N‑Doped\nCarbon Fiber-Encapsulated CoS₂/SnS₂ Heterostructures\nFacilitate Polysulfide Conversion\nfor Lithium–Sulfur Batteries

Abstract

Heterojunction structures as an advanced strategy may\npromote the\nsynergistic effect of different component materials; the rational\ndesign of heterojunctions allows them to exhibit various advantages\nwhen applied to lithium–sulfur batteries. Hollow CoSn(OH)₆ was used as a precursor, and polyacrylonitrile PAN and sulfur\npowder were used as raw materials. N-doped carbon nanofiber-encapsulated\nCoS₂/SnS₂ heterostructured materials CoS₂/SnS₂@CNFs were prepared by an electrostatic spinning\ntechnique and in situ vulcanization and applied to the lithium–sulfur\nbattery cathode. A hollow cubic material with structural stability\nand a physical domain-limiting effect, that is, the CoS₂/SnS₂ heterostructure, was effectively constructed, and\nrapid charge transfer was realized by a built-in electric field induced\nto form by the heterogeneous interface. Meanwhile, the fiber-like\nnetwork structure facilitates the wetting of the electrolyte and shortens\nthe ion transfer path. The results show that a CoS₂/SnS₂@CNFs@S-based battery exhibits an excellent electrochemical\nperformance. The initial discharge specific capacities were 1204.3\nmAh g^–1 at a current density of 0.1 C and 615.2\nmAh g^–1 at 4 C. The long-cycle performance showed\nthat the cells only exhibited an ultralow decay rate of 0.067% per\nweek on average after 1000 cycles at 2C. When the sulfur loading was\nincreased to 5.3 mg cm^–2 and the electrolyte/sulfur\nratio was 6 μL mg^–1, excellent cycling stability\nwas still demonstrated after 250 weeks of cycling at 0.2C.