Physical and electrochemical chattels of phosphonium ionic liquid-based solid and gel-polymer electrolyte for lithium secondary batteries

Abstract

In this work, a methodical study on the influence of ionic conductivity on polymer electrolyte with different weight percentages of ionic liquid and plasticizers had been investigated in detail. Solution casting method has been employed for preparing polymer electrolyte (PE) blend having poly(vinylidenefluoride-co-hexafluoropropylene) P(VdF-co-HFP) as polymer, trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) amide [P14,6,6,6][Tf2N] as ionic liquid and ethylene carbonate (EC) as well as propylene carbonate (PC) in 1: 1 ratio as plasticizers. The polymer electrolyte has been found out stable up to 450 °C, as measured from Thermal gravimetric analysis (TGA). Impedance spectral analysis reveals that the ionic conductivity of SPEs is 3.209 × 10–6 S/cm at 303 K with 25 wt% of ionic liquid. The addition of plasticizers (EC + PC (60 wt%)) results in two orders of magnitude of higher ionic conductivity (3.40 × 10–4 S/cm at 303 K), than that of SPEs. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) are performed to study the physico-chemical characteristics of polymer electrolytes. Electrochemical stability, potential window and discharge characteristics of the coin cell containing the electrolytes and LiFePO4 electrode were investigated using linear and cyclic voltammetry.