JPS5931571A - Electrolyte for lithium secondary battery - Google Patents

Abstract

PURPOSE:To increase charge-discharge performance of a lithium electrode by using an ethylenediaminetetraacetic acid derivative containing lithium ion as a lithium salt in a nonaqueous electrolyte prepared by dissolving lithium salt in an organic solvent. CONSTITUTION:An electrolyte prepared by dissolving a lithium salt in an organic solvent is used. An ethylenediaminetetraacetic acid derivative containing at least one lithium ion is used as a lithium salt. One reason to increase charge- discharge performance is that ethylenediamine tetraacetic acid forms a complex with Li<+> ion, and solvation of Li<+> ion and dissociation of lithium salt in an electrolyte are changed. The amount of lithium salt to be dissolved is preferable to limit to a range of 2.0mol/l or less.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-aqueous electrolyte used in a lithium secondary battery.

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.

V, O, as positive electrode active materials that can be secondaryized.

Metal oxides such as TiOt, TiSt, WS
I-type compounds such as 2 are known as compounds that undergo topochemical reactions with Li, and up to now titanium, zirconium, hafnium, niobium, and tantalum.

Batteries using vanadium sulfide, selenide, and telluride (see U.S. Patent No. 4089052) and heavy oil (J, ELE) using niobium selenide, etc.
ctrochem, Soc, + vol 124,
&l p. 968 and 325 Sada (1977))
etc. are disclosed.

However, compared to such research on positive electrode active materials for secondary batteries, the charging and discharging of Li4. Research on il properties is not sufficient, and in order to realize Li secondary skewers, the search for electrolytes with good charging/discharging properties such as charging/discharging efficiency and cycle life is a critical issue. .

As an attempt to improve the charging and discharging efficiency of Li poles,
Attempts to add additives such as nitromethane, SO, etc. to C10
chimica, Acta, vol 22 + 7th
5-83 (1977)) and attempts using L i CLOa /methyl acetate [Electrochjmi
ca, Acta, vol 22 + page 85~
91 (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 secondary batteries that has excellent charging and discharging characteristics of Li electrodes.

Therefore, the nonaqueous electrolyte for a lithium secondary battery according to the present invention is a nonaqueous electrolyte in which a lithium salt is dissolved in an organic solvent, and the nonaqueous electrolyte contains ethylenediamine tetracontaining at least one lithium ion as the lithium salt of the nonaqueous electrolyte. It is characterized by the use of an acetic acid derivative.

According to the present invention, by using an ethylenediaminetetraacetic acid derivative containing at least one lithium ion as the lithium salt in an electrolytic solution in which a lithium salt is dissolved in an organic solvent, lithium with good charging and discharging properties is produced. A secondary battery can be realized.

The present invention will be explained in more detail.

The solvent used in the non-aqueous electrolyte of the lithium secondary battery according to the present invention may be any solvent conventionally used in the persimmon electrolyte.

For example, propylene carbonate, tetrahydrofuran di', dimethyl sulfoxide, γ-butyrolactone, dioxolane, 1,2-dimethoxyethane.

1 selected from 2-methyltetrahydrofuran 1
Organic solvents with a capacity of 1J or more can be used.

In the present invention, the lithium salt used in the non-aqueous electrolyte is an ethylenediami/tetraacetic acid derivative containing at least 1 lithium ion. The reason why the charge/discharge characteristics are improved when such an ethylenediaminetetraacetic acid derivative is used is not necessarily clear. Ethylenediaminetetraacetic acid and Ll ion form a complex, which is thought to be one of the causes of a change in the solvation state of Li + ion and a change in the degree of yyr = v of lithium salt in the electrolyte.

The amount of the Li salt dissolved in the organic solvent is preferably 2
．． 0 mot/ is below. This is because if the concentration exceeds 2.0 mol/l, the dissolution will become too low and the charge/discharge characteristics will deteriorate significantly.

Next, examples of the present invention will be described.

