Constructing resilient solid electrolyte interphases on carbon nanofiber film for advanced potassium metal anodes

Stable cycling of potassium metal anodes in classic carbonate electrolytes remains a great challenge. Three-dimensional carbon hosts have been widely adopted to address the low Coulombic efficiency and devastated dendrite growth, but a correlation between the carbon microstructure and potassium plating/stripping stability has yet to be established. Here, stark contrasted carbonization temperatures, i.e., 800 and 2800 °C, are applied to electrospun carbon nanofiber (CNF) films for regulating graphitization degree. The resulted CNFs demonstrate distinct stability when serving as hosts for potassium metal anodes. We reveal that the carbon microstructure has a huge impact on not only the nucleation and diffusion of the K ions but also the mechanical properties of solid electrolyte interphases (SEIs). The maximum elastic deformation energy (U), which reveals the combined effects of Young's modulus and yield strain, is utilized to reflect the capability of SEI in accommodating the electrode deformation upon K deposition. The CNFs prepared at 2800 °C benefit the formation of a high U-value SEI. Consequently, it exhibits a small polarization and an ultra-long life of over 2000 h at 0.5 mA cm⁻² in the carbonate electrolyte.