Abstract
Understanding how cation identity governs charge storage is critical for next-generation batteries beyond lithium. Here we show that the amorphous Ca-Zn-PTtSA coordination polymer functions as a universal host for reversible electrochemical storage of all alkali-metal cations from Li(+) to Cs(+), including the rare case of reversible Rb(+) and Cs(+) electrochemical cycling in a positive electrode material. Despite the large variation in ionic radius, all cations yield nearly identical redox potentials, full material utilization (∼95 mAh g(-1)), and low hysteresis. Elemental and spectroscopic analyses confirm a cation storage mechanism without solvent co-intercalation. This behavior originates from the framework's amorphous flexibility and the delocalized electronic structure of the conjugated sulfonamide ligand, which together enable weak, reversible metal-ligand interactions and fast cation transport (D ≈ 10(-9) cm(2) s(-1)). Consequently, M(2)-Zn-PTtSA delivers high-rate capability and long-term cycling stability across the entire alkali-metal series, providing a platform that decouples ion size from electrochemical performance and supports "cation-of-choice" battery chemistries.