LixMnO2 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 super capacitors are assembled using LixMnO2 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.