Mechanically and kinetically reinforced bismuth/carbon microsheets anode for high-power and low-temperature sodium-ion capacitors

Sodium-ion capacitors (SICs), recognized for their low cost, safety and high-power output capabilities, have emerged as a promising complement to sodium-ion batteries. However, their hybrid design, which integrates a sluggish battery-type negative electrode with a fast capacitive positive electrode, presents a significant challenge: kinetics mismatch. This mismatch often results in reduced energy delivery at high rates. Herein, we introduce a novel composite structure where metallic Bi nanoparticles are uniformly embedded within amorphous carbon microsheets (referred to as Bi-C). This innovative design effectively mitigates the Na⁺ diffusion limitations and the substantial volume changes of Bi during sodiation, facilitating rapid and durable alloying processes. This Bi-C composite anode then can operate efficiently at high rates exceeding 100.0 A g^-1 and maintains stability over 10,000 cycles, effectively bridging the kinetic gap with a capacitive porous carbon cathode. A SIC based on this kinetically and mechanically optimized Bi-C composite anode achieves unprecedented levels of energy and power outputs, delivering a maximum energy density of 131 Wh kg^-1, an exceptionally high specific power of 112.5 kW kg^-1, and a long cycling life over 20,000 cycles. Moreover, this SIC demonstrates stable performance even at low temperatures down to -40°C.