AbstractThe aprotic Li‐CO₂ battery is emerging as a promising energy storage technology with the capability of CO₂ fixation and conversion. However, its practical applications are still impeded by the large overpotential. Herein, the general synthesis of a series of ultrathin 2D Ru‐M (M = Co, Ni, and Cu) nanosheets by a facile one‐pot solvothermal method is reported. As a proof‐of‐concept application, the representative RuCo nanosheets are used as the cathode catalysts for Li‐CO₂ batteries, which demonstrate a low charge voltage of 3.74 V, a small overpotential of 0.94 V, and hence a high energy efficiency of 75%. Ex/in situ studies and density functional theory calculations reveal that the excellent catalytic performance of RuCo nanosheets originates from the enhanced adsorption toward Li and CO₂ during discharge as well as the elevated electron interaction with Li₂CO₃ during charge by the in‐plane RuCo alloy structure. This work indicates the feasibility of boosting the electrochemical performance of Li‐CO₂ batteries by in‐plane metal alloy sites of ultrathin 2D alloy nanomaterials.