JP3418446B2 - Electrolyte for electrochemical cell and battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for an electrochemical cell and an electrochemical cell using the electrolytic solution.

[0002]

2. Description of the Related Art Conventionally, as an electrolytic solution for an electrochemical cell, a solution prepared by adding an alkali metal salt to a mixed solution of esters such as propylene carbonate and ethylene carbonate and ethers such as dimethoxyethane and tetrahydrofuran has been used.

Although the conventional electrolytic solution has excellent conductivity as a non-aqueous electrolytic solution, it has a chemical stability with respect to an electrode active material, a redox stability, and an electrochemical stability due to repeated charging and discharging. There's a problem.

In particular, the surface film formed by contacting Li and Li alloy with the electrolytic solution has a great influence on the reversibility of charge and discharge of the Li negative electrode and is greatly involved in dendrite formation. That is, it is greatly related to the charge / discharge efficiency of the Li negative electrode, which affects the charge / discharge cycle life of the Li secondary battery.

On the other hand, a method of adding an additive such as 2-methylfuran [J. Electrochem. Soc., 131, 2197
(1984) K.S. M. Abraham et al. And Matsuda et al. Power
Sources, 26,579 (1989)] and LiAsF ₆ + ethylene carbonate + 2-methyltetrahydrofuran systems [Hitoshi Okada Electrochem. Acta, 30, 1715 (1985)] and the like have been proposed, but they are still insufficient such as the interface resistance increasing.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic solution for an electrochemical cell which has a low interfacial film resistance and is excellent in charge / discharge reversibility of a negative electrode, and further excellent charge / discharge of a negative electrode. An object is to provide an electrochemical battery such as a secondary battery having high efficiency.

[0007]

The present invention contains a dialkyl (C = 1 to 16) pyrocarbonate and / or a dialkyl (C = 1 to 16) oxalate as a main component or an additive of an electrolytic solution. A lithium or lithium alloy negative electrode in which at least one alkyl group of has at least 4 carbon atoms and at least one alkyl group of the dialkyl oxalate has at least 5 carbon atoms.
And according to the electrolyte and batteries using the same for a secondary battery.

By using the electrolytic solution for an electrochemical cell of the present invention, the interface film resistance of the Li negative electrode can be reduced, and an electrochemical cell having a good charge / discharge cycle life can be obtained.

The dialkyl used in the present invention (C = 1 to 1
16) Pyrocarbonates and dialkyl (C = 1-16) oxalates can be prepared, for example, by reaction of the corresponding chloroformates with sodium alkyl carbonates [Kovalenko,
Zh. Obshch. Khim. 22, 1546 (1952)] and oxalyl chloride and the corresponding alcohols.

In the electrolyte containing the above compound as a main component, the alkyl group has 1 to 10 carbon atoms from the viewpoint of ionic conductivity.
4 is preferable, and methyl or ethyl is more preferable. Mixed alkyl substituents give equally good results.
Examples of these are dimethylpyrocarbonate, diethylpyrocarbonate, methylethylpyrocarbonate,
Methyl propyl pyrocarbonate, methyl butyl pyrocarbonate and / or dimethyl oxalate, diethyl oxalate, methyl ethyl oxalate, methyl propyl oxalate, methyl butyl oxalate etc. can be mentioned.

On the other hand, when used as an additive, the alkyl group may have a large number of carbon atoms, and those having 1 to 16 carbon atoms can be preferably used. For example, in addition to the preceding examples, methyldecylpyrocarbonate, ethyldodecylpyrocarbonate, ethylcetylpyrocarbonate, di-2-ethylhexylpyrocarbonate and / or methyldecyloxalate, ethyldodecyloxalate, ethylcetyloxalate, di-2-ethylhexyl. Examples thereof include oxalate.

In the present invention, known aprotic solvents for electrochemical cells can be used. Examples of such a solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran,
Dioxolane etc. can be mentioned.

