Core–shell structured carbon@tin sulfide@hard carbon spheres as high-performance anode for low voltage sodium-ion battery

Abstract

Transition metal sulfides (TMS) are promising candidates for sodium-ion battery anodes due to their high theoretical capacities. However, their practical application is limited by high operating voltages (vs. Na⁺/Na) and low initial Coulombic efficiency (ICE). In this study, we present the controlled synthesis of a core–shell structured composite, comprising tin sulfide (SnS) encapsulated within hard carbon microspheres (C@Sn_xS_y@HCS). This composite is prepared using a straightforward chemical bath deposition method followed by low-temperature annealing. The resulting material significantly lowers the average discharge voltage to 0.5 V vs. Na⁺/Na—a reduction of 71.4%—while achieving a relatively high ICE of 73.56%. The composite also exhibits excellent rate performance, delivering 212.5 mA h g⁻¹ at 5 A g⁻¹, and remarkable cycling stability, maintaining 153.3 mA h g⁻¹ after 1000 cycles at the same current density. The core–shell architecture effectively mitigates the volume expansion typically associated with tin sulfides, ensuring a stable solid electrolyte interphase (SEI) and robust electrode interface. This work offers a promising design strategy for developing low-voltage, high-performance sodium-ion battery anodes.