Structurally tunable characteristics of ionic liquids for optimizing lithium plating/stripping via electrolyte engineering

Electrolyte chemistry offers the opportunity to regulate the solid electrolyte interphase (SEI) and Li+ solvation, which is considered to be crucial to the growth of lithium crystals for safe lithium metal batteries (LMBs). Structurally tunable characteristics of ionic liquids (ILs) from anion type, cationic substituent chain length and cationic substituents, will contribute this field. Here, we explore the influence mechanism of imidazole-based ILs as electrolyte additives on Li+ solvation and the formation of SEI. ILs can participate into the formation of efficient SEI, together with cathode electrolyte interphase (CEI). Moreover, ILs can also regulate the sheath structure of Li+ solvation, to fasten the kinetics of Li. Furthermore, the imidazole-based cations with long alkyl chain can form an electrostatic shield around newly formed Li nucleus, and suppress further Li plating at this site. Under the optimized condition, the 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIm]TFSI) additive shows the best ability to enhance the electrochemical performance, endowing the Li||Li symmetric cell with a stable life (over 800 h) at 0.5 mA cm−2 and the Li||LiNi0.6Mn0.2Co0.2O2 (NMC622) full cell with a high capacity of 141.7 mAh g−1 after 200 cycles at 0.5 C.