Composite polymer electrolytes based on lithium salts: solubility and conductivity

Abstract

The paper highlights the results of composite polymer lithium-conducting films investigation. The films under discussion consist of solid polymer electrolytes filled by own lithium salt particles. The solubility limit in macromolecular solvent – fluoropolymer F-62 is determined for several salts solutions namely lithium perchlorate, hexafluorophosphate, fluoride and bromide. The composite films prepared by solvent casting from the joint solution of polymer and lithium salt with its content exceeding its solubility in polymer matrix leads to formation of large single crystals of inorganic salt. The preparation technique can hardly provide the desired uniform dispersion of filler nanoparticles. Transport characteristics of the films are determined by using impedance spectroscopy, DC interruption technique and measuring the DC resistance through the film. The ionic transport is shown to occur through both phases of composite according to their contents. Increasing of conductive filler content reduces the overall conductivity of composite electrolyte. Conductivity values of composites in a wide range of lithium salt concentration are found to be lower the conductivity values of individual phases. The most probable reason for such a behavior is connected with formation of relatively large filler particles with small interfacial area. These particles are unable to form the highly-conducting channels through the amorphous stuff.