A 3D coral-like structured NaVPO4F/C constructed by a novel synthesis route as high-performance cathode material for sodium-ion battery

A novel bottom-up synthesis route based on hydrogen bonds has been developed to prepare NaVPO4F/C (NVPF/C) composite as the cathode material for sodium ion batteries (SIBs). NVPF grains are anchored through effective hydrogen bonds between the fluorine ions and hydrogen atoms inside the sol-gel template, which endows the final product an interconnected and porous three-dimensional (3D) coral-like structure composed by oriented packing of uniform nanoparticles (15-20 nm). The as-prepared NVPF/C exhibits excellent rate capability and extraordinary cyclic stability. The corresponding discharge capacities at 1, 2, 5, 10, 20, 30 and 50 C range from 106, 102, 99, 98, 93, 90 to 88 mAh g(-1) respectively. At 5 C, it releases an initial capacity of 100 mAh g-1, and still maintains 70 mAh g(-1) after 2500 cycles, corresponding to a very low capacity fading of 0.012% per cycle. The uniform nanometers sized (15-20 nm) fundamental particles and nanopores (3-8 nm) of as-prepared NVPF/C endow the efficient transfer of both electrons and sodium ions. This work implies that the novel 3D coral-like structured NVPF/C is a very promising high-performance cathode for SIBs, and the new synthetic method can also be applied to prepare other fluorine contained polyanion-type materials.