Influence of Doping on performance of Solid Polymer Electrolyte for Lithium-ion Batteries

We investigate the influence of doping on the conductivity of high molecular weight, crystalline PEO₆ based solid polymer electrolytes (SPEs). Polyethylene oxide (PEO) based SPEs are an attractive alternative to the flammable liquid/gel electrolytes currently used in rechargeable lithium ion batteries. But, SPEs suffer from low ionic conductivity. The conductivity is linked to PEO segmental motion; In order to increase the segmental motion, we must reduce the glass transition temperature T_g. Unfortunately increase in polymer dynamics reduces mechanical strength of SPE. PEO₆-LiClO₄ complex is a tunnel like PEO/salt co-crystal which conducts Li⁺ based on a mechanism that decouples conductivity and segmental motion of the polymer. Inspired from ceramics, we dope small amounts of anions or cations to disrupt the PEO₆-LiClO₄ lattice. We vary the size of the anion, and cation to create defects in the crystal lattice. We observe up to 900% increase in the conductivity of doped samples even with small amount dopant (1 %). Interestingly, the increase in conductivity is not correlated with the decrease in Tg of the SPEs. With wide angle X-ray scattering, we observe transition from single crystalline phase to mixed phase morphology with increase of the dopant concentration.