Guidance KPF₆- and KFSI-based electrolytes in EC/DEC solvents selection for potassium-based batteries

Electrolytes play a key role in determining the electrochemical performance, safety, and lifespan of potassium-based batteries, making their selection and optimization a critical area of research. This study systematically investigates the effects of two major potassium-based battery electrolytes, potassium hexafluorophosphate (KPF₆) and potassium difluorosulfonimide (KFSI) in ethylene carbonate/diethyl carbonate (EC/DEC) solvents, on battery performance, solid electrolyte interphase (SEI) stability, aluminum (Al) current collector corrosion behavior, electrochemical stability window, and dendrite growth issue. Experimental results reveal that KFSI electrolyte significantly outperforms KPF₆ in terms of cycling stability, rate capability, and Coulombic efficiency (CE), primarily due to the formation of a high-quality SEI on electrode surface. Through X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) analyses, we construct the SEI structure for both electrolytes, and find that the SEI formed by KFSI is more uniform and stable. Additionally, KPF₆ exhibits weaker corrosivity towards the Al current collector compared to KFSI due to the formation of an AlF₃ layer with higher oxidation stability on Al surface. Furthermore, in-situ optical microscopy observations indicate that the dendrite growth in KFSI electrolyte is more uniform, preventing the aggregates. These findings provide essential experimental evidence and theoretical support for optimizing the electrolyte in potassium-based batteries.