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

Abstract

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.