Nanocomposite with fast Li+ conducting percolation network: Solid polymer electrolyte with Li+ non-conducting filler

Solid polymer electrolytes (SPEs) have attracted considerable research interest because they are expected to solve the safety problems caused by the liquid electrolytes. However, the low ionic conductivity limits their practical applications. Constructing Li+ fast conducting network in SPEs with Li+ highly conducting ceramic fillers following the mixed matrix membrane concept have shown their limits in raising the Li+ conductivity. Herein, a new strategy using Li+ non-conducting fillers like CeO2 nanowires, is proposed to construct a Li+ fast conducting network through SPEs. CeO2 nanowires can dissociate LiTFSI, which results in a high Li+ conductivity through the SPEs near to the fiber surface. This experimental finding is confirmed by analytics (FT-IR, Raman and NMR) and theoretical calculations (DFT-MD and COHP). As a result, the network of interwoven CeO2 nanowires helps form a continuous Li+ fast conducting percolation network through the SPEs. The ionic conductivity of the composite SPEs with 10 wt% CeO2 nanowires is greatly improved (1.1 × 10−3 S cm−1 at 60 °C). The Li symmetric cells with this composite electrolyte exhibit good cyclic stability (without short circuiting after 2000 h), and the all-solid-state LiFePO4/Li cells present a superior cycling performance (remained 140 mA h g−1 after 100 cycles at 1 C).