Surface Selenization Strategy for V2CTx MXene toward Superior Zn-Ion Storage

MXenes are promising cathode materials for aqueous zinc-ion batteries (AZIBs) owing to their layered structure, metallic conductivity, and hydrophilicity. However, they suffer from low capacities unless they are subjected to electrochemically induced second phase formation, which is tedious, time-consuming, and uncontrollable. Here we propose a facile one-step surface selenization strategy for realizing advanced MXene-based nanohybrids. Through the selenization process, the surface metal atoms of MXenes are converted to transition metal selenides (TMSes) exhibiting high capacity and excellent structural stability, whereas the inner layers of MXenes are purposely retained. This strategy is applicable to various MXenes, as demonstrated by the successful construction of VSe2@V2CTx, TiSe2@Ti3C2Tx, and NbSe2@Nb2CTx. Typically, VSe2@V2CTx delivers high-rate capability (132.7 mA h g-1 at 2.0 A g-1), long-term cyclability (93.1% capacity retention after 600 cycles at 2.0 A g-1), and high capacitive contribution (85.7% at 2.0 mV s-1). Detailed experimental and simulation results reveal that the superior Zn-ion storage is attributed to the engaging integration of V2CTx and VSe2, which not only significantly improves the Zn-ion diffusion coefficient from 4.3 × 10-15 to 3.7 × 10-13 cm2 s-1 but also provides sufficient structural stability for long-term cycling. This study offers a facile approach for the development of high-performance MXene-based materials for advanced aqueous metal-ion batteries.