Nanocomposite electrolytes with fumed silica and hectorite clay networks: Passive versus active fillers

The use of nanocomposites constitutes a versatile and robust approach in the development of novel electrolytes with tailored electrochemical and mechanical characteristics. In this study, we examine the morphology rheology and on transport proper ties of two types of nanocomposite electroyte gels, one consisting of branched silica nanoparticles and the other composed of hectorite clay. In the first system with hydrophobic (fumed) silica, oligomers of poly(ethlyene oxide) (PEO), and lithium salt-PEO electrolyte, allowing for ionic conductivies greater than 10(3) S cm(-1) at ambient temperature. At sufficient concentrations, the silica forms an elastic gel processing a large open network structure that provides for unimpeded ion mobility. In the second system, composed of lithium-exchanged hectorite filler the nanoscale platelets serve as the nation. This active filler yields ionic conductivities in excess of 10(4) S cm(-2) and lithium transference numbers approaching unity. Similar to fumed silica, the hectorite clay also forms an elastic gel network. However, the morphologies of the two systems are distinctively different both in terms of network structure and characteristic length scale. These morphological differences manifest themselves in different rheological responses with regard to gel modulus and yield stress.