Screening of the Role of the Chemical Structure in the Electrochemical Stability Window of Ionic Liquids: DFT Calculations Combined with Data Mining

Abstract

Ionic liquids have attracted the attention of researchers as possible electrolytes for electrochemical energy storage devices. However, their properties, such as the electrochemical stability window (ESW), ionic conductivity, and diffusivity, are influenced both by the chemical structures of cations and anions and by their combinations. Most studies in the literature focus on the understanding of common ionic liquids, and little effort has been made to find ways to improve our atomistic understanding of those systems. The goal of this paper is to explore the structural characteristics of cations and anions that form ionic liquids that can expand the HOMO/LUMO gap, a property directly linked to the ESW of the electrolyte. For that, we design a framework for randomly generating new ions by combining their fragments. Within this framework, we generate about 104 cations and 104 anions and fully optimize their structures using density functional theory. Our calculations show that aromatic cations are less stable ionic liquids than aliphatic ones, an expected result if chemical rationale is used. More importantly, we can improve the gap by adding electron-donating and electron-withdrawing functional groups to the cations and anions, respectively. The increase can be about 2 V, depending on the case. This improvement is reflected in a wider ESW.

Multiscale modeling for enhanced battery health analysis: Pathways to longevity

“…[67,68] Therefore, the electrochemical window is a comprehensive consideration of the characteristics of both the electrolyte and electrode materials. [69] F I G U R E 3 Simulations of electrolyte voltage window. (a) Calculated Redox potentials for the polymers and salts; (b) Lowest unoccupied molecular orbital (LUMO) orbitals and spin densities of the reduced states of LiTFSI, LiFSI, and LiCF 3 SO 3 .…”

“…[ 67,68 ] Therefore, the electrochemical window is a comprehensive consideration of the characteristics of both the electrolyte and electrode materials. [ 69 ]…”

Identification of Potential Electrolyte Additives via Density Functional Theory Analysis

“…as the determinant to screen reductive additives [5] . Very recently, Silva and co‐workers performed electrochemical stability analysis on a lot of ionic liquids (possible electrolyte), using the HOMO‐LUMO gap as the major determinant [11] …”

“…[5] Very recently, Silva and co-workers performed electrochemical stability analysis on a lot of ionic liquids (possible electrolyte), using the HOMO-LUMO gap as the major determinant. [11] Among the functional additives, vinylene carbonate (VC) is the most commonly used additive for the current LIBs. [4,12] The reactivity of VC comes from its functionality of polymerizable vinyl and its structure of high strain, which is caused by the sp 2 -hybridized carbons on the ring.…”