Sandwich-like\nSnS₂/Graphene/SnS₂ with Expanded Interlayer\nDistance as High-Rate Lithium/Sodium-Ion\nBattery Anode Materials

Abstract

SnS₂ materials have attracted broad attention in the\nfield of electrochemical energy storage due to their layered structure\nwith high specific capacity. However, the easy restacking property\nduring charge/discharge cycling leads to electrode structure instability\nand a severe capacity decrease. In this paper, we report a simple\none-step hydrothermal synthesis of SnS₂/graphene/SnS₂ (SnS₂/rGO/SnS₂) composite with ultrathin\nSnS₂ nanosheets covalently decorated on both sides of reduced\ngraphene oxide sheets <i>via</i> C–S bonds. Owing\nto the graphene sandwiched between two SnS₂ sheets, the\ncomposite presents an enlarged interlayer spacing of ∼8.03\nÅ for SnS₂, which could facilitate the insertion/extraction\nof Li⁺/Na⁺ ions with rapid transport kinetics\nas well as inhibit the restacking of SnS₂ nanosheets during\nthe charge/discharge cycling. The density functional theory calculation\nreveals the most stable state of the moderate interlayer spacing for\nthe sandwich-like composite. The diffusion coefficients of Li/Na ions\nfrom both molecular simulation and experimental observation also demonstrate\nthat this state is the most suitable for fast ion transport. In addition,\nnumerous ultratiny SnS₂ nanoparticles anchored on the graphene\nsheets can generate dominant pseudocapacitive contribution to the\ncomposite especially at large current density, guaranteeing its excellent\nhigh-rate performance with 844 and 765 mAh g^–1 for\nLi/Na-ion batteries even at 10 A g^–1. No distinct\nmorphology changes occur after 200 cycles, and the SnS₂ nanoparticles still recover to a pristine phase without distinct\nagglomeration, demonstrating that this composite with high-rate capabilities\nand excellent cycle stability are promising candidates for lithium/sodium\nstorage.