Weakly Polarized Organic Cation-Modified Hydrated Vanadium Oxides for High-Energy Efficiency Aqueous Zinc-Ion Batteries

Vanadium oxides, particularly hydrated forms like V₂O₅·nH₂O (VOH), stand out as promising cathode candidates for aqueous zinc ion batteries due to their adjustable layered structure, unique electronic characteristics, and high theoretical capacities. However, challenges such as vanadium dissolution, sluggish Zn²⁺ diffusion kinetics, and low operating voltage still hinder their direct application. In this study, we present a novel vanadium oxide ([C₆H₆N(CH₃)₃]_1.08V₈O₂₀·0.06H₂O, TMPA-VOH), developed by pre-inserting trimethylphenylammonium (TMPA⁺) cations into VOH. The incorporation of weakly polarized organic cations capitalizes on both ionic pre-intercalation and molecular pre-intercalation effects, resulting in a phase and morphology transition, an expansion of the interlayer distance, extrusion of weakly bonded interlayer water, and a substantial increase in V⁴⁺ content. These modifications synergistically reduce the electrostatic interactions between Zn²⁺ and the V-O lattice, enhancing structural stability and reaction kinetics during cycling. As a result, TMPA-VOH achieves an elevated open circuit voltage and operation voltage, exhibits a large specific capacity (451 mAh g^-1 at 0.1 A g^-1) coupled with high energy efficiency (89%), the significantly-reduced battery polarization, and outstanding rate capability and cycling stability. The concept introduced in this study holds great promise for the development of high-performance oxide-based energy storage materials.