Anion Engineering of LiVPO4F(1-x)Ox Enables Fast-Charge and Wide-Temperature Lithium-Ion Batteries

Abstract

The Tavorite-structured polyanionic lithium-ion batteries (LIBs) cathode material LiVPO₄F (LVPF) shows great promise for high-power applications due to its excellent safety and rapid charge–discharge capabilities. This study introduces a novel oxygen-substituted variant LiVPO₄F_(1-x)O_x, synthesized through a one-step hydrothermal method, producing a nanosheet structure. Advanced characterization confirms the formula of LiVPO₄F_0.69O_0.31 (LVPFO). Electrochemical evaluations indicate that replacing part of F with O lowers charge–discharge plateau voltage and polarization at high current densities. The material exhibits discharge capacities of 156.6–86.4 mAh g⁻¹ at various rates (0.1–15 C). It retains 90.1% of its capacity after 1000 cycles at 15 C. LVPFO further demonstrates fast ion/electron transport and excellent structural stability across an extensive temperature range (−40–50 °C). An experimental full-cell with carbon-coated TiNb₂O₇ (TNO@C) anode and LVPFO cathode achieves a capacity of 127.5 mAh g⁻¹ and an energy density of 319 Wh kg⁻¹ at 0.5 C, and a good capacity retention of 73.7% over 1000 cycles at 10 C. Density Functional Theory (DFT) calculations indicate that the partial substitution of F with O endows LVPFO with a lower Li⁺ diffusion energy barrier and improves electronic conductivity. This study offers valuable insights for the advancement of high-energy and power-density cathode materials in LIBs.