JPH0614468B2 - Lithium organic secondary battery - Google Patents

Description

The present invention relates to an improvement of a lithium organic secondary battery that uses lithium or a lithium alloy as a negative electrode active material, and aims to reduce the internal resistance, especially the lithium interface resistance, and to charge and discharge the secondary battery. The purpose is to improve the characteristics.

Conventionally, an organic electrolyte-based secondary battery using lithium or a lithium alloy as a negative electrode active material has not been sufficiently reversible in charge and discharge. The cause of this is that the morphology of the electrodeposited lithium becomes dendritic, and it grows, its tip penetrates the separator, causing an internal short circuit, or the electrodeposited lithium breaks from its root and cannot be used for charging and discharging. It was to do. That is, lithium is highly reactive and easily reacts with moisture, etc., and a film due to the reaction with moisture etc. is unevenly formed on the lithium surface to form a portion with high interfacial resistance, and a portion with low interfacial resistance during charging. The electric current is concentrated on the electrode, and lithium is selectively deposited there, so that the morphology of the electrodeposited lithium becomes dendritic, which grows and causes the internal short circuit and the like as described above.

This invention solves the above-mentioned drawbacks of the prior art.
In a lithium organic secondary battery using lithium or a lithium alloy as a negative electrode active material, at least one selected from the group consisting of polyethylene glycol, polyethylene oxide, polypropylene glycol, polypropylene oxide and ethylene oxide-propylene oxide copolymer is used as an electrolytic solution. The purpose was achieved by adding

Examples of the electrolytic solution in the present invention include 1,2-dimethoxyethane, 1,2-diethoxyethane, propylene carbonate, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1, 3-dioxolane, 4,4-dimethyl-1,3-dioxolane, 4,5-dimethyl-
1,3-dioxolane, 2-methyl-1,3-dioxolane, 2,4-dimethyl-1,3-dioxolane, (C
H ₃ O) ₃ P = 0, (C ₂ H ₅ O) ₃ P = 0, (C ₄ H
₉ O) ₃ P = 0, (C ₈ H ₁₇ O) ₃ P = 0, (ClCH
The ₂ CH _{2 O)} 3 alone or in a mixed solvent, such as _{P = 0, LiClO 4, LiPF} 6, LiBF 4, Li
AsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiB ₁₀ C
l ₁₀ , LiB ₁₂ Cl ₁₂ , LiB (C ₆ H ₅ ) ₄ , LiB
_{(P-FC 6 H 4)} 3 CH 3, LiB (p-FC
An organic electrolyte-based electrolytic solution in which an electrolyte such as ₆ H ₄ ) ₄ is dissolved is used.

If the amount of polyethylene glycol, polyethylene oxide, polypropylene glycol, polypropylene oxide, or ethylene oxide-propylene oxide copolymer added to the electrolytic solution is too small, the effect cannot be sufficiently considered, and if it is too large, the viscosity of the electrolytic solution increases. Since the electric conductivity is lowered, it is preferably 0.2 g to 8 g per 100 m of the electrolytic solution.

In the lithium organic secondary battery of the present invention, as the negative electrode active material, lithium, lithium and, for example, aluminum,
A lithium alloy with mercury, zinc, cadmium, etc. is used, and as the positive electrode active material, for example, titanium disulfide,
Iron sulfides such as iron disulfide, ferrous sulfide and ferric sulfide, manganese dioxide, niobium disulfide, V ₆ O ₁₃ , Cu ₅ V ₂ O ₁₀
Are used.

Next, the present invention will be described with reference to examples.

Example 1 LiB (C ₆ H ₅ ) ₄ was combined with 1,3-dioxolane and 1,2.
In a mixed solvent with a volume ratio of 75:25 with dimethoxyethane, 0.
2.4 mol / 100 of polyethylene glycol (average molecular weight 20,000) is added to the dissolved 6 mol / organic electrolyte electrolyte.
m was added and dissolved. In order to eliminate the influence of the counter electrode by using the electrolytic solution to which polyethylene glycol was added in this way, the charge / discharge characteristics were examined by a Li / Li model cell as shown in FIG. The charge / discharge characteristics were measured by charging / discharging the battery at a constant current of 1 mA and examining the number of cycles in which the polarization voltage between the test electrode and the counter electrode was 1 V or less.

In FIG. 1, 1 is a polypropylene pressing plate, a test electrode 2 is formed by pressure-bonding a lithium foil 4 to a stainless steel net 3 on both sides, and a counter electrode 5 is a stainless steel net 6 to which a lithium foil 7 is attached on both sides. It is formed by pressure bonding. 8 is a current collector lead on the test electrode side, 9 is a current collector lead on the counter electrode side, 10 and 11 are microporous polypropylene films, 12 and 13 are polypropylene non-woven fabrics, 14 is an electrolytic solution, and 15 is hermetically sealed. It is a glass container.

Comparative Example 1 The same electrolytic solution as in Example 1 was used except that polyethylene glycol was not added, and the same Li / L as in Example 1 was used.
The charging / discharging characteristic was investigated by the i model cell.

Table 1 shows the charge / discharge characteristics of Example 1 as an index when the charge / discharge characteristics of Comparative Example 1 were 100.

Example 2 LiB (C ₆ H ₅ ) ₄ was dissolved in a mixed solvent having a volume ratio of 4-methyl-1,3-dioxolane and 1,2-dimethoxyethane of 75:25 at 0.6 mol / mol to prepare an electrolyte solution. , Ethylene oxide-propylene oxide copolymer (average molecular weight 12,000) was added and dissolved at a rate of 4 g / 100 m.

The charge / discharge characteristics were examined by using the Li / Li model cell as shown in FIG. 1 using the electrolytic solution thus added with the ethylene oxide-propylene oxide copolymer.

