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.