JPS5887777A - Nonaqueous electrolytic solution for lithium secondary battery - Google Patents

Abstract

PURPOSE:To obtain a lithium secondary battery having a supeior charge and discharge characteristic of a Li electrode by using at least a kind of substance selected from a group consisting of ethylene diamine and its derivatives, as addition agent. CONSTITUTION:A cell is composed of a Pt electrode as an operating electrode, Li electrode as an opposite electrode, and Li as a reference electrode, and the charge and discharge characteristic of the Li electrode is measured by depositing Li on the Pt electrode. One N. of LiClO4/propylene carbonate (PO) added with ethylene diamine (EDA) in a volume mixed ratio of 3% is used as electrolytic solution. As seen from the figure, the charge and discharge cycle characteristic is improved clearly in the system (a) added with EDA in comparison with the single system (b).

Description

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

Batteries using RITECUM 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*Os -71 as a positive polarity hazard that can be secondaryized
Hedera's metal oxides, TIS lightning, W& and other layered materials are L
It is known as a compound that undergoes a topochemical reaction with 1, and to date, batteries using sulfides, selenides, and tellurides of titanium, zirconium, hafnium, niobium, tantalum, and vanadium (U.S. Pat. No. 40
No. 89052) and 9 cells using niobium selenide (J, Electrohem.

5oc-+ vol-124e NO-7 No. 968M and No. 325jj (1977)), etc. are disclosed. However, compared to such research on cathode active materials for secondary batteries, research on the charging and discharging characteristics of L12 electrodes is not sufficient, and in order to create secondary batteries in L, photodischarge efficiency and cycle life are required. Exploration of electrolytes with excellent charging and discharging properties has become a serious problem.

In an attempt to improve the photodischarge efficiency of Li #L,
An attempt was made to add thickening agents such as nitromethane and SO to iClO4/propylene carbonate (hereinafter abbreviated as PC) (E
l@etrochimiea, Aeta, , vo
L, 122, pp. 75-83 negative (1977)) and L.
Attempts have been made to use iC2On/methyl acetate, but it cannot necessarily be said to be a light component, and there is a need for a 11L solution for lithium secondary batteries with even better characteristics.

The present invention was made in response to the current situation, and its purpose is to provide a non-aqueous electrolyte for secondary electric currents etc. that has excellent charging and discharging properties for #iL1 poles.

Therefore, the nonaqueous electrolyte for lithium secondary batteries according to the present invention is a nonaqueous electrolyte in which a lithium salt is dissolved in an organic solvent, and is selected from the group consisting of ethylenediamine and its derivatives as an additive for the nonaqueous electrolyte. It is characterized by using one or more of the above.

According to the present invention, by using as the additive at least one IJI selected from the group consisting of ethylenediamine and its derivatives, a lithium secondary battery with good charge-discharge characteristics of Li electrodes can be realized.

The present invention will be explained in more detail.

The organic solvent used in the non-aqueous electrolyte for lithium secondary 11C ponds according to the present invention may be any organic solvent as long as it has been conventionally used in this type of electrolyte.

For example, an organic solvent selected from globylene carbonate, tetrahydro7rane, dimethyl sulfoxide, r-butyro2chton, dioxyrane, 1,2-dimethoxyethane, and 2-methyltetrahydro7rane and having a purity of 91 or more can be used. .

Further, as the lithium salt as a solute, a lithium salt generally used as a solution in a non-aqueous electrolyte, such as the above-mentioned organic selected lithium salt, can be effectively used.

The wrFi of the solute to be dissolved in the saturated solvent is 0.
It is 5-2.5N. If it is 0.5N, the charging 'fI
This is because the L% property decreases considerably, and if it exceeds 2.5N, dissolution becomes a national problem, the viscosity increases, and the charge/discharge characteristics become p-type. Particularly preferably, F'i is around 18, for example, in the case of L i CLOa.

In the present invention, the elephantine agent added to the organic solvent is ethylenediamine and one or more derivatives thereof. The reason why the addition of one or more of such ethylenediamine and its derivatives improves the charging and discharging 'wL% properties is not necessarily clear.

Ethylenediami/and its derivative HLi ion and -
There are many books that are easy to form, and by forming such a complex, p, Li ions become solvated! 1 and the degree of dissociation of the lithium salt in the electrolytic solution are considered to be contributing factors.

Examples of ethylenediamine and its derivatives that can form an integral body with Ll ions include ethylenediamine tetraacetate f
R(eth71ane diatnine tetra
etetle acid)sN, N, N: N'-
Tetramethylethylenediami/(N.

N, N', N'-tetrameth71
eth71ene diaynlns+),
Ethylene diamy-N+N'-2 acetic acid (etbyl
enediamln*-N+ N'-diacetic
acid), ethylenediamine-N, N'-cyanic acid-N, N'-jibu tetrabionic acid (
ethylene diamins-N, N'-dia
e@tie-NeN'-djproplonie ac
id), ethylenediaminetetraacetic acid (0-hydroxyphenylacetate) [etbylenedia
rnine-di (o-bydroxypheny
l ac@ticacid), ethylene diamine di L(+)-tartrate (etbylene
diamine dl-L-(+)-(-a
In the present invention, one or more of these compounds can be effectively used.

