Solid polymer electrolyte based on polyacrylonitrile

Details Solid polymer electrolyte based on polyacrylonitrile Solid polymer electrolyte based on polyacrylonitrile

1999-04-15

2001-09-18

Gupta, Yogendra N. (Department: 1751)

Compositions

Electrically conductive or emissive compositions

Elemental carbon containing

C252S503000, C252S506000, C252S509000, C252S518100, C252S062200, C429S199000, C429S199000, C429S199000, C429S199000

Reexamination Certificate

active

06290878

ABSTRACT:

The present invention relates to a solid polymer electrolyte based on polyacrylonitrile for use in a rechargeable lithium cell.
BACKGROUND OF THE INVENTION
“Gelled” solid polymer electrolytes comprise a polymer having, incorporated therein, a plasticizer containing organic solvents and a lithium salt. The plasticizer is trapped in the three-dimensional structure of the polymer. The resulting substance forms a single phase.
Gelled electrolytes based on polyacrylonitrile have poor mechanical behavior during cycling, and that gives rise, in particular, to a decrease in the thickness of the electrolyte layer. This creep contributes to premature aging of the cell and shortens the time during which it can be used. This phenomenon is made worse when the cell is required to operate at temperatures in excess of 45° C.
To remedy the problem, proposals have been made to add a reinforcing agent to the electrolyte in the form of an inorganic filler, in particular based on silica. That solution requires about 5% to 10% by mass of additive to be added, representing a large volume because of the low density of the filler, of the order of 36 mg/cm
3
.
U.S. Pat. No. 5,631,103 describes an electrolyte having a gelled polymer with a filler constituting more than 50% by weight of the electrolyte. The filler is either an inorganic material or an inert polymer.
Adding such a filler represents a considerable volume. It results in defects of wetting by the plasticizer, and in non-uniformity in filler distribution. This gives rise to dispersion in performance and to lifetime at high temperature that is not improved. In addition, those mixtures have poor pourability which makes them difficult to spread using industrial means.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to propose a gelled solid polymer electrolyte having mechanical strength that is satisfactory while it is in use in an electrochemical cell such that its lifetime is extended, in particular for use at temperatures greater than 45° C.
The present invention provides a solid polymer electrolyte comprising a polymer which is a polyacrylonitrile, a plasticizer made up of a lithium salt in solution in a liquid organic solvent, and a reinforcing agent which is an organic compound constituted by porous grains of a polymer having polyamide structural units.
The pore size of these grains is 0.7 &mgr;m±0.2 &mgr;m and their pore volume lies in the range 0.2 cm
3
/g to 0.6 cm
3
/g. A supply of plasticizer is thus constituted within the available pore volume, thereby contributing to extending the lifetime of the cell.
The density of the grains lies in the range 1 g/cm
3
to 1.2 g/cm
3
and their specific surface area lies in the range 1 m
2
/g to 30 m
2
/g. Their average size lies in the range 5 &mgr;m±1.5 &mgr;m to 60 &mgr;m±1.5 &mgr;m.
The content of said agent preferably lies in the range 1% to 10% by weight of said electrolyte.
The invention also provides a cell containing an electrolyte according to the invention, in which the negative active material is a carbon-containing material suitable for inserting lithium in its structure.
The present invention also provides a method of manufacturing a gelled solid polymer electrolyte of the invention. The method comprises the following steps.
Firstly the grains of the organic compound are impregnated with the solvent.
Secondly the plasticizer comprising the lithium salt in solution in the liquid organic solvent is mixed with the polymer. The polymer is preferably in powder form. This operation is preferably performed hot, but nevertheless at a temperature of less than 100° C. so as to avoid decomposition of the lithium salt. The mixture then takes on the viscous consistency of a gel.
Thereafter, the solvent-impregnated grains are introduced into the gelled mixture.
Finally, the electrolyte constituted by the mixture containing the grains is shaped, e.g. by pouring the mixture into a mold or onto a plate to form a film. This shaping operation is preferably performed hot, at a temperature of less than 100° C.
To avoid shearing the polymer chains, the gel can be pressed, e.g. between a plate of polytetrafluoroethylene (PTFE) and a sheet of aluminum. This makes it possible to obtain thin films of gel, e.g. films that are about 100 &mgr;m thick.


REFERENCES:
patent: 5426005 (1995-06-01), Eshbach
patent: 5631103 (1997-05-01), Eshbach et al.
patent: 5639573 (1997-06-01), Oliver et al.
patent: WO 97/08765 (1997-03-01), None
patent: WO 98/37589 (1998-08-01), None
Database WPI, Sechtion CH, Week 9521, Derwent Publications Ltd., London, GB; Class A14, AN 95-159125, XP002088820 corresponding to JP 07 082450 A (Matsushita Denki Sangyo KK) Mar. 28, 1995.
Chemical Abstracts, vol. 104, No. 2, Jan. 13, 1986, Columbus, OH, US; Abstract No. 8315, Tamura, Masatoshi et al, “Solid electrolyte”, XP00208819 corresponding to JP 60165058 A (Orient Wtach Co., Ltd.) Japan.
Morihiko Matsumoto et al, “Polymer Electrolytes with Multiple Conductive Channels Prepared from NBR/SBR latex Films Impregnated with Lithium salt and Plasticizer”, J. Electrochem. Soc., vol. 142, No. 9 Sep. 1995, pp. 3052-3057, XP002088818.

Affiliated with

Also associated with

Rating

Solid polymer electrolyte based on polyacrylonitrile does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Solid polymer electrolyte based on polyacrylonitrile, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solid polymer electrolyte based on polyacrylonitrile will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2512346