(4do) Nano Materials for Energy Storage Applications

Secondary batteries containing Li metal as anode provide one of the highest known energy densities. They are therefore desirable candidates for electric and hybrid electric vehicles. However, current liquid electrolytes cannot be employed with lithium metal anode because they allow dangerous lithium dendrite growth during the charge discharge cycles. Solid polymer electrolytes, on the other hand, are known to be effective in reducing dendrite growth and hence, there has been significant effort devoted by research groups world wide to the development of polymer and composite polymer electrolytes for use in lithium batteries. The best known ionic polymer conductor, polyethylene oxide, is crystalline and has low conductivity at room temperature. While polyethylene oxide oligomers exhibit good ionic conductivity as well as chemical and thermal stability, amorphous low molecular weight electrolytes lack mechanical strength. The addition of free inorganic particles as well as inorganic networks to polymer electrolytes has been shown to improve both mechanical properties and conductivity. We are developing a new class of organic-inorganic hybrid materials as solid electrolytes for lithium metal batteries. These novel electrolytes are based on nanoscale organic hybrid materials (NOHMs) comprised of silica nanoparticle cores covalently bonded to polyethylene glycol oligomers and ionic liquids tethered to ziriconia (ZrO2) nanoparticles. By varying the nanoparticle size and organic polymer molecular weight and grafting density, the volume fraction of the inorganic component can be systematically varied and mechanical properties of the hybrids manipulated over an unusually broad range. These novel organic-inorganic nanocompoite systens display rheology characteristic of yield-stress fluids termed soft-glasses. This presentation focuses on the conductivity and rheological properties of nanoscale hybrid electrolytes. The applicability of these hybrids as electrolytes in Li batteries will be discussed.