JPH06223875A - Electrolyte for lithium secondary battery - Google Patents

Abstract

PURPOSE:To obtain an electrolyte for forming a lithium secondary battery using lithium and the alloy thereof for a negative electrode, in which the growth of dendrite is restricted effectively and which has the excellent charge and discharge cycle life. CONSTITUTION:The organic compound having CidenticalC connection, CidenticalN connection, N-C=S connection or N=N connection is added to the electrolyte, which is obtained by dissolving metal salt in the organic solvent, at a ratio of 1ml/l. A lithium secondary battery having the excellent charge and discharge efficiency and the excellent discharge capacity or the like can be thereby obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution capable of suppressing the growth of dendrites and forming a lithium secondary battery having an excellent battery life.

[0002]

2. Description of the Related Art In a lithium secondary battery using lithium or an alloy thereof as a negative electrode for the purpose of improving electromotive force,
There is a problem that dendrite grows on the negative electrode due to repeated charging and discharging. Although dendrite is a dendritic growth of lithium, when it is generated, it causes a decrease in charge and discharge efficiency and a decrease in discharge capacity.Furthermore, when the grown dendrite penetrates the separator placed between the positive and negative electrodes to cause a short circuit. There is also. Therefore, in the lithium secondary battery described above, suppressing the growth of dendrites is an important issue for forming a practical battery.

Conventionally, as an electrolytic solution for suppressing the growth of dendrites in a lithium secondary battery, an electrolytic solution in which a metal salt is dissolved in an organic solvent is used as an electrolytic solution having a double bond such as thiophene, pyrrole or furan. Saturated heterocyclic compounds, aromatic hydrocarbons such as benzene and naphthalene,
Alternatively, it has been known that a saturated cyclic hydrocarbon such as cyclohexane is added. However, the effect of suppressing the growth of dendrites is poor, and the dendrites gradually grow to lower the charge / discharge efficiency and discharge capacity. The amount of decrease increases after about 50 times of charge / discharge, and the battery life is poor. was there. Generally, the number of times of repeating charging / discharging that can withstand practical use is about 100 times.

[0004]

DISCLOSURE OF THE INVENTION The present invention forms a lithium secondary battery using a lithium or an alloy thereof as a negative electrode, which has an excellent effect of suppressing dendrite growth and an excellent charge / discharge cycle life. The subject is the development of an electrolytic solution that can be used.

[0005]

According to the present invention, an electrolytic solution prepared by dissolving a metal salt in an organic solvent is added to a C≡C bond, a C≡N bond,
It is intended to provide an electrolytic solution for a lithium secondary battery, wherein an organic compound having an N—C═S bond or an N═N bond is added at a rate of 0.001 to 0.1 ml / l.

[0006]

By adding the organic compound having the above-mentioned bond, it is possible to obtain an electrolytic solution for a lithium secondary battery which can highly suppress the growth of dendrite. The mechanism for suppressing dendrite growth is unknown.

[0007]

EXAMPLE An electrolytic solution of the present invention is prepared by dissolving a metal salt in an organic solvent, and adding C≡C bond, C≡N bond, N—C = S to the electrolytic solution.
0.001 to an organic compound having a bond or N = N bond
It was added at a rate of 0.1 ml / l, which is for forming a lithium secondary battery.

As the organic solvent, an appropriate solvent that dissociates the metal salt may be used. Generally, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone, methyl formate, methyl acetate, 1,2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, 2-methyl. Tetrahydrofuran, 1,3-dioxolane, diethyl ether and the like are used. The organic solvent can use 1 type (s) or 2 or more types.

As the metal salt, for example, an appropriate one such as an alkali metal salt containing Li, Na, K or the like as a component may be used. Preferably, from the viewpoint of high electromotive force, for example, PF ₆ ions, ClO ₄ ions, BF ₄ ions, CF ₃ SO ₃ ions,
A lithium salt used in combination with an anion such as AlCl ₄ ion, AsF ₆ ion, or I ion is used. The amount of the metal salt used is generally 0.1 to 3 mol per liter of the organic solvent, but the amount is not limited to this and may be appropriately determined depending on the desired battery performance and the like.

The organic compound added to the electrolytic solution is 1,4-
Those having a C≡C bond in the molecule, such as butynediol and propargyl alcohol, those having a C≡N bond in the molecule, such as ethylene cyanohydrin, those having an N—C═S bond in the molecule, such as thiourea , Azo dyes and the like have N = N bonds in the molecule. One or two or more of such organic compounds may be added, and the addition amount is appropriately 0.001 to 0.1 ml / l based on the concentration in the electrolytic solution. If the amount added is outside the above range, the dendrite growth suppressing effect is poor.

