Synergistic dual co-solvents hybrid electrolyte design enabling high-voltage flexible aqueous lithium-ion fiber batteries

Flexible aqueous lithium-ion batteries are promising safe power sources for next-generation of portable and wearable electronic devices due to their intrinsic safety and eco-friendliness. However, water-related side reactions in aqueous electrolytes have greatly limited their operating voltage and electrochemical performance. Herein, we report a new family of 2.4 V high-voltage flexible aqueous lithium-ion fiber battery by designing a fluorine-free and high-voltage synergistic dual co-solvents aqueous hybrid electrolyte with high ionic conductivity, low cost, and high safety. Sulfolane and trimethyl phosphate are used as synergistic dual co-solvents, which can not only extend the electrochemical stability window of electrolyte to 3.3 V by suppressing the activity of water, but also form a S-/P-containing inorganics-rich solid electrolyte chlorination interphase for better electrochemical performance. Combined with novel flexible hybrid fiber electrodes, the resulting flexible aqueous fiber batteries exhibit high working voltage plateau (2.4 V, much higher than most reported flexible aqueous batteries), high energy density (146.5 Wh kg⁻¹), and superior cycling performance (500 cycles). In addition, these aqueous fiber batteries present impressive mechanical flexibility, which can be easily woven into clothes to power wearable electronics. This work is an inspiration for the design of next-generation of flexible batteries with both high energy and safety.