Oxygen Vacancy Modulated LiMn_xO_y@C Three-Dimensional Nanosheet Arrays on Nickel Foam for Lithium-Ion Capacitor with High Performance

The three-dimensional LiMnxOy@C (LMO@C) nanosheet arrays with rich oxygen vacancies were fabricated using a three-step method involving γ-MnO2 electrodeposition on Ni foam combined with hydrothermal lithiation and carbon coating. The open-framework and porous structure of the LMO@C can remarkably facilitate the fast insertion/extraction of lithium-ion and charge transfer. The introduced oxygen vacancies and conducting carbon-shell can significantly improve the electrochemical property of an integrated electrode. The LMO@C electrode presents a higher mass capacitance (239.2 mAh g–1 at 1 A g–1) and an enhanced cycling performance (nearly no decay after 10 000 cycles) compared with the LMO electrode. Additionally, a Li-ion capacitor (LIC) coin cell was assembled with Ni foam@LMO@C and activated carbon/Ni foam as the cathode and anode, respectively. The LIC can deliver 44.3 and 29.6 Wh kg–1 energy density at the power density of 800 and 8000 W kg–1, respectively, with superior cycling performance (80% capacitance retention after 4000 cycles). Thereby, the Ni foam@LMO@C electrode is promising for energy-storage devices due to its excellent electrochemical performance.