Robust VS4@rGO nanocomposite as a high-capacity and long-life cathode material for aqueous zinc-ion batteries.

Although vanadium (V)-based sulfides have been investigated as cathodes for aqueous zinc-ion batteries (ZIBs), the performance improvement and the intrinsic zinc-ion (Zn2+) storage mechanism revelation is still challenging. Here, VS4@rGO composite with optimized morphology is designed and exhibits ultrahigh specific capacity (450 mA h g-1 at 0.5 A g-1) and high-rate capability (313.8 mA h g-1 at 10 A g-1) when applied as cathode material for aqueous ZIBs. Furthermore, the VS4@rGO cathode presents long-life cycling stability with capacity retention of ∼82% after 3500 cycles at 10 A g-1. The structural evolution, redox, and degradation mechanisms of VS4 during (dis)charge processes are further probed by in situ XRD/Raman techniques and TEM analysis. Our results indicate that the main energy storage mechanism is derived from the intercalation/deintercalation reactions in the open channels of VS4. Notably, an irreversible phase transition of VS4 into Zn3(OH)2V2O7·2H2O (ZVO) during the charging process and the further transition from ZVO to ZnV3O8 during long-term cycles are also observed, which might be the main reason leading to the capacity degradation of VS4@rGO. Our study further improves the electrochemical performance of VS4 in aqueous ZIBs through morphology design and provides new insights into the energy storage and performance degradation mechanisms of Zn2+ storage in VS4, and thus may endow the large-scale application of V-based sulfides for energy storage systems.

Rational construction of K0.5V2O5 nanobelts/CNTs flexible cathode for multi-functional potassium-ion batteries.

Potassium-ion battery (KIB) is one of the emerging electrochemical energy storage technologies due to the abundance, low cost, and low redox potential of K. One of the most promising cathodes of KIBs is a layered vanadium-based compound, but it often suffers from fast capacity decay during repeated cycling. Herein, a K0.5V2O5/CNTs hybrid film composed of K0.5V2O5 nanobelt and carbon nanotube (CNT) network was synthesized by an electrostatic self-assembly and vacuum filtration process, and further used as the cathode in KIBs. The K0.5V2O5/CNTs cathode possessed a flexible and interconnected network structure, which not only offered fast kinetics for electron transfer and ion transportation, but also provided an elastic medium to buffer the large volume change of the K0.5V2O5 nanobelts during cycling. As a cathode for KIBs, the K0.5V2O5/CNTs electrode showed a reversible discharge capacity of ∼90 mA h g-1 at 50 mA g-1 and exhibited good cycling stability (88.8% capacity retention for 100 cycles at 50 mA g-1, 82.2% capacity retention for 300 cycles at 500 mA g-1) and excellent rate performance of ∼62 mA h g-1 at 500 mA g-1. K-Ion full battery testing further confirmed its good electrochemical performance by presenting a high reversible discharge capacity (68 mA h g-1 at 50 mA g-1) and long-term retention (>80% after 80 cycles). Interestingly, a cable-shaped KIB with the flexible K0.5V2O5/CNTs film as the cathode electrode was assembled and showed its further application potential as a power source for wearable electronics.