Phase engineering of vanadium sulfides as superior anodes for high-energy density sodium-ion half/full batteries

The development of electrode materials for Sodium-Ion Batteries (SIBs) has received more and more attention. Among them, vanadium sulfide, as a member of the transition metal sulfide family, owns the characteristics of rich electrochemical activity, high theoretical capacity and adjustable spatial structure. However, the complicated synthetic process, poor rate capability and intricate redox mechanism of vanadium sulfides make them less competitive for commercial use. In this work, a facile approach based on the ball-milling technique followed by adjusted annealing temperature is introduced to fabricate large-scale vanadium sulfides. This general phase-controlled method can bring three different crystal types of V5S8, V3S4 and V3S5. With homogeneous covering of super P and Carbon Nano Tubes (CNTs), a conductive network that favors the Na ions/electrons transport in the vanadium sulfides-based electrodes can be fabricated. The V5S8 exhibits the best performance in SIBs with specific capacity of 918 mAh g−1 at 0.1 A g−1 (100 cycles). Moreover, V5S8 electrode also exhibits an ultra-rate capability of 333 mAh g−1 at 50 A g−1 after cycling lifespan (4000 loops). The extremely high pseudo-capacitance characteristics of V5S8 is significant during the SIBs discharge/charge. Additionally, the V5S8 anode also shows the high energy density of 165 Wh kg−1 in SIBs full cell.