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 V ₅S ₈, V ₃S ₄ and V ₃S ₅ . 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 V ₅S ₈ exhibits the best performance in SIBs with specific capacity of 918 mAh g ⁻¹ at 0.1 A g ⁻¹ (100 cycles). Moreover, V ₅S ₈ 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 V ₅S ₈ is significant during the SIBs discharge/charge. Additionally, the V ₅S ₈ anode also shows the high energy density of 165 Wh kg ⁻¹ in SIBs full cell.