Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-06-21
2002-11-12
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C252S062200
Reexamination Certificate
active
06479191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel electrolyte for a lithium secondary battery capable of providing a lithium secondary battery having superior battery cycle characteristics and battery characteristics such as electrical capacity, storage characteristics, and also relates to a lithium secondary battery using the same.
2. Description of the Related Art
In recent years, lithium secondary batteries have been widely used as the power sources for driving compact electronic devices etc. Lithium secondary batteries are mainly composed of a cathode, a non-aqueous electrolyte and an anode. In particular, a lithium secondary battery having a lithium complex oxide such as LiCoO
2
as a cathode and a carbonaceous material or lithium metal as an anode is suitably used. Further, as the electrolyte for a lithium secondary battery, a cyclic carbonate such as ethylene carbonate (EC) or propylene carbonate (PC) is suitably used.
However, a secondary battery having an even more superior battery cycle characteristics and battery characteristics such as the electrical capacity is desired.
A lithium secondary battery using, as the cathode active material, for example, LiCoO
2
, LiMn
2
O
4
, LiNiO
2
, etc, suffers from a decrease in the battery performance since the solvent in the non-aqueous electrolyte is locally partially oxidized and decomposed at the time of charging and the decomposed products inhibit the desirable electrochemical reaction of the battery. This is believed to be due to the electrochemical oxidation of the solvent at the interface between the cathode active material and the non-aqueous electrolyte.
Further, a lithium secondary battery using a highly crystallized carbonaceous material such as natural graphite or artificial graphite, as an anode active material, sometimes suffers from peeling of the carbonaceous anode material which, depending on the extent of the phenomenon, makes the capacity irreversible. This peeling occurs due to the decomposition of the solvent in the electrolyte during charging, that is, is due to the electrochemical reduction of the solvent at the interface of the carbonaceous anode material and electrolyte. In particular, PC having a low melting point and high dielectric constant, has a high electroconductivity even at a low temperature. Nevertheless, when a graphite anode is used, there are problems that the PC cannot be used for the lithium secondary battery due to the decomposition thereof. Further, EC partially decomposes during the repeated charging and discharging thereof so that the battery performance is decreased. Therefore, the battery cycle characteristics and the battery characteristics such as the electrical capacity are not necessarily satisfactory at the present time.
SUMMARY OF THE INVENTION
The objects of the present invention are to solve the above-mentioned problems relating to an electrolyte for a lithium secondary battery and provide a non-aqueous electrolyte for a lithium secondary battery having superior battery cycle characteristics and battery characteristics such as electrical capacity and a lithium secondary battery using the same.
In accordance with the present invention, there is provided an electrolyte for a lithium secondary battery comprising (i) a non-aqueous solvent, (ii) an electrolyte salt dissolved therein and (iii) at least one alkyne derivative having the formulae (I), (II) and (III) or at least one alkyne carbonate derivative having the formula (IV):
R
1
—C≡C—R
2
(I)
wherein R
1
, R
2
, R
3
and R
4
independently indicate a C
1
to C
12
alkyl group, a C
3
to C
6
cycloalkyl group, a aryl group, or hydrogen atom, R
5
, R
6
and R
7
in Y
1
, Y
2
, and Y
3
independently indicate a C
1
to C
12
alkyl group, a C
3
to C
6
cycloalkyl group, or aryl group, and n is an integer of 1 or 2.
In accordance with the present invention, there is also provided a lithium secondary battery comprising (a) a cathode, (b) an anode, and (c) an electrolyte comprising (i) a non-aqueous solvent, (ii) an electrolyte salt dissolved therein and (iii) at least one alkyne derivative having the formulae (I), (II) and (III) or at least one alkyne carbonate derivative having the formula (IV):
R
1
—C≡C—R
2
(I)
wherein R
1
, R
2
, R
3
and R
4
independently indicate a C
1
to C
12
alkyl group, C
3
to C
6
cycloalkyl group, aryl group, or hydrogen atom, R
5
, R
6
and R
7
in Y
1
, Y
2
, and Y
3
independently indicate a C
1
to C
12
alkyl group, C
3
to C
6
cycloalkyl group, or aryl group, and n is an integer of 1 or 2.
