Effect of an inorganic additive on the cycling performances of lithium-ion polymer cells assembled with polymer-coated separators

Abstract

Gel polymer electrolytes were prepared by immersing a porous poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP))-coated separator in an electrolyte solution containing small amount of inorganic additive. Four kinds of inorganic compounds, aluminum fluoride, aluminum iodide, lithium fluoride and lithium iodide were used as inorganic additives. By using the gel polymer electrolytes containing different inorganic additives, lithium-ion polymer cells composed of carbon anode and LiCoO2 cathode were assembled and their cycling performance evaluated. Adding small amount of an inorganic additive led to less capacity fade and better high rate performance. Good cycling performances in the cell with these additives could be ascribed to the formation of a protective layer to cover active material in the electrode during cycling, which reduces the electrolyte decomposition.