Non-aqueous electrolyte and lithium secondary battery using...

Details Non-aqueous electrolyte and lithium secondary battery using... Non-aqueous electrolyte and lithium secondary battery using...

2000-09-20

2003-01-07

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S307000, C429S322000, C429S223000, C429S231100, C429S231800, C429S231950

Reexamination Certificate

active

06503662

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a non-aqueous electrolyte capable of providing a lithium secondary battery superior in the cycle characteristics and the battery characteristics such as the electric capacity and storage characteristics and a. lithium secondary battery using the same.
2. Description of the Related Art
In recent years, lithium secondary batteries have been widely used as sources of power for driving compact electronic devices etc. A lithium secondary battery is mainly composed of a cathode, a non-aqueous electrolyte and an anode. In particular, a lithium secondary battery using a lithium complex oxide such as LiCoO
2
as a cathode and a carbonaceous material or lithium metal as an anode is suitably being used. Further, as the non-aqueous electrolyte for such a lithium secondary battery, a carbonate such as ethylene carbonate (EC) or propylene carbonate (PC) and an electrolyte salt such as a lithium salt are suitably used.
However, a secondary battery having more superior characteristics in the cycle characteristics of the battery and the battery characteristics such as the electric capacity has been required.
In a lithium secondary battery using, for example, LiCoO
2
, LiMn
2
O
4
, LiNiO
2
, as the cathode, the solvent in the non-aqueous electrolyte is locally partially oxidized and decomposed at the time of charging. The decomposed products inhibit the desirable electrochemical reaction of the battery, and therefore, causes a decrease in the battery characteristics. This is believed due to the electrochemical oxidation of the solvent at the interface between the cathodic material and the non-aqueous electrolyte.
Further, in a lithium secondary battery using, for example, a highly crystallized carbonaceous material such as natural graphite or artificial graphite as the anode, the solvent in the non-aqueous electrolyte is reduced and decomposed at the anode surface at the time of charging. Furthermore, in EC, which is generally broadly used as a solvent for a non-aqueous electrolyte, partial reduction and decomposition occur during the repeated charging and discharging and, therefore, the battery performance is decreased. Thus, the cycle characteristics of the battery and the battery characteristics such as the electric capacity are not necessarily satisfactory.
SUMMARY OF THE INVENTION
The objects of the present invention are to solve the above-mentioned problems relating to the non-aqueous electrolyte for a lithium secondary battery and to provide a non-aqueous electrolyte for a lithium secondary battery capable of providing a lithium secondary battery superior in the cycle characteristics of the battery and the battery characteristics such as the electric capacity and storage characteristics in the charging state and also to provide a lithium secondary battery using the same.
In accordance with the present invention, there is provided a non-aqueous electrolyte comprising a non-aqueous solvent, an electrolyte salt dissolved therein and a tert-butylbenzene derivative having the formula (I):
wherein R
1
, R
2
, R
3
, R
4
and R
5
independently represent a hydrogen atom or C
1
to C
12
hydrocarbon group.
In accordance with the present invention, there is also provided a lithium secondary battery comprising a cathode, an anode, and a non-aqueous electrolyte comprising a non-aqueous solvent, an electrolyte salt dissolved therein and a tert-butylbenzene derivative having the formula (I):
