The free-standing N-doped Murray carbon framework with the engineered quasi-optimal Se/C interface for high–Se-loading Li/Na–Se batteries at elevated temperature

Lithium-selenium (Li–Se) and sodium-selenium (Na–Se) batteries have recently attracted increasing interest because of their high volumetric specific capacity. However, the practical application of the Se cathode is still hindered by volumetric expansion, slow redox reaction kinetics, low area Se-loading, and shuttle effect in ether electrolyte. In this work, we present hierarchically micro/meso/macroporous nitrogen-doped Murray carbon fibers (MCFs) inspired by generalized Murray's law with the engineered quasi-optimal Se/C interface as a free-standing high–Se-loading host for high-performance Li/Na–Se batteries at elevated temperature. Such a hierarchically porous framework not only provides adequate space to accommodate Se for reaction with structural stability but also ensures the rapid electron and ion transport to improve the redox reaction kinetics and to form uniform catholyte electrolyte interphase. At a high area Se-loading of 4 mg/cm², the Se@MCF cathode maintains a discharge capacity of 425 mAh/g at 5 C after 200 cycles for the Li–Se battery and a discharge capacity of 490 mAh/g at 0.5 C after 200 cycles for the Na–Se battery. Even at high temperatures of 50 and 80 °C, the Se@MCF cathodes demonstrate stable cycling performance and decreased polarization. Our work here not only presents significant progress in the development of the high–Se-loading cathode for ultra-stable and high-capacity Li/Na–Se batteries but also sheds some light on the preparation of advanced free-standing electrodes for other energy storage systems.