Bismuth nanospheres embedded in three-dimensional (3D) porous graphene frameworks as high performance anodes for sodium- and potassium-ion batteries

Bismuth (Bi) has been demonstrated as a promising anode material for both Na-ion batteries (NIBs) and K-ion batteries (KIBs) due to its high theoretical capacity (385mA h g(-1) for NIBs and KIBs). However, Bi undergoes a huge volume change during charge-discharge processes, leading to severe pulverization of Bi particles and structural degradation. Herein, a robust composite possessing a three-dimensional (3D) structure with Bi nanoparticles embedded in 3D macroporous graphene frameworks (Bi@3DGFs) is designed to address these issues. This 3D porous Bi@3DGF composite demonstrates high capacity and stable long-term cycling performance at various current densities for both NIBs and KIBs. As an anode for NIBs, it shows a reversible capacity of 180 mA h g(-1) at a current density as high as 50 A g(-1). The rate capability for KIBs is also unprecedented; it delivers a reversible capacity of 185.2 mA h g(-1) after 2000 cycles at a current density of 10 A g(-1). The excellent electrochemical performance of the Bi@3DGFs is ascribed to the unique structure. The 3D interconnecting pores facilitate the penetration of the electrolyte, leading to direct contact between electrochemically active Bi and the electrolyte, enhancing charge transfer kinetics.