JPS59219869A - Electrolyte for lithium battery - Google Patents

Abstract

PURPOSE:To obtain a lithium battery in which a lithium electrode has good charge-discharge performance by using a mixed solvent of 1,2-dibutoxyethane and nonproton solvent having a high dielectric constant exceeding a specific value as organic solvent of nonaqueous electrolyte. CONSTITUTION:A mixed solvent of 1,2-dibutoxyethane and a high dielectric constant solvent having a dielectric constant of 10 or more is used as organic solvent of electrolyte prepared by dissolving lithium salt in organic solvent. One or more of propylene carbonate, gamma-butyrolactone, dimethyl sulfoxide, sulfolane, N,N- dimethylformamide, N,N-dimethylacetamide are used as nonproton polar solvent of high dielectric constant. A mixing ratio of 1,2-dibutoxyethane and nonproton polar solvent is preferable to limit to 1:9-9:1. When the mixing ratio is in the outside of this limit, charge-discharge performance is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolyte for use in lithium primary and secondary batteries.

Batteries using lithium as a negative electrode active material are being researched as small-sized batteries with high energy density, but secondaryization has become a major problem.

■905, V6O1 as a positive electrode active material that can be secondaryized
Metal oxides such as 3, T i Ss, V Sg, etc.+7
) Layered compounds are known as compounds that undergo topochemical reactions with Li, and to date, batteries using sulfides, selenides, and tellurides of titanium, zirconium, hafnium, niobium, tantalum, and vanadium (U.S. (See Japanese Patent No. 4,089,052).

However, compared to such research on positive electrode active materials for secondary batteries, research on the charging and discharging characteristics of Li electrodes is not sufficient, and in order to realize Li secondary batteries, charging and discharging efficiency and cycle life are The search for electrolytes with good charge-discharge characteristics has become a serious issue. In an attempt to improve the charging and discharging efficiency of Li electrodes, an attempt was made to add additives such as nitromethane and Sop to LiCl0a/propylene carbonate (Hl
electrochimica, Acta, vol, 22+
75 to 83 (1977)], but these are not necessarily sufficient, and there is a need for an electrolytic solution for lithium secondary batteries with even better characteristics.

The present invention has been made in view of the current situation, and its purpose is to provide a non-aqueous electrolyte for lithium batteries with excellent charging and discharging characteristics of Li electrodes.

Therefore, the electrolytic solution for lithium batteries according to the present invention is an electrolytic solution for lithium batteries in which a lithium salt is dissolved in an organic solvent, and 1,2-dibutoxyethane is used as the organic solvent. This method is characterized by the use of a mixed solvent of aprotic polar solvents of 30% to 50%.

According to the present invention, Li A lithium battery with excellent charge and discharge characteristics can be realized.

The present invention will be explained in more detail.

A lithium battery is a battery that uses lithium as a negative electrode active material and a positive electrode active material that is electrochemically active and undergoes a reversible electrochemical reaction with Li+ ions.According to the present invention, lithium salt is used as a positive electrode active material. As the organic solvent of the electrolyte dissolved in an organic solvent, 1,2-dibutoxyethane and a dielectric constant of 10
A mixed solvent with the above high dielectric constant solvent is used.

As the high dielectric constant aprotic polar solvent to be mixed with the 1,2-dibutoxyethane, any high dielectric constant solvent having a relative dielectric constant of 10 or more, which is conventionally used in this type of battery, can be freely used. For example, propylene carbonate, γ-butyrolactone, dimethyl sulfoxide, sulfolane, N
, N-dimethylformamide, N,N-dimethylacetamide, and the like can be used.

The mixing ratio of the 1,2-dibutoxyethane and the high dielectric constant aprotic polar solvent is preferably 1:9 to 9:1. This is because if the mixture ratio deviates from this range, the charge/discharge characteristics will deteriorate.

As the solute dissolved in this, any solute conventionally used in this type of battery can be used. For example, LiClO
4, LiBF4, LiAsFe, LiP Fa, L
Inorganic salts such as 1Alc l 4, CF3303 Li.

Lithium salts such as one or more selected from organic salts such as CF3CO2Li can be used.

These solutes are added to the organic solvent preferably at a concentration of 0.5 to 2
．． 5N is dissolved. This is because if the solute to be dissolved is less than 0.5N, the charge/discharge characteristics will be significantly deteriorated, while if it exceeds 2.5N, the solute will be difficult to dissolve in the solvent.

