Electrolytic composition with polymer base for electrochemical generator

#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.

#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.

#FIG. 1 schematically illustrates generators with double composite electrodes (non-limiting) in four embodiments of the invention:

#A) Similar polymer matrix in the entire separator.

#B) Polymer matrix containing more solvent (more swollen) in each composite electrode. Example: Any polyether with control of the amount of crosslinking of the comonomers.

#Embodiments which account for this teaching are schematically illustrated in FIG. 1.

#It will be remembered that the high amount of swelling of the polymer matrix of the composite electrode may be obtained by utilizing, in the case of an all polyether system, a non cross-linkable or little cross-linked polyether.

#An alternative way of obtaining a high amount of solvent in composite electrodes consists inter alia of using a polymer matrix which is only slightly swollen and compensating for the porosity of the composite by a free liquid phase. This embodiment will be preferred for preparing high voltage cathodes≧4 V or still for giving a larger power capacity to a cathode of 3 V or more such as LiFePO4 or its analogous polyanions.