Water/Sulfolane Hybrid Electrolyte Achieves Ultralow-Temperature Operation for High-Voltage Aqueous Lithium-Ion Batteries

Aqueous batteries are promising candidates for large-scale energy storage due to their high safety and low cost. However, the narrow electrochemical stability window (ESW, 1.23 V) and high melting point (0 °C) of water limit the energy density and low-temperature operation of aqueous batteries. In this work, sulfolane is introduced as a co-solvent to obtain a water/sulfolane hybrid electrolyte, which participates in the solvated sheath of lithium ions, strengthens the O  H bond of water, and disrupts the large-scale hydrogen bond network. Such an elaborate strategy not only expands the ESW of the hybrid electrolyte to 3.8 V, but also lowers the glass-transition temperature to −110 °C. As proof of concept, the LiMn 2 O 4 /Li 4 Ti 5 O 12 full batteries assembled by the hybrid electrolyte display high voltage (2.7 V) and excellent low-temperature performance of 98% capacity retention from 0 to −20 °C, which can even discharge normally and illume an LED light (rated power of 0.02 W, excitation voltage of 1.8 V) at −65 °C.