Methyl Asymmetric Interference-Enhanced Dipole-Dipole Interaction for High-Performance Potassium-Graphite Battery...

Potassium-ion batteries are the only new alkali metal battery system, apart from lithium-ion batteries, that can directly use graphite as the anode. However, the development of potassium-graphite batteries has been restricted due to the lack of high-voltage electrolytes compatible with graphite anodes. To address this issue, a graphite-compatible high-voltage electrolyte is designed based on methyl asymmetric interference-enhanced dipole-dipole interactions. The formulated electrolyte achieves an initial Coulombic efficiency of 86.5% by reducing the desolvation energy of K⁺ ions and forming a sulfur-rich inorganic solid electrolyte interface. At a low current density of 1 µA cm^-2, the maximum stable electrochemical window of the electrolyte reaches 4.6 V, which is compatible with the currently used Prussian blue analogue cathodes. Notably, the potassium-graphite battery with K_1.92Fe[Fe(CN)₆]_0.94·0.5H₂O as the cathode and untreated graphite as the anode can deliver an energy density of 265.6 Wh kg^-1 (based on the total mass of cathode and anode) with a capacity retention of 81.3% after 600 cycles. When K_1.68Mn[Fe(CN)₆]_0.92·1.36H₂O is used as the cathode, the energy density can reach 306.2 Wh kg^-1. A five-stacked pouch full cell with a capacity of ∼24 mAh can rapidly drive a small motor, demonstrating the application potential of the electrolyte.