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

The consensus practice in research of high energy density energy storage devices is to simultaneously achieve high areal capacity and high intrinsic specific capacity. Increasing the areal capacity of batteries necessitates the maximization of their mass loading. However, batteries usually deliver mass loading-dependent electrochemical performance. Take selenium (Se) cathode with a theoretically high specific capacity as an example, Se reaction kinetics, utilization and cycling lifespan seriously deteriorate with increased Se mass loading. Here, we propose an electrocatalytic Se reduction/oxidation reaction strategy to realize high-Se-loading Zn||Se batteries with fast kinetics and high Se utilization. Specifically, the synergetic effects of Cu and Co transition-metal species inside channel structure of host can effectively immobilize and catalytically convert Se_n during cycling, which thus facilitates Se utilization and 6-electron (Se⁴⁺ \(\leftrightarrow\) 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 highest current response for Se oxidation. Accordingly, the Zn battery employing 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 3.3 % and outstanding cyclic stability with 9.4 % initial capacity retained after 400 cycles at exceedin 98 % Coulombic efficiency.