Impact of Trifluoromethylation of Adiponitrile on Aluminum Dissolution Behavior in Dinitrile-Based Electrolytes

Abstract

Aluminum dissolution behavior of adiponitrile (ADN) and its trifluoromethylated derivative 3-(trifluoromethyl)adiponitrile (ADN-CF3) as single or co-solvent with propylene carbonate (PC) was determined in electrolytes with lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) as conducting salt via selected electrochemical, spectroscopic and physicochemical methods. ADN-CF3 is introduced as a promising electrolyte solvent affording reduced aluminum dissolution in the presence of imide salts. In cases where neither electrolyte components nor decomposition products thereof enable the formation of protective surface layers on aluminum current collectors, both the viscosity and relative permittivity of the solvents could be identified as key parameters for reducing aluminum dissolution. High viscosities reduce the mobility of involved species yielding increased complex formation of Li+ and TFSI− ions or solvent molecules, hindering a reaction of TFSI− anions with the passivating aluminum oxide surface to Al(TFSI)x. Low relative permittivity yields lesser ionic dissociation of the lithium salt and lower solubility of Al(TFSI)x species in viscous electrolytes. Hence, reduced aluminum dissolution was observed by substituting electrolyte solvents from PC to ADN to ADN-CF3. The obtained results significantly contribute to better understanding of anodic aluminum dissolution behavior, while encouraging future design of advanced electrolytes with high viscosities and low-permittivity solvents that possess high oxidative stabilities.