Electrocatalytic Selenium Redox Reaction for High-Mass-Loading Zinc-Selenium Batteries with Improved Kinetics and Selenium Utilization

Batteries usually deliver mass loading-dependent electrochemical performance. Taking the selenium cathode as an example, the Se reaction kinetics, utilization, and cycling lifespan seriously deteriorate with increased Se mass loading. Here, an electrocatalytic Se reduction/oxidation reaction strategy to realize high-Se-loading Zn||Se batteries with fast kinetics and high Se utilization is proposed. Specifically, the synergetic effects of Cu and Co transition-metal species inside the channel structure of the host can effectively immobilize and catalytically convert Se_n during cycling, which thus facilitates Se utilization and 6-electron (Se⁴⁺ ↔ Se^2–) conversion kinetics. In particular, the Cu[Co(CN)₆] host exhibits a remarkably low energy barrier (1.63 kJ mol^–1) and low Tafel slope (95.23 mV dec^–1) for the Se reduction, and the highest current response for Se oxidation. Accordingly, the Zn battery employing a Se-in-Cu[Co(CN)₆] cathode delivers a capacity of 664.7 mAh g^–1 at 0.2 A g^–1, an excellent rate capability with 430.6 mAh g^–1 achieved even at 10 A g^–1, and long-cyclic life over 6000 cycles with 90.6% capacity retention. Furthermore, an A-h-level (≈1350 mAh) Zn||Se pouch-type battery with high Se loading (≈12.3 mg_(Se) cm^–2) shows a high Se utilization of 83.3% and outstanding cyclic stability with 89.4% initial capacity retained after 400 cycles at exceeding 98% Coulombic efficiency.