to a lithium battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte in which a solute is dissolved in a non-aqueous solvent. The positive electrode and the negative electrode are improved to increase the internal resistance of the lithium battery during storage. This is characterized in that a lithium battery excellent in storage characteristics can be obtained.

  In recent years, lithium batteries have been used as a power source for various devices, and lithium batteries with high storage characteristics have been demanded.

For this reason, in recent years, it has been proposed to use β-VOPO ₄ which is stable to some extent and has little reaction with the non-aqueous electrolyte during storage as a positive electrode active material in a lithium battery (for example, Non-Patent Document 1). reference.).

However, even in such a lithium battery using β-VOPO ₄ as the positive electrode active material, when this lithium battery is stored, vanadium gradually dissolves in the non-aqueous electrolyte from β-VOPO ₄ in the positive electrode. The vanadium dissolved in this way covers the surface of lithium in the negative electrode, which makes it impossible to properly discharge lithium in the negative electrode, increasing the internal resistance of the lithium battery after storage and deteriorating the storage characteristics. There was a problem.
Journal of Electrochemical Society, 146 (12) 4375-4379 (1999)

The present invention is a lithium battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which a solute is dissolved in a non-aqueous solvent, and the above-described problem when β-VOPO ₄ is used as an active material of the positive electrode. In the storage, the surface of lithium in the negative electrode is suppressed from being covered with vanadium dissolved from the above β-VOPO ₄ in the positive electrode, and the discharge of lithium from the negative electrode is reduced. Therefore, it is an object of the present invention to prevent the internal resistance of the lithium battery from increasing during storage and to obtain a lithium battery having excellent storage characteristics.

In the present invention, in order to solve the above problems, in a lithium battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which a solute is dissolved in a non-aqueous solvent, -VOPO ₄ was used, and a lithium alloy containing at least aluminum was used as the negative electrode active material.

When the above-described β-VOPO ₄ is used as the positive electrode active material and a lithium alloy containing at least aluminum is used as the negative electrode active material, β-VOPO in the positive electrode can be obtained when the lithium battery is stored. _{Even if} vanadium gradually dissolves in the non-aqueous electrolyte from ₄ , the dissolved vanadium is bonded to the aluminum contained in the lithium alloy of the negative electrode, preventing the lithium surface of the negative electrode from being covered with vanadium. Become so.

Here, in the above lithium battery, with respect to the amount of aluminum contained in the above lithium alloy which is the active material of the negative electrode, if the amount is small, vanadium dissolved from β-VOPO ₄ is not sufficiently bonded to the aluminum. As a result, vanadium covers the surface of lithium in the negative electrode, but if the amount is too large, the portion of aluminum bonded to vanadium increases, and in any case, lithium discharge in the negative electrode is suppressed. Become so. For this reason, the amount of aluminum contained in the lithium alloy is preferably in the range of 0.01 to 5% by weight, more preferably in the range of 0.05 to 2% by weight.

Further, in the lithium battery of the present invention, commonly used solutes in the non-aqueous electrolyte can be used, for example, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO _{2) 2, LiN (C 2} F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3 LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , Li ₂ B ₁₂ Cl ₁₂ , a mixture thereof, or the like can be used. In particular, when lithium trifluoromethanesulfonate LiCF ₃ SO ₃ is used, even if vanadium is dissolved in the non-aqueous electrolyte from the positive electrode, the dissolved vanadium is dissolved in the anion and V (CF ₃ SO ₃ ) ₃ in this solute. Since V (CF ₃ SO ₃ ) ₃ has a low solubility, vanadium does not move to the negative electrode, but precipitates in the vicinity of the positive electrode in the state of V (CF ₃ SO ₃ ) ₃ and dissolves from the positive electrode. It is further suppressed that the surface of lithium in the negative electrode is covered with vanadium.

Further, as the non-aqueous solvent in the non-aqueous electrolyte, those generally used can be used, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, A chain carbonate such as diethyl carbonate, an ether solvent such as 1,2-dimethoxyethane, 1,2-diethoxyethane, or a mixed solvent thereof can be used. In particular, when a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane is used as a non-aqueous solvent, the solubility of V (CF ₃ SO ₃ ) ₃ is further lowered, and nickel dissolved from the positive electrode moves to the negative electrode. Thus, the lithium surface of the negative electrode is further prevented from being covered with vanadium dissolved from the positive electrode.

