Unlocking vanadium diboride as a high-performance cathode for zinc-ion batteries

Abstract

Aqueous zinc-ion batteries (ZIBs) are increasingly valued for safe, large-scale and green energy storage applications. However, conventional Mn-based and V-based cathode materials suffer from inferior structural stability and poor conductivity-induced unsatisfactory electrochemical performance. This work proposes structure-reorganized vanadium diboride (VB₂) materials to realize advanced high-capacity and stable cathodes for ZIBs. Layer-structured VB₂ materials exhibit metal-like electrical conductivity, whereas they present poor ion-storage capability such as a low capacity of 29 mAh g⁻¹ in ZIBs, since their high crystallinity coupled with the small interlayer spacing restricts the Zn²⁺ diffusion-storage. A constant-voltage electrochemical activation induces the transformation of VB₂ into an amorphous—nanocrystalline heterostructure with abundant defects, not only guaranteeing high electric conductivity but also allowing ions to easily diffuse to the active sites, i.e., triangular bipyramids constructed from V–B atoms, thereby realizing a large reversible capacity of 398 mAh g⁻¹, impressive rate performance and excellent cycling stability with 99% capacity retention over 3500 cycles. A Zn²⁺/H⁺ co-storage mechanism, which is dominated by Zn²⁺ storage, is elucidated for the structure reorganized VB₂ cathode. This work provides a green methodology and theoretical foundation for exploring diborides as a new family of advanced cathode materials for ZIBs.