Development of a novel type of solid polymer electrolyte for solid state lithium battery applications based on lithium enriched poly (ethylene oxide) (PEO)/poly (vinyl pyrrolidone) (PVP) blend polymer

In the present study, flexible and freestanding solid polymer electrolyte (SPE) films based on poly ethylene oxide (PEO) and poly (vinyl pyrrolidone) (PVP) complexed with lithium nitrate (LiNO₃) have been developed by solution casting method. Morphological features of the synthesised SPE films have been investigated in detail using X-ray Diffraction, Fourier Transform Infra-Red Spectroscopy and Field Emission-Scanning Electron Microscopy techniques. These films have smooth surface morphology and porous nature along with good thermal stability above 400 °C. The novelty of the present work is the introduction of these flexible SPE films for Li storage applications. The films exhibit room temperature ionic conductivity around 1.13 × 10⁻³ S cm⁻¹ which is quite comparable to that of liquid electrolytes. For these SPE films, the total ion transport number and lithium ion transference number are 0.9997 and 0.332 respectively. Electrochemical characterizations have been carried out by assembling prototype Li-ion cells with LiFePO₄ as the cathode active material, lithium as the anode and the SPE film of the present work serving both as the separator film and the solid electrolyte. These cells show an open circuit voltage of 3.26 V and good electrochemical activity as evidenced from the cyclic voltammetry studies. These novel type of flexible SPE films from PEO/PVP/LiNO₃ composites with remarkable room temperature ionic conductivity, good thermal stability and promising electrochemical activity offer excellent application prospects for realizing all solid state Li ion cells and other solid state, electrochemical energy storage devices.