Enabling high-voltage aqueous dual-ion batteries capable of working at −40 °C in a low-concentration salt electrolyte

Graphite positive electrode-based anion-intercalation aqueous dual-ion batteries using bis(trifluoromethanesulfonyl)imide anion intercalations show the potential because of the high discharge plateau (>1.4 V vs. the standard hydrogen electrode at 25 °C ± 2 °C) for anion chemistry. However, currently, the electrochemical performance of aqueous dual-ion batteries based on bis(trifluoromethanesulfonyl)imide anion intercalation can only be achieved in highly concentrated salt electrolytes. This dependence on high anion concentration to activate intercalation inevitably leads to high costs and prevents operation at low temperatures (e.g., < −20 °C). In this context, we explore a hydrogel electrolyte rich in dipole molecules, incorporating only 1 M lithium bis(trifluoromethanesulfonyl)imine and 2 M zinc chloride, with expanded electrochemical stability windows (>4.6 V at −40 °C) to activate bis(trifluoromethanesulfonyl)imide anion insertion into the graphite positive electrode through high-voltage scanning to 3.0 V. The assembled aqueous dual-ion batteries based on bis(trifluoromethanesulfonyl)imide anion intercalation demonstrate high discharge plateaus of 1.9 V at −20 °C and 1.7 V at −40 °C, along with a specific energy of 595 Wh kg−1 (normalized to the 1 mg cm−2 of the graphite positive electrode). Graphite-based anion intercalation aqueous dual-ion batteries using TFSI⁻ are limited by the need for highly concentrated salt electrolytes. Here, the authors develop a dipole molecule-rich hydrogel electrolyte enabling high specific energy at −40 °C.