Oxygen-reduced surface-terminated MXenes as cathodes for enhanced reversible Li–CO2 batteries

Li–CO₂ batteries have garnered global attention due to their dual attributes of high energy density and effective CO₂ capture. However, they still face a formidable challenge in decomposing the discharge products Li₂CO₃, resulting in subpar battery performance. MXene has been proposed as a promising candidate owing to its high electrical conductivity and effective CO₂ activation performance. Nevertheless, unavoidable surface terminations (such as –O and –OH) during synthesis strongly influence their catalytic properties, posing a significant hurdle for high-performance Li–CO₂ batteries. Herein, a thermal annealing approach is proposed to control the surface termination groups of MXene to reduce the generation of lithium hydroxide byproducts, thereby accelerating Li₂CO₃ decomposition kinetics and enhancing the reversibility of the battery. The systematic annealing of MXene in the range of 500–800 °C confirmed optimal surface terminations at 500 °C (TC500). The TC500, when tested as a catalyst in a Li–CO₂ battery, exhibited enhanced performance metrics, such as low voltage gap (1.98 V), high specific capacity (15,740.38 mA h g⁻¹ at 100 mA g⁻¹), and prolonged cycle stability (700 h at 200 mA g⁻¹). The proposed work offers an effective strategy for regulating MXene surface termination groups via simple annealing treatments to achieve high-performance Li–CO₂ batteries.