Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-06-12
2004-10-19
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S249000, C429S231800, C029S623500, C029S623100, C427S058000
Reexamination Certificate
active
06806002
ABSTRACT:
TECHNICAL FIELD
The present invention concerns electrolytic compositions based on polymers, for electrochemical generators. More specifically, the invention is directed to aprotic electrolytic compositions characterized in that they consist of at least one alkali metal salt and a polymer matrix consisting of a polyether and at least another polymer matrix, which are separated microscopically, and are swollen by means of at least one polar aprotic organic solvent, said solvent or mixture of solvents being unequally distributed between the matrices.
PRIOR ART
During the last ten years, lithium batteries of the primary and rechargeable type have been the object of a considerable number of research and development works. The intent was to develop a battery which is safe, inexpensive, having a large energetic content and good electrochemical performances. In this context, a plurality of a battery designs were developed to meet different applications, such as micro-electronics, telecommunications, portable computers and electrical vehicles, to name only a few.
Electrochemical batteries or generators, whether rechargeable or not, are all made of an anode which can consist of a metal such as lithium, or an insertion compound which is reversible towards lithium, such as carbon, a cathode which consists of an insertion compound which is reversible towards lithium such as cobalt oxide, a mechanical separator placed in between the electrodes and an electrolytic component. The term electrolytic component means any material placed inside the generator and which is used as ionic transport except electrode materials in which the ions Li
+
may be displaced at the level of the separator as well as in at least one composite electrode. During the discharge or charge of the generator, the electrolytic component ensures the transport of ionic species through the entire generator from one electrode to the other and even inside the composite electrodes. In lithium batteries, the electrolytic component is generally in the form of a liquid which is called liquid electrolyte or a dry or gel polymer matrix which may also act as mechanical separator.
When the electrolytic component is in liquid form, it consists of all alkali metal salt which is dissolved in an aprotic solvent. In the case of a lithium generator, the more common salts are LiPF
6
, LiBF
4
and LiN(SO
2
CF
3
)
2
and the polar aprotic solvents may be selected from propylene carbonate, ethylene carbonate, &ggr;-butyrolactone and 1,3-dioxolane or their analogs to name only a few. At the level of the separator, the liquid electrolyte is generally impregnated in a porous polymer matrix which is inert towards the aprotic solvent used, or in a fiberglass paper. The use of a liquid electrolyte which is impregnated in an inert polymer matrix enables to preserve a sufficient ionic mobility to reach a level of conductivity of the order of 10
−3
Scm
−1
at 25° C. At the level of the composite electrodes, when the latter are made of an insertion material which is bound by a polymer matrix which is towards aprotic solvents, which have only little interaction with the latter, the liquid electrolyte compensates for the porosity of the electrode. Examples of batteries utilizing a liquid electrolytic component are found U.S. Pat. No. 5,422,203; U.S. Pat. No. 5,626,985 and U.S. Pat. No. 5,630,993.
When the electrolytic component is in the form of a dry polymer matrix, it consists of a high molecular weight homo or copolymer, which is cross-linkable or non cross-linkable and includes a heteroatom in its repeating unit, such as oxygen or nitrogen for example, in which an alkali metal salt is dissolved such as LiN(SO
2
CF)
2
, LiSO
3
CF
3
and LiClO
4
. Polyethylene oxide is a good example of a polymer matrix which is capable of solvating different alkali metal salts. Armand, in U.S. Pat. No. 4,303,748 describes families of polymers which may be used as electrolytic component ill lithium batteries. More elaborated families of polymers (cross-linkable or non cross-linkable co-polymers and terpolymers) are described in U.S. Pat. Nos. 4,578,326; 4,357,401; 4,579,793; No. 4,758,483 and in Canadian Patent No. 1,269,702. The use of a high molecular weight polymer enables to provide electrolytes in the form of thin films (of the order of 10 to 100 &mgr;m) which have sufficiently good mechanical properties to be used entirely as separator between the anode and the cathode while ensuring ionic transport between the electrodes. In the composite, the solid electrolyte serves as binder for the materials of the electrode and ensures ionic transport through the composite. The use of a cross-linkable polymer enables to utilize a polymer of lower molecular weight, which facilitates the preparation of the separator as well as the composite and also enables to increase the mechanical properties of the separator and, by the same token, to increase its resistance against the growth of dendrites when using a metallic lithium anode. Contrary to a liquid electrolyte, a solid polymer electrolyte cannot escape nor be evaporated from the generator. Its disadvantage results from a lower ionic mobility obtained in these solid electrolytes which restricts their uses at temperatures between 60 and 100° C.
The gel electrolytic component is itself generally constituted of a polymer matrix which is solvating or non-solvating for lithium salts, an aprotic solvent and an alkali metal salt being impregnated in the polymer matrix. The most common salts are LiPF
6
. LiBF
4
and LiN(SO
2
CF)
2
and the polar aprotic solvents may be selected from propylene carbonate, ethylene carbonate, butyrolactones and 1,3-dioxolane, to name only a few. The gels may be obtained from a high molecular weight homo or copolymer which is cross-linkable or non cross-linkable or from a cross-linkable homo or copolymer. In the latter case, the dimensional stability of the gel is ensured by cross-linking the polymer matrix. Polyethers including cross-linkable functions such as alkyls, acrylates or methacrylates are good examples of polymers which may be used in formulating a gel electrolyte, such as described in U.S. Pat. No. 4,830,939. This is explained by their capacity to solvate lithium salts and their compatibility with polar aprotic solvents as well as their low cost, and ease of handling and cross-lining. A gel electrolyte has the advantage of being handled as a solid and of not escaping or going out of the generator as is the case with liquid electrolyte generators. Ionic transport efficiency is associated with the proportion of aprotic solvent incorporated in the polymer matrix. Depending on the nature of the polymer matrix, the salt, the plasticizing agent and its proportion in the matrix, a gel may reach an ionic conductivity of the order of 10
−3
Scm
−1
at 25° C. while remaining macroscopically solid. As in the case of a dry electrolyte, a gel electrolyte may be used as separator between the anode and cathode while ensuring ionic transport between the electrodes. In the composite electrode(s) of the generator, the gel electrolyte is used as binder for the materials of the electrode(s), and ensures ionic transport through the composite electrode(s). However, the loss of mechanical property resulting from the addition of the liquid phase (aprotic solvent) should generally be compensated by the addition of solid fillers, by cross-linking the polymer matrix whenever possible, or in some cases, when the proportion of liquid is too high, by using a porous mechanical separator which is impregnated with the gel which serves as electrolytic component in the separator. Examples of a generator utilizing a gel electrolytic component are described in U.S. Pat. No. 5,443,927 and U.S. Pat. No. 4,830,939. Takeda et al., in U.S. Pat. No. 5,658,687 claim a battery and a process of manufacturing said battery which comprises an electrolytic component consisting of a specific, cross-linkable and high molecular weight polyether. This high molecular weight polyether is obtained by esterification of a
Armand Michel
Belanger Andre
Besner Simon
Choquette Yves
Gauthier Michel
Hydro-Duebec
Weiner Laura
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