Synergistic PF₆₋ and FSI⁻ intercalation enables stable graphite cathode for potassium-based dual ion battery

Potassium-based dual ion batteries have emerged as promising alternatives to the prevailing lithium-ion batteries due to the advantages in cost and sustainability. Single-anion intercalation into graphite takes place on the cathode side, but it usually delivers a low capacity with poor Coulombic efficiency in potassium-based systems. We demonstrate the performance could be significantly boosted through synergistic dual-anion intercalation of FSI⁻ and PF₆⁻. The presence of PF₆⁻ helps the formation of an effective cathode electrolyte interface to allow high anionic stability up to 5.5 V, while FSI⁻ intercalation brings about superior rate capability and long-term cyclic stability. Concurrent intercalation of FSI⁻ and PF₆⁻ is tracked by in-situ Raman spectroscopy and ex-situ XRD. It reveals the formation of stage I graphite intercalation compounds (GICs) upon charging, leading to a reversible capacity of over 100 mAh g⁻¹ with an average potential of 4.65 V (vs. K⁺/K). Furthermore, the graphite-potassium cell delivers an exceptional capacity of 94 mAh g⁻¹ at 0.3 A g⁻¹ and shows capacity retention of 96% after 250 cycles. The strategy provides a novel avenue toward stable dual-ion battery via intercalation chemistry regulation.