▎ 摘　　要

We systematically diagnose here the various phases formed at the electrodes in a Li-CO2 battery. The CO2 cathode comprises a mixture of two-dimensional electrocatalysts, MXene and graphene oxide (MXene/GO), configured on Ni foam. The observed overpotential for MXene/GO (2.4 V) is lower than that for GO (2.8 V). MXene/ GO also outperforms GO in terms of battery stability and performance. The overall battery reaction (Li2CO3 ? Li + CO2) is more efficient in the case of MXene/GO than in the case of GO. This is convincingly demonstrated using ex situ high-resolution synchrotron X-ray diffraction and Raman scattering spectroscopy, which strongly indicates that the MXene/ GO composite is more capable than GO in converting Li2CO3 to Li and CO2. When the Li anode is probed, CO2 crossover is evident via the observation of the formation of LiOH/ Li2CO3 phases, the proportions of which change during successive cycles.