High Transference Number Composite Lithium Electrolytes: From "Soggy Sand"� Electrolytes to Infiltrated Mesoporous Silica

High lithium transference number (t_Li⁺) electrolytes are greatly beneficial as they could solve the problem of ion concentration gradients within the lithium cell which limit its lifetime and energy density. In composite “soggy sand” electrolytes (insulating oxide nanoparticles dispersed in lithium salt solution), lithium conductivity is enhanced in the space charge zones due to the coupled effects of anionic adsorption and association-dissociation equilibrium while the long range transport is enabled by beneficial particle network formation.¹ When mesoporous silica particles are used as a solid phase, lithium can be efficiently transported through the interconnected pores (MSU-H, 7/15 nm).² A convenient way of circumventing kinetical issues is infiltration of solid mesoporous silica pellets or monoliths (prepared by sol-gel method) with liquid electrolyte (1M lithium triflate in polyethylene glycol or dimethyl sulfoxide). Galvanostatic DC polarization measurements performed in a specially designed cell under controlled atmosphere indicate t_Li⁺≈0.5 integrated with high AC conductivity (≈ 1 mS cm^-1).³ The pertinence of such materials is remarkable as they could make lithium battery separators dispensable offering excellent contact/adhesion with high power nanostructured electrodes. Additionally, by careful choice of solvent, hybrid electrolytes can be made transparent which is beneficial for potential photoelectrochemical applications.

1. C. Pfaffenhuber, M. Göbel, J. Popovic, J. Maier, Phys. Chem. Chem. Phys., 2013, 15, 18318.
2. C. Pfaffenhuber, F. Hoffmann, M. Fröba, J. Popovic, J. Maier, J. Mat. Chem. A, 2013, 1, 12560.
3. J. Popovic et. al., in preparation