Reformulation of Liquid Electrolytes for Extreme Fast Charging of Lithium-Ion Batteries

Although lithium-ion batteries (LIBs) have found an unprecedented place in the portable electronic devices owing to their unique 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, engineering of electrolytes plays a key role in enhancing the fast-charging capability of LIBs. Here, we have employed a combination of electrolyte additives in order to improve its charge-discharge properties. Further we have also synthesized a novel -viologen that contains 4,4’-bipyridinium unit and a terminal carboxylic acid group with positive charges that confines PF₆ anions and accelerates the migration of lithium-ions due to electrostatic repulsion and thus increases the rate capability of lithium-ion batteries. The lithium-ion cells comprising LiFePO₄/Li with viologen-added in the electrolyte exhibited a discharge capacity of 110 mAh g^-1 at 6 C –rate with 95 % of capacity retention even after 500 cycles. The added-viologen not only enhanced the electrochemical properties but also significantly reduces the self-extinguishing time. The fast-charging ability and better cycling performances at 6C –rate is attributed to the formation of a stable, robust and conductive solid electrode/electrolyte interface with less corrosive aluminum current collector.

e-mail: amstephan@cecri.res.in