Influence of surface charged Al2·67O4 nanofiller on conductivity and stability in plasticized green hydroxypropyl methylcellulose/pectin incorporated with LiClO4 polymer composite electrolyte

Abstract

In essence, the green polymer electrolyte with cationic deficient insulating oxide nanofillers gaining importance due to their significant influence on enhancing ionic conductivity and electrochemical stability. Specifically, in this work, the spinel Al_2·67O₄ nanoparticles were synthesized via solution combustion technique and free standing 10 wt % pectin/90 wt % Hydroxypropyl methylcellulose/25 wt % Glycerol/10 wt% spinel Al_2·67O₄/7.5 wt % LiClO₄ solid polymer electrolyte has been fabricated via solution casting technique. X-ray diffraction pattern of calcined aluminum oxide reveals a cation-deficient cubic Al_2·67O₄ spinel phase, with an average crystallite size of 5.08 nm and a strain of 0.77 %, while the polymer electrolyte shows major amorphous nature even with the nanofiller. ATR-FTIR studies have confirmed the types of functional groups in the polymer chain. Thermal differential scanning calorimetry analysis shows that the prepared electrolytes exhibit endothermic peak at 46 °C corresponds to the Transition temperature (T_g). The surface of the optimized polymer electrolyte became rougher, with randomly spread nano pores as nanofiller and salts are added. Further, the electrolyte exhibits a maximum conductivity of 0.11 mScm⁻¹ with a good stability window of 3.36 V and a maximum cation transference number of 0.74. Dielectric spectroscopic studies confirm that nanofillers are involved in enhancing the flexibility of the polymer electrolyte with a lower tangent loss and dielectric relaxation time at higher frequencies. The structural relaxation time associated flexible motion of chains found to decrease from 179.6 to 3.17 μs with the addition of Li salt. The mechanical tensile strength of the optimized polymer electrolyte with salt found to be 11.28 MPa with lower stiffness and higher young's modulus of 551.02 MPa.