Confining hollow ZnSe/NiSe microspheres in freestanding carbon nanofibers for flexible potassium-ion batteries

Self-supporting electrode materials play a pivotal role in advancing the progress of flexible potassium-ion batteries (PIBs). However, crafting self-supporting electrodes with unique compositions and structures to surmount the volume effect and sluggish kinetics resulting from the significant size of K+ during potassium storage continues to pose a formidable challenge. In this study, we introduce a novel approach by uniformly encapsulating heterostructured hollow ZnSe/NiSe microspheres within N-doped carbon nanofibers (ZnSe/NiSe@NC) to create freestanding anodes for PIBs. Leveraging its sophisticated composition and structure, the ZnSe/NiSe@NC electrode demonstrates a high initial Coulombic efficiency, substantial reversible capacities, exceptional rate capability, and extended cycling stability, surpassing the performance of most previously reported anodes for PIBs. We elucidate the mechanism behind its high potassium storage capacity through in situ XRD and ex situ TEM measurements, shedding light on the charge storage behavior and mass transfer kinetics using various electrochemical techniques, thus demonstrating its superior rate performance. Theoretical calculations further elucidate the intrinsic mechanism of the heterostructured material in facilitating K-ion adsorption and diffusion. Moreover, we have successfully integrated this designed electrode into full cells, unexpectedly yielding high energy and power densities. Notably, the foldable soft-packed cell we fabricated maintains a high capacity and cycling stability even under high current densities, showcasing its potential for flexible device applications. This research contributes significantly to advancing the rational design, fabrication, and utilization of freestanding electrodes in PIBs and beyond. Flexible ZnSe/NiSe@NC anodes exhibit a remarkable Coulombic efficiency, rate capability, and cycling stability. Leveraging their sophisticated composition and structure, high-capacity and long-life foldable potassium-ion batteries can be achieved.