The Effects of Morphological Architectures of ZIF-8-Derived N-Doped Nanoporous Carbon as Cathodes on the Electrochemical Performances of Li–Se Batteries

The morphological structures, hierarchical porosity, heteroatom doping, and catalytically active centers of MOF-derived porous carbon as Se cathodes play essential roles in the electrochemical performances of Li–Se batteries. It is highly desirable to establish the structure–property relationship between the tunable architectures of MOF-derived porous carbons and their electrochemical performances in Li–Se batteries. In this study, nitrogen-doped porous carbon materials were derived from ZIF-8 precursors with precisely tuned morphologies by using particle-size adjustment and controlled tannic acid etching, which served as Se hosts for electrochemical analysis. Compared with the medium- and large-sized ZIF-8-derived porous carbon, the small-sized nitrogen-doped porous carbon (NPC) can effectively shorten ion and electron transport pathways and increase the fraction of surface-accessible active sites, which feasibly accelerates selenium conversion kinetics and enhances both capacity and cycling stability. Small-sized Se@NPC-S electrode possessed high reversible capacities of 670 mAh g–1 at 0.1 C and 446 mAh g–1 at 5 C. For the acid etched nitrogen-doped porous carbon (ENPC), the Se@ENPC-R2 cathode with moderate shell thickness exhibits a superior balance between capacity, rate capability, and long-term cycling stability which exceeded that of insufficiently etched and excessively etched counterparts. Se@ENPC-R2 delivers a reversible capacity of 480 mAh g–1 after 200 cycles at 0.1 C, and it sustains about 400 mAh g–1 after 800 cycles at 1 C. Electrochemical analyses reveal the improved Li+ diffusivity in Se@ENPC-R2, in which its moderate shell thickness can preserve continuous electronic pathways and provide sufficient internal space to accommodate volume variation and facilitate ion transport. These findings establish a clear correlation between the structural regulation and electrochemical behavior and suggest a practical route toward promising Li–Se batteries with a high discharge capacity, a superior rate capability, and excellent cycling stability built from MOF-derived porous carbons.