Fast lithium storage in defect-rich carbon encapsulated Fe3C nanoparticles as anode material toward high-energy lithium-ion capacitors

Lithium-ion capacitors (LICs) can combine the high energy density of battery-type electrode and high power density of capacitor-type electrode, which is considered as one of the most promising electrochemical storage devices. The challenge of developing superior performance LICs is designing suitable electrode materials to overcome the kinetic imbalance between the battery-type anode and the capacitor-type cathode. Herein, defect-rich carbon encapsulated Fe3C nanoparticle (Fe3C@DRC) was obtained via a modified sol-gel method with a calcination process. The defect-rich and microporous structure effectively boosts kinetics and provides additional reaction sites for lithium-ion intercalation/deintercalation process, which leads to an excellent capacity (215 mAh g(-1) at 1 A g(-1) after 800 cycles) and rate capability (128.8 mAh g(-1) even at 10 A g(-1)). Then a novel Fe3C@DRC//AC LIC was consisted using Fe3C@DRC as anode and activated carbon as cathode. The Fe3C@DRC//AC LIC demonstrates a wide potential window (0-4 V), delivers a high energy density of 187.8 Wh kg(-1) at a power density of 200 W kg(-1), reached a high power density of 4000 W kg(-1) at an energy density of 80 Wh kg(-1), and coupled with a reasonable life span (84.8% after 6000 cycles at a current density of 1 A g(-1)). The study indicates that the introduction of defect-rich strategy may push the practical application of high-rate and high-energy LIC anode materials in energy fields.