wherein R
1
, R
2
, R
3
, R
4
and R
5
independently represent a hydrogen atom or C
1
to C
12
hydrocarbon group.
The non-aqueous electrolyte of the present invention is used as a component of a lithium secondary battery. The components of the lithium secondary battery other than the non-aqueous electrolyte are not particularly limited. Various components generally used in the past may be used.
In this specification and in the claims which follow, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
In the tert-butylbenzene derivative having the above formula (I) contained in the non-aqueous electrolyte containing the non-aqueous solvent and the electrolyte salt dissolved therein, R
1
, R
2
, R
3
, R
4
and R
5
are independently a hydrogen atom; a linear alkyl group such as a methyl group, ethyl group, propyl group and butyl group; or a branched alkyl group such as an isopropyl group, isobutyl group, sec-butyl group, and tert-butyl group. Further, it may be a C
3
to C
6
cycloalkyl group such as a cyclopropyl group and cyclohexyl group. Further, it may be a phenyl group, benzyl group, or an alkyl-group substituted phenyl group or benzyl group such as a tolyl group, tert-butylphenyl group, or tert-butyl benzyl group. It preferably has a C
1
to C
12
hydrocarbon group.
As specific examples of the tert-butyl benzene derivative having the above formula (I), for example, tert-butylbenzene (i.e., R
1
═R
2
═R
3
═R
4
═R
5
=hydrogen atom), 2-tert-butyltoluene (i.e., R
1
=methyl group, R
2
═R
3
═R
4
═R
5
=hydrogen atom), 3-tert-butyltoluene (i.e., R
2
=methyl group, R
1
═R
3
═R
4
═R
5
=hydrogen atom), 4-tert-butyltoluene (i.e., R
3
=methyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 1-(tert-butyl)-2-ethylbenzene (i.e., R
1
=ethyl group, R
2
═R
3
═R
4
═R
5
=hydrogen atom), 1-(tert-butyl)-3-ethylbenzene (i.e., R
2
=ethyl group, R
1
═R
3
═R
4
═R
5
=hydrogen atom), 1-(tert-butyl)-4-ethylbenzene(i.e., R
3
=ethyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 3-tert-butyl-o-xylene(i.e., R
1
═R
2
=methyl group, R
3
═R
4
═R
5
=hydrogen atom), 4-tert-butyl-o-xylene(i.e., R
2
═R
3
=methyl group, R
1
═R
4
═R
5
=hydrogen atom), 4-tert-butyl-m-xylene(i.e., R
1
═R
3
=methyl group, R
2
═R
4
═R
5
=hydrogen atom), 5-tert-butyl-m-xylene(i.e., R
2
═R
4
=methyl group, R
1
═R
3
═R
5
=hydrogen atom), 2-tert-butyl-p-xylene(i.e., R
1
═R
4
=methyl group, R
2
═R
3
═R
5
=hydrogen atom), 3-iso-propyl-1-tert-butylbenzene (i.e., R
2
=iso-propyl group, R
1
═R
3
═R
4
═R
5
=hydrogen atom), 4-iso-propyl-1-tert-butylbenzene(i.e., R
3
=iso-propyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 4-n-butyl-1-tert-butylbenzene(i.e., R
3
=n-butyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 4-iso-butyl-1-tert-butylbenzene(i.e., R
3
=iso-butyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 4-sec-butyl-1-tert-butylbenzene(i.e., R
3
=sec-butyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 3-cyclohexyl-1-tert-butylbenzene(i.e., R
2
=cyclohexyl group, R
1
═R
3
═R
4
═R
5
=hydrogen atom), 4-cyclohexyl-1-tert-butylbenzene(i.e., R
3
=cyclohexyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 4,4′-di-tert-butyldiphenylmethane(i.e., R
3
=4-tert-butylbenzyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 4,4′-di-tert-butylbiphenyl(i.e., R
3
=4-tert-butylphenyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 1,3-di-tert-butylbenzene(i.e., R
2
=tert-butyl group, R
1
═R
3
═R
4
═R
5
=hydrogen atom), 1,4-di-tert-butylbenzene(i.e., R
3
=tert-butyl group, R
1
═R
2
═R
4
═R
5
=hydrogen atom), 1,2,4-tri-tert-butylbenzene(i.e., R
1
═R
3
=tert-butyl group, R
2
═R
4
═R
5
=hydrogen atom), 1,2,3-tri-tert-butylbenzene(i.e., R
1
═R
2
=tert-butyl group, R
3
═R
4
═R
5
=hydrogen atom), 1,3,5-tri-tert-butylbenzene(i.e., R
2
═R
4
=tert-butyl group, R
1
═R
3
═R
5
=hydrogen atom), 1,2,3,5-te

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