Theoretically predicting the feasibility of highly-fluorinated ethers as promising diluents for non-flammable concentrated electrolytes

Abstract

The practical application of nonflammable highly salt-concentrated (HC) electrolyte is strongly desired for safe Li-ion batteries. Not only experimentalists but also theoreticians are extensively focusing on the dilution approach to address the limitations of HC electrolyte such as low ionic conductivity and high viscosity. This study suggests promising highly-fluorinated ethers to dilute the HC electrolyte based on non-flammable trimethyl phosphate (TMP) solvent. According to the quantum mechanical and molecular dynamics calculations, the fluorinated ether diluents showed a miscibility behavior in HC TMP-based electrolyte. While such miscibility behavior of the diluent with TMP solvent has been significantly enhanced by increasing its degree of fluorination, i.e., the “fluorous effect”, it is remarkable that the self-diffusion constant of Li+ and the ionic conductivity should be significantly improved by dilution with bis(1,1,2,2-tetrafluoro ethyl) ether (B2E) and bis(pentafluoro ethyl) ether (BPE) compared to other common hydrofluoroether diluents. In addition, the fluorinated-ether diluents have high ability to form a localized-concentrated electrolyte in HC TMP-based solution, leading to high expectation for the formation of a stable and a compact inorganic SEI film.

Enhanced Li+ Transport in Ionic Liquid‐Based Electrolytes Aided by Fluorinated Ethers for Highly Efficient Lithium Metal Batteries with Improved Rate Capability

“…As discussed above, in the presence of BTFE, Li + is more strongly coordinated with FSI − since BTFE does not solvate Li + , but favors for a stronger solvation of Li + by FSI − . [ 44 ] The previously described Li + ‐FSI − complex could be (part of) this new, larger structure observed in the SAXS.…”

“…The relatively lower average CE in Li/NMC cells versus Li/LFP cells demonstrates accelerated side reactions on the cathode/electrolyte interface because of a higher operation potential and NMC's catalytic effect in enhancing the electrolyte decomposition. [57] Considering the anodic stability potential window of the electrolyte and the current per- formance, we can infer that further optimization of the cathode material, for example, the structure, morphology, and surface engineering, [58] as well as the electrolyte, for example, different fluorinated ether, [29,44] and use of additives, is feasible to improve the performance of the Li/NMC cells.…”

Applying Classical, Ab Initio, and Machine-Learning Molecular Dynamics Simulations to the Liquid Electrolyte for Rechargeable Batteries

“…The strong interaction between cations and anions in HCEs delivers several disadvantages, including low conductivity and high viscosity. , One innovative solution to these drawbacks is introducing inert cosolvents to dilute the concentrated electrolytes, namely, LHCEs (Figure a). ,,,,− LHCEs can be regarded as HCEs mixed with diluents. Diluents should be inactive not only in chemical reactions but also in coordination with cations to maintain unique solvation structures in HCEs. ,− In this regard, the above-mentioned DIPE and DIPS share the same properties with diluents.…”

Development of advanced electrolytes in Na-ion batteries: application of the Red Moon method for molecular structure design of the SEI layer

“…Until today, SEI layer is considered one of the most important but least understood components in rechargeable batteries, regarding the complexity of its formation's chemical and electrochemical reactions and the insufficient direct measurement of its physical properties. 35 Various computational methods have been applied, especially to enrich the understanding of the initial reduction of electrolyte components such as quantum chemical (QC) calculations, [36][37][38][39][40][41][42] rstprinciple or ab initio-molecular dynamics (ab initio-MD), [43][44][45][46][47][48][49][50] classical molecular dynamics (MD), 51,52 and reaction force eld (ReaxFF-MD) approaches. 53,54 Indeed, multiple QC calculations studies were conducted to predict the reduction decomposition mechanism of electrolyte compounds.…”

“…On the other hand, regarding force eld molecular simulation methods, classical MD simulations were used mainly to investigate the electrolyte properties and the electric double layer. 51,52 Nevertheless, ReaxFF-MD, which can qualitatively describe the forming/breaking of chemical bonds, was performed to analyze chemical reactions in rather large systems beyond the scope of ab initio-MD. 53,54 However, the progress on the understanding of SEI remained still humble regarding the complexity of its heterogeneous substructure.…”