Tunable synthesis of LixMnO2 nanowires for aqueous Li-ion hybrid supercapacitor with high rate capability and ultra-long cycle life

Li_xMnO₂ nanowires with controllable morphology and excellent electrochemical performance are synthesized by a hydrothermal method with tunable lithium contents. Both double layer capacitive process and diffusion-controlled Faradaic process play roles in the charging-discharging process. Aqueous Li-ion hybrid supercapacitors are assembled using Li_xMnO₂ nanowires as the positive electrode and activated carbon as the negative electrode. The hybrid devices deliver high energy density of 88.56 Wh kg^-1 and 25.2 Wh kg^-1 at the high power density of 151.8 W kg^-1 and 2155.8 W kg^-1, respectively. The device also shows superb cycling life with capacitance retention of 95.2% after 10,000 cycles and 85.2% after 20,000 cycles.