The salt used in the electrolytic solution of the present invention can be variously selected according to the purpose, and examples thereof include alkali metal salts, alkaline earth metal salts and quaternary ammonium salts. Specifically, LiClO ₄ , LiBF ₄ , Li
PF ₆ , LiAsF ₆ , CF ₃ SO ₃ Li, LiCl, NaBr,
LiOCH ₃ , Mg (ClO ₄ ) ₂ , Al (ClO ₄ ) ₃ , (C ₂
H ₅ ) ₄ NClO ₄ , tetraethylammonium tosylate and the like can be exemplified.

The present invention also relates to an electrochemical cell using each of the above electrolytic solutions. The electrochemical cell referred to in the present invention is
The positive electrode and the negative electrode are in contact with each other via the electrolytic solution, and the electron conduction is electrically separated by the electrolytic solution. As is commonly used, the entire redox reaction between the electrodes is an electromotive force. Or a combination of two electrodes arranged such that their state changes when energy is applied to the cell. Electrochemical cells include primary and secondary cells, fuel cells, ion selective sensors, electrochemical displays, electronic integrators and the like.

[0015]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the examples.

[0016]Reference example 1 Evaluation of electrolyte by interface film resistance Dimethylpyrocarbonate (DMPY): Propylene Carbohydrate
Carbonate (PC): Dimethoxyethane (DME) =
1 mol / l in the solvent prepared in a weight ratio of 1: 1: 1
Like LiClO_FourDissolve and use this solution as an electrode for metal Li
Was injected into the measuring cell at 10 kHz to 10^-3Between Hz
The complex impedance was measured. Measured by Solartron 125
Using a complex impedance measuring device that connects 0 and 1286
I went.

In the obtained Cole-Cole Plot, a small arc and a straight line portion showing the diffusion-controlling rate are recognized on the low frequency side, and the interface film resistance value obtained from the intersection of the arc and the horizontal axis is 10Ω.
It was.

Comparative Example 1 The Cole-Cole Plot of an electrolyte solution of propylene carbonate (PC): dimethoxyethane (DME) = 1: 1, which was similarly prepared and measured for comparison, showed only a large arc,
The interface film resistance value obtained from the intersection of the arc with the horizontal axis is
It was 75Ω.

Examples 1 to 4, Reference Examples 2 to 4 and Comparative Example 2
˜4 LiClO ₄ was dissolved in a solvent prepared in a predetermined weight ratio so as to be 1 mol / l, and the interface film resistance values obtained from the complex impedance measurement as in Reference Example 1 are summarized below.

Reference Example 2 Dimethyl oxalate: PC:
DME = 1: 1: 1 12 Ω Example 1 Methyl butyl pyrocarbonate: PC: EC
= 1: 1: 1 15Ω Example 2 Methyldecylpyrocarbonate: PC: dioxolane = 5: 50: 45 16Ω Example 3 Ethylcetyloxalate: EC: DMC =
5:45:50 20Ω Reference Example 3 Diethylpyrocarbonate: EC: 2-methyl THF = 1: 1: 110Ω Reference Example 4 DMPY: Dipropyloxalate: PC:
DME = 1: 1: 1: 114 Ω Example 4 Di-2-ethylhexyl pyrocarbonate:
PC: EC = 1: 1: 118Ω Comparative Example 2 EC: DMC = 1: 173Ω Comparative Example 3 2-Methylfuran: PC: DME = 5: 50:
45 90Ω Comparative Example 4 2-Methyl THF: EC = 1: 1 50Ω

[0021]Reference example 5 Amorphous V as positive electrode material_TwoO₅70% by weight as an active material,
25% by weight of acetylene black, polytetrafluoroe
Mixture pellet containing 5% by weight of ethylene (16mmφ, thickness
0.4 mm) and lithium aluminum alloy as the negative electrode material.
Gold (lithium content 85%), microporous porosity as separator
Polypropylene sheet and polypropylene non-woven fabric, electrolyte
do itreference1 yen coin size Richiu using the electrolyte of Example 1
Battery was prepared.

The lithium battery was subjected to a charge / discharge test at room temperature at a current value of 1 mA and a voltage range of 2 V to 3.5 V to evaluate the charge / discharge characteristics. The change in discharge capacity with respect to the number of charge and discharge cycles was 90% of the initial value even at the 300th cycle, which was a very good result.

