JPH0359962A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To remarkably enhance repeated charging/discharging characteristics by forming electrolyte solution of lithium salt and solvent in a specified ether series. CONSTITUTION:Electrolyte solution is composed of lithium salt and solvent in an ether series represented by an equation I in a lithium secondary battery wherein conductive high molecules are used as a positive electrode active material. In the equation I, R2 represents an alkyl group with the carbon numbers of 2 to 4, and R1 and R3 represent alkyl groups with the carbon numbers of 1 to 4. In this battery, when conductive high molecules are doped by anion or cation, energy is stored, and energy is released through an external circuit when the high molecules are dedoped. in addition, since said doping and de- doping can be reversibly carried out, the battery can be used as a secondary one. This constitution enables an reduction in capacity due to repeated charging and discharging to be restrained.

Description

Detailed Description of the Invention [Prior Art] Organic polymer compounds having conjugated double bonds can be electrochemically doped with anions such as ClO4-BH3-PF6AsF6- or cations such as Li1 ammoniums. It is known that it becomes a P-type or n-type conductive polymer, [J, C, S, Chem, Com
M, (1979) P 594-595 ], various electrochemical functional devices using these polymer compounds have been studied by taking advantage of the fact that doping and dedoping reactions occur through redox.

In particular, the development of batteries using conductive polymers as electrode active materials is progressing.

The redox characteristics and repeated charge/discharge stability of lithium secondary batteries using these conductive or semiconductive polymer materials as active materials vary greatly depending on the composition of the electrolyte.

BACKGROUND ART Conventionally, electrolytes for lithium batteries have been used by adding a low viscosity solvent such as dimethoxyethane to a solvent having a high dielectric constant such as propylene carbonate. However, these solvents are not sufficient because they cannot provide an electrolytic solution with a high salt concentration necessary to achieve the desired performance, and cannot suppress deterioration due to repeated charging and discharging.

[Problems to be Solved by the Invention] In view of these circumstances, the present invention provides a lithium secondary battery that has high energy capacity and high energy density and uses a conductive or semiconductive polymer as a positive electrode active material. The purpose is to

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors have conducted extensive studies on the electrolyte solution of the lithium secondary battery, and have found that:
Ishikawa discovered that an electrolytic solution consisting of a lithium salt and a specific ether solvent was used, leading to the present invention.

That is, the present invention is a lithium secondary battery using a conductive polymer as a positive electrode active material, in which the electrolytic solution is composed of a lithium salt and an ether solvent represented by the following formula.

R+ O+ R20+ R3 (wherein R2 is an alkyl group having 2 to 4 carbon atoms, R1 and R
(3 is an alkyl group having 1 to 4 carbon atoms) The battery of the present invention basically consists of a positive electrode, a negative electrode, an electrolyte, and a separator, and a conductive or semiconductive polymer material is used as the electrode active material of the positive electrode. .

In the battery of the present invention, a conductive polymer is doped with anions or cations to store energy, and the energy is released through an external circuit by dedoping. Furthermore, in the battery of the present invention, this doping-dedoping is performed reversibly, so it can be used as a secondary battery.

The conductive or semiconductive polymer material used in the positive electrode active material of the present invention is a conductive material made by polymerizing pyrrole, thiophene, furan, benzene, azulene, aniline, diphenylbenzidine, diphenylamine, triphenylamine, or a derivative thereof. Examples include semiconductive polymers. These polymers form a complex with an electrolyte anion at the same time as they are polymerized, and the anion enters and exits with the redox reaction, resulting in doping and dedoping.

Due to doping, these polymers have high electrical conductivity and can store energy at the same time.

Examples of ions that form complexes with conductive polymers include:
Complex anions such as ClO4-, PF6-AsP6BP4-, paratoluenesulfonate anion, nitrobenzenesulfonate anion, Pe(CN)6CP(CN)6-, or AlCl3, PeCl3,
Lewis acids such as Gael 3 can be mentioned.

These conductive polymers are obtained by chemical polymerization or electrolytic polymerization.

Electrolytic polymerization methods are generally described in, for example, J, Electrochem, Soc, Vol.
130. No. 7.15013-1509 (1983)
, EIectroche IIl, Acta, , Vol.
27. No, 1.61-65 (19H), J, Chem
, 5oc1. CheLCommun,, 1199~(1
984), a solution in which a monomer and an electrolyte salt are dissolved in a solvent is placed in a predetermined electrolytic bath, and an electrode is immersed.
This can be carried out by causing an electrolytic polymerization reaction by anodic oxidation or cathodic reduction.

