JPS58214281A - Nonaqueous electrolyte for lithium secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolyte for a lithium secondary battery in which charge-discharge performance of a lithium electrode is good by using a nitrobenzene derivative as an additive of an nonaqueous electrolyte. CONSTITUTION:In a nonaqueous electrolyte prepared by dissolving a lithium salt in an organic solvent, a nitrobenzene derivative is used as an additive of the electrolyte. By adding the derivative, charge-discharge performance of a lithium electrode is increased. Although the reason is not always clear, it presumes that when an aromatic nitrocompound is added, a Li<+> ion conductive film is formed on the lithium surface and this film effectively acts in charge-discharge performance of a Li electrode. As effective nitrocompounds, 2,4,7-trinitro-9-fluorenone, nitramine, or 5-nitrobenzotriazole is used. 10<-1>mol/l or less of a nitrobenzene is preferably added. Addition of more than 10<-1>mol/l decreases charge-discharge performance of the Li electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a feed liquid used in lithium 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 failure point.

V20s +LiO as a positive active proboscis that can be secondaryized
Layered metal materials such as metal oxides such as 2 and 'l' iSt + WS2 have been used as compounds that undergo topochemical reactions with Li. , batteries using vanadium sulfide, selenide, telluride (see U.S. Pat. No. 4,089,052) and batteries using niobium selenide (J, Electrochem)
aoc, vol, 124, mu 7, pages 968 and 3
25 Sada (1977)) etc. have been disclosed.

However, compared to such research on the active properties of Li-Q batteries, research on the charging and discharging characteristics of LIQ is more important. light emission
A battery with good photodischarge characteristics such as efficiency and cycle life.
! ! Exploration of liquids has become an important goal. In an attempt to improve the photodischarge efficiency of the LI pole, an attempt was made to add a silicate agent such as nitromethane, SOz, etc. to LiC1o</globylene carbonate (Electrochimica).

Acra, Vol. 22, pp. 75-83 (197
7)) and Li C10 < /Methyl acetate [Ele-ctrochimica Acta,
Vol. 22, pp. SSA-91 (1977):], etc., but these are not necessarily sufficient, and there is a need for a heavy decomposition solution for linium 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 with excellent charging and discharging characteristics of Li electrodes.

Therefore, in the non-aqueous electrolyte for lithium secondary batteries according to the present invention, eg, lithium salt f: the non-aqueous electrolyte solution made with a shoulder injection solvent, a nitrobenzene derivative is used as an additive for the non-aqueous saliva. It is characterized by hata.

According to the present invention, by adding a nitrobenzene derivative to an electrolytic solution in which lithium is dissolved in an IS4 solvent, a lithium secondary battery with good charge/discharge percentage of Li electrode can be realized.

Non-invention will be explained in more detail.

The organic solvent used in the non-aqueous wax solution of the secondary lithium cutting pond according to the present invention may be any organic solvent conventionally used in the formation of this structure. For example, one or more organic solvents selected from glopyrene carbonite, tetrahydrofuran, dimethyl sulfoxide, γ-butyrolactone, dioxirane, 1,2-cytoxyethane, and 2-methyltetranohydrofuran can be used.

Furthermore, the lithium salt that is the solute is not limited to the above-mentioned organic solvent. For example, L I CZO4+LiBF
+, LiAsFa, LiPFa, LiAtC.

Lithium salts generally used as solutes in non-aqueous liquids, such as one or more selected from CF35o, Li, and CFiCO2Li, can be effectively used.

The density of the solute dissolved in the solvent is preferably 0.5 to 2.
．． It is 5N. If it is less than 0.5N, the charging and discharging characteristics will deteriorate significantly, and if it still exceeds 2.5N, there will be disadvantages such as difficulty in dissolving, increased viscosity, and worsening of charging and discharging characteristics. It is from. For example, in the case of Li CLO4, the thickness is preferably around 1.25N, LiBF4
The fundamental tone is around 0.75N.

The additive used in the present invention is a nitrobenzene derivative. The reason why the addition of such a nitrobenzene derivative improves the charge-discharge characteristics is not necessarily clear.

When lithium, such as a lithium metal plate, is used as it is as a lithium negative electrode, when the discharging or charging current increases, a local reaction may occur (due to this, holes may form in the lithium negative electrode, or dendrite-like lithium may form during charging). Phenomena such as precipitation and falling off from the negative electrode occur.This is a cause of decreasing the charging and discharging efficiency of the Li electrode.

When a nitrobenzene derivative is used as an additive, the charge/discharge characteristics of a lithium electrode are improved. The reason for this is not necessarily clear as mentioned above, but when an aromatic nitro compound is added, a Li+ ion conductive film is formed on the lithium metal surface, which effectively affects the charging and discharging of the Li electrode. Things can also be considered.

Examples of nitrobenzene derivatives exhibiting this powerful effect include those represented by the following general formula (1).

(Left below) NOl Here, R is a cyclic substituent including hydrogen, halogen, alkyl group, phenyl group, alkoxy group, N-alkyl ester amino group, carbonyl chloride group, nitro group, and petro atom,
It represents a substituent such as pyridyl, benzyl, phenylketone, quinone, etc., and X represents the number of these substituents.

