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

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 (CM ≥ 3 M) 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 LiPF6 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 PF6
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- 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.