Stable lithium-ion batteries based on a hybrid aqueous/organic electrolyte

Moving from organic to aqueous lithium-ion batteries (ALIBs) would be an interesting feat. As of today, we have water-in-salt electrolytes (WISEs) that were developed primarily to expand the electrochemical stability window of traditional aqueous electrolytes. However, their cathodic limits do not enable the use of high-capacity negative electrodes and the very high concentrations of expensive heavily fluorinated salts, often >20 mol kg−1, hinder any feasible implementation of LIBs based on WISEs. A hybrid organic/aqueous electrolyte based on LiFTFSI dissolved in sulfolane and water is here presented as an alternative, where sulfolane is used to tune and reduce the water activity, by altering the Li+ cation first solvation shell, and thereby the cathodic limit can be pushed to <1.0 V vs. Li+/Li even at a comparatively moderate salt concentration (7.8 mol kg−1). This enables long-term operation of an Li4Ti5O12⎪hybrid electrolyte⎪LiMn2O4 2.4 V cell with a specific energy of 156 Wh kgAM−1.