The electrolytic solution of the present invention contains lithium or Li as the negative electrode.
For forming a lithium secondary battery using a lithium alloy such as -Al, Li-Al-Mg, Li-C,
There is no particular limitation on the positive electrode of the battery. A material capable of generating a high electromotive force such as a lithium / cobalt-based electrode may also be used. The way electrode for such a positive electrode, for example, the general formula: such as _{Li w Co 1-xy M x} P y O 2 + represented by those such as in _z those with active substances. M in the above formula is N
Two or more transition metals such as i may be contained. Further, w is 0 <w ≦ 2, and x is 0 ≦ x <1. Furthermore, y is 0 ≦ y <1 and z is −1 ≦ z ≦ 4.

An active material having a particularly high electromotive force is a composite oxide containing at least lithium, cobalt and phosphorus. Specific examples thereof include LiCo _0.5 P _0.5 O ₂ and LiCo
_0.4 P _1.6 O ₂ , LiCo _1.6 P _0.4 O ₂ , LiCo _0.3 Ni _0.3 P
Examples thereof include _0.4 O ₂ , LiCo _0.2 Ni _0.2 P _0.6 O _{2, and the} like, but are not limited thereto. The production of such a composite oxide is performed by, for example, a solid phase method, a sintering method, a sol-gel method, a CVD method, a P method.
It can be performed by a ceramic manufacturing method such as a VD method, a thermal spraying method, or a thermal decomposition method.

The electrode using the active material is obtained, for example, by molding the active material into an electrode form using a binder such as polytetrafluoroethylene or polyethylene, or polyolefin oxide or polyvinyl alcohol, if necessary. You can A solid electrolyte or the like may be used as the binder. The electrodes may contain a conductive material such as acetylene black or Ketjen black.

In addition to the method of using the electrolytic solution of the present invention as it is when forming a lithium secondary battery, for example, a method of holding it by impregnating it with an appropriate polymer, a porous support, or a gel-like substance. Can be used in any method.

Example 1 Propylene carbonate having a water content of 50 ppm or less and 1,
LiClO ₄ vacuum-dried at 200 ° C. for 24 hours was dissolved in a mixed solvent of 50/50 (volume ratio) of 2-dimethoxyethane to obtain a solution having a concentration of 1 mol / liter, and 0.01 ml of propargyl alcohol was added to the solution. / L was added to obtain an electrolytic solution.

Example 2 An electrolytic solution was obtained in the same manner as in Example 1 except that ethylene cyanohydrin was added at a rate of 0.01 ml / l instead of propargyl alcohol.

Example 3 In place of propargyl alcohol, thiourea was added in an amount of 0.01 ml /
An electrolytic solution was obtained in the same manner as in Example 1 except that the electrolyte solution was added at a ratio of 1.

Example 4 In place of propargyl alcohol, 0.01 of azobenzene was used.
An electrolytic solution was obtained in the same manner as in Example 1 except that the solution was added at a ratio of ml / l.

Comparative Example 1 0.01 ml of thiophene was used instead of propargyl alcohol.
An electrolytic solution was obtained in the same manner as in Example 1 except that the electrolyte was added at a ratio of 1 / l.

Comparative Example 2 The addition ratio of propargyl alcohol was 0.0001 ml / l.
An electrolytic solution was obtained in the same manner as in Example 1 except that.

Comparative Example 3 An electrolytic solution was obtained in the same manner as in Example 1 except that the addition ratio of propargyl alcohol was 0.3 ml / l.

Using the electrolytic solutions obtained in Examples and Comparative Examples, L
A cell having iCo _0.5 P _0.5 O ₂ as a positive electrode and Li as a negative electrode was formed, and the lithium secondary battery was charged with a charging current of 0.5 mA.
The cycle characteristics were investigated by repeating the operation of charging for a time and then discharging. The results are shown in Table 1.

[0023]

[Table 1]

[0024]

According to the electrolytic solution of the present invention, it is possible to obtain a lithium secondary battery in which dendrite is less likely to grow on the negative electrode composed of a lithium-based electrode and which has excellent cycle life such as charge / discharge efficiency and discharge capacity.

Claims (1)

[Claims] 1. An electrolytic solution in which a metal salt is dissolved in an organic solvent is added to a C≡C bond, a C≡N bond, an N—C═S bond or an N═
0.001-0.1 ml / l of organic compound having N bond
An electrolyte solution for a lithium secondary battery, which is added in a ratio of.