Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-07-30
2001-07-03
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S329000, C429S337000, C429S339000, C429S341000, C429S224000, C429S231100, C429S231950
Reexamination Certificate
active
06255021
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improvement in the storage property of a nonaqueous electrolyte battery which uses lithium as a negative electrode active material, i.e., a lithium battery.
BACKGROUND OF THE INVENTION
Lithium batteries which use lithium as the negative electrode active material have lately attracted attention as high energy density batteries, and much active research has been conducted.
As a solvent of the nonaqueous electrolyte for these types of batteries, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, sulfolane, 1,2-dimethoxydiethane, tetrahydrofuran and dioxolane and the like can be used alone or in the form of a mixture of two or three of these substances. As a solute dissolved in the solvent there can be mentioned LiPF
6
, LiBF
4
, LiClO
4
, LiCF
3
SO
3
, LiAsF
6
, LiN (CF
3
SO
2
)
2
, LiCF
3
(CF
2
)
3
SO
3
or the like.
It is a problem that an organic solvent and a negative electrode having lithium as an active material react chemically in nonaqueous electrolyte consisting of a solute and, as a solvent, dioxolane alone or a two or three component solvent including dioxolane and reduce battery capacity after storage. Therefore, it is very important to inhibit self-discharge during storage to put this kind of battery to practical use.
Japanese patent publication (Laid-Open) Sho 60-91565 discloses a battery having improved properties and which uses a nonaqueous electrolyte including dioxolane as a solvent. However, it is a problem when dioxolane is used as solvent that a negative electrode in which lithium is an active material reacts chemically with the dioxolane, and reduces battery capacity after storage.
Japanese patent publication (Laid-Open) Sho 49-108525 discloses that pyridine is added to an electrolyte to improve storage properties. However, even if pyridine is added to an electrolyte, sufficient improvement is not obtained in a battery in which an organic solvent containing dioxolane is used. Further improvement is required.
OBJECT OF THE INVENTION
An object of the present invention is to reduce self-discharge during storage of a nonaqueous electrolyte battery and to provide a nonaqueous electrolyte battery having excellent storage properties.
SUMMARY OF THE INVENTION
The present invention provides a nonaqueous electrolyte battery having a positive electrode, a negative electrode comprising lithium or a material capable of absorbing and desorbing lithium, an organic solvent containing dioxolane and a solute, wherein the dioxolane is 10 wt % or more of the organic solvent, and the organic solvent contains a storage stabilizing additive selected from the group consisting of an oxygen acid ester, isoxazole, oxazole, oxazoline and derivatives thereof.
When the storage stabilizing additive selected from the group consisting of an oxygen acid ester, isoxazole, oxazole, oxazoline and derivatives thereof is added to an organic solvent containing 10 wt % or more of dioxolane, the additive reacts with lithium, and a coating or film of good quality is formed on the negative electrode which comprises a metal oxide. The coating prevents direct contact of lithium and the solvent, and reduces decomposition of the nonaqueous electrolyte caused by the contact of lithium and the solvent. As a result, the storage properties are improved.
As the oxygen acid ester, trimethyl phosphate [(CH
3
O)PO], tetrabutyl titanate [(C
4
H
9
O)
4
Ti], trimethyl borate [(CH
3
O)
3
B], triethyl phosphate [(C
2
H
5
O)
3
PO], tetraisopropyl titanate [(C
3
H
7
O)
4
Ti], triethyl borate [(C
2
H
5
O)
3
B], or the like can be illustrated.
Trimethyl phosphate is most preferable among the above mentioned oxygen acid esters to inhibit self-discharge. It is believed that the best coating on the negative electrode is formed or that trimethyl phosphate is the easiest of the oxygen acid esters to be adsorbed on the negative electrode.
