Localized High‐Concentration Electrolytes Boost Potassium Storage in High‐Loading Graphite

Reversible intercalation of potassium‐ion (K+) into graphite makes it a promising anode material for rechargeable potassium‐ion batteries (PIBs). However, the current graphite anodes in PIBs often suffer from poor cyclic stability with low coulombic efficiency. A stable solid electrolyte interphase (SEI) is necessary for stabilizing the large interlayer expansion during K+ insertion. Herein, a localized high‐concentration electrolyte (LHCE) is designed by adding a highly fluorinated ether into the concentrated potassium bis(fluorosulfonyl)imide/dimethoxyethane, which forms a durable SEI on the graphite surface and enables highly reversible K+ intercalation/deintercalation without solvent cointercalation. Furthermore, this LHCE shows a high ionic conductivity (13.6 mS cm−1) and excellent oxidation stability up to 5.3 V (vs K+/K), which enables compatibility with high‐voltage cathodes. The kinetics study reveals that K+ intercalation/deintercalation does not follow the same pathway. The potassiated graphite exhibits excellent depotassiation rate capability, while the formation of a low stage intercalation compound is the rate‐limiting step during potassiation. A localized high‐concentration electrolyte is designed by adding a highly fluorinated ether into the concentrated potassium bis(fluorosulfonyl)imide/dimethoxyethane, which forms a durable potassium fluoride (KF)‐rich passivation layer on the graphite surface and enables highly reversible K+ intercalation/deintercalation without solvent cointercalation. The potassium‐ion batteries with the high‐loading graphite (≈8 mg cm−2) anode can operate over 300 cycles with negligible capacity decay.