Preparation of Expanded Graphite-VO₂ Composite Cathode Material and Performance in Aqueous Zinc-Ion Batteries

Due to safety problems caused by the use of organic electrolytes in lithium-ion batteries and the high production cost brought by the limited lithium resources, water-based zinc-ion batteries have become a new research focus in the field of energy storage due to their low production cost, safety, efficiency, and environmental friendliness. This paper focused on vanadium dioxide and expanded graphite (EG) composite cathode materials. Given the cycling problem caused by the structural fragility of vanadium dioxide in zinc-ion batteries, the feasibility of preparing a new composite material is explored. The EG/VO₂ composites were prepared by a simple hydrothermal method, and compared with the aqueous zinc-ion batteries assembled with a single type of VO₂ under the same conditions, the electrode materials composited with high-purity sulfur-free expanded graphite showed more excellent capacity, cycling performance, and multiplicity performance, and the EG/VO₂ composites possessed a high discharge ratio of 345 mAh g^-1 at 0.1 A g^-1, and the Coulombic efficiency was close to 100%. The EG/VO₂ composite has a high specific discharge capacity of 345 mAh g^-1 at 0.1 A g^-1 with a Coulombic efficiency close to 100%, a capacity retention of 77% after 100 cycles, and 277.8 mAh g^-1 with a capacity retention of 78% at a 20-fold increase in current density. The long cycle test data demonstrated that the composite with expanded graphite effectively improved the cycling performance of vanadium-based materials, and the composite maintained a stable Coulombic efficiency of 100% at a high current density of 2 A/g and still maintained a specific capacity of 108.9 mAh/g after 2000 cycles.