Plasticized Polymer Composite Single-Ion Conductors for Lithium Batteries
Lithium bis(trifluoromethane) sulfonamide (TFSI) is a promising electrolyte salt in lithium batteries, due to its good conductivity and high dissociation between the lithium cation and its anion. By tethering N-pentane trifluoromethane sulfonamide (C5NHTf), a TFSI analogue molecule, onto the surface of silica nanoparticle as a monolayer coverage should increase the Li<sup>+</sup> transference number to unity since anions bound to particles have reduced mobilities. Silica polymer composite has better mechanical property than that of the pure PEO. Analogously trifluoromethane sulfonic aminoethyl methacrylate (TfMA), a TFSI analogue vinyl monomer, was polymerized on silica nanoparticle surface as a multilayer coverage. Anchored polyelectrolytes to particle surfaces offer multiple sites for anions, and in principle the carrier concentration would increase arbitrarily and approach the carrier concentration of the bulk polyelectrolyte. Monolayer grafted nanoparticles have a lithium content of 1.2 × 10<sup>-3</sup> g Li/g, and multilayer grafted nanoparticles have a lithium content over an order higher at 2 × 10<sup>-2</sup> g Li/g. Electrolytes made from monolayer grafted particles exhibit a weak conductivity dependence on temperature, exhibiting an ionic conductivity in the range of 10<sup>-6</sup> S/cm when temperatures increase to 80 °C. While electrolytes made from multilayer grafted particles show a steep increase in conductivity with temperature with an ionic conductivity increase to 3 × 10<sup>-5</sup> S/cm at 80 °C, with an O/Li ratio of 32.