Fast Screening Suitable Doping Transition Metals to Na₃V₂(PO₄)₂F₃ for Sodium-Ion Batteries with High Energy Density...

Screening the suitable doping elements for Na₃V₂(PO₄)₂F₃ (NVPF) through the traditional trial-and-error method to enhance its intrinsic electronic conductivity and electrochemical performance is a time-exhausted task. Here, a new strategy of theoretical prediction-assisted chemical synthesis is proposed to fast filter the suitable doping elements to NVPF by first calculating the band gaps of various transition metals doped NVPF and then verifying by the experimental results. Single crystal NVPF-M (Na₃V_1.85M_0.15(PO₄)₂F₃, M = Ru, Fe, Ni, Ti, and Cd, etc.) materials are synthesized to compare their electrochemical performances. Excellent cycling performance (2000 cycles with high Coulombic efficiencies), remarkable rate capacity (20 C), and wide-temperature range (-30-60 °C) application capability are witnessed in the NVPF-Ru/Fe cathodes in both half and full cells. In situ X-ray diffraction patterns have confirmed that they followed the consisting of multi-phase reactions (Na₃ ↔ Na_2.4 ↔ Na_2.2 ↔ Na₁) and a solid-solution reaction (Na_1.8 ↔ Na_1.3) with small changes of lattice volume and strains. Compromising the cost and performance, the NVPF-Fe cathode is regarded as the optimized cathode for sodium-ion batteries with a high energy density and wide temperature application features.