Solid polymer electrolyte membranes based on organic/inorganic nanocomposites with star-shaped structure for high performance lithium ion battery

Solid polymer electrolyte membranes (SPEMs) with star-shaped structure, consisting of octavinyl octasilsesquioxane (OV-POSS) with nanoscale organic/inorganic hybrid structure and poly(ethylene glycol) methyl ether methacrylate (PEGMEM), have been prepared by one-step free radical polymerization. OV-POSS with eight functional corner groups was used to produce star-shaped nanocomposites and PEGMEM was used as the polymer matrix to dissolve lithium ion. For comparison, SPEMs based on the corresponding linear copolymers, containing POSS moieties and PEGMEM segments, were also prepared. The SPEM with star-shaped structure containing 5.1 mol% POSS exhibits the highest ionic conductivity of 1.13×10−4 S cm−1 and Li+ transference number of 0.35 at 25 °C, which are about two times of that of SPEM with linear structure containing the same POSS content. Moreover, the Li/LiFePO4 cell assembled with such star-shaped SPEM delivers the highest discharge capacity of 137.1 mAh g−1 under a current density of 0.5 C at 25 °C. At an evaluated temperature of 80 °C, this cell exhibits an initial discharge capacity of 163.8 mAh g−1 at 0.5 C, and even at high discharging C-rates of 5 and 10 C, the discharge capacity of 75.6 and 45.7 mAh g−1 can still be obtained, respectively.