Synthesis and characterization of reversible thermosensitive methylated chitin and its application in zinc‐ion battery thermal runaway

Abstract Novel water‐soluble methylated chitins (MCHs) were synthesized homogeneously in aqueous alkaline solution. The relatively mild reaction conditions resulted in the MCH with high degree of acetylation (DA >0.76). The chemical structure of the obtained MCHs was analyzed and the degree of methylation substitution (DS) and DA were determined by proton NMR in both D 2 O and 20% DCl/D 2 O. The MCH aqueous solutions (DS = 0.46 ~ 0.71) showed a reversible thermosensitive sol–gel–sol transition upon heating and cooling. The gel transition temperature of these MCHs (in the range of 15–85 °C) increased with increasing DS and decreasing polymer concentration. Thermal runaway has been an important safety issue impeding the development of high‐energy‐density zinc‐ion batteries. A smart thermosensitive reversible electrolyte was prepared based on this MCH for the aqueous zinc‐ion battery to prevent thermal runaway. When the temperature of zinc‐ion battery rises or even gets out of control, the thermosensitive electrolyte can quickly gel and inhibit the migration of zinc ions, resulting in increase of the internal resistance and realizing intelligent and efficient thermal self‐protection. Thus the novel thermosensitive methylated chitin shows promise for safe aqueous zinc‐ion batteries.