Significant contribution of single atomic Mn implanted in carbon nanosheets to high-performance sodium-ion hybrid capacitors

Sodium-ion hybrid capacitors (SIHCs) hold great promise in large-scale energy storage by compromising the merits of sodium-ion batteries and electrochemical capacitors; however, the mismatch of kinetics and capacity between battery-type anode and capacitive-type cathode is still the Achilles' heel of this technology. Herein, nanohybrids with Mn single atoms implanted in N, F co-doped ultrathin porous carbon nanosheets (MnSAs/NF-CNs) have been developed as both the anode and cathode of SIHCs. The systematic experimental study coupled with theoretical calculations reveal that N-coordinated Mn atoms (Mn-N 4 ) can act as sites not only for reversible Na + storage with reduced energy barrier but also for improving the pseudocapacitance, thus making great contribution to accelerating the reaction kinetics of the anode and enhancing the capacity for the cathode in SIHCs. We demonstrate that the Janus-featured MnSAs/NF-CNs endows SIHCs with an impressively high energy/power density (maximum 197 W h kg −1 /9350 W kg −1 ) and ultralong cycling life over 10 000 cycles. Single Mn atoms in carbon nanosheets with compatible properties can compromise the kinetics and capacity mismatches between the anode and cathode for sodium-ion hybrid capacitors.