The structural formula of isoxazole is shown below:
The structural formula of oxazole is shown below:
The structural formula of oxazoline is shown below:
The derivatives of isoxazole described above are those in which at least one of the hydrogens bonded to a carbon atom of the isoxazole is substituted by methyl(—CH
3
), ethyl(—C
2
H
5
) or halogen (fluorine (F), chlorine (Cl) etc.). 3,5-Dimethyl isoxazole is illustrated as one of the derivatives of isoxazole. The chemical structure of 3,5-dimethyl isoxazole is shown below:
The derivatives of oxazole are also defined the same as the derivatives of isoxazole, that is, at least one of the hydrogens bonded to a carbon atom of the oxazole is substituted by methyl (—CH
3
), ethyl(—C
2
H
5
) or halogen (fluorine (F), chlorine (Cl) etc.). 4-Methyloxazole is illustrated as one of the derivatives of oxazole. The chemical structure of 4-methyloxazole is shown below:
Derivatives of oxazoline are also defined the same as the derivatives of isoxazole or oxazole, that is, at least one of the hydrogens bonded to a carbon atom of the oxazole is substituted by methyl(—CH
3
), ethyl(—C
2
H
5
) or halogen (fluorine (F), chlorine (Cl) etc.). 2-Methyl-2-oxazoline is an example of the derivatives of oxazoline. The chemical formula of 2-methyl-2-oxazoline is shown below:
3,5-Dimethyl isoxazole, oxazole and 2-methyl-2-oxazoline are preferable additives among those described above, because these compounds form easily the most suitable coating on the negative electrode or are adsorbed easily on the negative electrode. It is believed that these compounds (IV, II and VI) have structures which contact lithium easily, and react with lithium easily, or the electron distribution intramolecular of these compounds makes them easy to be adsorbed by lithium metal. Among these three compounds, when 3,5-dimethyl isoxazole is used as the additive, self-discharge rate can be well suppressed.
The amount of the additive is 0.01 wt % or more and 30.0 wt % or less based on the weight of the organic solvent. 0.1 wt % or more and 20.0 wt % or less are more preferable from the standpoint of reduction of the amount of discharge after storage of the nonaqueous electrolyte battery.
As a solute for the battery, LiPF
6
, LiBF
4
, LiClO
4
, LiCF
3
SO
3
, LiAsF
6
, LiN(CF
3
SO
2
)
2
, LiN(C
2
F
5
SO
2
)
2
, LiCF
3
(CF
2
)
3
SO
3
, LiC(CF
3
SO
2
)
3
, or the like. The solute is, of course, not limit to these and other solutes that do not adversely affect the storage property of the battery can be used.
As an organic solvent for this battery, there can be used dioxolane alone or an organic solvent containing 10 wt % or more of dioxolane mixed with ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, sulfolane and/or tetrahydrofuran.
A metal oxide containing at least one of manganese, cobalt, nickel, vanadium or niobium can be used as the positive electrode. Other materials that do not adversely affect the storage property of the batteries can be used.
The negative electrode for this battery is a material capable of absorbing and desorbing lithium ion electrochemically, or is metallic lithium. Graphite, coke, carbon materials (for example, calcined organic materials), and a lithium alloy are illustrative of the materials capable of absorbing and desorbing lithium ion electrochemically. As the lithium alloy, lithium-aluminum alloy, lithium-magnesium alloy, lithium-indium alloy, lithium-tin alloy, lithium-thallium alloy, lithium-lead alloy and lithium-bismuth alloy can be used.
REFERENCES:
patent: 4419422 (1983-12-01), Leger et al.
patent: 4489144 (1984-12-01), Clark
patent: 4737424 (1988-04-01), Tobishima et al.
patent: 5393620 (1995-02-01), Manaresi et al.
patent: 5478673 (1995-12-01), Funatsu
patent: 5558953 (1996-09-01), Matsui et al.
patent: 5580684 (1996-12-01), Yokoyama et al.
patent: 62-90869 (1987-04-01), None
patent: 62-219475 (1987-09-01), None
patent: 6-10995 B2 (1994-02-01), None
Kusumoto Yasuyuki
Nishio Koji
Nohma Toshiyuki
Yoshimura Seiji
Kubovcik & Kubovcik
Sanyo Electric Co,. Ltd.
Weiner Laura
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