Electrospun MOF-based ZnSe nanocrystals confined in N-doped mesoporous carbon fibers as anode materials for potassium ion batteries with long-term cycling stability

Potassium ion batteries (KIBs) are promising energy storage systems for large-scale applications. However, owing to the large diameter of K+, these batteries show limited electrochemical performance, particularly in terms of cycling stability. Thus, it is essential to design novel electrode materials for practical applications of KIBs. In this study, novel N-doped porous carbon nanofibers embedded with ultrafine ZnSe nanocrystals were successfully prepared as an advanced anode material for KIBs via electrospinning of a Zn-based zeolitic imidazolate framework (ZIF-8) and subsequent thermal treatment. Numerous mesopores were generated within the nanofibers by the transformation of ZIF-8 nanoparticles into a hollow carbon frame during thermal treatment. The unique 1D structure provided sufficient active sites for K+ storage, shortened the diffusion path for ions, and enhanced the structural robustness of the electrode. The N-doped carbon matrix also effectively alleviated the mechanical stress in the ZnSe nanocrystals and improved the electrical conductivity. Consequently, the 1D porous nanostructured electrodes exhibited excellent long-term cycling stability for 1000 cycles when tested as anodes for KIBs, with a reversible capacity of 270 mA h g−1 at 0.5 A g−1 and a high-rate capacity of 139 mA h g−1 at 2.0 A g−1.