Regulating the interfacial chemistry enables fast-kinetics hard carbon anodes for potassium ion batteries

Whether carbon anodes could sustain the high-rate potassium ion batteries (PIBs) remains controversial, owing partly to the distinct electrode preparation protocols and electrolyte systems in reported works. Herein, we adopt a freestanding carbon nanofiber (CNF) film as a model system to explore the charge transfer kinetics in carbon anodes. Without the interference of binders and additives, we probe the effect of interfacial chemistry and boost the kinetics through a tetrahydrofuran-based electrolyte. The weak solvent-cation interaction promotes the rapid desolvation of potassium ions. More importantly, such an electrolyte also benefits the formation of a thin and uniform solid electrolyte interphase. Consequently, the CNFs anode exhibits fast kinetics evidenced by a capacity of 143 mAh g⁻¹ at a large current density of 1.5 A g⁻¹ (∼5.4C) and 200 mAh g⁻¹ at a low temperature of 0 ^○C, significantly outperforming the performance in classical carbonate electrolytes. This work demonstrates the critical roles of electrode/electrolyte interfaces in determining the stability and kinetics of PIBs.