Enhanced sodium storage in MXene transition metal chalcogenides anode through dual molten salt etching

Abstract

Referred to as potential options for anodes in sodium-ion batteries, transition metal chalcogenides (TMCs) exhibit unique electronic and structural characteristics. However, the limited electrical conductivity inherent in them poses a hindrance to electron transport, while their tendency to undergo volumetric expansion during cycling exacerbates structural instability, thereby imposing constraints on practical applications. Herein, a dual molten salt etching strategy followed by a sulfidation-selenidation process was employed to anchor multi-component sulfides FeS₂/NiS and FeSe/NiSe onto conductive Ti₃C₂T_x MXene, achieving superior sodium storage performance. Owing to the enhanced Na⁺ and faster kinetics of electronic transport, mechanical strain is effectively reduced, and strong covalent interactions are formed at the interface, significant enhancement in the cycling stability is observed for the anodes of Ti₃C₂T_x@FeS₂/NiS and Ti₃C₂T_x@FeSe/NiSe (with specific capacities of 309.4 and 162.6 mAh g⁻¹, respectively, after 1000 cycles at 5 A g⁻¹, with a former retention capacity rate that can reach as high as 87.8 %) and exceptional rate performance (252.1 and 207.8 mAh g⁻¹, respectively, at 8 A g⁻¹). Furthermore, full cells assembled by pairing Ti₃C₂T_x@FeS₂/NiS and Ti₃C₂T_x@FeSe/NiSe with Na₃V₂(PO₄)₃ cathodes also demonstrate excellent cycling performance, with both configurations achieving up to 500 cycles. The suggested approach enables efficient utilization of byproducts from Lewis acidic etching, expanding possibilities for synthesizing high-performance anodes in sodium-ion batteries consisting of MXene and TMCs.