Rational design of sulfone-based electrolytes for dual-ion batteries

• Synergy of two salts was used to make sulfone-based electrolytes functional in DIB. • A rational physicochemical approach to the design of such electrolytes was shown. • Series of electrolytes, stable over a wide potential range, was developed. • The effects of preparation procedures and cycling protocols were studied. • Further improvements of the concept as well as economical aspects were discussed. Dual-ion batteries (DIB) with a graphitic cathode represent an intriguing concept, which remains challenging to commercialise. One of the key obstacles is selection of an electrolyte with a sufficiently broad window of electrochemical stability (0 V ≤ E ≤ 5.5 V vs. Li + /Li). Often, modern studies suggest either use of super-concentrated electrolytes ( C M ≥ 3M) or chemical modification of the solvent to walk round this problem. These approaches, however, result in decreased power density, a narrowed operating temperature window and increased cost of the final battery system. Another option is to avoid using the super-concentration concept by selecting an appropriate combination of an electrochemically stable solvent and a combination of salts. This was realised in our work. We re-considered sulfones, known for their exceptionally high oxidative stability, as electrolyte solvents. Their instability within the anodic range of electrochemical potentials was tackled by mixing LiFSI and LiPF 6 salts. This resulted into following synergy: the presence of FSI - anions ensured electrolyte compatibility with metallic lithium and graphite, serving as anodes, while a sufficient concentration of PF 6 - anions reduced the impact of current collector corrosion. Before long-term electrochemical tests, we conducted a preliminary physicochemical characterisation of a series of sulfone-based electrolytes, which can serve as a method for their rational development. Particular attention was paid to the impact of preparation and testing protocols onto long-term cycling behaviour. Besides, fundamental ways of improving the sulfone-based electrolytes were discussed. Ultimately, the most promising electrolyte-candidate was selected based on performance, sustainability, and price.