Strategy on enhancing ionic conductivity of biocompatible hydroxypropylmethylcellulose/polyethylene glycol polymer blend electrolyte with TiO2 nanofillers and LiNO3 ionic salt

A biocompatible and biodegradable polymer in the fabrication of solid polymer electro­lytes for high energy density rechargeable batteries is gaining interest owing to their safety, compatibility and flexibility. In this study, a polymer electrolyte based on hydroxy­propyl methylcellulose (HPMC)/polyethylene glycol (PEG) biopolymers, incorporating TiO2 nano­fillers and LiNO3 as a lithium source, was fabricated using the solution casting method. Mixed-phase TiO2 nanofillers were synthesized via hydrolysis of tita­nium tetraisopropoxide. The crystal structure, phase morphology, and electro­chemical impedance spectra of the films and nanofillers were investigated. X-ray dif­frac­tion analysis confirmed the amorphous nature of the polymer electrolyte and crystalline nature of nanofiller. In addition, it was noted that the amorphous phase of the polymer blend remained unaltered despite the incorporation of TiO2 and LiNO3. Thermo­gravi­metric analysis and differential thermal analysis confirmed that the pure blend exhibited a melting point of around 60°C and complete degradation of around 340 °C, while the blend electrolyte with additives de­monstrated thermal stability with a broad melting point. The blend containing 5 wt.% TiO2 fillers and 10 wt.% LiNO3ionic salt exhibited the highest ionic conductivity of 0.213 mS cm-1 at room temperature. The polymer blend electrolyte displayed a narrow electrochemical stability window of 2.85 V, with the highest cationic transfer number of 0.323. The temperature-dependent ionic conduc­tivity of the prepared polymer blend electrolyte followed Arrhenius behaviour, with an activation energy of 0.1 eV. The study examined and reported the effect of aging on the interfacial resistance of polymer blend electrolyte. The mechanical properties of the optimized HPMC/PEG/TiO2/LiNO3 polymer blend electrolyte were investigated and reported. Thus, this research elucidated the role of nanofillers and ionic salt in enhancing the performance of biocompatible polymer electrolytes.