Combining Ultrafine Co₃V₂O₈ Nanoparticles and Hollow Carbon Spheres for Lithium Storage Applications

Large volume changes and low electronic conductivity limit the advancement of mixed metal vanadate oxides as anode materials in lithium-ion batteries. Herein, ultrafine Co3V2O8 nanoparticles with a diameter of 7–9 nm are embedded in situ within the walls of hollow carbon combination spheres (HCCSs) through spray drying and calcination process. Each unit sphere of HCCS has an internal cavity of 170 nm and a wall thickness of 12 nm. When tested in lithium-ion half-cells, Co3V2O8/HCCS sustains a high reversible capacity of 1043 mAh g–1 at 0.2 A g–1 after 120 cycles, 832 mAh g–1 at 0.5 A g–1 after 580 cycles, and 759 mAh g–1 at 1.0 A g–1 after 800 cycles. Kinetics investigation uncovers a noticeable pseudocapacitive effect. Li+ diffusion coefficient ranges from 1.12 × 10–12 to 6.62 × 10–14 cm2 s–1. Electrochemical impedance spectroscopy revealed low Ohmic resistance and charge transfer resistance, confirming efficient Li+ diffusion. The full cell also exhibits excellent cycling performance and rate capability. The exceptional electrochemical performance is associated with the unique hollow carbon combination sphere and the embedded structure of ultrafine Co3V2O8 nanoparticles. The former improves the structural strength, facilitates ion transport and electronic conduction, and prevents Co3V2O8 detachment from the composite. The latter further suppresses the volume variation of Co3V2O8 and enhances its electrochemical activity.