Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
1999-04-14
2001-07-17
Weriner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S247000, C429S246000
Reexamination Certificate
active
06261721
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention concerns a cell comprising a separator comprising a macroporous matrix and a porous polymer and the method of manufacturing it.
2. Description of the prior art
Conventional cells comprise solid electrodes on opposite sides of a separator containing the liquid electrolyte. A separator can be a macroporous body impregnated with the electrolyte, for example. Another, modern type of conventional “separator” is a porous or non-porous gelled polyvinylidene fluoride polymer containing the liquid electrolyte.
Various methods of manufacturing this type of cell have been proposed, including processes involving the separate manufacture of the electrodes and the separator followed by their combination using various techniques. These techniques include rolling (BellCore, U.S. Pat. No. 5,456,000, U.S. Pat. No. 5,460,904, U.S. Pat. No. 5,540,741, U.S. Pat. No. 5,552,239) and adhesive bonding (Electrofuels, U.S. Pat. No. 5,437,692, U.S. Pat. No. 5,512,389).
Also, document U.S. Pat. No. 5,639,573 describes a separator comprising a multiphase polymer support structure comprising at least a porous first phase and a polymer second phase dispersed in the pores of said porous first phase. The dispersed polymer phase absorbs the organic electrolyte; it is not porous.
These techniques are not entirely satisfactory, however, because the separator is sometimes crushed, which causes short circuits. Assembly also requires careful handling.
Moreover, the skilled person is still confronted with the standard problem of the loss of mechanical properties to the detriment of conductivity properties, and vice versa.
An aim of the invention is therefore a new cell comprising a separator having increased mechanical resistance to crushing and enabling easy assembly.
SUMMARY OF THE INVENTION
Accordingly, the invention provides a cell comprising a separator comprising a macroporous matrix the pores of which contain a microporous polymer, placed in said macroporous matrix by impregnating said matrix with a solution containing said polymer. Generally, the microporous polymer, after having been placed in said macroporous matrix chemically by impregnation, is gelled following its impregnation by the electrolyte.
The cell in accordance with the invention advantageously comprises a separator of homogeneous structure, even in the presence of a few localized heterogeneities, because it is prepared chemically, by impregnating practically all of the macroporous matrix with a solution including the microporous polymer. The separator of the cell in accordance with the invention is therefore practically single-layered.
Another advantage of the cell in accordance with the invention is that the porosity of the separator in said cell is high, the final porosity generally being in the range from 35% to 90% and preferably in the range from 50% to 90%. This facilitates manufacture of said cell by the methods generally employed, which will be explained hereinafter. In particular, the possibility of crushing said separator during manufacture, which leads to unwanted short circuits, is greatly reduced or even virtually eliminated.
The microporous polymer typically has a pore volume in the range from 35% to 95%. It typically has pores with an average diameter in the range from 0.1 &mgr;m to 5 &mgr;m, generally in the order of 1 &mgr;m.
The microporous polymer can be selected from polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polybutyl methacrylate (PBMA), polyacrylonitrile (PAN), polyvinylformal, cellulose polyacetate, a polysulfone, a polyether, a polyolefin such as polyethylene (PE), polyethylene oxide (PEO), polypropylene (PP), their copolymers, copolymers of polyvinylidene fluoride and polyethylene tetrafluoride and copolymers of polyvinylidene fluoride and polyhexene hexafluoride, copolymers of polyvinyl acetate and polyvinyl alcohol, and their alloys, and alloys of polyvinylidene fluoride with a polymer selected from a polysulfone, polymethyl methacrylate and polyvinylpyrrolidone.
The microporous polymer is advantageously polyvinylidene fluoride, a copolymer thereof or an alloy thereof.
The macroporous matrix is “impregnated” with the microporous polymer. The matrix for the microporous polymer is substantially rigid.
The macroporous matrix typically has an initial pore volume in the range from 35% to 95%. It typically has pores whose average diameter is in the range from 5 &mgr;m to 50 &mgr;m, generally in the order of 10 &mgr;m.
The macroporous matrix can be selected from, for example, organic or inorganic felts, especially polymer felts, woven separators, macroporous materials obtained by processes such as phase inversion or by mechanical means. A preferred matrix is a polymer felt formed of a woven or non-woven fabric defining interstices (or pores) between the fibers. The felt can be made from a polyolefin (PE, PP, etc) or polyamide or any other material.
The pores or interstices of the matrix and of the polymer have average diameters enabling the polymer to occupy the pores or interstices of the matrix. In general, the ratio of the average pore diameter of the macroporous matrix to the average pore diameter of the microporous polymer is in the range from 2 to 50, and this ratio is conventionally in the order of 10.
The polymer may also comprise an elastomer (which in some cases can completely replace it), and possibly an inorganic substance.
The elastomer can be a polyurethane, an acrylonitrile/butadiene copolymer, a styrene/butadiene/styrene copolymer, a styrene/isoprene/styrene copolymer, a polyester or polyether with amide blocks, etc. The elastomer can be present in various amounts. The inorganic substance can be silica.
The separator in accordance with the invention is of standard thickness, which can be in the range from 10 &mgr;m to 100 &mgr;m.
In one embodiment of the invention the separator is made by a preparation method that comprises forming the microporous polymer in situ in the pores of the macroporous matrix.
All conventional processes of forming the microporous polymer in situ in the pores of the macroporous matrix are appropriate; for example, a solution of the polymer in a solvent with a plasticizing agent can be used, by evaporating the solvent and extracting the plasticizer.
The microporous polymer is preferably prepared using the phase inversion technique.
In a first embodiment, which operates by immersion, the method of making the separator of the cell in accordance with the invention comprises the following steps:
a solution of said polymer dissolved in a solvent, possibly with additives, is produced;
said macroporous matrix is impregnated with said solution;
the impregnated matrix is immersed in a non-solvent that is miscible with said solvent; and
said impregnated matrix is dried to eliminate said solvent and said non-solvent.
In a second embodiment, which operates by evaporation, the method of making the separator of the cell in accordance with the invention comprises the following steps:
a solution of said polymer dissolved in a solvent, possibly with additives, is prepared, said solution further containing a non-solvent that is miscible with said solvent, in a proportion that is insufficient to precipitate said polymer;
said macroporous matrix is impregnated with said solution; and
said macroporous matrix is dried to eliminate said solvent and said non-solvent.
The impregnation can be performed by dipping the matrix into a bath or by coating it with the solution or by any other appropriate method. The solutions can be heated before the macroporous matrix is impregnated.
The term “solvent” means an organic solvent in which the polymer (and possibly the elastomer) dissolves easily at the working temperature and which can be easily eliminated by heating to a moderate temperature. The term “non-solvent” means a liquid in which the polymer (and possibly the elastomer) is not soluble (strong non-solvent) or only very slightly soluble (weak non-solvent) at the working temperature.
The boi
Andrieu Xavier
Boudin François
Jehoulet Christophe
Alcatel
Sughrue Mion Zinn Macpeak & Seas, PLLC
Weriner Laura
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