Toward Theoretical Capacity and Superhigh Power Density for Potassium–Selenium Batteries via Facilitating Reversible Potassiation Kinetics

Potassium-selenium (K-Se) batteries attract tremendous attention because of the two-electron transfer of the selenium cathode. Nonetheless, practical K-Se cells normally display selenium underutilization and unsatisfactory rate capability. Herein, we employ a synergistic spatial confinement and architecture engineering strategy to establish selenium cathodes for probing the effect of K+ diffusion kinetics on K-Se battery performance and improving the charge transfer efficiency at ultrahigh rates. By impregnating selenium into hollow and solid carbon spheres with similar diameters and porous structures, the obtained parallel Se/C composites possess nearly identical selenium loadings, molecular structures, and heterogeneous interfaces but enormously different paths for K+ diffusion. Remarkably, as the solid-state K+ diffusion distance is significantly reduced, the K-Se cell achieves 96% of 2e- transfer capacity (647.1 mA h g-1). Reversible capacities of 283.5 and 224.1 mA h g-1 are obtained at 7.5 and 15C, respectively, corresponding to an unprecedented high power density of 8777.8 W kg-1. Quantitative kinetic analysis demonstrated a twofold higher capacitive charge storage contribution and a 1 order of magnitude higher K+ diffusion coefficient due to the short K+ diffusion path. By combining the determination of potassiation products by ex situ characterization and density functional theory (DFT) calculations, it is identified that the kinetic factor is decisive for K-Se battery performances.