Properties and potential application of silica-gelled electrolytes for lithium-ion batteries

The properties of gelled electrolytes based on liquid organic electrolytes are investigated. The gelation agents are highly dispersed silica (HDS) which are added in a quantity of a few wt.%. Drying conditions for the HDS are described as well as the analytical values for the residual water. Two basically different types of HDS are investigated: (i) hydrophilic and (ii) hydrophobic material. Whereas the hydrophilic HDS contains SiOH groups on the surface of the silica particles, in the hydrophobic HDS, these SiOH are normally methylated. With hydrophilic HDS, thixotropic gels can be prepared. Conductivity data for EC-DMC/LiTFMSI gels are comparable with the values obtained for the liquid electrolyte. The electrochemical stability window for such a gel electrolyte is at least between 0-4.1 V versus lithium. Metallic lithium and the intercalation cathodes (LiCoO2, LiMn2O4) can be reversibly cycled in this electrolyte. No specific detrimental effects due to the addition of HDS were observed. (C) 1997 Elsevier Science S.A.