Example 1 By assembling a cell using Li as a working electrode and using Li with reference to 17 and 17, and depositing Li on the Pt electrode, the charge-discharge characteristics of Li1M were determined. Measured. The electrolyte contains 1 mo of 4Li ion 1a-exchanged ethylenediaminetetraacetic acid (hereinafter referred to as 4Li-EDTA). , /l *Propylene carbonate (
(hereinafter referred to as PC) was used.

The measurement was carried out for 1 minute with a 5 mA current without switching, using PT and other high-quality Li? : After deposition and photoelectric charging, a cycle experiment was performed in which the Li deposited on Pt(?) was discharged as Ll ions using a constant radio wave of 5 mA/i.The charge/discharge efficiency was determined from the potential change of the Pt electrode, and The amount of electricity required to turn the precipitated Li into waste paper as Ll ions, and the amount of electricity required to turn the deposited Li into waste paper.
q was calculated from the ratio of the amount of electricity required to deposit .

FIG. 1 is a diagram showing the relationship between the charging/discharging efficiency of the L l lump and the number of cycles. In the figure, (a) is the case when - the above electrolyte is used, and (b) is the case when the above electrolyte is used. 04/PC
The charging and discharging characteristics when used as an electrolyte are shown in reference figure 1.

As shown in FIG. 1, the charge/discharge cycle and r♀ property are clearly improved in the system (a) using 4Li-EDTA compared to the reference i+1J (b).

Example 2 As an electrolyte, 3Li ion t+! 1 mat of 4'-substituted ethylenediaminetetraacetic acid (3Li-EDTA)
The charging and discharging characteristics of the Li electrode were measured in the same manner as in Example 1 except that a mixture of Li/lPC was used.

Figure 2 is a diagram showing the relationship between charging and discharging tK efficiency and cycle number, and (2) in (1) is the case when the above electrolyte is used, and (b) is when lNLiC40a/PC is The charging and discharging characteristics when used in the following are shown as a reference example.

As can be seen from Figure 2, compared to reference example (b), 3Li-
In the system (a) using EDTA, the photodischarge cycle characteristics are clearly improved.

Example 3 The charging and discharging characteristics of a Li kite were measured in the same manner as in Example 1, except that a mixture of 2Ll ion-substituted ethylenetetraacetic acid (2Li-EDTA) at 1 mot/lPC was used as the electrolyte. .

FIG. 3 is a diagram showing the relationship between charge/discharge efficiency and cycle number, in which (a) is the case when the above-mentioned solution is used, and (b) I NL i C10< /P C The charging and discharging characteristics when used as an electrolyte are shown as a reference example.

As can be seen from Figure 3, compared to the reference subsystem (b), 2Li
- In the system (a) using EDTA, the charge/discharge cycle characteristics are clearly improved.

Example 4 As a tube liquid, 4L, 1-EDTA/PC (2mot
/l) was used in the same manner as in Example 1, and measurements were made for T, i-love's fullness' (!toshi-ability).

, n4 diagram is a diagram showing the relationship between charging/discharging/electric vehicles and the number of cycles, and (a) in the diagram is the above-mentioned ``Pinging?'' (b) ij: I N L i C10< /P
The charging and discharging characteristics of Meiso using C for electrolysis are shown as a reference example.

As can be seen from Figure 4, compared to the reference subsystem (b), 4L
In the system (a) using i-K DTA, the photodischarge cycle characteristics are clearly improved.

Example 5 Electrolyte and [7,3 Li -El)TA/PC (0
, 1 m ot/l) was used in the same manner as in Example 1, and Li4+ was charged and discharged at a lower rate of 1 J and 1 m ot/l.

Figure 735 (・This is a diagram showing the relationship between the light emission efficiency and the number of cycles. In the figure, (a) is the case where the above solution is used, and (b) is the case where I Nl, i C10

From Figure 45, compared to the reference subsystem (b), 3.
In the system (a) using Li-EDTA, the charge/discharge cycle time is clearly the same as above.

Example rtt, as liquid: Li-EDTA/PC (0
.

Figure 46 is a diagram showing the relationship between the charging and discharging efficiency and the number of cycles, in which (a) is the lifting platform using the above-mentioned slag liquid, and (b) is the I NL i C104/ The charging and discharging characteristics when PC is used as the electrolyte are shown as a reference example.

