A Series of Polyhydric Esters As Novel Candidates for Battery Solvents in Lithium Metal Cells: Electrochemical Investigations and Influences of Moisture and Alcohol Residues in Contact with Lithium Metal

Abstract

In recent years, the lithium metal anode has aroused great interest, not at least through the development of the lithium//sulfur and the lithium//air battery technologies, in all-solid-state batteries. However, the application of lithium metal anodes is limited by safety issues and several failure mechanisms, including, dendrite growth and direct chemical reactions with electrolyte components like battery solvents, which leads to fast capacity losses. In this context, a new series of polyhydric propyl-based esters were investigated, namely n-propyl acetate, isopropyl acetate (monohydric esters), trimethylene diacetate, 1,2-propylene glycol diacetate (dihydric esters) and triacetin (trihydric ester) as attractive and environmental friendly candidates for electrolyte solvents in lithium metal battery applications.The above mentioned organic esters were examined in respect to their reactivity in contact with lithium metal, influenced by water or alcohol impurities. The resulting reaction products were analyzed and determined via 1H-NMR spectroscopy. Additional experiments were performed and the resulting products compared to anticipated reaction products which were prepared separately, to evidence possible reaction mechanisms like the occurrence of a CLAISEN-condensation. Furthermore, the here mentioned propyl-based esters and the reaction products were analyzed by cyclic voltammetry against copper, platinum and aluminum as working electrode to evaluate the anodic and cathodic stability, as well as possible anodic dissolution reactions in the presence of LiTFSI as conducting salt. In both cases, the reactivity in contact with lithium metal and the anodic dissolution of aluminum, a reactivity could be observed whereupon the trihydric esters were least reactive followed by the dihydric and monohydric esters. In absence of water and alcohols all investigated esters show no detectable reaction with lithium metal. ACKNOWLEDGMENT The authors want to acknowledge the German Federal Ministry for Economic Affairs and Energy (BMWi) for funding within the project FesKaBat (03ET6092E). The authors also acknowledge the analytical group of Sascha Nowak (MEET Battery Research Center, University of Münster) for all performed TXRF measurements.