Greenhouse-inspired light-driven inorganic molten salt Li-CO2 battery operating at room temperature

Lithium-carbon dioxide (Li-CO₂) batteries using high ion-conductive inorganic molten salt electrolytes have recently attracted much attention due to the high energy density and potential application of carbon neutrality. However, the poor Li-ion conductivity of the molten-salt electrolytes at room temperature (RT) makes these batteries lose most of their capacity and power as the temperature falls below 80 °C. Here, inspired by the greenhouse effect, we report an RT molten salt Li-CO₂ battery where solar energy can be efficiently harvested and converted into heat that is further localized on the cathode consisting of plasmonic ruthenium (Ru) catalysts and Li₂CO₃-based products via a greenhouse-like phenomenon. As a result, the solar-driven molten salt Li-CO₂ battery demonstrates a larger full discharge/charge capacity of 9.5 mA h/8.1 mA h, and a longer cycle lifespan of 250 cycles at 500 mA/g with a limited capacity of 500 mA h/g at RT than the molten salt Li-CO₂ battery at 130 °C. Notably, the average temperature of the cathode increases by 8 °C after discharge to 0.75 mA h, which indicates the infrared radiation from Ru catalysts can be effectively suppressed by discharged Li₂CO₃-based products. This battery technology paves the way for developing low-temperature molten salt energy storage devices.