COMPOSITE POLYMER ELECTROLYTES WITH MODIFIED MESOPOROUS SILICA FILLER FOR LI-ION BATTERIES

Dispersing fine ceramic particles in polymer matrices has proved to be one of the most effective ways of enhancing key structural and electrochemical parameters of polymer electrolytes for rechargeable lithium batteries. It is now widely recognized that the phase composition, morphology and surface chemistry of the filler all exert a clear impact on the way it interacts with the polymer host, thus contributing to the final outcome in terms of ionic mobility, thermal, mechanical, chemical and electrochemical stability in lithium cells. In the present contribution we manufactured microporous polymer membranes based on copolymer poly(vinylidene fluoride-hexafluoropropylene) (PVdF/HFP) using a two-step approach originally proposed by Bellcore. A mesoporous silica filler MCM-41 was synthesized and functionalized with chlorosilane. After the effect of functionalization was verified by means of FTIR spectroscopy, the fillers were incorporated in the polymer matrices and the resulting dry composite membranes showed a well-developed porous structure and a high ability to absorb liquid media with the formation of stable gels. The good physical properties of the membranes were attributed to the enhanced compatibility of the filler with the fluoropolymer matrix. The composite gel electrolytes were prepared by soaking the dry membranes with a conventional lithium cation conducting liquid electrolyte and their electrochemical characteristics were determined in terms of the temperature dependence of ionic conductivity and electrochemical window. During the experimental studies we observed high conductivities at room temperatures exceeding about 2*10(-3) S/cm and decidedly better anodic stability for composite gel electrolytes with an addition of mesoporous silica with and without surface modification.