Abstract:

Recently, there has been rapid and profound progress with respect to the energy and power density of sodium-ion batteries. However, the conventional liquid organic electrolyte/separator system tends to evaporate and burst into flame, leading to wide concerns about its inherent low safety. To develop sodium ion batteries with high energy density and improved safety, solid electrolytes have gained attention, especially polymer-based electrolytes including solid and gel types. This article begins by reviewing the progress in fundamental mechanism and physical chemistry theoretical models for polymer electrolytes, followed by advancements in both solid and gel polymer electrolyte application in sodium ion batteries along with assessments of various material modification techniques, synthesis procedures, and novel material design. Based on the analysis, polymer electrolyte adopting oligomer, inorganic filler, and molecule design strategies are given for the successful conversion of a solid battery operation temperature from 90°C to room temperature or lower. A gel electrolyte relies on intermolecular forces and renders greater solvation effects for sodium salts, realizing quasi-solid batteries coupled with various electrodes generally at room temperature. In addition, a brief comment on hydrogel electrolytes concerning their great potential in aqueous sodium ion batteries is provided. Finally, an appeal is made concerning critical parameters, including volume and mass, in future reports, as well as a brief outlook concerning possible perspectives considering material design, and an in-situ polymer electrolyte technique in sodium ion batteries is proposed.

Key words: sodium ion battery, solid electrolyte, gel electrolyte, composite material, energy storage