In situ thermally polymerized solid composite electrolytes with a broad electrochemical window for all-solid-state lithium metal batteries

Solid composite electrolytes are prepared by polymerizing a liquid precursor containing Li6.25Ga0.25La3Zr2O12 (Ga-LLZO) nanoparticles. The composite electrolyte shows an ionic conductivity of 1.8 x 10(-4) S cm(-1) and a Li-ion transference number of 0.58 at 30 degrees C. Moreover, polymerized composite electrolytes (PCEs) are electrochemically stable up to 6.5 V versus Li/Li+ at room temperature. Li/PCEs/Li symmetric cells maintain stable cycling for more than 1000 h at 0.5 mA cm(-2), and the dendrite formation is effectively inhibited, showing compatibility with lithium anodes. Using in situ polymerization, PCEs retain conformal interfacial contacts with all electrodes, and the interfacial resistance of solid-state batteries is decreased by half. Coupled with LiNi0.6Co0.2Mn0.2O2 (NCM622) and LiNi0.85Co0.05Al0.1O2 (NCA) cathodes, solid-state Li metal batteries with PCEs exhibit good cycling performances, including superior specific capacity, high coulombic efficiency and a long cycle lifetime at room temperature. This work offers an approach to meet both the bulk and interfacial requirements of solid-state Li metal batteries and extends the applications of solid composite electrolytes to high-voltage cathodes.