Reversible Cycling of Graphite Electrodes in Propylene Carbonate Electrolytes Enabled by Ethyl Isothiocyanate

As one of the greatest inventions in the history of electrochemistry, the lithium-ion battery (LIB) has radically transformed human beings' daily life by powering portable electronics and electric vehicles. When we look back upon the long and arduous effort devoted to the development of the LIB technology, it is found that the birth of LIBs could have been even earlier if reversible cycling of the graphite electrode had been realized in the propylene carbonate (PC) electrolyte, one of the few dominating electrolytes extensively used in nonaqueous electrochemistry long before the concept of LIBs. In this work, a functional electrolyte additive, that is, ethyl isothiocyanate, has been identified to enable the reversible Li⁺ ion intercalation/de-intercalation into/out of the graphite electrode in PC electrolyte by forming a high-quality solid electrolyte interphase (SEI) on the graphite electrode. A wide range of advanced in situ and ex situ spectroscopic characterization techniques coupled with theoretical calculations have been employed to understand the SEI formation mechanism. The results reported here rejuvenate the promise of PC as the primary electrolyte solvent for LIBs by artificially rectifying the interfacial electrochemical processes.