Hierarchical/mesoporous V3S4@C/Graphene composite with conversion pseudocapacitance effect for a high-rate Mg-Li hybrid battery

As a next-generation energy storage system, the practical application of non-aqueous rechargeable Mg batteries (RMBs) is hindered by limited energy density and sluggish Mg²⁺ diffusion kinetics. To overcome these challenges, this study proposes a dual-carbon engineered cathode: a V-MOF-derived hierarchical mesoporous V₃S₄@C/graphene (V₃S₄@C/G) composite synthesized through high-temperature vulcanization and graphene hybridization. The pyrolyzed carbon framework mitigates volume expansion during cycling, while graphene enhances electronic conductivity and Mg²⁺/Li⁺ co-transport. Coupled with APC + LiCl/Mg hybrid electrolyte, the V₃S₄@C/G cathode delivers an exceptional initial discharge capacity of ∼500 mAh g⁻¹ at 100 mA g⁻¹, maintaining 83.5 % capacity retention after 100 cycles. Remarkably, the discharge capacity maintains 148 mAh g⁻¹ even after 2000 cycles at 1000 mA g⁻¹, outperforming conventional Mg battery cathodes. Mechanistic studies via ex-situ XRD/XPS uncover a two-step reaction pathway involving Mg²⁺/Li ⁺ intercalation followed by conversion to metallic V⁰ and Li₂S. DFT calculations reveal that sulfur vacancies in V₃S₄ and Li-affinity carbon interfaces synergistically enable pseudocapacitive charge storage, with reduced Li⁺ diffusion barriers of 0.28 eV. This work not only demonstrates a high-performance sulfide cathode design but also establishes a material optimization paradigm combining defect engineering and hybrid ion transport for multivalent batteries.