Multicore–Shell Bi@N‐doped Carbon Nanospheres for High Power Density and Long Cycle Life Sodium‐ and Potassium‐Ion Anodes

Bismuth (Bi) is an attractive material as anodes for both sodium‐ion batteries (NIBs) and potassium‐ion batteries (KIBs), because it has a high theoretical gravimetric capacity (386 mAh g −1 ) and high volumetric capacity (3800 mAh L −1 ). The main challenges associated with Bi anodes are structural degradation and instability of the solid electrolyte interphase (SEI) resulting from the huge volume change during charge/discharge. Here, a multicore–shell structured Bi@N‐doped carbon (Bi@N‐C) anode is designed that addresses these issues. The nanosized Bi spheres are encapsulated by a conductive porous N‐doped carbon shell that not only prevents the volume expansion during charge/discharge but also constructs a stable SEI during cycling. The Bi@N‐C exhibits unprecedented rate capability and long cycle life for both NIBs (235 mAh g −1 after 2000 cycles at 10 A g −1 ) and KIBs (152 mAh g −1 at 100 A g −1 ). The kinetic analysis reveals the outstanding electrochemical performance can be attributed to significant pseudocapacitance behavior upon cycling.