BEST MODE FOR CARRYING OUT THE PRESENT INVENTION
The alkyne derivative contained in the electrolyte is reduced and decomposed, prior to the reduction and decomposition of the organic solvent, at the surface of the carbonaceous anode at the time of charging. A part of the decomposed product is believed to form a passivation film on the surface of the highly crystallized carbonaceous anode due to the activity of the natural graphite, artificial graphite, etc., whereby the reduction and decomposition of the organic solvent in the electrolyte are prevented in advance.
Further, a part of the decomposed product is believed to oxidize and decompose, prior to the reduction and decomposition of the organic solvent in the electrolyte at the slight excess voltage portion where the potential of the surface of the cathode material becomes high transitionally, whereby the oxidation and decomposition of the organic solvent in the electrolyte are prevented in advance.
Due to the above mechanism, it is believed there is the effect of suppressing decomposition of the electrolyte, without impairing normal reactions of the battery.
In the alkyne derivative contained in the electrolyte composed of the electrolyte salt dissolved in the non-aqueous solvent, R
1
, R
2
, R
3
, and R
4
in the alkyne derivative of the formulae (I) and (II) are preferably, independently C
1
to C
12
alkyl groups such as a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, octyl group and decyl group. The alkyl group may also be a branched alkyl group such as an isopropyl group or isobutyl group. Further, it may be a C
3
to C
6
cycloalkyl group such as a cyclopropyl group or cyclohexyl group. Further, it may include a C
1
to C
12
aryl group such as a phenyl group, benzyl group, or p-tolyl group. Further, a hydrogen atom is also possible.
Further, R
5
, R
6
, and R
7
in Y
1
, Y
2
, and Y
3
in the alkyne derivative of the general formulae (II) and (III) are preferably, independently from each other, a C
1
to C
12
alkyl group such as a methyl group, ethyl group, propyl group, butyl group, pentyl group, and hexyl group. Further, the alkyl group may be a branched alkyl group such as an isopropyl group or isobutyl group. Further, it may also be a C
3
to C
6
cycloalkyl group such as a cyclopropyl group or cyclohexyl group. Further, it may include a C
1
to C
12
aryl group such as a phenyl group, benzyl group, or p-tolyl group. However, n is an integer of 1 or 2.
The specific examples of the alkyne derivative having the formula (I) are 2-pentyne (R
1
=a methyl group, R
2
=a ethyl group), 1-hexyne (R
1
=hydrogen atom, R
2
=a butyl group), 2-hexyne (R
1
=methyl group, R
2
=propyl group), 3-hexyne (R
1
=R
2
=ethyl group), 1-heptyne (R
1
=hydrogen atom, R
2
=pentyl group), 1-octyne (R
1
=hydrogen atom, R
2
=hexyl group), 2-octyne (R
1
=methyl group, R
2
=pentyl group), 4-octyne (R
1
=R
2
=propyl group), 1-decyne (R
1
=hydrogen atom, R
2
=octyl group), 1-dodecyne (R
1
=hydrogen atom, R
2
=decyl group), phenylacetylene (R
1
=phenyl group, R
2
=hydrogen atom), 1-phenyl-1-propyne (R
1
=phenyl group, R
2
=methyl group), 1-phenyl-1-butyne (R
1
=phenyl group, R
2
=ethyl group), 1-phenyl-1-pentyne (R
1
=phenyl group, R
2
=propyl group), 1-phenyl-1-hexyne (R
Abe Koji
Hamamoto Toshikazu
Ito Akikazu
Matsumori Yasuo
Takai Tsutomu
Morgan & Lewis & Bockius, LLP
Tsang-Foster Susy
Ube Industries Ltd.
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