Chemical polymerization methods include, for example, conducting poly
mers.

105 (1987), etc.

In batteries that use conductive or semiconductive polymer materials as active materials, ions in the electrolyte are doped into and dedoped into the electrodes during charging and discharging, so the concentration of the electrolyte is used to dope the active material. It requires more than the theoretical amount. In order to create a lightweight and compact battery, the smaller the amount of electrolyte, the more
Since it is preferable, the higher the concentration of the electrolyte, the better.

That is, the battery of this system requires an electrolytic solution that dissolves a highly concentrated electrolyte salt.

The electrolytic solution of the present invention has a lower electrolyte than conventionally used carbonate-based or carbonate-based and ether-based mixed solutions.
It became possible to significantly improve the solubility of electrolyte salts.

In addition, the charging capacity of the battery in this system gradually decreases when charging and discharging are repeated in a system with a small amount of electrolyte. This tendency is particularly noticeable when charging and discharging is performed at a relatively high current density per unit area of the negative electrode.

Although the reason for this is not clear, it is thought that the capacity decreases because lithium reacts with electrolyte components or solvents in the electrolytic solution, such as decomposition, during charging and discharging. The electrolytic solution of the present invention can suppress a decrease in capacity due to repeated charging and discharging compared to conventional electrolytic solutions.

The electrolytic solution used in the present invention consists of an electrolyte salt and an ether solvent. The ether solvent is represented by the following general formula.

RI O (R20), R3n≧1 (R2 is an alkyl group having 2 to 4 carbon atoms, R1 and R3 are alkyl groups having 1 to 4 carbon atoms) Among these, especially in the asymmetric ether where R1≠R3, the above characteristics were obtained.

Specific examples of asymmetric ethers include methoxyethoxyethane, methoxypropoxyethane, methoxyisopropoxyethane, methoxybutoxyethane, methoxy-te
Examples include rt-butoxyethane, ethoxypropoxyethane, ethoxyisopropoxyethane, diethylene glycol methoxyethoxy ether, diethine glycol ethoxypropoxy ether, and the like.

As an electrolyte salt, SCN C1''' Brl-B
F4″″ PF5- CF35O3SbF6-
Anions such as ASF&-Cl04B CC6Hs)4- and Li"Na"
Alkali metal cations such as K+, (C4H9)4N”
Examples include electrolyte salts consisting of cations such as organic cations such as (C2H5)4N+.

The amount of electrolyte salt to be added is 3 mol/kg to 15 m
o1/kg1 preferably 3mol/kg to lOmol/
kg is good.

Basically, the negative electrode used in the present invention may be any negative electrode that causes a Li:Li+ reaction upon charging and discharging. Specific examples include lithium metal, lithium alloy, wood metal, and lithium intercalation compound.

[Example] This will be explained below using examples.

Preparation example of positive electrode Dissolve aniline in 1M hydrochloric acid to a concentration of 0.6M,
A solution of ammonium sulfate dissolved in IM hydrochloric acid to a concentration of 0.25 M was added dropwise thereto while controlling the temperature from 0 to 10°C, and the mixture was reacted for 2 hours to obtain polyaniline. The obtained polyaniline was washed and then subjected to a reduction treatment using a 20% hydrazine methanol solution. This was thoroughly washed, mixed with 10% graphite, and pressure molded at 30 kg/cm' to produce a 0.25 g polyaniline electrode.

The polyaniline prepared in the battery test positive electrode preparation example was used as a positive electrode active material.
A battery shown in FIG. 1 was prepared using Li/A 1 alloy as a negative electrode active material, a stainless mesh as a current collector, and a glass fiber nonwoven fabric as a separator.

The electrolyte composition at this time is shown in Table-1. Electrolyte salt is L
iBF4 was used. 2.5-3 at charging/discharging current value 4mA
．． Charging and discharging were repeated at 7V, and the discharge capacity at this time is shown in Table 1.

Table [Effects of the Invention] As explained above, the lithium secondary battery of the present invention has a lithium salt and a specific ether-based solvent for the electrolyte, so that the repeated charging and discharging characteristics can be significantly improved. can.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a lithium secondary battery of the present invention.

Claims (1)

[Scope of Claims] A lithium secondary battery using a conductive polymer as a positive electrode active material, wherein the electrolytic solution comprises a lithium salt and an ether solvent represented by the following formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_2 is an alkyl group with 2 to 4 carbon atoms, R_1 and R_3 are alkyl groups with 1 to 4 carbon atoms)