Nanostructure Engineering of Copper Sulfide Nanosheets Enables Reversible and Kinetically Boosted Magnesium Storage

Copper sulfide (CuS) is regarded as a highly promising cathode candidate for rechargeable magnesium batteries (RMBs) owing to its high theoretical specific capacity, stable voltage plateau, and low-cost merit. Nevertheless, the sluggish Mg2+ diffusion kinetics and severe structural degradation of conventional cathode materials severely restrict their practical application. Herein, a two-dimensional CuS nanosheet (CuS NS) cathode is rationally designed via nanostructure engineering to address the above challenges. Compared with CuS nanoparticle (CuS NP) and commercial CuS, the CuS NS electrode exhibits enhanced reversible capacity, reduced electrochemical polarization, superior rate performance, and excellent long-cycle stability. Kinetic analyses demonstrate that the nanosheet architecture effectively shortens Mg2+ migration pathways, promotes interfacial charge transfer, and realizes a synergistic diffusion-capacitive magnesium storage mechanism. Combined with ex situ XRD, XPS, and HRTEM characterizations, a reversible multi-step conversion reaction mechanism is clearly elucidated. The CuS NS cathode undergoes sequential phase transformation of CuS → Cu2S → metallic Cu during discharging and reconstructs its original crystal structure after charging. This work establishes a clear structure–performance relationship of CuS-based cathodes, providing an efficient structural optimization strategy and in-depth mechanistic insight for the development of high-performance sulfide cathode materials for advanced magnesium-ion batteries.