Synergistic effect of bifunctional catalytic sites and defect engineering for high-performance Li–CO2 batteries

Abstract Li–CO2 batteries have been regarded as a promising energy storage system due to their high energy density, CO2 fixation ability and environmental friendliness. However, Li–CO2 batteries are still suffering from large overpotential and poor cycling performance, which severely hinder their practical applications. Therefore, it is vital to design highly efficient cathode catalysts to improve the performance of Li–CO2 batteries. Here, we designed a highly efficient synergistic catalyst by incorporating ultrafine Ru nanoparticles on N, S co-doped graphene (Ru/NS-G) as cathode for Li–CO2 batteries. The ultrafine Ru catalyst can reduce the decomposition voltage of the discharge product Li2CO3. In addition, N, S co-doped graphene (NS-G) with a three-dimensional structure provides excellent conductivity and adequate space for the reversible reactions in batteries. The Ru/NS-G catalyst achieves enhanced catalytic activities for the CO2 reduction/evolution reactions, assigned to the strong synergistic effect between the bifunctional catalyst Ru nanoparticles and the NS-G substrate with numerous defect structures and accessible active sites. The batteries achieve an impressive discharge capacity (12,448 ​mA ​h ​g−1 ​at a current density of 100 ​mA ​g−1), high Coulombic efficiency (94.6%) and excellent cycling stability (over 100 cycles) with a low overpotential of 1.40 ​V. This work provides an engineering strategy on the cathode design for metal-gas batteries and other devices that are not limited to Li–CO2 batteries.