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 degrees C confirmed optimal surface terminations at 500 degrees 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.