Formation of toroidal Li2O2 in non-aqueous Li–O2 batteries with Mo2CTx MXene/CNT composite

Abstract

Due to the growing demand for high energy density devices, Li–O₂ batteries are considered as a next generation energy storage system. The battery performance is highly dependent on the Li₂O₂ morphology, which arises from formation pathways such as the surface growth and the solution growth models. Thus, controlling the formation pathway is important in designing cathode materials. Herein for the first time, we controlled the Li₂O₂ formation pathway by using Mo₂CT_x MXene on a catalyst support. The cathode was fabricated by mixing the positively charged CNT/CTAB solution with the negatively charged Mo₂CT_x solution. After introducing Mo₂CT_x, important battery performance metrics were considerably enhanced. More importantly, the discharge product analysis showed that the functional groups on the surface of Mo₂CT_x inhibit the adsorption of O₂ on the cathode surface, resulting in the formation of toroidal Li₂O₂ via the solution growth model. It was supported by density functional theory (DFT) calculations that adsorption of O₂ on the Mo₂CT_x surface is implausible due to the large energy penalty for the O₂ adsorption. Therefore, the introduction of MXene with abundant functional groups to the cathode surface can provide a cathode design strategy and can be considered as a universal method in generating toroidal Li₂O₂ morphology.