Viologen as an Electrolyte Additive for Extreme Fast Charging of Lithium‐Ion Batteries

ABSTRACT Although lithium‐ion batteries (LIBs) have found an unprecedented place among portable electronic devices owing to their attractive properties such as high energy density, single cell voltage, long shelf‐life, etc., their application in electric vehicles still requires further improvements in terms of power density, better safety, and fast‐charging ability (i.e., 15 min charging) for long driving range. The challenges of fast charging of LIBs have limitations such as low lithium‐ion transport in the bulk and solid electrode/electrolyte interfaces, which are mainly influenced by the ionic conductivity of the electrolyte. Therefore, electrolyte engineering plays a key role in enhancing the fast‐charging capability of LIBs. Here, we synthesize a novel propionic acid‐based viologen that contains a 4,4′‐bipyridinium unit and a terminal carboxylic acid group with positive charges that confine PF 6 ‒ anions and accelerate the migration of lithium ions due to electrostatic repulsion, thus increasing the overall rate capability. The LiFePO 4 /Li cells with 0.25% of viologen added to the electrolyte show a discharge capacity of 110 mAh g ‒1 at 6C with 95% of capacity retention even after 500 cycles. The added viologen not only enhances the electrochemical properties, but also significantly reduces the self‐extinguishing time.