Controllable construction of yolk–shell Sn–Co@void@C and its advantages in Na-ion storage

Abstract

In the family of anodes for sodium-ion batteries, alloy-type anodes possess higher theoretical specific capacity than carbon anodes. The theoretical specific capacity of metallic Sn is 847 mAh·g−1. However, the tin-based material undergoes a large volume expansion during the sodium-ion intercalation process, which leads to the crack and pulverization of the electrode, consequently resulting in a significant capacity loss. In this paper, a yolk–shell-structured Sn–Co@void@C composite composed of a Sn–Co alloy core, a carbon shell and void space between the core and shell is designed and synthesized. Compared with the carbon-encapsulated SnCo without void space (Sn–Co@C) and carbon-encapsulated pure Sn core shell with void space (Sn@void@C), this composite exhibits improved reversibility, cyclic performance and rate capability. This work highlights the important roles of Co in the alloy and the void space between the core and the shell. The former can not only buffer the volume expansion of Sn, but also act as an electrical conductor. The void space can further tolerate the volume expansion of the Sn–Co core. Owing to this unique microstructure, the Sn–Co@void@C composite shows an initial reversible capacity of 591.4 mAh·g−1, at a current density of 50 mA·g−1. After 100 charge/discharge cycles at 100 mA·g−1, the composite still delivers 330 mAh·g−1.