A Moisture‐Assisted Rechargeable Mg−CO₂ Battery

New sustainable energy conversion and storage technologies are required to address the energy crisis and CO 2 emission. Among various metal–CO 2 batteries that utilize CO 2 and offer high energy density, rechargeable Mg−CO 2 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−CO 2 batteries have been proposed with moisture assistance in a CO 2 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−CO 2 battery is revealed to be 2 Mg+3 CO 2 +6 H 2 O↔2 MgCO 3 ⋅3 H 2 O+C. It is anticipated that the moisture‐assisted rechargeable Mg−CO 2 batteries would stimulate the development of multivalent metal‐CO 2 batteries and extend CO 2 fixation and utilization for carbon neutrality.