Cu3.21Bi4.79S9: Bimetal superionic strategy boosts ultrafast dynamics for Na-ion storage/extraction

Traditional metal sulfides used as anodes for sodium-ion batteries are hindered by sluggish kinetics, which limits their rate performance. Previous attempts to address this issue focused on nanostructured configurations with conductive frameworks. However, these nanomaterials often suffer from low packing density and the tendency for nanoparticles to agglomerate, posing significant challenges for practical applications. To overcome these limitations, this study presents a novel bimetal superionic anode material Cu_3.21Bi_4.79S₉, which effectively resolves the conflict between sluggish kinetics and micrometer-scale particle size. By leveraging the vacancies created by free Cu and Bi atoms, this material forms rapid migration channels during sodium insertion and extraction, significantly reducing the migration barriers for sodium ions. The development of micrometer-scale Cu_3.21Bi_4.79S₉ enables ultrafast charging-discharging capabilities, achieving a reversible capacity of 325.5 mAh g⁻¹ after 4000 cycles at a high rate of 45 C (15 A g⁻¹). This work marks a significant advancement in the field by offering a solution to the inherent trade-off between high capacity and rate performance in coarse-grained materials, reducing the need for reliance on nanostructured configurations for next-generation high-capacity anode materials.