Elevated Energy Density and Cyclic Stability of LiVPO₄F Cathode Material for High-rate Lithium Ion Batteries

Simultaneous realization of superior energy density and cyclic stability of a cathode material under high rate is imperative for practical applications in rechargeable lithium-ion batteries (LIBs). In the present work, the effects of a marginal amount of K substitution of Li on the electrochemical properties of the Li1-xKxV0.98Nb0.02PO4F@C (L1-xKxVNPF@C, x = 0-0.01) cathode materials are investigated. As a result, K substitution of Li has a great influence on the electronic conductivities, ionic conductivities, charge transfer resistances, and Li+ diffusion coefficients of the L1-xKxVNPF@C (x = 0.003-0.01) cathode materials. Substantially improved discharge capacities and energy densities are observed in the L1-xKxVNPF@C (x = 0.003-0.01) cathodes under high charge/discharge current densities of 0.4-1 A g-1. In particular, because of the highest Li+ conductivity and diffusivity, the L0.995K0.005VNPF@C cathode exhibits an optimal electrochemical performance at both 25 and 50 °C. It delivers a high discharge capacity of 101 mA h g-1 at 10 C with a capacity retention of 95.3% after 1000 cycles at 25 °C. Correspondingly, the initial discharge energy density and energy retention is 396.2 Wh kg-1 and 96.4%, respectively. Even evaluated at 9 C and 50 °C, the initial discharge energy density and energy retention after 500 cycles is 420.6 Wh kg-1 and 92.9%, respectively, which is highly promising for practical applications. The present work may provide a valuable guidance to elevate the energy density and cyclic stability of a cathode material for high-rate LIBs.