Chemically Binding Vanadium Sulfide in Carbon Carriers to Boost Reaction Kinetics for Potassium Storage.

Potassium-ion batteries (PIBs) have received widespread interest on account of low redox potential, low price, and high abundance of potassium. However, attributing to the large radius of K+ ions, the structure of electrode material is easily damaged during the potassiation/depotassiation process. Herein, the unique chemical bonding of encapsulating V5.45S8 nanoparticles in N,S codoped multichannel carbon nanofibers (CB-VS@NSCNFs) is designed through electrospinning and in situ vulcanization techniques. The anchoring effect (V-C chemical bonding) of the V5.45S8 nanoparticles with carbon carriers assists in shortening the K+/e- transport path and alleviating the structural changes, which is highlighted to acquire a stable cycle lifespan. Also, codoped multichannel carbon nanofibers provide abundant active sites for pseudocapacitive behavior to achieve fast kinetics. As a synergistic result, when CB-VS@NSCNFs are evaluated as anode material for PIBs, they exhibit a high reversible capacity of 411 mA h g-1 at 0.1 A g-1, decent rate property with a capacity of up to 123 mA h g-1 at 6 A g-1, and good cycling stability of 500 cycles at 1 A g-1.

Structure Engineering of Vanadium Tetrasulfides for High-Capacity and High-Rate Sodium Storage.

Structure engineering of electrode materials can significantly improve the life cycle and rate capability of the sodium-ion battery (SIB), yet remains a challenging task due to the lack of an effective synthetic strategy. Herein, the microstructure of VS4 hollow spheres is successfully engineered through a facile hydrothermal method. The hollow VS4 microspheres possess rich porosity and are covered with 2D ultrathin nanosheets on the surface. The finite element simulation (FES) reveals that such heterostructures can effectively relieve the stress induced by the sodiation and thereby enhance the structural integrity. The SIB with the hollow VS4 microspheres as anode displays impressively high specific capacity, excellent stability upon ultra-long cycling, and extraordinary rate capacity, e.g., a reversible capacity of ≈378 mA h g-1 at ultra-high 10 A g-1 , while retaining 73.2% capacity after 1000 cycles. The Na storage mechanism is also elucidated through in situ/ex situ characterizations. Moreover, the hollow VS4 microspheres demonstrate reliable rate performance at a low temperature of -40 °C (e.g., the capacity is ≈163 mA h g-1 at 2 A g-1 ). This work provides novel insights toward high-performance SIBs.