Cu-based prussian blue analogs/iodine composite cathode with reversible cuI conversion for sodium metal batteries

Prussian Blue Analogs (PBAs) stood out as promising candidates for sodium metal batteries cathode, leveraging their unique open-framework architecture, straightforward synthesis, and cost-effectiveness. However, PBAs were plagued by limited capacity arising from insufficient redox-active sites. Additionally, iodine cathode with high theoretical capacity (211 mAh g⁻¹) suffer from poor practical performance due to the shuttle effect of polyiodides and slow kinetic conversion. The complex cathode to construct conversion reaction might be a better method to improve the capacity and easy to implement. Herein, we reported the design of a Cu-based PBAs/iodine composite cathode, where the PBAs framework serves as an iodine host and a conversion reaction mechanism via copper‑iodine coupling within PBAs cavities was established to enhance capacity. Various characterization results demonstrated that the Cu-based PBAs framework enabled favorable iodine encapsulation and facilitated CuI coupling, enabling reversible conversion during charge/discharge progress. Density Functional Theory (DFT) simulations confirmed that the complexation of Cu-based PBAs with iodine represents a thermodynamically favorable process. Thereby, the assembled full battery achieved a high specific capacity of 276.4 mAh g⁻¹ at 0.1 A g⁻¹ and a capacity retention of 80.9 % after 1000 cycles at 0.3 A g⁻¹. This work introduced a novel Cu-based PBAs/iodine complexed conversion cathode, offering an innovative insight for the development of high-performance sodium metal batteries.