Sascha Franz-Josef LEYENDECKER1, Leonard DICK1, Jan BLASIUS1, Koen BINNEMANS2, Barbara KIRCHNER1
1University of Bonn, Bonn, Germany
2KU Leuven, Leuven, Belgium
Aiming towards developing alternative battery technologies, the design of novel electrolytes is one of the key ways to enhance the properties of batteries. The experimental screening of novel electrolytes, however, is a tedious venture as new compounds need to be synthesized and tested thoroughly. At the same time, the environmental aspect plays a major role, as broad experimental screening of a plethora of trial electrolytes is inefficient and creates a lot of chemical waste. Therefore focusing the experimental screening of electrolytes on more promising candidates may be key to not only accelerate the progress in this area of research but also to do it in an environmentally friendly manner.
Herein, a theoretical study is presented, focused on obtaining structure-property relationships of a variety of solvent-salt combinations to set a guideline for experimental research on promising candidates for novel battery electrolytes. As solvents, two ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2C1Im][NTf2]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2C1Im][BF4]), are proposed. As for the salt, the monovalent s-block metal cations lithium and sodium are paired together with fluorohydridoborate (BH4–nFn–, n = 0 − 4) and cyanohydridoborate (BH4–n(CN)n–, n = 1 − 3) based anions. All combinations of ionic liquid solvent, metal cation and borate anion are studied to obtain data regarding the influence of each component on structural, dynamical and electrochemical properties. By performing molecular dynamics (MD) simulations, the dynamics of each solvent-salt combination is modeled. Clusters including all ligands in the first solvation shell of the central metal cation are harvested from the MD simulation and are then optimized with static quantum chemical calculations. Using these structures, the cation-ligand coordination in regard to system composition is determined and trends in structure and reduction potential are evaluated.