Formation of toroidal Li 2 O 2 in non-aqueous Li-O 2 batteries with Mo 2 CT x MXene/CNT composite.

Due to the growing demand for high energy density devices, Li-O 2 batteries are considered as a next generation energy storage system. The battery performance is highly dependent on the Li 2 O 2 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 Li 2 O 2 formation pathway by using Mo 2 CT x MXene on a catalyst support. The cathode was fabricated by mixing the positively charged CNT/CTAB solution with the negatively charged Mo 2 CT x solution. After introducing Mo 2 CT x , important battery performance metrics were considerably enhanced. More importantly, the discharge product analysis showed that the functional groups on the surface of Mo 2 CT x inhibit the adsorption of O 2 on the cathode surface, resulting in the formation of toroidal Li 2 O 2 via the solution growth model. It was supported by density functional theory (DFT) calculations that adsorption of O 2 on the Mo 2 CT x surface is implausible due to the large energy penalty for the O 2 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 Li 2 O 2 morphology.