Mildly Oxidized MXene (Ti3C2, Nb2C, and V2C) Electrocatalyst via a Generic Strategy Enables Longevous Li-O2 Battery under a High Rate.

Lithium-oxygen batteries (LOBs) with ultrahigh theoretical energy density have emerged as one appealing candidate for next-generation energy storage devices. Unfortunately, some fundamental issues remain unsettled, involving large overpotential and inferior rate capability, mainly induced by the sluggish reaction kinetics and parasitic reactions at the cathode. Hence, the pursuit of suitable catalyst capable of efficiently catalyzing the oxygen redox reaction and eliminating the side-product generation, become urgent for the development of LOBs. Here, we report a universal synthesis approach to fabricate a suite of mildly oxidized MXenes (mo-Nb2CTx, mo-Ti3C2Tx, and mo-V2CTx) as cathode catalysts for LOBs. The readily prepared mo-MXenes possess expanded interlayer distance to accommodate massive Li2O2 formation, and in-situ-formed light metal oxide to enhance the electrocatalytic activity of MXenes. Taken together, the mo-V2CTx manages to deliver a high specific capacity of 22752 mAh g-1 at a current density of 100 mA g-1, and a long lifespan of 100 cycles at 500 mA g-1. More impressively, LOBs with mo-V2CTx can continuously operate for 90, 89, and 70 cycles, respectively, under a high current density of 1000, 2000, and 3000 mA g-1 with a cutoff capacity of 1000 mAh g-1. The theoretical calculations further reveal the underlying mechanism lies in the optimized surface, where the overpotentials for the formation/decomposition of Li2O2 are significantly reduced and the catalytic kinetics is accelerated. This contribution offers a feasible strategy to prepare MXenes as efficient and robust electrocatalyst toward advanced LOBs and other energy storage devices.