Highly concentrated electrolyte enabling high-voltage application of metallic components for potassium-ion batteries

Abstract

Abstract A clear understanding of the electrochemical stability of metal components is needed to ensure the sustainability of potassium-ion battery (KIB) materials. Herein, the effect of highly concentrated 7\xa0M potassium-bis(fluorosulfonyl)imide (KFSI) in dimethoxyethane (DME) electrolyte is investigated to determine the electrochemical stability of the Cu, Al, and 316L stainless steel components. Dynamic- and transient-mode polarization reveal that the Cu is passivated with a Cu–O (CuO or Cu2O) layer below 3.55\xa0V vs. K+/K. Above this threshold potential, dissolution of Cu2+ ions is inevitable, causing general corrosion of the Cu metal. Strikingly, Al and 316L stainless steel are passivated even at 5\xa0V vs. K+/K in the highly concentrated electrolyte, with two double layers; namely, an outermost M\xa0−\xa0F (MF3, M: Al, Fe, or Cr) layer, below which inner M\xa0−\xa0O (M2O3) layers sit on the metal bulk. In contrast, progressive dissolution of metal ions occurs for these metals in diluted electrolyte with 0.5\xa0M KFSI salt. This finding suggests the electrochemical availability of Al and 316L stainless steel, indicating the potential application of these metals as both current collectors and cell cases for high-voltage KIBs.