Polymer-coated silica dual functional fillers to improve the performance of poly(ethylene oxide)-based solid electrolytes

The application of solid polymer electrolytes (SPEs) is mainly hindered by their low ionic conductivity and the limited mechanical properties. Adding functional small molecules and inorganic fillers are two of the simplest and most effective ways to improve the performance of SPEs. However, most of the time, both methods cannot be implemented concomitantly, and may even inhibit each other. Here, an original dual functional filler, consisting of hollow porous SiO2 nanospheres three-dimensionally wrapped by poly(2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMPM), is blended with poly(ethylene oxide) (PEO) and LiClO4 to obtain a composite solid electrolyte (CSE). Compared to the reference PEO SPE, the room-temperature ionic conductivity of the synthesized CSE is improved by 4 orders of magnitude reaching 1.3 × 10−4 S cm−1. Moreover, a lithium ion transference number value as high as 0.81 is obtained. The CSE membrane is further assembled with a Li anode and a standard LiFePO4 cathode to obtain an all-solid-state battery showing high capacity (149.3 mAh g−1 at 0.1 C) and long-term stability (0.68‰ loss of capacity per cycle, over 100 cycles). The peculiar structure of the PEO/PTMPM interface is thought to be at the origin of the enhanced LiClO4 dissociation and mobility of lithium ions. Remarkably, the well-known toughening effect of SiO2 fillers is preserved in the CSE.