Iodine-Doped Sodium Vanadate Cathode for Improved Zn Ion Diffusion Kinetics

The electrostatic interaction between zinc ions and the host structure significantly limits the practicality of vanadium-based cathodes in aqueous zinc-ion batteries (AZIBs). Herein, an anion doping strategy is demonstrated to mitigate electrostatic resistance and steric hindrance during zinc ion insertion by incorporating iodine atoms into the lattice of the cathode material, Na₂V₆O₁₆·3H₂O. Iodine doping reduces the adsorption energy at the most stable site, thereby weakening the Zn²⁺-host interaction and lowering the Zn²⁺ diffusion energy barrier, resulting in a one-order-of-magnitude increase in the diffusion coefficient. Moreover, the large atomic size of iodine expands the host lattice, creating ample space for increased zinc ion storage capacity, further supported by the introduced oxygen vacancies. As a result, the iodine-doped Na₂V₆O₁₆·3H₂O cathode achieves an impressive specific capacity of 528.8 mAh g⁻¹ at a current density of 0.5 A g⁻¹, and retains 262 mAh g⁻¹ after 12,000 cycles at a high current rate of 10 A g⁻¹. This work provides new insights into the design of high-performance cathode materials for AZIBs.