Unique Spindle-Like Bismuth-Based Composite toward Ultrafast Potassium Storage.

Bismuth (Bi)-based materials have attracted great attention as anodes in potassium ion batteries (PIBs) for their high theoretical capacity and suitable voltage range. Herein, the authors report a unique spindle-like structured Bi@N-doped carbon composite (SPB@NC) consisting of interconnected nano-Bi coated heteroatom-doped hard carbon layer via an interesting in situ carbon thermal reduction method. The special interconnected Bi nanoparticles gradually form porous structure with ample inner voids for accommodating volume variations while the N-doped carbon layer not only keeps the electrode stable, but also contributes to rapid electron/ion transfer. As a result, such a robust framework endows SPB@NC fast potassium storage with outstanding capacity of 276.5 mAh g-1  at 30 A g-1 (i.e., 1 min for discharge/charge) and durable cycling performance of 299.3 mAh g-1  at 5 A g-1  after 2000 cycles. Notably, a full cell assembled with potassium vanadate cathode is promising for practical applications. A series of ex situ techniques reveals the in-depth potassium storage mechanism and kinetics reactions. This work illuminates helpful insights into Bi-based anodes for PIBs.