Enhancing electrochemical performance by triggering a local structure distortion in lithium vanadium phosphate cathode for Li ion batteries

Abstract

The development of high-energy Li ion batteries (LIBs) with a long cycle life is essential for meeting the energy requirements in next-generation large-scale applications. Monoclinic Li₃V₂(PO₄)₃ has emerged as a promising cathode for high-energy LIBs owing to its robust three-dimensional structure, high working voltage (>4.0 V), and high theoretical capacity (197 mA h g⁻¹) compared with LiFePO₄. Recently, attempts have been made to improve the electrochemical performance by doping various elements, among which Ti⁴⁺ is considered to be promising. However, no in-depth studies have been conducted on the cause of performance improvement in Ti-doped Li₃V₂(PO₄)₃ materials, in terms of the structure, during electrochemical reactions. Here, we demonstrate that Ti doping triggers the distortion of the VO₆ octahedron and expands the space composed of Li and O ions, enhancing Li ion diffusion. Moreover, the lattice mismatch is mitigated, suppressing incomplete phase transitions and enhancing structural reversibility. Furthermore, the distortion of VO₆ becomes more severe at the end of charging after Ti doping, making “the S-shaped curve” clearer during the discharge process and leading to low overpotential and high discharge capacity. These findings provide valuable opportunities for understanding electrochemically induced phase distortions and possible approaches for utilizing the distortions in high-energy-voltage cathode materials for LIBs.