Dual-Driven Ion/Electron Migration and Sodium Storage by In Situ Introduction of Copper Ions and a Carbon-Conductive...

Tin sulfide (SnS) has emerged as a promising anode material for sodium ion batteries (SIBs) due to its high theoretical capacity and large interlayer spacing. However, several challenges, such as severe insufficient electrochemical reactivity, rapid capacity degradation, and poor rate performance, still hinder its application in SIBs. In this study, in situ introduction of copper ions and a carbon conductive framework to form SnS nanocrystals embedded in a Cu₂SnS₃ lamellar structure heterojunction composite (SnS/Cu₂SnS₃/RGO) with graphene as the supporting material is proposed to achieve dual-driven sodium ion/electron migration during the continuous electrochemical process. The designed structure facilitates the preferential electrochemical reduction of copper ions into copper nanocrystals during the discharge process and functions as a catalytically active center to promote multivalence tin sodiation reaction. Furthermore, during the charging process, the presence of copper nanocrystals also facilitates efficient desodiation of NaSn and further activates to form higher valence state sulfides. As a result, the SnS/Cu₂SnS₃/RGO composite demonstrates high cycling stability with a high reversible capacity of 395 mAh g^-1 at 5A g^-1 after 500 cycles with a capacity retention of 85.6%. In addition, the assembled Na₃V₂(PO₄)₃∥SnS/Cu₂SnS₃/RGO sodium ion full cell achieves 93.7% capacity retention after 80 cycles at 0.5 A g^-1.