JPS5812991B2 - battery - Google Patents

Description

Detailed Description of the Invention The present invention relates to a negative electrode whose main active material is a light metal such as lithium, magnesium, or an alloy mainly composed of these, a positive electrode whose active material is solid carbon fluoride, and a non-aqueous solvent and a solute. The present invention relates to a so-called organic electrolyte battery having an electrolyte consisting of.

Conventionally, this type of battery uses propylene carbonate, γ-
An electrolyte is used in which an ion-dissociable salt such as lithium perchlorate or lithium borofluoride is dissolved in a cyclic ester such as butyrolactone to impart ionic conductivity.

When using these electrolytes, especially at a current density of 10 mA/
During high rate discharge of about cm' or more, the discharge pressure decreases,
There was a problem that the utilization rate of battery active material was low.

The object of the present invention is to improve the characteristics of this type of battery during high rate discharge.

The present invention is characterized in that ethylene carbonate and 1,2-dimethoxyethane are used as main components as an electrolyte solvent, and a part of the ethylene carbonate is propylene carbonate or γ-butyloctone, and 1,2-dimethoxyethane is used as the main component. A portion of 2-dimethoxyethane may be substituted with tetrahydrofuran or 1,3-dioxolane, respectively.

The present invention will be explained in detail below with reference to Examples.

A nickel net current collector is embedded in a metal lithium plate with a size of 10 x 25 mm and a thickness of 0.3 mm to serve as a negative electrode, and the positive electrode contains 10 parts by weight of carbon fluoride, 1 part by weight of acetylene black as a conductive material, and a binder. A mixture of 2 parts by weight of fluororesin powder was pressure-molded onto a nickel net current collector, and the size was 10 x 2.
5mm, thickness 0. A 3 mm one was used.

A test battery was constructed by placing one each of these positive and negative electrodes in a polyethylene case filled with various electrolytes shown in the following table, with a polypropylene nonwoven fabric separator interposed between them.

In the table, PC is propylene carbonate and BL is r-
Butyrolactone, DME is 1,2-dimethoxyethane,
EC represents ethylene carbonate, THF represents tetrahydrofuran, and DOX represents 1,3-dioxolane.

FIGS. 1 and 2 show the discharge characteristics of batteries using the various electrolytes described above when discharged at a constant resistance of 75Ω at 20°C.

As is clear from Figure 1, ethylene carbonate and 1
, 2-dimethoxyethane improves the discharge characteristics of a lithium-fluorocarbon battery compared to an electrolyte using propylene carbonate or γ-butyrolactone as a single solvent.

That is, the discharge pressure is increased and the active material utilization rate is improved.

Ethylene carbonate has a freezing point of 39°C, and even if lithium borofluoride LiBF4 is dissolved to lower the freezing point, it is solid at 20°C, so it cannot be used alone as an electrolyte solvent, and it cannot be used alone as an electrolyte solvent. It can only be used by mixing it with a solvent.

By the way, the freezing point of 1,2-dimethoxyethane is -69℃.
It is.

In general, the solvent for this type of electrolyte must have appropriate freezing point, boiling point, viscosity, and dielectric constant, but in particular when using carbon fluoride, carbon fluoride has high water repellency and is difficult to wet. It is necessary to select a material that is compatible with this and can be sufficiently wetted.

Low polar ether solvents such as (1),2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, and ethyl ether are known as solvents that wet fluorocarbon well.

Among these, 1,2-dimexyethane has a boiling point of 85°C, which is higher than that of 1,3-dioxolane at 78°C, tetrahydrofuran at 66°C, and ethyl ether at 34.5°C. For example, when stored at a high temperature such as 70° C., it is excellent in that there is no deterioration in battery characteristics due to an increase in battery internal pressure or leakage.

Among the ether solvents, 1,4- with a boiling point of 101℃
There is also dioxane, but its viscosity is 1.2 at 25°C.
It is unsuitable because the centipoise is high and the resistance of the electrolyte becomes large.

(2) The viscosity of 2-dimethoxyethane is 0.46 centipoise at 25°C.

Contrary to ether solvents, propylene carbonate, γ
- Highly polar solvents such as butyrolactone are difficult to wet fluorocarbons.

Wetting is also not good for ethylene carbonate.

An electrolyte using a mixed solvent of ethylene carbonate and 1,2-dimethoxyethane wets the positive electrode containing fluorocarbon very well, and bubbles were observed to form on the surface of the positive electrode just by placing the positive electrode in the electrolyte. , it can be seen that the electrolyte rapidly permeates into the inside of the positive electrode.

