Due to the capability of CO2 uptake and the high theoretical energy density, Li–CO2 batteries have attracted a great deal of attention as a novel and promising energy storage system which is based on the reversible reaction between lithium and CO2. However, the insulating Li2CO3 formed upon the discharge process, which is difficult to be decomposed during recharge process due to the lack of effective cathode catalyst, leads to the poor cycling performance and huge overpotential of the Li–CO2 batteries. In this work, the Ru nanosheets were directly grown on one side of the three-dimensional nickel foam through a galvanic replacement reaction to form the Ru/Ni electrode, which was further used in the Li–CO2 batteries. The highly dispersed Ru nanosheets in the Ru/Ni cathode effectively promote the decomposition of discharge product Li2CO3 and thus reduce the charge overpotential. Moreover, the typical porous and binder-free Ru/Ni electrode not only has a sturdy construction to suppress the side reaction in the Li–CO2 batteries, but also enables the rapid permeation of CO2 and electrolyte/electron into the active sites of the Ru/Ni electrode. As a result, the Ru/Ni cathode-based Li–CO2 battery exhibits the superior discharge capacity (9502 mAh g−1), good coulombic efficiency (95.4%) and excellent rate performance (3177 mAh g−1 at 500 mA g−1) at the full discharge/charge condition. When operated at the limited capacity of 1000 mAh g−1, this cell can run for over 100 cycles with the charge potential below 4.1 V. The findings provide a snapshot towards improving the reversibility of Li–CO2 batteries by designing the binder-free stable cathodes.