Excellent electrochemical performance based on covalently crosslinked chitosan hydrogel electrolytes induced structural stability against alkali

Abstract

Alkali-resistant electrolytes are suitable for high-power equipment and harsh environments. However, most hydrogels lose stability in a strong alkaline environment. As such, the development of hydrogel electrolytes having an outstanding alkali resistance is desirable. In the work reported here, the quaternary ammonium group was introduced to chitosan to achieve excellent hydrophilicity and conductivity. Then, an alkali-resistant hydrogel polymer electrolyte was prepared by graft copolymerizing and crosslinking chitosan quaternary ammonium salt with acrylamide. The fracture elongation of the resulting hydrogel polymer electrolyte can reach 300%. The electrolyte has a high ionic conductivity of 1.66 × 10^–1 S·cm⁻¹ after being soaked in a strong alkaline solution. Meanwhile, salt solutions were used to further enhance the ionic conductivity that reached 2.42 × 10^–1 S·cm⁻¹. The potential window of the device prepared expanded from 1.0 to 1.3 V. The energy density and the power density reached 5.49 Wh·kg⁻¹ and 346.66 W·kg⁻¹, respectively. Finally, it was explored from a molecular level, for the first time, that free ions and solvent-separated ion pairs proceed with ionic migration to enhance ionic conductivity. Our findings provide valuable insights into the application of gel polymer electrolytes in future energy devices.