Screening of Ionic Liquid-Based Electrolytes for Al Dual-Ion Batteries: Thermodynamic Cycle and Combined MD-DFT Approaches

Abstract

The electrochemical window (ECW) of the ionic liquid (IL) is the fundamental parameter to understand the stability of the electrolyte for a given electrode material. Here, we have considered room-temperature and molten salt-based 16 IL-based electrolytes, consisting of imidazolium-, pyrrolidinium-, urea-, and acetamide-based cations coupled with AlCl4 and OTf (trifluoromethanesulfonate) anions. Three different high-throughput computational screening techniques have been implemented to calculate the ECW of these electrolytes for dual-ion batteries (DIBs). The thermodynamic cycle method has been employed to calculate the oxidation and reduction potentials with respect to the Al3+/Al reference electrode for the individual ions of the IL. Classical molecular dynamics followed by DFT methods (MD + DFT) have been considered to calculate anodic and cathodic limiting potentials. From the MD + DFT, we have classified two methods, AIMD-min and AIMD-sp. The calculated ECWs for all considered ILs using the AIMD-min method are found to be close to experimental outcomes compared to other two methods. We show that the alkyl group of the imidazolium ring has a very limited effect on the ECW values. On the other hand, aromatic imidazolium rings are more prone to reduction compared to the nonaromatic pyrrolidinium ring. Moreover, we have investigated the contribution of cations and anions in cathodic and anodic potentials, from the study of density of states. Along with that, we have tested the robustness capability of the AIMD-min method and established a superior technique for other liquid systems to calculate the ECW. This work facilitates a step forward in selecting nonaqueous electrolytes for rechargeable DIBs. © 2023 American Chemical Society.