Polymer electrolyte and rechargeable cell comprising the same

Details Polymer electrolyte and rechargeable cell comprising the same Polymer electrolyte and rechargeable cell comprising the same

2000-11-22

2003-05-13

Ryan, Patrick (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S231800, C429S231950, C429S306000, C429S309000

Reexamination Certificate

active

06562520

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a polymer electrolyte, which can be used in electrochemical equipment such as cells, capacitors, etc., prevent the liquid leakage, and is easily produced, and a rechargeable cell comprising the same.
PRIOR ART
Hitherto, in the production of polymer electrolytes, various polymers such as polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, etc. or monomers which are polymerized with radical polymerization initiators or the irradiation of UV rays are used as gelation agents to gel liquid electrolytes.
However, polyethylene oxide, polyvinylidene fluoride or polyacrylonitrile requires heating to gel the liquid electrolytes. During the heating step, the electrolyte salts may be decomposed. In addition, such polymers have high viscosity and therefore their workability is low.
When the monomers are polymerized with the radical polymerization initiators, heating is usually necessary, and it takes a long time until the polymerization reaction is completed. In addition, the polymerization may not be carried out in the air since radicals are deactivated with oxygen. When the monomers are polymerized with the irradiation of UV ray, the polymerization may proceed at room temperature but it is difficult to produce polymers having the same properties required at any time in a dry air because of the generation of radicals. In addition, the monomers used are mostly polyfunctional, and thus the polymers generated usually becomes fragile easily.
SUMMARY OF THE INVENTION
One object of the present invention is to develop a polymer which can be quickly prepared at room temperature in a dry air and is used as a gelation agent for the preparation of a polymer electrolyte.
Another object of the present invention is to provide a polymer electrolyte which can be easily prepared and prevent the liquid leakage from electrochemical equipment.
A further object of the present invention is to provide a rechargeable cell comprising a polymer electrolyte, which can avoid the liquid leakage.
Accordingly, the present invention provides a polymer electrolyte comprising an electrolyte salt, a non-aqueous solvent, and a polymer as a gelation agent which comprises repeating units of the formulas:
—(R
1
—O)
n
—,
and
—[CH (R
2
)—CH
2
—O]
m
—
wherein n is 0 or a positive number (n≧0) and m is 0 or a positive number (m≧0) provided that the sum of n and m is at least 5 (n+m≧5), R
1
is an alkyl group having 1 to 6 carbon atoms, and R
2
is an alkyl group having 1 to 6 carbon atoms or a benzyl group, and a urea structure of the formula (I):
in which R
3
and R
4
are the same or different and represent, an alkyl group having 1 to 6 carbon atoms or a hydrocarbon group comprising an aromatic group and having 7 to 11 carbon atoms in total, and R
5
is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydrocarbon group comprising an aromatic group and having 7 to 11 carbon atoms in total, which may be prepared by polymerization through the reaction of an amine compound and a urethane.
Furthermore, the present invention provides a rechargeable cell comprising a positive electrode, a negative electrode and a film of the polymer electrolyte of the present invention, which is interposed between the positive and negative electrodes.
The polymer contained in the polymer electrolyte of the present invention has a decreased crystallinity and a low glass transition temperature because of the introduction of, for example, propylene oxide segments in ethylene oxide segments. Therefore, such a polymer itself has a good ion conductivity even at or below room temperature in comparison with the conventional polymer gelation agents.
Furthermore, the retention of the liquid electrolyte can be controlled by the adjustment of the ratio of the ethylene oxide segments to the propylene oxide segments.
The above polymer used in the present invention is prepared by the polymerization through the reaction of an amine compound and a urethane. This reaction can be carried out in a dry air since it is a polyaddition reaction in which no radicals are generated as intermediates. Thus, the production process of the polymer electrolyte can be simplified.
In addition, the reaction of the active hydrogen of the amine and the isocyanate group of the urethane can be carried out at room temperature, since it proceeds very quickly. The reaction rate can be controlled easily using the difference of the reactivity of a primary amine, a secondary amine and a polyamine and/or the content of the amino group.
In the polymer structure of the present invention, the structures represented by —(R
1
—O)
n
—, and —[CH(R
2
)—CH
2
—O]
m
— are derived from either the amine compound or urethane. The group R3 in the urea structure represented by the formula (I) is derived from the urethane, while R4 and R5 are derived from the amine compound. Thus, those having the above structures are selected as the amine comound and the urethane to synthesize the polymer used in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The amine compound used is preferably a primary amine, a secondary amine or polyaminoamide having a polymeric chain of an alkylene oxide, or their derivatives, which preferably has at least two amino groups. Specific examples of such an amine compound include Jeffamine (trade name) comprising polypropylene glycol the both terminals of which are changed to amine groups, diethylene glycol bispropylamine comprising a linear aliphatic diamine into which an ether group is introduced [H
2
N(CH
2
)
p
O(CH
2
CH
2
O)
q
—(CH
2
)
p
—NH
2
], etc.
Preferably, the urethane is an aliphatic urethane, an alicyclic urethane, an aromatic urethane or derivatives thereof with a compound comprising polymeric alkylene oxide chain. Preferably, the urethane has at least two isocyanate groups. Specific examples of such a urethane include 2,4-tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), dianisidine diisocyanate, tolylene diisocyanate, m-xylene diisocyanate, hexamethylene diisocyanate, polymethylenepolyphenyl polyisocyanate, and their addition products with polyols.
Examples of the electrolyte salt are halides and perchlorates of alkali metals, perchlorates of alkaline earth metals, salts of fluorine-containing compounds such as salts of trifluoromethanesulfonic acid, and mixtures thereof. Specific examples of such an electrolyte salt include sodium fluoride, sodium chloride, sodium iodide, lithium bromide, lithium perchlorate, lithium trifluoromethanesulfonate, lithium tetraborofluoride, lithium bistrifluoromethylsulfonylimide, lithium thiocyanate, magnesium perchlorate, magnesium trifluoromethanesulfonate, sodium tetraborofluoride, etc.
Specific examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, &ggr;-butyrolactone, dimethoxyethane, dimethylsulfoxide, dioxolane, sulfolane, methylethyl carbonate, etc. They may be used singly or in a mixture.
The polymer electrolyte of the present invention may be produced by any preparation method used to produce conventional polymer electrolytes using the above components.
Also the amounts of the polymer, the electrolyte salt and the non-aqueous solution may be the same as those for the conventional polymer electrolytes.
The rechargeable cell of the present invention has the same construction as that of the conventional rechargeable cell comprising a polymer electrolyte. That is, the rechargeable cell comprises a positive electrode, a negative electrode, and the film of the polymer electrolyte of the present invention.
The active material of the positive electrode can be lithium-containing composite oxides such as lithium cobalt composite oxides (e.g. LiCoO
2
, etc.), lithium manganese composite oxides (e.g. LiMn
2
O
4
, etc), lithium nickel composite oxides (e.g. LiNiO
2
, etc.), and those derivatives in which a part of the metals are replaced with other metals (e.g. LiNi
0.7
Co
0.2
Al
0.1
O
2
, etc.) Other metal oxides (e.g. manganese dioxide, vanadium pentoxide

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