Addition of these ethylenediamine and its derivatives! lF
i Preferably, the molar ratio to L1 ion concentration is 2 or less,
Most preferably, Fil is 5 or less.

If it exceeds 2, it will charge and discharge! This is because the quality decreases.

Example 1 A cell was assembled using Ll with a Pt electrode as a counter electrode and Li as a reference electrode, and Li was placed on the Pt image.
The charging and discharging characteristics of the Ll electrode were measured by depositing . Electrolyte solution KFi, I NLLllO4/propylene carbonate (hereinafter abbreviated as PC) to which ethylenediamine (hereinafter abbreviated as EDA) was added at a volume mixing ratio of 3 times was used. The structural formula of the above-mentioned subadditive is shown in the following formula (I). The equivalent conductivity of the above electrolyte is 6.20-”mol
-'m'' is 5, I NLICtO, /PC alone system equivalent conductivity is 6,00-'mot-'eat''
It was more expensive.

NH* CHs CH Snow NH, (I) First, Pt best KL with constant current of 5 m sea for 1 minute
After depositing and charging i, conduct a cycle test to discharge Ll deposited on pt & with a constant current of 5 mA/cd as +"r=s? ion.9. Photodischarge efficiency Fip
t Determine the potential change and change the Ll deposited on the Pt layer to L
It was calculated from the ratio of the amount of electricity required to discharge one ion to the amount of electricity required to deposit Ll on the Pt electrode.

FIG. 1 is a diagram showing the relationship between the charge/discharge efficiency of Li and the number of cycles, in which (A) is the case when the above electrolyte is used, and (b) FiI NLIC/:04/PC alone. The charging and discharging characteristics when using the system electrolyte are shown as a reference example. As can be seen from Figure 1, compared to the single system (b) K, EDA
In the system (a) with the addition of , the charge/discharge cycle characteristics are clearly improved.

fire! ? Example 1 except that N,N,N-N'-tetramethylethylenediamine (hereinafter abbreviated as TMEDA) was added as an electrolytic solution at a volume mixing ratio of INLiCtO4/PCK3- and a round one was used. The charging and discharging characteristics of the Li electrode were measured in the same manner as above. The equivalent conductivity of the above electrolyte is 6.5.
Ω-mot″″-Ashi, I NL i CLo4/P
6,00-'mot-' which is the equivalent conductivity of C alone system
-It was expensive. The structural formula of the above cooling agent is shown in formula (++).

(CHs) ChildrenNCHICHsN (CHI)I
(Iris) Figure 2 shows the charge/discharge efficiency and cycle number r!
This is a diagram showing the kA ratio, in which (a) is the case where solution solution is used in the above 1, and (ra) is the case where I NLiCAO4/PC is used.
As a reference example, we have shown the charging and discharging US characteristics when an electrolyte produced by JLK was run down a river.

As can be seen from the M2 diagram, compared to the single system (b), TMED
In the system containing A-), the charge-discharge cycle characteristics are clearly improved.

Implementation Fil 3 ss solution (, I NLiCtO, /PC to o, ss
Other charge/discharge characteristics were determined in the same manner as in Example 1 except that TMFDA was added at a volumetric mixing ratio of 1.
The equivalent conductivity of the upper itsg is 6.20-'rno
It was higher than 6,00-'moj-1, which is t-'J, which is the equivalent weight of I NLICjO4/PC 4th degree.

Figure 3 is a diagram showing the relationship between photodischarge efficiency and number of cycles.
The charging and discharging characteristics when using an electrolyte solution of C single yarn are shown as a reference example.

As can be seen from Figure 8143, compared to the single system (b), TMh:
In the system in which DA was added at lI), the charge/discharge characteristics were clearly improved.

Example 4 The same procedure was carried out except that ethylene cyanotetraacetic acid (hereinafter abbreviated as EDTA) was added at a molar ratio of 5:1 to the L1 ion # degree in 1NLictO,/PC as the electrolytic solution. The charging and discharging WL characteristics of the Li electrode were measured in the same manner as in Example 1. The structural formula of the above additive is shown in the formula (sodium).

(HOOCCHm )tNcHt C)(IN(CH
m C00H)t (1) Figure 4 is a diagram showing the relationship between charge/discharge efficiency and cycle number, in which (a) is the case when the above electrolyte is used, and (b)
a/PC* Charging and discharging characteristics when using a-based electrolyte are shown as a reference example.

As can be seen from Figure 4, compared to the single system (b), EDTA
In the system (a) in which the compound was added, the photodischarge cycle characteristics were clearly the same as above.

As is clear from the above explanation, according to the present invention, by adding ethylenediamine and one or more of its derivatives to an electrolytic solution in which a lithium salt is dissolved in an organic solvent, lithium oxide with good charge-discharge characteristics of a Li electrode can be obtained. It is possible to dissolve non-aqueous liquid for secondary batteries.

[Brief explanation of the drawing]

FIGS. 1 to 4 are diagrams showing the relationship between the charge/discharge efficiency of lithium electrodes and the number of cycles in Examples of the present invention. Applicant's agent: Tadashi Ergu

Claims (1)

[Claims] A nonaqueous electrolyte for a lithium secondary battery, characterized in that the nonaqueous electrolyte is a nonaqueous electrolyte in which a lithium salt is dissolved in an organic solvent, and one or more of nylene diamine and its derivatives is used as an additive in the nonaqueous electrolyte. .