Highly stable H2V3O8/Mxene cathode for Zn-ion batteries with superior rate performance and long lifespan

Low electrical conductivity of the cathode for rechargeable aqueous Zn-ion batteries (RAZIBs) significantly limits the rate capability and shortens the cycling life. Herein, a highly stable composite is developed as a promising cathode by directly growing non-oriented H2V3O8 nanowires on 2D Mxene sheets. This composite architecture shows enhanced electrical conductivity and faster diffusion for charge transportation, resulting in improved rate performance and prolonged cycling life. Compared with the pristine H2V3O8 (306 mAh·g−1 at 0.2 A·g−1 and 900 cycles at 5 A·g−1), the resultant H2V3O8/Mxene composite exhibits larger specific capacities (365 mAh·g−1 at 0.2 A·g−1) and longer cycling life (≈84% capacity retention over 5600 cycles at 5 A·g−1). Even at 10 and 20 A·g−1, this composite cathode also delivers capacities of 164 and 73 mAh·g−1 for over 1900 and 500 cycles, respectively. Such superior electrochemical performance of RAZIB is ascribed to the enhanced electrical conductivity and improved charge transport kinetics. Furthermore, the reversible co-intercalation electrochemical reaction mechanism of Zn2+ and water was systemically demonstrated through various ex-situ characterizations. Additionally, highly safe and flexible solid-state ZIBs with polyacrylamide/cellulose nanofiber (CNF) hydrogel electrolyte deliver high capacities (317.4 mAh·g−1 at 0.2 A·g−1) and long cycle life (over 6600 cycles at 10 A·g−1). The solid-state batteries are still workable even at different harsh environments, such as freezing at −18 ℃ (152.5 mAh·g−1 at 0.5 A·g−1) and heating at 40 ℃ (307.3 mAh·g−1 at 0.5 A·g−1).