Dual-ion synergy in boosting reaction kinetics and conductivity of a VO2·xH2O cathode for stable zinc-ion batteries

Abstract

VO₂ has emerged as a promising cathode material for aqueous zinc-ion batteries, attributed to its unique one-dimensional tunnel structure and reversible Zn²⁺ de/intercalation. However, its practical application is hindered by intrinsically poor conductivity, slow ion diffusion and structural instability during long-term cycling. In this study, we introduce a novel dual-ion synergy strategy by co-doping NH₄⁺ and F⁻ to systematically address these challenges. The combined effects of NH₄⁺-induced lattice expansion and F⁻-mediated electronic modulation significantly enhance the electrochemical performance of VO₂·xH₂O (VONF-0.4). Specifically, NH₄⁺ increases the tunnel spacing for facile Zn²⁺ diffusion and stabilizes the V–O framework via the “pillar” effect and hydrogen bonding, while the partial substitution of O²⁻ with F⁻ enhances conductivity and suppresses vanadium dissolution by forming a hydrophobic interface. The optimized VONF-0.4 cathode delivers satisfactory rate capability and a high initial specific capacity of 415.4 mAh g⁻¹ at 1.0 A g⁻¹, which can be maintained at 371.1 mAh g⁻¹ after 300 cycles. Notably, it shows outstanding long-term stability and retains 99.4% of its initial capacity after 1400 cycles at 10 A g⁻¹. This work demonstrates the feasibility of dual-ion engineering in designing advanced cathode materials for high-performance aqueous zinc-ion batteries.