Active Component Design of Amorphous SnP_x/SnS_x and Interfacial Bonding Engineering in N/P/S-Doped Hard Carbon for High-Rate Sodium-Ion Hybrid Capacitors

Sodium-ion hybrid capacitors （SIC）face critical challenges from the kinetic mismatch and cycling life imbalance between battery-type anodes and capacitive cathodes. A slope-dominant N/P/S-doped hard carbon anode (Sn0.1@NSPC) with nearly plateau-free sloping charge–discharge curves, embedded with amorphous SnP_x/SnS_x composites, is developed. This unique design delivers a high reversible capacity of 412.8 mAh g⁻¹ at 0.05 A g⁻¹ while retaining 180.7 mAh g⁻¹ at 10 A g⁻¹, coupled with 90% capacity retention over 10 000 cycles. The amorphous SnP_x/SnS_x enables isotropic Na⁺ diffusion and volume expansion suppression, while interfacial Sn─P/Sn─S bonding activates the redox potential of P/S for sodium storage through reversible Na₃P/Na₂S formation. Density functional theory calculations demonstrate that Sn doping enhances electronic states near the Fermi level and reduces sodium-ion diffusion barriers, improving conductivity and ion transport. Pseudocapacitive-dominated kinetics with reduced charge transfer resistance are achieved, synergizing with alloying/conversion reactions. In SIC paired with activated carbon, the system exhibits an energy density of 360 Wh kg⁻¹ (anode-mass-based), a power density of 38 kW kg⁻¹, and 91% capacity retention after 3000 cycles. This work establishes a universal heterostructure design via amorphous engineering and interfacial coupling, addressing trade-offs between high capacity, rapid kinetics, and long-term cycling stability in advanced SIC.