Electrolyte Design Enables Stable and Energy‐dense Potassium‐ion Batteries

Free from strategically important elements such as lithium, nickel, cobalt, and copper, potassium‐ion batteries (PIBs) are heralded as promising low‐cost and sustainable electrochemical energy storage systems that complement the existing lithium‐ion batteries (LIBs). However, the reported electrochemical performance of PIBs is still suboptimal, especially under practically relevant battery manufacturing conditions. The primary challenge stems from the lack of electrolytes capable of concurrently supporting both the low‐voltage anode and high‐voltage cathode with satisfactory Coulombic efficiency (CE) and cycling stability. Herein, we report a promising electrolyte that facilitates the commercially mature graphite anode (> 3 mAh cm‐2) to achieve an initial CE of 91.14% (with an average cycling CE around 99.94%), fast redox kinetics, and negligible capacity fading for hundreds of cycles. Meanwhile, the electrolyte also demonstrates good compatibility with the 4.4 V (vs. K+/K) high‐voltage K2Mn[Fe(CN)6] (KMF) cathode. Consequently, the KMF||graphite full‐cell without precycling treatment of both electrodes can provide an average discharge voltage of 3.61 V with a specific energy of 316.5 Wh kg‐1‐(KMF+graphite), comparable to the LiFePO4||graphite LIBs, and maintain 71.01% capacity retention after 2000 cycles.