Design Rules for Selecting Fluorinated Linear Organic Solvents for Li Metal Batteries

Abstract

Fluorinated linear organic solvents have great potential in improving the safety and lifetime of next-generation Li metal batteries. However, this group of solvents is underexplored. Here, we investigate the molecular and interfacial reactivity properties of seven partially and fully fluorinated linear carbonates designed based on conventional solvents. Using density functional theory, we find the highest occupied molecular orbital levels decrease with increasing substitution of the fluorinated functional groups, implying that fluorination, to a first approximation, improves the stability toward high voltage cathodes. On the basis of the simulated decomposition mechanisms and statistical analyses, we find that a fluorinated linear carbonate with partial fluorination at the methyl component is more accessible in terms of degradation and LiF nascence formation, leading to a potentially LiF-rich solid electrolyte interphase (SEI). The molecular design concepts and the computational techniques presented are transferable to ester and ether systems, facilitating the navigation in a large chemical design space.

High Energy Density Rechargeable Batteries Based on Li Metal Anodes. The Role of Unique Surface Chemistry Developed in Solutions Containing Fluorinated Organic Co-solvents

“…We discovered the positive effect that can be reached by adding trans -difluoroethylene carbonate (DFEC) as a co-solvent to FEC-based solutions. This doubly fluorinated cyclic organic carbonate co-solvent was shown to be a promising additive to the commonly used organic carbonates for cycling NCA/SiO@C and Li|NCM 622 cells, as well as to sulfone based electrolyte solutions for stable cycling of graphite|NCM 532 cells . An electrolyte solution with DFEC enabler was applied for stabilization of the cells with Li metal anodes and NCM 622 cathodes with areal capacity of 1.75 mAh cm –2 .…”

“…Fluorinated organic solvents display unique physicochemical properties because of the very high electronegativity, high ionic potential, and low polarizability of the fluorine atoms . Replacing hydrogen atoms with fluorine atoms decreases the HOMO and LUMO energy levels, thus leading to an increased anodic stability . However, the significance of fluorine atoms is not only their presence but also their position in the structure of molecules considered as functional electrolyte solutions’ components.…”

“…41 Replacing hydrogen atoms with fluorine atoms decreases the HOMO and LUMO energy levels, thus leading to an increased anodic stability. 51 However, the significance of fluorine atoms is not only their presence but also their position in the structure of molecules considered as functional electrolyte solutions' components. Hence, not all fluorinated organic solvents can contribute to LiF formation on the electrodes' surfaces in Li batteries.…”

Growth Mechanism of Micro/Nano Metal Dendrites and Cumulative Strategies for Countering Its Impacts in Metal Ion Batteries: A Review

“…The metal anodic terminal, which works as the battery's negative electrode, is lithiated to a potential of ~0.09 V vs. Li/Li + [104] in the presence of organic electrolytes such as ethylene carbonate, dimethyl carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, etc. The anodic oxidation-reduction energy levels lie below the lowest unoccupied molecular orbital (LUMO) of the above-mentioned electrolytes, giving rise to electrode decomposition [105][106][107]. However, during the charging process, a stable passivation layer or SEI blocks the electrode-electrolyte decomposition.…”

A Minimal Information Set To Enable Verifiable Theoretical Battery Research

“…Once published, we suggest that the filled-out checklist be a part of the Supporting Information and provide the necessary background to the readers. To give examples of filled-out checklists for different theoretical studies, each author populated a checklist for at least one of their published articles. ,,,− We aimed to cover many different types of battery modeling paradigms in the author-populated checklists. It also serves as a good starting reference for battery modeling best practices and shortcomings.…”