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 can then 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.