Composite Solid Polymer Electrolyte with Garnet Nanosheets in Poly(ethylene oxide)

Solid electrolytes potentially provide safety, Li dendrites blocking, and electrochemical stability in Li-metal batteries. Large efforts have been devoted to disperse ceramic nanoparticles in a poly(ethylene oxide) (PEO) matrix to improve the ions transport. However, it is challengeable to create efficient framework for ions transport with nanoparticles. Here we report for the first time garnet nanosheets to provide interconnected Li-ions transport pathway in a PEO matrix. The garnet nanosheet fillers would not only facilitate ions transport but also enhance ionic conductivity in comparison with their nanoparticle counterparts. A composite solid polymer electrolyte containing 15 wt % garnet nanosheets exhibits a practically useful conductivity of 3.6 × 10–4 S cm–1 at room temperature. Besides, the composite electrolyte can robustly isolate Li dendrites in a symmetric lithium metal-composite electrolyte battery during reversible Li dissolution/deposition at a relatively low temperature of 40 °C. The symmetric cell with composite electrolyte shows flat voltage and low interfacial resistance over a galvanostatic cycling of 200 h at a current density of 0.1 mA cm–2. A solid-state Li/LiFePO4 battery with the composite polymer electrolyte exhibits a capacity of 98.1 mAh g–1 and a capacity retention of 97.5% after 30 cycles at a temperature of 40 °C. This finding provides a strategy to explore superionic conductors.