Facile Construction of Nano-Dimensional Bi Encapsulated in N-Doped Porous Carbon Frameworks for High-Performance Sodium-Ion Hybrid Capacitors

As a promising anode candidate for sodium storage, the adhibition of metallic Bi is limited by severe volume expansion and modest conductivity. To solve the issues, optimizing and designing both structures and compositions of Bi-based anodes are highly necessary. Herein, Bi nanoparticles encapsulated in N-doped porous carbon frameworks (Bi@NPC) are synthesized via a facile but efficient chemical blowing method. The size and dispersion of Bi NPs in the interconnected carbon frameworks are accurately adjusted through the control of reaction temperatures and nitrogen doping. Thanks to its attractive structural/componential merits, the optimized Bi@NPC anode shows that an excellent high-rate capability of 207.6 mA h g –1 is achieved at a high rate of 50 A g –1 . In addition, it can still present a stable reversible capacity of 243.9 mA h g –1 over 2000 cycles at 10 A g –1 . Furthermore, the assembled sodium-ion hybrid capacitors with Bi@NPC as the anode and commercial active carbon as the cathode realize an exceptional energy/power density of 94.2 W h kg –1 /200 W kg –1 and a low capacity decay rate of 0.014% per cycle for 2400 cycles at 1 A g –1 . The contribution here will guide future design of alloy-type anode materials toward advanced sodium-ion hybrid capacitors.