Encapsulation of MnS Nanocrystals into N, S-Co-doped Carbon as Anode Material for Full Cell Sodium-Ion Capacitors

Sodium-ion capacitors (SICs) have received increasing interest for grid stationary energy storage application due to their affordability, high power, and energy densities. The major challenge for SICs is to overcome the kinetics imbalance between faradaic anode and non-faradaic cathode. To boost the Na⁺ reaction kinetics, the present work demonstrated a high-rate MnS-based anode by embedding the MnS nanocrystals into the N, S-co-doped carbon matrix (MnS@NSC). Benefiting from the fast pseudocapacitive Na⁺ storage behavior, the resulting composite exhibits extraordinary rate capability (205.6 mAh g^-1 at 10 A g^-1) and outstanding cycling stability without notable degradation after 2000 cycles. A prototype SIC was demonstrated using MnS@NSC anode and N-doped porous carbon (NC) cathode; the obtained hybrid SIC device can display a high energy density of 139.8 Wh kg^-1 and high power density of 11,500 W kg^-1, as well as excellent cyclability with 84.5% capacitance retention after 3000 cycles. The superior electrochemical performance is contributed to downsizing of MnS and encapsulation of conductive N, S-co-doped carbon matrix, which not only promote the Na⁺ and electrons transport, but also buffer the volume variations and maintain the structure integrity during Na⁺ insertion/extraction, enabling its comparable fast reaction kinetics and cyclability with NC cathode.