Fabrication and electrical properties of Li3PO4-based composite electrolyte films

A new type of Li3PO4-based composite electrolyte films was fabricated with an approach similar to Bellcore technology. The films are composed of Li3PO4 fine powder, SiO2 nanoparticles, dibutyl(o-)phthalate (DBP) and a polymer matrix poly(vinyldiene fluoride). X-ray diffraction, scanning electron microscopy and photo scattering techniques were employed to analyze the Li3PO4 powder synthesized by a chemical precipitation method. AC impedance spectroscopy was used to measure the electrical properties of the composite electrolyte films. The effect of the addition of different concentration nanoparticles SiO2 and DBP on the conductivities of the Li3PO4-based composite electrolyte was analyzed. It is found that the optimized starting composition with a mass ratio Li3PO4:SiO2:DBP:Kynar 2801 (PVDF-12% HFP):acetone equal to 30:5:30:35:100 gives rise to the highest ionic conductivity of 2.4 x 10(-8) S/cm at 30 degrees C and 1.7 x 10(-7) S/cm at 100 degrees C with an activation energy of 0.32 eV. It is comparable with that of Li3PO4 thin films obtained from sputtering or electrostatic spray deposition (ESD) techniques. The presence of the plasticizer DBP and nanoparticles SiO2 plays an important role to minimize the resistance for lithium-ion conduction between Li3PO4 particles. In addition, for the graphite/composite/graphite measurement cell, the apparent conductivity for the charge-transfer process between the electrolyte film and the graphite electrode is about one order of magnitude lower than that of the composite electrolyte with an activation energy of 0.56 eV. The development of such composite films opens opportunities to thermally stable electrolytes for rechargeable lithium batteries. (c) 2005 Elsevier B.V. All rights reserved.