Safer Electrolytes for Lithium‐Ion Batteries: State of the Art and Perspectives

Abstract

Lithium-ion batteries are becoming increasingly important for electrifying the modern transportation system and, thus, hold the promise to enable sustainable mobility in the future. However, their large-scale application is hindered by severe safety concerns when the cells are exposed to mechanical, thermal, or electrical abuse conditions. These safety issues are intrinsically related to their superior energy density, combined with the (present) utilization of highly volatile and flammable organic-solvent-based electrolytes. Herein, state-of-the-art electrolyte systems and potential alternatives are briefly surveyed, with a particular focus on their (inherent) safety characteristics. The challenges, which so far prevent the widespread replacement of organic carbonate-based electrolytes with LiPF6 as the conducting salt, are also reviewed herein. Starting from rather "facile" electrolyte modifications by (partially) replacing the organic solvent or lithium salt and/or the addition of functional electrolyte additives, conceptually new electrolyte systems, including ionic liquids, solvent-free, and/or gelled polymer-based electrolytes, as well as solid-state electrolytes, are also considered. Indeed, the opportunities for designing new electrolytes appear to be almost infinite, which certainly complicates strict classification of such systems and a fundamental understanding of their properties. Nevertheless, these innumerable opportunities also provide a great chance of developing highly functionalized, new electrolyte systems, which may overcome the afore-mentioned safety concerns, while also offering enhanced mechanical, thermal, physicochemical, and electrochemical performance.

Gel Polymer Electrolytes for Electrochemical Energy Storage

“…However, the reported solid polymer electrolytes mostly deliver low ionic conductivities (10 −8 −10 −5 S cm −1 ) and poor interfaces with electrodes, resulting in deteriorated cycle performance. [1][2][3][4] The inferior mechanical property has also limited their developments. To this end, combined the advantages of both the liquid and solid electrolytes, gel polymer electrolytes (GPEs) have attracted increasing attentions as they can function as not only electrolytes but also separators.…”

Ion Transport in Solvent-Free, Crosslinked, Single-Ion Conducting Polymer Electrolytes for Post-Lithium Ion Batteries

“…Post-lithium ion batteries, including those based on lithium metal and other more abundant materials, are under active investigation. Next-generation battery electrolytes that allow for improved safety, maintained or longer device lifetimes, and that support post-lithium ion platforms are highly desired [1][2][3][4][5][6].…”

“…These electrolytes exhibit high Li-ion conductivity and support an adequate solid-electrolyte-interface (SEI) formation, but they present many practical disadvantages, such as being volatile and flammable [1,5,7,8]. One class of electrolytes that are seen as a possible alternative are polymer electrolytes (PE).…”

Towards Li-Ion Batteries Operating at 80 °C: Ionic Liquid versus Conventional Liquid Electrolytes

“…The key issues to address to ensure a continuous increase in the use of LIBs for large scale electrical energy storage are safety [1] and sustainability [2]. Since high operating or storage temperatures (i.e., above 50 • C) can give rise to significant fading for most commercial LIBs [3,4], cooling systems are generally required.…”