Controlling ligand field of Li3VO4 to enhance the electrochemical performance for lithium-ion batteries
摘要
Electrochemical potential and ion diffusion of electrode materials restrain the energy and power densities of lithium-ion batteries, and these challenges also remain in the intercalation-type Li3VO4 (LVO). In this work, the local [VO4] coordination symmetry in LVO is broken by a higher concentration of oxygen vacancies (Vö), resulting in an increased average V–O bond length and a larger ligand field splitting. These alterations reduce the energy level of the lowest unoccupied orbitals (e*) and lift the electrochemical potential, resulting in a higher voltage output. Additionally, the broken local symmetry in Vö-LVO is found to reduce the band gap and expand the ion transport channels, which favors enhancing electronic conductivity and facilitates ion diffusion, thereby improving the electrochemical kinetics in the energy storage process. The local symmetry broken sample (Vö-LVO) achieves a significantly improved capacity of 532 mAh/g at 0.1 A/g in comparison with 394 mAh/g of pristine LVO, and long cycling stability with retained capacity of 398 mAh/g at 1 A/g over 500 cycles compared with 236 mAh/g of the pristine LVO. The fundamental understanding paves the way to exploit high-performance electrodes via ligand field engineering for next-generation rechargeable batteries.