As can be seen from Figure 6, compared to the reference subsystem (b), 3Li
- The yarn (a) using EDTA clearly has improved charging/discharging cycle characteristics.

Example 7 3hi-EDTA/PC ((
The charge/discharge characteristics of Li were measured in the same manner as in Example 1 except that 1.25 mol/l) was used.

FIG. 7 is a diagram showing the relationship between charging/discharging, electric vehicle, and cycle number. In the diagram, (a) is the case when the above-mentioned electrolyte is used, and (b) is I NL i Clck /P C The low charging and discharging characteristics when used as an electrolyte are shown as a reference example.

As can be seen from Figure 7, compared to the reference subsystem (b), 3Li
In the system (a) using -EDTA, the photodischarge cycle characteristics are clearly improved.

Example 8 2Li-EDTA/PC as tli, If 'i
The charge/discharge characteristics of the Li electrode were measured in the same manner as in Example 1 except that (0.5 moL/l) was used.

FIG. 8 is a diagram showing the relationship between charge/discharge efficiency and cycle number, and (a) in the diagram is the case when the above 'electrolyte solution is used,
(b) shows the charging characteristics as a reference example when I NL i C104/PC was used as the electrolyte.

As can be seen from Figure 8, compared to the reference subsystem (b), 2Li
- In the system (a) using EDTA, the charge/discharge cycle characteristics are clearly the same as above.

Example 9 2Li-EDTA/PC (0,75 mo
Li%
The charging and discharging characteristics of X were measured.

FIG. 9 is a diagram showing the relationship between charge/discharge efficiency and cycle number, and (a) in the figure is. This is the case where the above electrolyte was not used, and (b) shows the charge/discharge characteristics when I NL i Clo4/P C was used as the α-folding liquid as a reference example.

As can be seen from Figure 9, compared to the reference subsystem (b), 2Li
- In the system (a) using EDTA, the charging and discharging cycle characteristics are clearly improved.

Example 10 i! S, as a solution, 2 L i -BDTA/P C
The charge/discharge characteristics of the Li electrode were measured in the same manner as in Example 1 except that (025 mot/l) was used.

Figure 10 shows the relationship between the charge/discharge efficiency and the number of cycles. In the figure, (a) is the case when the above r17 solution is used, and (b) is the case when INLiCtO</PC is electrolyzed. (c) Charging and discharging characteristics when used at night are shown as a reference example.

As can be seen from Figure 10, compared to the reference side system (b), 2L
In the system (a) using i-EDTA, the charging/discharging vehicle % property is clearly improved.

Above implementation 1+l f is 2Li-EDTA, 3Li-ED
TA, 4L i -EDTA were all dissolved in various solvents.
Although an example was shown in which four batteries were used, the system using ILi-EDTA also had better charge-discharge characteristics than the four systems using INLtClo4/PC as the electrolyte.

As is clear from the above explanation, in accordance with the invention, in a non-aqueous solution in which a lithium salt is dissolved in an organic solvent, an ethylenesimaminetetraacetic acid compound containing at least one lithium ion is used as a lithium salt. By using this, it is possible to create a non-aqueous electrolyte for lithium secondary batteries with good charging and discharging 1E characteristics for Li electrodes.

[Brief explanation of the drawing]

FIGS. 1 to 10 are diagrams showing the relationship between the charging and discharging efficiency of the lithium electrode and the number of cycles in Examples of the present invention. Out; Tadashi Amane Miya Tadashi Kisuif number Figure 2 Buik + Mosquito number 3 @ Buik + Soft figure 4 Reiku no L Soft Figure 5 Cycle number Figure 6 Cyclic number Saif 4 Kei Figure 8 Buikatsu L Broadcasting No. 9 @ Cycle Number Zuik) L, -Save

Claims (1)

[Claims] In a non-aqueous electrolytic solution in which a lithium salt is dissolved in a specific solvent, at least one
An acid solution for lithium secondary batteries that uses an ethylenediaminetetraacetic acid derivative containing 50% lithium.