A Moisture-Assisted Rechargeable Mg-CO2 Battery.

New sustainable energy conversion and storage technologies are required to address the energy crisis and CO2 emission. Among various metal-CO2 batteries that utilize CO2 and offer high energy density, rechargeable Mg-CO2 batteries based on earth-abundant and safe magnesium (Mg) metal have been limited due to the lack of a compatible electrolyte, operation atmosphere, and unambiguous reaction process. Herein, the first rechargeable nonaqueous Mg-CO2 batteries have been proposed with moisture assistance in a CO2 atmosphere. These display more than 250 h cycle life and maintain the discharge voltage over 1 V at 200 mA g-1 . Combining with the experimental observations and theoretical calculations, the reaction in the moisture-assisted Mg-CO2 battery is revealed to be 2 Mg+3 CO2 +6 H2 O↔2 MgCO3 ⋅3 H2 O+C. It is anticipated that the moisture-assisted rechargeable Mg-CO2 batteries would stimulate the development of multivalent metal-CO2 batteries and extend CO2 fixation and utilization for carbon neutrality.