Electrocatalytic reduction of carbon dioxide (CO₂ER) in rechargeable Zn–CO₂ battery still remains a great challenge. Herein, a highly efficient CO₂ER electrocatalyst composed of coordinatively unsaturated single-atom copper coordinated with nitrogen sites anchored into graphene matrix (Cu–N₂/GN) is reported. Benefitting from the unsaturated coordination environment and atomic dispersion, the ultrathin Cu–N₂/GN nanosheets exhibit a high CO₂ER activity and selectivity for CO production with an onset potential of −0.33 V and the maximum Faradaic efficiency of 81% at a low potential of −0.50 V, superior to the previously reported atomically dispersed Cu–N anchored on carbon materials. Experimental results manifest the highly exposed and atomically dispersed Cu–N₂ active sites in graphene framework where the Cu species are coordinated by two N atoms. Theoretical calculations demonstrate that the optimized reaction free energy for Cu–N₂ sites to capture CO₂ promote the adsorption of CO₂ molecules on Cu–N₂ sites; meanwhile, the short bond lengths of Cu–N₂ sites accelerate the electron transfer from Cu–N₂ sites to *CO₂, thus efficiently boosting the *COOH generation and CO₂ER performance. A designed rechargeable Zn–CO₂ battery with Cu–N₂/GN nanosheets deliver a peak power density of 0.6 mW cm⁻², and the charge process of battery can be driven by natural solar energy.