Hydrogel electrolytes are promising in developing flexible and safe batteries, but the presence of large amounts of free solvent water makes battery chemistries constrained by parasitic H2 evolution and electrode dissolution.
Recently, researchers from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences (CAS) have developed an unconventionally salt-concentrated hydrogel electrolyte with salt fraction up to 44 mol% without phase separation, which essentially suppresses water-induced side reactions and thus enables practical long-cycling operation of aqueous sodium-ion batteries.
The study was published in Angewandte Chemie International Edition on Sept. 5.
Inspired by the role of protein methylation in regulating intracellular phase separation, the researchers transformed protic polymer backbones into aprotic ones by polymer methylation modification, which substantially weakened pristine polymeric H-bonding network and enhanced the solvation of metal cations from the polymer matrices in the hydrogel electrolytes.
Based on this fundamental, stable hydrogel electrolytes could be realized with extremely high salt contents, far beyond the limits that traditional hydrogels and even saturated aqueous solutions could reach.
As such, almost all water molecules were confined within the primary solvation shell of cations, providing the depressed water activity and mobility towards electrode dissolution and self-decomposition. The assembled aqueous sodium ion batteries could retain ~89.6% capacity with an average coulombic efficiency of 99.1% after 400 cycles.
