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.