Organic Heterophase Composites Induced Sulfur Vacancies and Internal Electric Field Enhancement for Advanced Magnesium Storage of Copper Sulfide Cathodes

Abstract

Rechargeable magnesium-ion batteries (MIBs) hold significant promise for safe and efficient large-scale energy storage, but the lack of high-performance cathodes hinders their development for practical applications. In this work, a series of nanocomposites consisting of π-conjugated perylene-3,4,9,10-tetracarboxylic dianhydride annealed at 450 °C and copper sulfide (CuSP) are synthesized solvothermally to explore their utility as a host for Mg²⁺ storage in MIBs. The carbonyl organics in the hybrid materials modify the predominant CuS phase, expanding interlayer spacing and enriching sulfur vacancies through modifications of the internal electric field. This synergistic interaction enhances magnesium storage performance and accelerates reaction kinetics. Using chlorine-free Mg[B(hfip)₄]₂/DME electrolytes, the CuSP91 cathode containing an appropriate organic content displays a remarkably high reversible capacity of 285 mAh g⁻¹ at 50 mA g⁻¹, and demonstrates a stable capacity of 220 mAh g⁻¹ at 100 mA g⁻¹, surpassing pure CuS cathode in terms of shorter activation time. The CuSP91 cathode maintains a discharge capacity of 55 mAh g⁻¹ over 1000 cycles at 500 mA g⁻¹. A co-redox mechanism is revealed through in/ex situ investigations and analyses. Overall, this research contributes valuable insights targeting the development of advanced organic–inorganic hybrid composite cathode materials in next-generation energy storage systems.