A high-entropy carbon-coated Na3V1.9(Mg, Cr, Al, Mo, Nb)0.1(PO4)2F3 cathode for superior performance sodium-ion batteries

Abstract

A NASICON-type high-entropy carbon-coated Na3V1.9(Mg, Cr, Al, Mo, Nb)0.1(PO4)2F3 (NVPF-HE@C) material was synthesized through the sol-gel route. The incorporation of high entropy elements (Mg, Cr, Al, Mg, Nb) improved the stability of Na2 sites in NVPF without altering its crystal structure, which suppressed the intermediate reactions of Na3V2(PO4)2F3 phase at low potential of 3.4V. This improvement further lifted the specific capacity, capacity retention and Na+ diffusion coefficient of NVPF-HE@C cathode. The fluctuation of Na+ diffusion coefficient at low voltage region decreased 10−14-10−10cm2s−1 to 10−12-10−10cm2s−1. NVPF-HE@C cathode displays the initial specific capacities of 128 mAhg−1 at 1C and 82 mAhg−1 at 5C, while maintaining a low capacity decay of 17% over 800 cycles. The introduction of high-entropy doping provides an effective approach as promoting the electrochemistry properties of NVPF cathode, with potential applicability to other electrode materials in energy storage applications.