Mechanistic insights into polaron-mediated lithium ion diffusion in monolayer V₂O₅ cathodes

Monolayer V₂O₅ is a compelling cathode material, yet its performance is limited by poorly understood coupled ion diffusion and electron transport mechanisms. We employ first-principles calculations to reveal a strong synergistic migration mechanism between Li⁺ and small electronic polarons in the material. Our findings demonstrate that Li⁺ diffusion and polaron migration are interdependent, forming a dynamic coupled system. Specifically, polaron formation significantly promotes near-neighbor Li⁺ diffusion along the [010] direction, drastically lowering the barrier from 0.27 eV to a record-low 0.12 eV via electrostatic shielding. Concurrently, Li⁺ insertion reduces the polaron near-neighbor migration barrier along [100] from 0.32 eV to 0.20 eV, eliminating electrostatic traps. Critically, the Li⁺-polaron synergistic diffusion pair is essential for highly efficient transport. While isolated Li⁺ or polaron migration faces high barriers (0.47 eV and 0.51 eV respectively), the cooperative mechanism reduces the shared barrier for both species to just 0.27 eV. This synergy is driven by strong Coulombic interactions: the Li⁺ electrostatically stabilizes the polaron, providing a favorable, low-energy migration pathway. This work microscopically clarifies the dynamic "ion-polaron" coupling in monolayer V₂O₅, validating the superiority of coupled diffusion. It highlights the critical role of engineering electron transport to simultaneously optimize ionic and electronic conductivity for next-generation vanadium-based cathodes.