Large scale preparation of Na₃V₂(PO₄)₂F₃ with cross-linked double carbon network for high energy density sodium ion batteries at -20 C

Na3V2(PO4)2F3 (NVPF) is considered as one of the most promising cathode materials for high-voltage sodium ion batteries, because of its high energy density and rapid ion diffusion ability. Yet, the insulating nature of (PO4)3and the perishable F- cause the NVPF suffers from poor rate performance and short cycle durability. Herein, a particular three-dimensional double carbon network-intertwined NVPF nanospheres (notated as NVPF/CNTs) are successfully prepared by spray drying method. The coting carbon on the surface of NVPF can collect electrons at same time effectively improve lattice stability. And the unique conductive three-dimensional CNTs network framework has significantly improved the electrical conductivity between particles and enlarged the contact area between the cathode and electrolyte. Thanks to the unique structure, the electrochemical properties of NVPF/ CNTs electrode has been significantly improved, showing awesome rate capability (127.7 mAh g-1 at 0.1 A g-1 and 77.7 mAh g-1 at 10 A g-1) and ultra-long cycle life (92.1 % capacity reminded after 20,000 cycles at 10 A g-1). In addition, it has excellent adaptability to low temperature (96.8 mAh g-1 at 0.1 A g-1, 98 % capacity retention after 500 cycles at -20 degrees C) and considerable energy density of 353.4 Wh kg-1 in NVPF/CNTs||hard carbon full-cells. These excellent properties further enhance the competitiveness of NVPF/CNTs to achieve high performance of sodium-ion batteries.