Quasi-solid-state plasticized chitosan biopolymer electrolyte with enhanced Mg²⁺ ion mobility for next-generation Mg ion battery

Developing electrolytes with high Mg²⁺ ion mobility and compatibility with magnesium electrodes is of the utmost importance for the development of next-generation magnesium ion batteries. Here, we report the findings related to the physicochemical properties of the quasi-solid state chitosan biopolymer electrolyte prepared with a highly polar plastic crystal succinonitrile plasticizer. The prepared biopolymer electrolytes exhibited ionic conductivity in the order of 10⁻² S cm⁻¹ which is very much comparable to the conductivity of a liquid electrolyte used in commercial batteries. Besides, the prepared electrolyte shows decreased crystallinity ( \({\chi }_{c}\) ${\chi }_c$ ) and glass transition temperature (T_g) values, widened electrochemical window (2.5 V), good transference number ( \({t}_{{Mg}^{2+}}\) $t_{{\mathit{Mg}}^{2+}}$ ~0.6), reduced activation energy E_a (25 kJ mol⁻¹), and increased dielectric values (ε). These results confirm the enhanced Mg²⁺ ion kinetics owing to the addition of SCN with high dissociate property and oxidative stability. Furthermore, the interfacial stability of the best-conducting chitosan biopolymer electrolyte is evaluated using CV analysis against Mg electrodes (vs. Mg/Mg²⁺). Also, a prototype Mg battery is constructed using the prepared electrolyte, MoO₃ cathode, and Mg metal anode which showed an initial specific capacity of 277 mAh g⁻¹ analyzed through galvanostatic charge/discharge studies. Therefore, in light of the results, we believe that adding succinonitrile to polymer electrolytes could be a practical approach to enhancing the electrochemical properties suitable for magnesium ion batteries.