Ionic Conductivity Study On PEO-based Composite Polymer Electrolyte For Lithium Batteries

Composite polymer electrolyte has extensive application promise in the lithium ion battery, fuel cells, transducer and capacitor, etc. The solid polymer electrolytes (SPE) have many advantages like non-leakage, volumetric stability, solvent free condition, easy handling and wide electrochemical stability windows over liquid electrolytes. However, ambient temperature conductivity of PEO based electrolytes that depend on the continuous movement of PEO chain descend after PEO has partially crystallized. It is the major problem that hamper the application of PEO based electrolytes, thus the current research are focused on how to decrease crystallinity of PEO based polymer electrolytes. In order to enhance the efficiency and transport properties, liquid plasticizers such as ethylene carbonate (EC) or propylene carbonate (PC) are added to the polymer matrix. However, the addition of the liquid components promotes deterioration of the electrolytes' mechanical properties and increases its reactivity toward the lithium metal anode. The development of polymeric composite materials filled with nanosized rigid particles has attracted both scientific and industrial interest.1. We measured the ionic conductivities of PEO-based polymer electrolytes containing different concentrations of lithium salt, results showed that the ionic conductivity is the highest in polymer electrolytes containing LiClO₄ with molar ratio of O/Li=16. The effects of PC on ionic conductivities of polymer electrolytes were studied; it could be found that the ionic conductivity increased with the increase of the addition of PC. The chemical stability, mechanical strength, and sub-ambient temperature conductivity of polymer gel electrolytes were investigated. A polymer gel electrolyte sample with a gradually varying concentration of plasticizer had been examined by Electrochemical impedance spectroscopy (EIS). The temperature dependence of the ionic conductivity of the polymer electrolyte films followed the Arrhenius equation and Vogel-Tamman-Fulcher (VTF) equation in different temperature scope, and the ionic conductivity at ambient temperature reached a value close to 5×10^-4 S cm^-1. The effects of three kinds of plasticizers (PC, DEC, PEGDME) on the electrochemical properties of polymer electrolytes were studied.2. The nanosized inorganic particles composite polymer electrolytes PEO₁₆-LiC1O₄-SiO₂ were prepared. These polymer electrolytes were studied in detailed using DSC, TGA and AC impedance analysis. The conductivity enhancement could be attributed to the addition of ceramic filler that yielded a significant increase of surface to volume ratio related to the decrease in glass transition temperature values in the composite polymer electrolyte. Differential scanning calorimetry (DSC) analysis revealed that the crystalline phase and crystallinity were slightly decreased with the addition of SiO₂ to the PEO-LiClO₄ system. The conductivity was increased with increasing SiO₂ content, peaked at a SiO₂ content of 8 wt.%, and subsequently decreased because the decreasing surface area of nanoparticles reduced the hydrophilicity of the SiO₂ surface groups. Nano-particle oxide fillers including TiO₂, SiO₂ and ZnO had been shown to have significant effects on the properties of polymer electrolytes in this article.3. It is generally accepted that the electrical conduction in solid polymer electrolytes (SPE) is strongly temperature dependent: an Arrhenius dependence is observed at low temperatures, while a non-Arrhenius Vogel-Tamman-Fulcher (VTF) behavior is seen at high temperatures. At room temperature, the SPEs' ionic conductivity was low and the effects of temperature on ionic conductivity were significantly. In addition, a critical transition temperature at which the electrical conductivity behavior changes from Arrhenius-like to VTF-like is determined analytically. For PEO-salt-ceramic composite electrolytes, it has been reported that the equilibration time of the ionic conductivity under isothermal conditions is very long, ranging in a matter of months. We present a study on the conductivity relaxation of ceramic-free PEO-LiClO₄-PC-SiO₂ electrolytes at isothermal condition. The heating/cooling temperature dependence of the ionic conductivity is also measured and compared.