Selenium-infiltrated metal-organic framework-derived porous carbon nanofibers comprising interconnected bimodal pores for Li-Se batteries with high capacity and rate performance

The rational design of cathode materials for lithium-selenium (Li-Se) batteries is essential to achieve high-performance electrochemical properties with long cycle life and excellent rate capability. In this paper, novel porous carbon nanofibers with bimodal pores (micro/meso), as efficient cathode hosts for Li-Se batteries, were successfully synthesized by carbonization of electrospun zeolitic imidazole framework-8/polyacrylonitrile (ZIF-8/PAN) nanofibers and further chemical activation. Mesopores originated from carbonization of ZIF-8 embedded in the carbon nanofiber, and micropores were further introduced via KOH activation. During the activation step, micropores were introduced to the ZIF-8-derived meso porous carbon cages and within the carbon nanofibers, resulting in the formation of bimodal porous carbon nanofibers with enlarged pore volumes. Owing to their mesopores for easy access of electrolyte and high utilization of chain-like selenium with low-range ordering within the micropore, the selenium-loaded bimodal porous carbon nanofibers exhibited high discharge capacity and superb rate performance. The discharge capacities of the nanofibers at the 2^nd and 300^th cycle at a current density of 0.5C were 742 and 588 mA h g^-1, respectively. The capacity retention calculated from the 2^nd cycle was 79.2%. In addition, a discharge capacity of 568 mA h g^-1 was obtained at an extremely high current density of 10.0C.