Surface Amorphization of Vanadium Dioxide (B) for K-Ion Battery

Given the merits of low cost, fast ionic transport in electrolyte, and high operating voltage, potassium ion batteries (PIBs) are promising alternatives to lithium-ion batteries. However, developing suitable electrode materials that can reversibly accommodate large potassium ions is a great challenge. Here, guided by density functional theory (DFT) calculations, it is demonstrated that the strategy of interfacial engineering via surface amorphization of VO2 (B) nanorods (SA-VO2), which results in the formation of a crystalline core/amorphous shell heterostructure, enables superior K+ storage performance in terms of large capacity, outstanding rate capability, and long cycle stability working as an anode for PIBs. DFT calculations reveal that the created crystalline/amorphous heterointerface in SA-VO2 can substantially lower the surface energy, narrow the band gap, and reduce the K+ diffusion barrier of VO2 (B). These conditions enable enhanced K+ storage capacity and rapid K+/electron transfer, which result in large capacity and outstanding rate capability. Using in situ X-ray diffraction and in situ transmission electron microscopy complemented by ex situ microscopic and spectroscopic techniques, it is unveiled that the superior cycling stability originates from the excellent phase reversibility with negligible strain response and robust mechanical behavior of SA-VO2 upon (de)potassiation.