Li4.4Sn encapsulated in hollow graphene spheres for stable Li metal anodes without dendrite formation for long cycle-life of lithium batteries

Abstract

Lithium (Li) metal has always faced serious challenges of dendritic growth and low Coulombic efficiency due to the nonuniform electric field distribution and the dynamically changed interface situation. In this paper, the interconnected and closed hollow graphene spheres with an internal load of lithiophilic Li4.4Sn nanoparticles (Li4.4Sn/SG) is prepared to improve Li deposition behavior. Both the density functional theory calculations and experimental studies indicate that Li4.4Sn has higher binding energy and lower nucleation overpotential toward Li than graphene, thus guiding the deposition of Li metal inside the hollow graphene spheres to avoid the generation of uncontrolled Li dendrites and formation of solid electrolyte interface (SEI) on the fresh Li surface. Furthermore, the surface of the non-tip graphene spheres can greatly avoid the uneven distribution of charge caused by the tip effect, so as to continuously guide the uniform deposition of Li on the surface of the spheres after the spheres are completely filled with Li, thus achieving a dense Li metal layer free of dendrites. In consequence, the Li4.4Sn/SG electrode exhibits a long lifespan up to 1000 h and an exceptionally low overpotential (<18 mV). It is believed that the design of the closed hollow spherical structure with lithiophilic nanoparticle seeds inside is a promising strategy to construct high performance Li metal anodes for lithium batteries.