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.