On the other hand, an electrolyte using propylene carbonate or γ-butyrolactone alone as a solvent does not sufficiently penetrate into the inside of the positive electrode even if vacuum impregnation is performed.

By using a mixed solvent electrolyte of ethylene carbonate and 1,2-dimethoxyethane that penetrates well into the positive electrode, the effective reaction surface area of the positive electrode increases, which increases the discharge pressure and improves the utilization rate of the active material. It is thought that this was connected to.

However, an electrolyte using ■,2-dimethoxyethane alone as a solvent is better than one using a mixed solvent with ethylene carbonate in terms of positive electrode wetting, but ■,2-dimethoxyethane itself has a dielectric constant of 25°C. Because it is as low as 7.2,
The resistance of the electrolyte increases and the battery performance deteriorates as in waste 3.

In order to lower the resistance of the electrolyte, it is preferable to mix a highly polar solvent with a large dielectric constant with 1,2-dimethoxyethane.

FIG. 2 shows the difference in battery performance depending on the solvent mixed with 1,2-dimethoxyethane.

From the comparison of 44 and 7.8, ethylene carbonate is the best among γ-butyrolactone, propylene carbonate, and ethylene carbonate.

This difference in battery performance corresponds to the magnitude of the dielectric constant.

That is, the dielectric constants of γ-butyrolactone and propylene carbonate are each 39.64 at 25°C,
Ethylene carbonate is 89 at 40°C.

No. 12.13, we see that ethylene carbonate and 1
Even if a third solvent is added to the mixed solvent of ethylene carbonate and 2-dimethoxyethane, that is, even if a part of the ethylene carbonate is replaced with γ-butyrolactone or propylene carbonate, the mixed solvent of ethylene carbonate and 1,2-dimethoxyethane cannot be used. It can be seen that characteristics close to those used were obtained.

FIG. 3 shows the discharge characteristics during 75Ω constant resistance discharge at -20°C.

No. 3 in Figure 3. A comparison of 4, 9, 10, and 11 reveals the difference in low-temperature characteristics of the battery due to the difference in solute when a mixed solvent of ethylene carbonate and 1,2-dimethoxyecune is used.

The characteristics of lithium perchlorate are particularly bad;
This is because it hardly dissolves in ,2-dimethoxyethane.

The solubility of lithium perchlorate in 1,2-dimethoxyethane is 0.1 mol/l or less even at 20°C,
At -20°C, even in a mixed solvent system of 1,2-dimethoxyethane and ethylene carbonate, lithium perchlorate precipitates on the electrode surface and impedes discharge.

414.15, it can be seen that the low temperature characteristics can be improved by replacing a part of 1,2-dumethoxyethane with another ether solvent in which lithium perchlorate has a high solubility.

Note that lithium perchlorate is tetrahydrofuran, 1,3-
The solubility in dioxolane is 1 mol/mole at 20°C.
l or more.

As described above, for lithium-carbon fluoride batteries, an electrolyte using a mixed solvent of ethylene carbonate and 1,2-dimethoxyecune is particularly effective in improving high rate discharge characteristics.

The mixing ratio EC/DME of ethylene carbonate and 1,2-dimethoxyethane is suitably in the range of 1/1 to 1/2 by volume.

Further, when a portion of ethylene carbonate or 1,2-dimethoxyethane is replaced by a third solvent, it is desirable that the third solvent be used in a range not exceeding 50% by volume.

The concentration of the solute is suitably in the range of 0.5 to 1.5 mol/l.

As a way to improve the low-temperature properties when using lithium peroxyoxide as a solute, it is possible to partially replace it with other solutes that have high solubility in 1,2-dimethoxyethane, such as lithium borofluoride, but in that case, perchloric acid 50 mol% or more of lithium is desirable.

As detailed above, according to the present invention, the high rate discharge characteristics of a light metal carbon monofluoride battery can be improved.

[Brief explanation of the drawing]

Figures 1 and 2 compare the characteristics of lithium-fluorocarbon batteries using various electrolytes during 75Ω constant resistance discharge at 20°C, and Figure 3 compares the characteristics during 75Ω constant resistance discharge at -20°C. This is a comparative diagram.

Claims (1)

[Claims] 1 It has a negative electrode made of a light metal as an active material, a positive electrode made of solid fluorocarbon as an active material, and an electrolyte made of a solvent and a solute, and the solvent is ethylene carbonate or a part of ethylene carbonate converted into propylene carbonate or 1. A battery comprising one in which γ-butyrolactone is substituted, and one in which 1,2-dimethoxyethane or a portion of 1,2-dimethoxyethane is substituted with tetrahydrofuran or 1,3-dioxolane.