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

Abstract

Solid composite electrolytes are prepared by polymerizing a liquid precursor containing Li_6.25Ga_0.25La₃Zr₂O₁₂ (Ga-LLZO) nanoparticles. The composite electrolyte shows an ionic conductivity of 1.8 × 10⁻⁴ S cm⁻¹ and a Li-ion transference number of 0.58 at 30 °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 LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) and LiNi_0.85Co_0.05Al_0.1O₂ (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.