Synthesis Of Solid Polysiloxane Electrolytes And Fabrication Of All-solid-state Lithium Ion Batteries

All-solid-state polymer lithium ion batteries (LIBs) can operate in a broad working temperature range and have higher safety than conventional lithium ion batteries due to the use of thermally stable solid polymer electrolyte (SPE) instead of flammable liquid electrolyte. However, most SPEs exhibit low room temperature ionic conductivity that prevents them from applications in LIBs. In this thesis, two electrolytes with higher room temperature ionic conductivity were obtained by structure design for polysiloxane molecules. Based on these electrolytes, all-solid-state LIBs were assembled and can work in a wide temperature range.A combed poly(ethylene oxide)(PEO) mono-substituted polysiloxane was prepared by the hydrosilylation of polymethylhydrosiloxane with vinyl tris(2-methoxyethoxy) silane. Electrolyte membranes consisting of the polysiloxane, poly(vinylidene fluoride) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were fabricated by the solvent casting method. Its ionic conductivity reaches5.7×10-5S cm-1at25℃and4.5×10-4S cm-1at80℃when20wt%LiTFSI was added.In addition, a cyclic propylene carbonate (PC) and combed PEO mix-substituted polysiloxane was synthesized by the simultaneous reaction of polymethylhydrosiloxane with cyclic [(allyloxy)methyl]ethylene ester carbonic acid and vinyl tris(2-methoxyethoxy) silane. When PC/PEO ratio is6:4and LiTFSI is20wt%, the electrolyte has an ionic conductivity of1.6×10-4S cm-1at25℃, which is nearly3times of mono-substituted electrolyte. The LiFePO4/Li batteries based on the electrolyte achieve the initial discharge capacities of88.2mAh g-1(25℃) and140mAh g-1(100℃) at1C rate, and the discharge capacities in the100th cycle are79.8mAh g-1(25℃) and130mAh g-1(100℃), presenting excellent cycling performance in the wide temperature range.