Closely packed Si@C and Sn@C nano-particles anchored by reduced graphene oxide sheet boosting anode performance of lithium ion batteries

Abstract

Both silicon and tin are promising anodes for new generation lithium ion batteries due to high lithium storage capacities (theoretically 4200 mA h g−1 and 992 mA h g-1, respectively). However, their large volumetric expansions (both are above 300 %) usually lead to poor cycling stability. In this case, we synthesized closely packed Si@C and Sn@C nano-particles anchored by reduced graphene oxide (denoted as Si@C/Sn@C/rGO) by the way of solution impregnation and subsequent hydrogenation reduction. Sn particles with a diameter of 100 nm are coated by carbon and surrounded by Si@C particles around 40 nm in average diameter through the high-resolution transmission electron microscopy. Expansions of Si and Sn are alleviated by carbon shells, and reduced graphene oxide sheets accommodate their volume changes. The prepared Si@C/Sn@C/rGO electrode delivers an enhanced initial coulombic efficiency (78 %), rate capability and greatly improved cycle stability (a high reversible capacity of nearly 1000 mA h g−1 is achieved after 300 cycles at a current density of 1000 mA g−1). It can be believed that packing Sn@C nano-particles with Si@C relieves the volume expansion of both and releases the expansion stresses. Sn@C particles enhance anode process kinetics by reducing charge transfer resistance and increasing lithium ion diffusion coefficient. The present work provides a viable strategy for facilely synthesizing silicon-tin-carbon composite anode with long life.