Next, the present invention will be explained in detail.

Example 1 A cell was assembled using a PT electrode as a working electrode, Li as a counter electrode, and Li as a reference electrode, and Li was deposited on the PT electrode to measure the charge/discharge characteristics of the Li electrode.

The electrolytic solution used was one in which 2N LiClO4 was dissolved in a mixed solvent of 1,2-dibutoxyethane and propylene carbonate at a volume ratio of 1:1.

The measurement was first carried out at a constant current of 5 mA/cA for 1 minute.
After depositing Li on the PT electrode and charging, 5mA/c+l
Li deposited on the PT electrode for 1 minute at a constant current of L 1
A cycle test was conducted in which the battery was discharged as + ions. The charge/discharge efficiency is determined from the change in the potential of the PT electrode, and is the ratio of the amount of electricity required to discharge l and t deposited on the PT electrode as Li+ ions to the amount of electricity required to deposit Li on the PT electrode. Calculated from.

FIG. 1 is a diagram showing the relationship between charge/discharge efficiency and cycle number, and in the figure, (a) is the case when the solvent of the present invention is used. In addition, (b) in the figure shows IN LiCl0a as a reference example.
/ shows the charge/discharge characteristics when propylene carbonate is used.

As can be seen from FIG. 1, the charge/discharge characteristics of the mixed system (a) according to the present invention are clearly improved compared to the single system (b).

Example 2 In the same manner as in Example 1, LiCl0a was dissolved in a 5:5 volume ratio mixed solvent of 1,2-dibutoxyethane and propylene carbonate as the electrolyte.
The charge and discharge characteristics of the battery were measured.

First, measure 0.5mA/cI! for 1 minute at a constant current of P
After depositing Li on the t electrode and charging, 5 mA/
Li deposited on the PT electrode for 1 minute with a constant current of C1 is
A cycle test was conducted in which the battery was discharged as ions.

FIG. 2 is a diagram showing the relationship between the charge/discharge efficiency of Li electrodes and the number of cycles. In the figure, (a) is the 2N LiC1 of this example.
04/1.2-dibutoxyethane/propylene carbonate (volume mixing ratio 5:5) is used as the electrolyte, and (b) in the figure is a reference example of IN LiCl0.
a/Charge and discharge characteristics of a Li electrode when a propylene carbonate single solvent electrolyte is used.

As can be seen from Figure 2, compared to the single system (b), the mixed system (
In case a), the charge/discharge characteristics are clearly improved.

Example 3 The same procedure as in Example 2 was used except that I N Li C10a was dissolved in a mixed solvent of γ-butyrolactone and 1,2-dibutoxyethane at a volume ratio of 5:5. The charge/discharge characteristics of the Li electrode were measured.

FIG. 3 is a diagram showing the relationship between the charging/discharging efficiency of Li electrodes and the number of cycles, in which (a) shows the INL i CI of the present invention.
This is the case where Oa/1.2-dibutoxyethane/7-butyrolactone (volume mixing ratio 5:5) is used as the electrolyte, and (b) in the figure is a reference example of 0.75N Li
This figure shows the charge/discharge characteristics of a Li electrode when using a C104/γ-butyrolactone single solvent electrolyte.

As can be seen from Figure 3, compared to the single system (b), the mixed system (
In case a), the charge/discharge characteristics are clearly improved.

As is clear from the above description, according to the present invention, in a non-aqueous electrolyte in which a lithium salt is dissolved in a solvent as a solute, 1,2-dibutoxyethane is used as the organic solvent and a high dielectric constant of 10 or more is used. By using a dielectric constant aprotic polar solvent, it is possible to provide a non-aqueous electrolyte for lithium batteries with excellent Li charging and discharging characteristics.

[Brief explanation of the drawing]

Figures 1 to 3 show L when using the electrolyte according to the present invention.
FIG. 3 is a diagram showing the relationship between the charging/discharging efficiency of an i-pole and the number of cycles. Applicant's agent Tadashi Amemiya Figure 1: Number of Tsuikuno L Figure 2: Number of cycles Figure 3: Cyclo ν Maki

Claims (1)

[Claims] In an electrolytic solution for lithium batteries in which a lithium salt is dissolved in an organic solvent, a mixed solvent of 1,2-dibutoxyethane and an aprotic polar solvent with a high dielectric constant of 10 or more is used as the organic solvent. An electrolyte for lithium batteries characterized by: