Distinct roles: Co-solvent and additive synergy for expansive electrochemical range and low-temperature aqueous batteries

Abstract

The present study addresses the challenges encountered by aqueous lithium-ion batteries (ALiBs), specifically the limited electrochemical stability window and inadequate low-temperature energy retention. We propose a binary solvent electrolyte system comprising N,N-Dimethylformamide (DMF) as a co-solvent and 3-sulfolene (3SF) as an additive (5 wt.% 3SF in 9 M LiTFSI H2O/DMF with a molar ratio of 1:1). The H2O solvent ensures non-flammability and high safety, while DMF reduces the freezing point and enhances low-temperature conductivity. Additionally, DMF actively solvates Li+ ions, thereby reducing interfacial H2O content. Moreover, through the incorporation of the 3SF additive along with LiTFSI, a stable bilayer interphase film is formed on the anode surface effectively expanding the electrochemical stability window to 4.37 V. By leveraging the distinct roles played by solvents and additive, exceptional performance at both room temperature and low-temperature is achieved for the LiMn2O4/Li4Ti5O12 cell. Specifically, at room temperature, the cell demonstrates an initial coulombic efficiency reaching 90 %. Moreover, even after undergoing 300 cycles at 1 C, the capacity remains as high as 156.3 mAh g−1 (with a remarkable capacity retention rate of 96 %). Notably, in extremely low-temperatures of -30 °C, the cell exhibits excellent cycling performance which can still maintain a capacity retention rate of 98.8 % after 50 cycles. The proposed electrolyte design strategy, which takes into account both the bulk electrolyte and interfacial chemistry, presents a practical and feasible approach for the development of safe, low-temperature, and high-energy density ALiBs.