In the lithium battery of the present invention, as described above, β-VOPO ₄ is used as the positive electrode active material, and a lithium alloy containing at least aluminum is used as the negative electrode active material. Therefore, when this lithium battery is stored, Even if vanadium is gradually dissolved in the non-aqueous electrolyte from β-VOPO ₄ in the positive electrode, the dissolved vanadium is combined with aluminum contained in the lithium alloy of the negative electrode, and the lithium surface in the negative electrode is covered with vanadium. To be prevented.

  As a result, in the lithium battery of the present invention, the lithium discharge at the negative electrode is suppressed from being reduced by the vanadium coating, the internal resistance of the lithium battery is prevented from increasing during storage, and lithium having excellent storage characteristics A battery can be obtained.

  Hereinafter, the lithium battery according to the present invention will be described in detail with reference to examples, and in the lithium battery according to this example, the increase in internal resistance after storage is suppressed and storage characteristics are improved. Is clarified with a comparative example. The lithium battery of the present invention is not limited to those shown in the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof.

Example 1
In Example 1, a negative electrode, a positive electrode, and a nonaqueous electrolytic solution prepared as described below were used.

[Production of positive electrode]
In producing the positive electrode, β-VOPO ₄ powder was used as the positive electrode active material, and the positive electrode active material, the carbon black powder of the conductive agent, and the fluororesin powder of the binder were in a weight ratio of 85: 10: 5. To prepare a positive electrode mixture. The positive electrode mixture was cast into a disk shape and dried in a vacuum at 250 ° C. for 2 hours to produce a positive electrode.

[Production of negative electrode]
In producing the negative electrode, a Li—Al alloy plate material containing 0.01% by weight of aluminum was punched into a disc shape to produce a negative electrode.

[Preparation of non-aqueous electrolyte]
In preparing the non-aqueous electrolyte, lithium trifluoromethanesulfonate LiCF as a solute in a mixed solvent in which ethylene carbonate (EC) and 1,2-dimethoxyethane (DME) were mixed at a volume ratio of 1: 1. ₃ SO ₃ was dissolved at 1 mol / liter to prepare a non-aqueous electrolyte.

[Production of battery]
In producing a battery, as shown in FIG. 1, a separator 3 made of a polypropylene nonwoven fabric impregnated with the above non-aqueous electrolyte is interposed between the positive electrode 1 and the negative electrode 2 produced as described above. The positive electrode 1 is connected to the positive electrode can 4a via the positive electrode current collector 1a, while the negative electrode 2 is connected to the positive electrode can 1a through the positive electrode current collector 1a. Is connected to the negative electrode can 4b through the negative electrode current collector 2a, and the positive electrode can 4a and the negative electrode can 4b are electrically insulated by the insulating packing 5 made of polypropylene, so that the diameter becomes 24 mm and the thickness becomes 3 mm. A flat coin-type lithium battery of Example 1 was obtained.

(Examples 2 to 5)
In Examples 2-5, only the Li-Al alloy used for the negative electrode and the Lithium-Al alloy used for the negative electrode were changed, and other than that, Examples 2-5 were performed in the same manner as in Example 1 above. Each lithium battery was prepared.

  Here, as the Li—Al alloy, in Example 2, an Li—Al alloy containing 0.05% by weight of aluminum was used. In Example 3, an Li—Al alloy containing 0.2% by weight of aluminum was used. In Example 4, a Li—Al alloy containing 2% by weight of aluminum was used, and in Example 5, a Li—Al alloy containing 5% by weight of aluminum was used.

(Comparative Example 1)
In Comparative Example 1, a lithium battery of Comparative Example 1 was produced in the same manner as in Example 1 except that Li metal containing no aluminum was used for the negative electrode.

  Then, an alternating voltage of 1 mV and 1 kHz was applied to each of the lithium batteries of Examples 1 to 5 and Comparative Example 1 immediately after being produced as described above, and the current at that time was measured to determine the inside of each lithium battery. As a result of calculating the resistance, the internal resistance of any lithium battery was about 20Ω.

