Safer electrolyte components for rechargeable batteries

Among the electrochemical energy storage systems, rechargeable lithium batteries are considered very promising candidates for the next generation power sources because of their high gravimetric and volumetric energy density with respect to other cell chemistries. The lithium-ion battery technology is based on the use of electrode materials able to reversibly intercalate lithium cations, which are continuously transferred between two host structures (negative and positive electrodes) during the charge and discharge processes. Commercial lithium-ion batteries commonly use liquid electrolytes based on suitable lithium salts (solute) and organic compounds (solvents). The latter, volatile and flammable, represent serious concerns for the safety of the electrochemical devices, this so far preventing their large diffusion in applications as automotive, storage from renewable sources, smart grids.

One of the most appealing approaches is the partial or total replacement of the organic solvents with safer, less hazardous, electrolyte components. Here, a concise survey of ones of the most investigated types of alternative electrolyte components, proposed for safer and more reliable rechargeable lithium batteries, is reported.

Graphical Abstract:

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

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.