Development of Safe and Sustainable Dual-Ion Batteries Through Hybrid Aqueous/Nonaqueous Electrolytes

In this study, a new dual-ion battery (DIB) concept based on an aqueous/non-aqueous electrolyte is reported, combining high safety in the form of a nonflammable water-in-salt electrolyte, a high cathodic stability by forming a protective interphase on the negative electrode (non-aqueous solvent), and improved sustainability by using a graphite-based positive electrode material. Far beyond the anodic stability limit of water, the formation of a stage-2 acceptor-type graphite intercalation compound (GIC) of bis(trifluoromethanesulfonyl) imide (TFSI) anions from an aqueous-based electrolyte is achieved for the first time, as confirmed by ex-situ X-ray diffraction. The choice of negative electrode material shows a huge impact on the performance of the DIB cell chemistry, i.e., discharge capacities up to 40 mAh g−1 are achieved even at a high specific current of 200 mA g−1. In particular, lithium titanium phosphate (LiTi2(PO4)3; LTP) and lithium titanium oxide (Li4Ti5O12; LTO) are evaluated as negative electrodes, exhibiting specific advantages for this DIB setup. In this work, a new DIB storage concept combining an environmentally friendly, transition-metal-free, abundant graphite positive electrode material, and a nonflammable water-based electrolyte is established, thus paving the path toward a sustainable and safe alternative energy storage technology.