  Next, each of the lithium batteries of Examples 1 to 5 and Comparative Example 1 produced as described above was stored in a temperature atmosphere of 80 ° C. for 1 month, and then 1 mV and 1 kHz AC as described above. A voltage was applied, the current at that time was measured, the internal resistance of each lithium battery after storage was calculated, and the results are shown in Table 1 below.

  As a result, each of the lithium batteries of Examples 1 to 5 using the Li—Al alloy containing aluminum in the negative electrode was compared with the lithium battery of Comparative Example 1 using Li metal containing no aluminum in the negative electrode. The internal resistance after storage was greatly reduced, and the storage characteristics of the lithium battery were greatly improved. In particular, in each of the lithium batteries of Examples 2 to 4 using a Li—Al alloy containing aluminum in the range of 0.05 to 2% by weight, the internal resistance after storage was further reduced, and the lithium battery The storage characteristics were further improved.

(Examples 6 to 8)
In Examples 6-8, in the same manner as in Example 3 above, an Li-Al alloy containing 0.2% by weight of aluminum was used for the negative electrode and a non-aqueous electrolyte was prepared. In Example ₆ , lithium hexafluorophosphate LiPF ₆ is used as a solute, in Example 7, lithium tetrafluoroborate LiBF ₄ is used as a solute, and in Example 8, propylene carbonate (PC) and 1 are used as solvents. , 2-dimethoxyethane (DME) was mixed in a volume ratio of 1: 1, and other than that, each lithium in Examples 6 to 8 was used in the same manner as in Example 1 above. A battery was produced.

  And also about each lithium battery of Examples 6-8 produced in this way, the internal resistance after storing for one month in the temperature atmosphere of 80 degreeC was calculated like the above-mentioned case, and the result Are shown in Table 2 below together with the results of the lithium battery of Example 3.

  As a result, each of the lithium batteries of Examples 6 to 8 in which the solute and the solvent used in the non-aqueous electrolyte were changed as compared with the lithium battery of Comparative Example 1 using Li metal that does not contain aluminum in the negative electrode. As a result, the internal resistance after storage was greatly reduced, and the storage characteristics of the lithium battery were greatly improved.

When comparing the lithium batteries of Examples 3 and 6 to 8 above, lithium trifluoromethanesulfonate LiCF ₃ SO ₃ was used as the solute of the non-aqueous electrolyte, and ethylene carbonate (EC ) And 1,2-dimethoxyethane (DME) in a 1: 1 volume ratio, the lithium battery of Example 3 uses lithium hexafluorophosphate LiPF _{6 as} the solute of the non-aqueous electrolyte. And lithium batteries of Examples 6 and 7 using lithium tetrafluoroborate LiBF ₄ , and 1: 1 volume of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) as a solvent for the non-aqueous electrolyte. Compared with the lithium battery of Example 8 using a mixed solvent mixed at a ratio, the internal resistance after storage was further reduced, and the storage characteristics of the lithium battery were further improved. Which was.

It is a schematic sectional drawing of the lithium battery produced in the Example and comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 2 Negative electrode 2a Negative electrode collector 3 Separator 4 Battery case 4a Positive electrode can 4b Negative electrode can 5 Insulation packing

Claims (5)

In a lithium battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which a solute is dissolved in a non-aqueous solvent, β-VOPO ₄ is used as an active material of the positive electrode, and at least the active material of the negative electrode is A lithium battery using a lithium alloy containing aluminum.   2. The lithium battery according to claim 1, wherein aluminum is contained in the lithium alloy in the negative electrode in an amount of 0.01 to 5% by weight.   2. The lithium battery according to claim 1, wherein aluminum is contained in the lithium alloy in the negative electrode in a range of 0.05 to 2% by weight.   The lithium battery according to any one of claims 1 to 3, wherein lithium trifluoromethanesulfonate is used as a solute of the non-aqueous electrolyte.   The lithium battery according to any one of claims 1 to 4, wherein a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane is used as the non-aqueous solvent of the non-aqueous electrolyte. Lithium battery.

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