Example5 Ethylene carbonate (E with a weight mixing ratio of 1: 1: 0.05)
C) / dimethoxyethane (DME) / ethylcetylpyro
CF in carbonate at a concentration of 1.5 mol / l_ThreeSO_ThreeLi
Dissolved into electrolyte and heat treated MnO_Two 85wt%,
Acetylene black 12wt%, polytetrafluoroethyl
Cathode pellet consisting of 3 wt% len and lithium ano
The microporous polypropylene sheet and polypropylene
Face each other with a woven fabric separator
I made a lithium battery. This battery up to 2V at 30kΩ
When discharged and the battery capacity was measured, the result was good as shown in Table 1.
I got the result. In this way, the compound of the present invention is also good as an additive.
It showed good results.

[0024]

[Table 1]

[0025]Reference example 6 Propylene carbonate (P: 1: 1: 1 by weight)
C) / dimethoxyethane (DME) / methylethyloxy
CF in salate at a concentration of 1.5 mol / l_ThreeSO_ThreeMelt Li
Dissolve into electrolyte and use amorphous V as positive electrode material_TwoO₅Live
70% by weight as a substance, 25% by weight of acetylene black,
Mixture mixture containing 5% by weight of polytetrafluoroethylene
Use a let (16 mmφ, thickness 0.4 mm) as a negative electrode material.
Titanium aluminum alloy (lithium content 85%), Sepa
Microporous polypropylene sheet and polypropylene
Len non-woven fabric is used to make a 1-yen coin size lithium battery
Made With this lithium battery at room temperature, a current value of 1 mA,
Perform charge / discharge test in the voltage range of 2V to 3.5V,
The sex was evaluated. Of discharge capacity against the number of charge / discharge cycles
Change keeps 90% of the initial value even at the 300th cycle
And showed very good results.

Example6 Ethylene carbonate (E with a weight mixing ratio of 1: 1: 0.05)
C) / dimethoxyethane (DME) / methyldecyloxy
CF in salate at a concentration of 1.5 mol / l_ThreeSO_ThreeDissolve Li
Made into electrolyte and heat treated MnO_Two 85wt%, acetylene
12% by weight, polytetrafluoroethylene 3%
% Of cathode pellet and lithium anode
Made of polypropylene sheet and polypropylene non-woven fabric
1 yen coin size lithium battery
I created a pond. This battery is discharged to 2V at 30kΩ and charged.
When the pond volume was measured, good results were obtained as shown in Table 2.
It was In this way, the compound of the present invention has good results as an additive.
The result was shown.

[0027]

[Table 2]

[0028]

INDUSTRIAL APPLICABILITY The electrolytic solution of the present invention has a small interfacial film resistance to be produced, is excellent in charge / discharge reversibility, and can improve the charge / discharge efficiency and storage stability of the negative electrode of an electrochemical cell.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-333594 (JP, A) JP-A-6-267590 (JP, A) JP-A-6-267589 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 10/40

Claims (3)

(57) [Claims] 1. A dialkyl (C = 1 to 16) pyrocarbonate and / or a dialkyl (C = 1 to 16) oxalate is contained as a main component or additive of an electrolytic solution, and at least one alkyl group of the dialkylpyrocarbonate is Lithium having at least 4 carbon atoms and at least one alkyl group of the dialkyl oxalate having at least 5 carbon atoms;
Alternatively, an electrolytic solution for a secondary battery including a lithium alloy negative electrode . 2. Propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane,
A solution of at least one selected from tetrahydrofuran, 2-methyltetrahydrofuran and dioxolane and a salt is added to a dialkyl (C = 1 to 16) pyrocarbonate and / or
Or a dialkyl (C = 1 to 16) oxalate,
At least one alkyl group of the dialkylpyrocarbonate has 4 or more carbon atoms, and at least one alkyl group of the dialkyl oxalate has a lithium or lithium alloy negative electrode formed by adding one having 5 or more carbon atoms.
Electrolyte for secondary battery. 3. Lithium using the electrolytic solution according to claim 1 or 2.
Secondary battery with a lithium or lithium alloy negative electrode .