Wide-temperature rechargeable Li metal batteries enabled by an in-situ fabricated composite gel electrolyte with a hierarchical structure.

Lithium metal batteries (LMBs) are well recognized as promising next-generation high energy density batteries, but the uncontrollable Li dendrites growth and the volatilization/gas production of electrolytes, which become extremely worse at low and high temperatures, restrict their practical utilizations. In this work, a hierarchically structured polymerized gel electrolyte (HGE), which was composed of an inorganic (LiGaIn alloy and LiCl salt)/organic (polymerized tetrahydrofuran (THF)) hybrid layer and the bulk polymerized THF electrolyte, was proposed to achieve a steady performance of LMBs over a wide temperature range of -20-55 °C. The HGE fabrication can be completed within assembled cells with a simultaneously occurring replacement-polymerization-alloying reaction, which helps decrease the interfacial resistance and enhance the stability and ion diffusion under both low and high temperatures. The use of THF with low polarity also ensures high ion conductivity under low temperatures. With such HGE, the Li symmetric cells showed low overpotential under 10 mA/cm with a capacity of 10 mAh/cm over a 1200 h cycling, and the full cell coupled with LiTiO demonstrated high capacity retention over 5000 cycles at room temperature. Besides, the symmetric cells showed low overpotentials of 12 mV at 55 °C and 80 mV at -20 °C at 2 mA/cm after a 1000 h cycling, and the full cell revealed the high capacity retention of 93.5% at 55 °C and 88.8% at -20 °C after 1500 cycles under a high current density of 1000 mA/g. This work shows a hierarchically structured polymerized electrolyte design for advanced Li batteries workable under broad temperatures.