JPS5812990B2 - battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in electrolytes for batteries using light metals such as lithium and magnesium as negative electrode active materials.

In this type of battery, an organic electrolyte has been used in which ion conductivity is imparted by dissolving an ion dissociative salt such as lithium borofluoride or lithium perchlorate in a cyclic ester such as γ-butyrolactone or propylene carbonate.

When these organic electrolytes are used, there is a problem that the discharge voltage decreases and the utilization rate of the battery active material decreases, especially at low temperatures of 0° C. or lower.

The object of the present invention is to improve the discharge characteristics of this type of battery at low temperatures.

The present invention is characterized in that the electrolyte is composed of at least one solute and two solvents, one of the solvents being dimethoxymethane and the other being γ-butyrolactone or propylene carbonate.

Generally, the electrical conductivity of the electrolyte is used as a measure of the effect of the electrolyte on battery performance.

A battery using an electrolyte with a higher conductivity has a lower internal resistance and a lower polarization during discharge.

The present invention is based on the results of studies from this perspective.

Hereinafter, the present invention will be explained with reference to examples thereof.

FIG. 1 shows the electrical conductivity at -20° C. of electrolytes in which LiC 104 is dissolved at various concentrations in dimethoxymethane.

As can be seen from the figure, the concentration of L I C 104 is 3.5
The maximum peak of electrical conductivity exists near mol/l.

FIG. 2 shows the electrical conductivity at -20° C. of electrolytes prepared by dissolving LiC 104 at various concentrations in a solvent containing a mixture of γ-butyrolactone and dimethoxymethane at a volume ratio of 1:1.

In this case, the conductivity reaches its maximum value when the concentration of LiC 104 is 2.5 mol/l.

Figure 3 shows LiCl04 in a solvent containing propylene carbonate and dimethoxymethane mixed at a volume ratio of 1:2.
It shows the electrical conductivity at -20°C of an electrolyte in which .

From the figure, the electrical conductivity reaches its maximum value when the LiC 104 concentration is around 2 mol A.

Curve A in Figure 4 shows L i C for propylene carbonate.
Curve B shows the electrical conductivity at -20°C of LiCl04 dissolved in γ-butyrolactone.

Comparing Figures 1 and 4, it is clear that the polarization associated with low-temperature discharge of batteries using electrolytes with dimethoxymethane as the solvent is significantly lower than that with electrolytes composed of conventional solvents such as γ-butyrolactone or propylene carbonate. It is expected that this will be smaller than the polarization of the battery.

Comparing Figures 2 and 3 with Figures 1 and 4, we can see that by using a solvent in which dimethoxymethane is mixed in an appropriate ratio to the conventional solvent γ-butyrolactone or propylene carbonate, dimethoxymethane alone can be used as a solvent. Alternatively, it can be seen that the low-temperature properties of the electrolyte can be expected to be further improved than when using γ-butyrolactone or propylene carbonate as a sole solvent.

That is, the maximum value of the electrical conductivity of various electrolytes at -20°C decreases in the following order.

(1) Li C 1 is added to a solvent in which propylene carbonate and dimethoxymethane are mixed at a ratio of 1:2 (volume ratio).
Electrolyte (2) with 2.0 mol/l of LiCl04 dissolved in a 1:1 ratio of γ-butyrolactone and dimethoxymethane (3) Electrolyte with 2.0 mol/l of LiCl04 dissolved in dimethoxymethane alone 3.5 mol/l LiC
Electrolyte (4) in which IO4 is dissolved 1.0 mol/l L in γ-butyrolactone
Electrolyte (5) 1.0 mol/Z Li in propylene carbonate in which IC 104 is dissolved
Electrolyte with CIO4 dissolved Next, we will show the results of a comparison of the discharge characteristics at low temperatures of carbon monolithium fluoride batteries using each of the above electrolytes. The negative electrode was constructed by embedding a lithium metal plate with a size of 20×20 mm and a thickness of 0.5 mm in a nickel net current collector.

The positive electrode is made of carbon fluoride (CFx) n, xkl, acetylene black, and fluororesin powder as a binder in a weight ratio of 10:1.
: A powder mixed in a ratio of 2:2 was pressure-molded onto a nickel net current collector, measuring 20 x 20 mm and having a thickness of 0.2 mm. 5mm
I used the one from

The theoretical capacity of this positive electrode is 350mAh.

The positive electrode, the negative electrode, and the polypropylene nonwoven fabric separator interposed between the two electrodes were enclosed in a polyethylene case filled with the electrolytic solution to prepare five types of batteries.

FIG. 5 shows the discharge characteristics when these batteries were discharged at a constant resistance of 150Ω at -20°C.

The numbers attached to the curves in the figure correspond to batteries using the electrolytes with the respective numbers above.

As is clear from Figure 5, a battery using a mixed solvent electrolyte of dimethoxymethane and propylene carbonate or γ-butyrolactone has better low-temperature characteristics than a battery using a single solvent electrolyte of γ-butyrolactone and propylene carbonate. is excellent in terms of discharge pressure and active material utilization.

Furthermore, this mixed system has the advantage that the amount of solute used can be reduced compared to a dimethoxymethane-only system.

That is, as is clear from Figures 1 to 3, in order to obtain the maximum conductivity, dimethoxymethane alone requires 3.5 mol/l.
A LiC 104 concentration of 2.5 mol/l or 2 mol/l is required in mixed systems, whereas maximum conductivity has been obtained at 2.5 mol/l or 2 mol/l.

This is advantageous in reducing the cost of practical batteries.

In the above example, carbon fluoride was used as the positive electrode active material, but silver chromate, copper sulfide, copper oxide, and other materials used in this type of organic electrolyte battery can also be used.

Note that when carbon fluoride is used for the positive electrode, dimethoxymethane improves wetting of the positive electrode with the electrolyte, and the effect of improving low-temperature characteristics is greater than when using other active materials.

In addition to L i C 104, the solutes include lithium thiocyanate, L s BF4 , L t P F
6 or a mixture thereof can be used.

As described above, according to the present invention, the low-temperature characteristics of an organic electrolyte battery can be significantly improved.

[Brief explanation of drawings]

1 to 4 show the relationship between the solute concentration and conductivity of electrolytes using various solvents, and FIG. 5 shows the discharge characteristics of fluorocarbon-lithium batteries using various electrolytes.

Claims (1)

[Claims] 1 having a positive electrode, a negative electrode using a light metal as an active material, and an electrolyte consisting of at least one solute and two solvents,
A battery characterized in that one of the solvents is dimethoxymethane and the other solvent is γ-butyrolactone or propylene carbonate.