Porous polymer-in-silica hybrid electrolyte for all-solid-state Li-ion battery applications

Abstract

Porous hybrid electrolytes based on Poly(Ethylene Glycol) (PEG) and mesoporous silica (SBA-15) were prepared by a post-synthetic modification of the silica matrix. The complex composed of the lithium salt (LiTFSI) and PEG is embedded in the silica pores, which offers mechanical properties for the hybrid electrolyte. The textural properties and composition of pure SBA-15 and the hybrid materials were characterized by several techniques. It was evidenced that the inner pores of the inorganic matrix (hexagonally packed cylindrical mesochannels) surface were uniformly coated with the complex PEG-LiTFSI and that the hybrid materials remained slightly mesoporous after the post-synthetic modification. To study the ionic conductivity, the hybrid powders were shaped as a pellet having both inter- and intraparticle porosity. The parameters whose influence were addressed are: the filling of the inter- and intraparticle porosity with PEG-LiTFSI complex, the lithium ion concentration and the PEG molecular weight. First, filling the interparticle porosity is necessary to the formation of continuous lithium conducting pathways while the intraparticle conductivity appeared to be mandatory to improve the overall conductivity. The hybrid of SBA-15 with PEG having a molecular weight of 600 gmol-1 gives the highest conductivity (1.6 x 10−6 S cm−1 at 30 °C) when used with the optimum molar ratio nEO/nLi of 10 found in this study. Preliminary analysis showed that the conductivity is governed by the segmental dynamics of the polymer chains (VTF model) in the whole temperature range. Finally, this material has an electrochemical window compatible with classical Li ion batteries cathode materials.