Specifically, examples of the above-mentioned nitrobenzene derivatives include the following compounds. i.e. nitrobenzene,
Nitroacenaphthene, nitroacetanilide, nitroacetophenone, nitroaminoanisole, nitroaminoanilin diazonium salt, nitroaminobensitrifluoride, nitroaminophenol, nitroaminopyridine, nitroaminothiazole, nitroaminotoluene, nitroaniline, Nitroanisidine, nitroanisidine, nitroanthraquinone, nitrobenzaldehyde, nitrobenzamide, nitrobenzenesulfenyl chloride, nitrobenzenesulfonic acid, nitrobenzenethiol, nitrobenzoic acid, nitrobenzonitrile, nitrobenzophenone, nitrobenzotriazole, nitrobenzoyl chloride, Nitrobenzyl acetate, Nitrobenzyl alcohol, Nitrobenzyl promite, Nitrobenzyl chloride, γ-(
P-nitrobenzyl) pyridine, nitrochlorobenzene, nitrotoluene, trinitrotoluene, dinitrobenzene, trinitropenze, nitrofluorene, trinitrofluorene, tetranitrofluorenone, nitrophthalic acid, nitroquinoline, and the like. Among these nitrobenzene derivatives, 2,4.7-1-
Dinitro-9-fluorenone, nitramine, P-nitrobenzoyl chloride, m-nitrobenzoyl chloride, 0-nitrobenzonitrile, m-nitrobenzonitrile, P-nitropenzonitrile, P-nitrobenzophenone, γ-
(P-nitrobenzyl)pyridine and 5-nitrobenzotriazole are preferred. The nitrobenzene derivative is preferably added at less than 10-' moL/.

This is because if it exceeds 10-' mat/l, the charging/discharging efficiency of the Li electrode will deteriorate.

The present invention will be explained in detail below.

Example 1 A battery was assembled using Li as the working electrode and Li (linear Li pellets with a thickness of approximately 3 mm, Electrogen Surface Tomb 1.ff1) as the reference electrode, and a Pt electrode as the counter electrode. The charge/discharge characteristics of the Li electrode were measured by depositing Li.

For the measurement, first, Li was deposited on the Pt electrode and charged for 1 minute at a constant current of 5 Am, and then a cycle test was performed in which the Li deposited on the Pt electrode was discharged as Ll ions at a constant current of 5 mA. Charge/discharge efficiency is pt 4
The Li deposited on the Pt electrode is calculated from the potential change of L
It was calculated from the ratio of the amount of electricity required to convert Li into bioions and the amount of electricity t''Th required to deposit Li on pt and i.

Figure 1 is a diagram showing the relationship between charge/discharge efficiency and cycle number, and a in the diagram indicates 5 to 2NLiC4/PC as an electrolyte.
This is the case where 2.4.7-dolinitro-9-fluorenone (TNE) of When using P.C.
This figure shows the charging and discharging characteristics of Li electrodes.

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

Implementation row 2 Pt electrode was heated, Li thin piece (thickness 0.5 mm
Electricity area 1c! /L) was used as a reference material, and a battery using Li was assembled, and Li was deposited on the Pt layer, thereby aiming at the charge-discharge characteristics of Li.

The measurement was first performed with a constant current of 1 mA/c++t for 1 minute.
Theory of optical astronomy by precipitating Li on the top, 11TIA/d
A cycle test was conducted in which Li deposited on Pt4 was discharged as Li + ions at a constant current of . The charge/discharge efficiency was determined from the upright change of the Pt box, and was calculated by comparing the amount of electricity required to discharge the precipitated i on PtCt as Li+ ions and the amount of electricity required to deposit Ll on the Pt top. Calculated from the ratio.

Figure 2 shows the charge/discharge efficiency and number of stoppages in -A system r/PC
(6) in the figure is a reference example (D I
NL i C1O< /P The charge/discharge characteristics of the Li electrode when used as a lamination solution are shown.

As can be seen from FIG. 4, the charge/discharge characteristics of the mixed system (a) are clearly improved compared to the single system (b).

Example 3 As an electrolyte, I
L
The charge/discharge characteristics of the i-pole were measured.

FIG. 3 is a diagram showing the relationship between charge/discharge efficiency and number of cycles; a in the diagram is the case when pancreatic juice is used; The charging and discharging characteristics when using a single electrolyte are shown as a reference example. As you can see in Figure 3, the sword is a single system (
Compared to b), the charging/discharging characteristics of the mixed system (a) are clearly improved.

By using a nitrobenzene derivative as an additive in a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent, a non-aqueous chamber solution for lithium secondary batteries with good lithium balance charge-discharge characteristics can be created. liquid can be realized.

[Brief explanation of drawings]

FIGS. 1 to 3 are diagrams showing the relationship between the charging and discharging efficiency of lithium and the number of cycles in practical examples of the present invention.

Claims (1)

[Claims] A non-aqueous electrolyte for a lithium secondary battery, characterized in that a non-aqueous electrolyte is prepared by adding a lithium salt to an organic solvent, and a nitrobe/ze/derivative is used as an additive in the non-aqueous electrolyte. .