Carbon layer-confined MoS2/Ni3S2 heterostructure with enhanced sodium and potassium storage performance

Transitional metal sulfides have received widespread attention as efficient anode materials for sodium-/potassium-ion batteries (SIBs/PIBs), benefitting from their high theoretical capacities and strong structural reversibility. Nevertheless, their poor electrical conductivity and severe volume variation result in unsatisfactory performance, seriously hindering their practical applications. Herein, a robust carbon layer-confined MoS2/Ni3S2 heterostructure (MoS2/Ni3S2@C) was designed and synthesized by a facile one-step hydrothermal method with a subsequent sulfidation process. The Ni3S2 ultrafine nanoparticles are embedded between ultrathin MoS2 nanosheets, which are surrounded by a thin carbon layer. When used as an anode material for SIBs and PIBs, the heterostructure displays high specific capacities, excellent cycling stability and outstanding rate capability. The superior performance results from the elaborate heterostructure, which forms numerous heterointerfaces, provides more Na+/K+ storage sites, shortens the Na+/K+ diffusion path and accelerates the charge transfer. Moreover, the carbon layer confinement further promotes the electrical conductivity, enhances the reaction kinetics and accommodates the volume expansion of the heterostructure. The sodium/potassium reaction mechanism and the performance enhancement origin of MoS2/Ni3S2@C were verified by kinetic analyses, multiple ex situ characterizations and density functional theory (DFT) calculations. The carbon layer-confined heterostructure strategy could shed light on the rational design of bimetallic sulfides for high-performance SIBs/PIBs.