Fluorine‐Free Electrolytes for Lithium and Sodium Batteries

Abstract

Fluorinated components in the form of salts, solvents and/or additives are a staple of electrolytes for high‐performance Li‐ and Na‐ion batteries, but this comes at a cost. Issues like potential toxicity, corrosivity and environmental concerns have sparked interest in fluorine‐free alternatives. Of course, these electrolytes should be able to deliver performance that is on par with the electrolytes being in use today in commercial batteries. This begs the question: Are we there yet? This review outlines why fluorine is regarded as an essential component in battery electrolytes, along with the numerous problems it causes and possible strategies to eliminate it from Li‐ and Na‐ion battery electrolytes. The examples provided demonstrate the possibilities of creating fully fluorine‐free electrolytes with similar performance as their fluorinated counterparts, but also that there is still a lot of room for improvement, not least in terms of optimizing the fluorine‐free systems independently of their fluorinated predecessors.

Liquid electrolyte chemistries for solid electrolyte interphase construction on silicon and lithium-metal anodes

“…Alternatively, LiF-rich SEIs 170 can be generated using electrolytes exclusively composed of fluorinated solvents 232 and supplements such as hexafluoroisopropyl trifluoromethanesulfonate (HFPTf), trimethylsilyl(fluorosulfonyl)( n -nonafluorobutanesulfonyl)imide (TMS-FNFSI), 2,2,2-trifluoroethyl trifluoroacetate (TFE), 2-fluoropyridine (2-FP), difluoroethylene carbonate (DFEC), 2,2,2-trifluoroacetate (TFA), and 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM). 233–237 Despite the advantages of fluorinated solvents and salts, their widespread use for cell operation under practical conditions is hindered by several problems 238 such as cost-effectiveness, scalability for large-scale production, stability during long-duration storage, environmental concerns, and the inherently high density of fluorinated solvents. 239,240 Fluorinated salts and solvents are expensive and currently unsuitable for mass production.…”

Practical Cathodes for Sodium‐Ion Batteries: Who Will Take The Crown?

“…However, it should be noted that FEC is not a perfect electrolyte additive as it does not match with some anodes and is prone to decomposition at elevated temperatures. [ 341 ] On the other hand, although fluorinated electrolyte components exhibit high electrochemical stability, the production of toxic byproducts (HF, NaF) can pose safety and environmental hazards. Therefore, it is suggested to develop novel functional electrolytes that are inexpensive, non‐toxic, and can form thin and uniform interface layers on the cathode and anode, so as to further promote the development of SIBs.…”

Eco-friendly electrolytes via a robust bond design for high-energy Li metal batteries

“…15,40,41 Despite these advances, the high fluorine content, either from high-concentration salts or from fluorinated solvents/diluents, leads to considerably higher production cost and greater environmental burden. 37,42 In addition, the reduction of fluorinated organic solvents generates parasitic organic components, but the reduction of fluorinated inorganic salts produces only an inorganic SEI, which is preferred in Li metal batteries. Therefore, designing novel less-fluorinated electrolytes that are eco-friendly and low cost but still possess good compatibility with both LMA and high-voltage cathodes is highly desirable to advance the commercialization of practical LMBs.…”