Open-Structured Vanadium Dioxide as an Intercalation Host for Zn Ions: Investigation by First-Principles Calculation and Experiments

Zinc-ion batteries are emerging as next-generation rechargeable batteries that can operate in aqueous electrolytes. We first examine the feasibility of open-structured VO₂(B) as a Zn²⁺ intercalation host. A bond-valence sum energy map predicts that four Zn²⁺-ion sites (Zn_C, Zn_A1, Zn_A2, and Zn_C′) can exist in the structure. Using first-principles calculations, we verified that 0.5 mol of Zn²⁺ ions can be reversibly (de)intercalated with an average voltage of ∼0.61 V (vs Zn²⁺/Zn), which is comparable with the experimental results. The specific capacity of VO₂(B) at 50 mA g^-1 is maintained up to ∼365 mAh g^-1 corresponding to the storage capacity of ∼0.57 mol of Zn²⁺ ions in the framework of VO₂(B), and its redox reaction occurs at ∼0.61 V. The high capacity is maintained for 200 cycles, with capacity retention of 80% (288 mAh g^-1). Moreover, the capacity delivered by the VO₂(B) electrode is stable even with cycling at a rate of 5C (1750 mA g^-1) at approximately 110 mAh g^-1. This high-power capability of VO₂ is supported by the theoretical approach based on first-principles calculation, which shows the activation barrier for Zn²⁺ diffusion in the VO₂(B) structure. These findings demonstrate the potential of open-structured VO₂(B) as a new candidate material.