Sandwich-like SnS2/Graphene/SnS2 with Expanded Interlayer Distance as High-Rate Lithium/Sodium-Ion Battery Anode Materials

SnS₂ materials have attracted broad attention in the field of electrochemical energy storage due to their layered structure with high specific capacity. However, the easy restacking property during charge/discharge cycling leads to electrode structure instability and a severe capacity decrease. In this paper, we report a simple one-step hydrothermal synthesis of SnS₂/graphene/SnS₂ (SnS₂/rGO/SnS₂) composite with ultrathin SnS₂ nanosheets covalently decorated on both sides of reduced graphene oxide sheets via C-S bonds. Owing to the graphene sandwiched between two SnS₂ sheets, the composite presents an enlarged interlayer spacing of ∼8.03 Å for SnS₂, which could facilitate the insertion/extraction of Li⁺/Na⁺ ions with rapid transport kinetics as well as inhibit the restacking of SnS₂ nanosheets during the charge/discharge cycling. The density functional theory calculation reveals the most stable state of the moderate interlayer spacing for the sandwich-like composite. The diffusion coefficients of Li/Na ions from both molecular simulation and experimental observation also demonstrate that this state is the most suitable for fast ion transport. In addition, numerous ultratiny SnS₂ nanoparticles anchored on the graphene sheets can generate dominant pseudocapacitive contribution to the composite especially at large current density, guaranteeing its excellent high-rate performance with 844 and 765 mAh g^-1 for Li/Na-ion batteries even at 10 A g^-1. No distinct morphology changes occur after 200 cycles, and the SnS₂ nanoparticles still recover to a pristine phase without distinct agglomeration, demonstrating that this composite with high-rate capabilities and excellent cycle stability are promising candidates for lithium/sodium storage.