Bi-salt electrolyte for aqueous rechargeable aluminum battery

Abstract The exertion of superior high-energy density based on multivalent ions transfer of rechargeable aluminum batteries is greatly hindered by limited electrochemical stability window of typical water in salt electrolyte (WiSE). Recently, it is reported that a second salt addition to the WiSE can offer further suppression of water activities, and achieves a much wider electrochemical window compared with aqueous WiSE electrolytes. Hence, we demonstrate a class of water in bi-salt electrolyte containing the trifluoromethanesulfonate (OTF), which exhibits an ultra-wide electrochemical window of 4.35 V and a very low overpotential of 14.6 mV. Moreover, the interface chemistry between cathode and electrolyte is also confirmed via kinetic analysis. Surprisingly, we find the electrolyte can effectively suppress Mn dissolution from the cathode, alleviate self-discharge behavior, and ensure a stable electrode–electrolyte interface based on the interface concentrated-confinement effect. Owing to these unique merits of water in bi-salt electrolyte, the AlxMnO2·nH2O material delivers a high capacity of 364 mAh g−1 and superb long-term cycling performance > 150 cycles with a capacity decay rate of 0.37% per cycle with coulombic efficiency at ca. 95%.