Comparative Example 2 The same electrolytic solution as in Example 2 was used except that the ethylene oxide-propylene oxide copolymer was not added,
The charge / discharge characteristics were examined using a Li / Li model cell in the same manner as in Example 2.

Table 2 shows the charging / discharging characteristics of the example 2 in the index when the charging / discharging characteristics of the comparative example 2 is 100.

Example _{3 LiB (p-FC 6 H} 4) 3 CH 3 4-methyl-1,
Polypropylene glycol (average molecular weight 4,000) in an electrolytic solution prepared by dissolving 1.0 mol / mol of a solvent mixture of 3-dioxolane and 1,2-dimethoxyethane in a volume ratio of 75:25.
Was added and dissolved at a rate of 1 g / 100 m.

Using the electrolytic solution thus added with polypropylene glycol, the charge / discharge characteristics were examined by a Li / Li model cell as shown in FIG.

Comparative Example 3 The same electrolytic solution as in Example 3 was used except that polypropylene glycol was not added, and Li /
The charge / discharge characteristics were examined using a Li model cell.

Table 3 shows the charging / discharging characteristics of Example 3 as an index when the charging / discharging characteristics of Comparative Example 3 is 100.

As shown in Tables 1 to 3, addition of polyethylene glycol, ethylene oxide-propylene oxide copolymer, polypropylene glycol, etc. improved the charge / discharge characteristics.

Next, the complex plane solution diagrams of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in FIGS. The measurement was performed in the range of 65kHz to 20mHz. FIG. 2 shows before charge / discharge, and FIG. 3 shows after 10 cycles of charge / discharge. In addition, in FIG.
Is A, Example 2 is B, Example 3 is C, Comparative Example 1 is U, Comparative Example 2 is V, and Comparative Example 3 is W.

As is clear from the results shown in FIGS. 2-3, in the example of the present invention, the interfacial resistance of lithium, that is, the resistance value corresponding to the diameter of the semicircle in the figure, is smaller than that of the comparative example. In the examples, it can be seen that the lithium surface film is less produced. This is considered to be because these additives used are effective in removing the lithium surface coating.

Example 4 A button type battery having a diameter of 20 mm and a height of 1.6 mm was assembled by using the same electrolytic solution as in Example 1 to which polyethylene glycol was added. The battery is composed of a mixture of a microporous polypropylene film and a polypropylene non-woven fabric with a lithium negative electrode and a titanium disulfide positive electrode active material for the positive electrode. It was arranged so as to face the negative electrode surface.

Comparative Example 4 A button type battery was assembled in the same manner as in Example 4 except that the same electrolytic solution as in Comparative Example 2 was used.

Example 5 A button-type battery was assembled in the same manner as in Example 4 except that the same electrolytic solution containing the same ethylene oxide-propylene oxide copolymer as in Example 2 was used.

Comparative Example 5 A button type battery was assembled in the same manner as in Example 5 except that the same electrolytic solution as in Comparative Example 2 was used.

Example 6 A button-type battery was assembled in the same manner as in Example 4 except that the same electrolytic solution containing polypropylene glycol as in Example 3 was used.

Comparative Example 6 A button type battery was assembled in the same manner as in Example 6 except that the same electrolytic solution as in Comparative Example 3 was used.

Examples 4 to 6 and Comparative Examples 4 to 6 obtained as described above
The closed circuit voltage of the above battery was measured after discharging at 300C for 5 seconds at 20 ° C. The results are shown in Table 4.

Next, at 20 ° C. of the batteries of Examples 4 to 6 and Comparative Examples 4 to 6,
FIG. 4 shows the discharge characteristics when continuously discharged with a constant resistance of 2 kΩ. In FIG. 4, the battery of Example 4 is D,
The battery of Example 5 is indicated by E, the battery of Example 6 is indicated by F, the battery of Comparative Example 4 is indicated by X, the battery of Comparative Example 5 is indicated by Y, and the battery of Comparative Example 6 is indicated by Z.

As shown in Table 4 and FIG. 4, each of the batteries of the present invention has a higher closed circuit voltage and a longer discharge duration than the corresponding battery of the comparative example. It is considered that this is because the resistance at the lithium interface was lowered by the addition of polyethylene glycol, ethylene oxide-propylene oxide copolymer, polypropylene glycol or the like.

[Brief description of drawings]

FIG. 1 is a sectional view showing a Li / Li model cell, and FIGS. 2 to 3 are Examples 1 to 3 (indicated by A to C) and Comparative Examples 1 to 1.
3 (indicated by U to W) is a complex plane solution diagram, FIG. 2 shows a state before charge and discharge, and FIG. 3 shows a state after charge and discharge for 10 cycles. FIG. 4 shows batteries of Examples 4 to 6 (indicated by D to Z).
And the discharge characteristic diagrams of the batteries of Comparative Examples 4 to 6 (indicated by X to Z). 2 ... Test electrode, 5 ... Counter electrode, 14 ... Electrolyte

Front page continuation (72) Inventor Toshikatsu Manabe 1-88 No. 1-Tora, Ibaraki-shi, Osaka Prefecture Hitachi Maxell Co., Ltd. (56) References JP-A-58-35874 (JP, A)

Claims (1)

[Claims] 1. A lithium organic secondary battery using lithium or a lithium alloy as a negative electrode active material, wherein the electrolytic solution is selected from the group consisting of polyethylene glycol, polyethylene oxide, polypropylene glycol, polypropylene oxide and ethylene oxide-propylene oxide copolymer. At least one of the
A lithium organic secondary battery, characterized in that 0.2 g to 8 g of each is added.