Elucidating the role of graphene and porous carbon coating on nanostructured Sb2S3 for superior lithium and sodium storage

Abstract Antimony sulfide (Sb2S3) is a promising anode for alkali metal ion batteries owing to its high theoretical specific capacity derived from sequential conversion and alloying reactions with lithium/sodium. However, volume variance during (de)lithiation/(de)sodiation complemented with sluggish reaction kinetics leads to severe capacity decay and cycle instability. Carbon in various forms has been explored with Sb2S3 to absorb the volumetric strain by rationale materials and electrode design. However, identifying the suitable carbon composite structure for improved electrochemical performance in lithium-ion and sodium-ion batteries remains a subject of investigation. The present work sheds light on the difference between lithium and sodium storage behavior in Sb2S3/carbon composite by designing two different structures. Therefore, a core-shell structure of Sb2S3 nanoparticle confined within a porous carbon shell (~100 nm thick) and Sb2S3 nanoparticles reinforced with planar graphene sheets were synthesized, followed by binder-free electrode fabrication by electrophoretic deposition. The electrochemical results demonstrate that core-shell Sb2S3@C shows improved electrochemical performance in lithium-ion batteries with rate capacity reaching ~215 mAh.g−1 at ~4 Ag−1 current rate and long cycle life (~283 mAh.g−1 at ~1Ag−1 over 500 cycles with ~99.6% Coulombic efficiency). On the contrary, Sb2S3/RGO showed favorable results in sodium-ion batteries with an average specific capacity of ~300 mAh.g−1 at ~0.1 Ag−1 current rate up to 100 cycles and good rate capability (~210 mAh.g−1 at ~1 Ag−1 current rate with ~99% Coulombic efficiency). The difference electrochemical performance of Sb2S3@C and Sb2S3/RGO in lithium-ion and sodium-ion batteries attributed to the difference in charge transfer resistance, SEI resistance, and phase evolution as confirmed by electrochemical impedance spectroscopy, ex situ XANES, and XRD study of cycled electrodes. Also, superior Na-ion and Li-ion reaction kinetics in Sb2S3/RGO and Sb2S3@C was verified by diffusion coefficient (DNa and DLi) measurements. These results demonstrate that Sb2S3/carbon composite architecture selection is an important factor for designing conversion-cum-alloy anodes in lithium and sodium batteries.