Pyrrolidinium‐based ionic liquids as electrolytes for lithium batteries: A Computational Study

Electrochemical windows (ECWs) of the cyclic ammonium based ionic liquids formed by the combination of two common pyrrolidinium cations—N,N‐butylmethyl pyrrolidinum(Pyr14) and N,N‐hexylmethyl pyrrolidinium(Pyr16) and five anions—dicyanamide, trifluoroacetate, fluoromethane sulfonate, bis((trifluoromethylsulfonyl)imide, and bis(fluorosulfonyl)imide were investigated. The ECW of each ionic liquid was obtained from the oxidation and reduction potentials of these ionic liquids with respect to a Li+/Li reference electrode by using thermodynamic cycle method. The work reveals that the ECWs of these ionic liquids are solely decided by the HOMO energy of pairing anions. The ECWs were also computed using HOMO‐LUMO method employing Møller‐Plesset perturbation theory to the second order and M06L methods with a basis set of 6‐31 + G(d, p). The ECW computed using M06L functional with an extended basis set of 6‐311++G(d, p) showed better agreement with experimental values suggesting accurate computation of ECW is possible at lower computational cost. Electrochemical windows (ECW) of pyrrolidinium‐based ionic liquids computed for their use as lithium battery electrolytes for the first time. HOMO energy of pairing anions is identified as a decisive factor to determine the ECW. DFT functional M06L in conjunction with HOMO‐LUMO method is demonstrated as a viable method for accurate computation of ECW.