Combining Ultrafine Co<sub>3</sub>V<sub>2</sub>O<sub>8</sub> Nanoparticles and Hollow Carbon Spheres for Lithium Storage\nApplications

Large\nvolume changes and low electronic conductivity limit the\nadvancement of mixed metal vanadate oxides as anode materials in lithium-ion\nbatteries. Herein, ultrafine Co<sub>3</sub>V<sub>2</sub>O<sub>8</sub> nanoparticles with a diameter of 7–9 nm are embedded in situ\nwithin the walls of hollow carbon combination spheres (HCCSs) through\nspray drying and calcination process. Each unit sphere of HCCS has\nan internal cavity of 170 nm and a wall thickness of 12 nm. When tested\nin lithium-ion half-cells, Co<sub>3</sub>V<sub>2</sub>O<sub>8</sub>/HCCS sustains a high reversible capacity of 1043 mAh g<sup>–1</sup> at 0.2 A g<sup>–1</sup> after 120 cycles, 832 mAh g<sup>–1</sup> at 0.5 A g<sup>–1</sup> after 580 cycles, and 759 mAh g<sup>–1</sup> at 1.0 A g<sup>–1</sup> after 800 cycles.\nKinetics investigation uncovers a noticeable pseudocapacitive effect.\nLi<sup>+</sup> diffusion coefficient ranges from 1.12 × 10<sup>–12</sup> to 6.62 × 10<sup>–14</sup> cm<sup>2</sup> s<sup>–1</sup>. Electrochemical impedance spectroscopy revealed\nlow Ohmic resistance and charge transfer resistance, confirming efficient\nLi<sup>+</sup> diffusion. The full cell also exhibits excellent cycling\nperformance and rate capability. The exceptional electrochemical performance\nis associated with the unique hollow carbon combination sphere and\nthe embedded structure of ultrafine Co<sub>3</sub>V<sub>2</sub>O<sub>8</sub> nanoparticles. The former improves the structural strength,\nfacilitates ion transport and electronic conduction, and prevents\nCo<sub>3</sub>V<sub>2</sub>O<sub>8</sub> detachment from the composite.\nThe latter further suppresses the volume variation of Co<sub>3</sub>V<sub>2</sub>O<sub>8</sub> and enhances its electrochemical activity.