Preparation of Si/Ti Mesoporous Molecular Sieve and Its Application in P(VDF-HFP)-based Composite Polymer Electrolytes

Graphical abstract: Cycle stability and coulombic efficiency curves of the Li/CPE/LiCoO₂ cell with 10% Si/Ti molecular sieve at different C-rates, where the insert shows the constructional diagrams of the assembled Li/CPE/LiCoO₂ cell. - Abstract: The mesoporous Si/Ti molecular sieve was successfully synthesized from tetrabutyl titanate, tetraethoxysilane and EO₂₀PO₇₀EO₂₀ by sol-gel combined with following pyrolysis processes and confirmed by XRD and TEM. The poly (vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))-based composite polymer electrolyte (CPE) membranes doped with Si/Ti molecular sieve were fabricated by phase inversion method and the desirable CPEs were obtained after being activated in liquid electrolytes, which are investigated by SEM, XRD, TG, LSV and EIS measurements. The results show that the CPE doped with 10% Si/Ti molecular sieve (vs P(VDF-HFP) in weight) presents the most uniform surface with abundant interconnected micro-pores and possesses excellent mechanical tensile strength with high decomposition temperature about 400 °C and wide electrochemical working window about 4.7 V; adding Si/Ti molecular sieve into the system can significantly decrease the crystallinity and improve the ionic conductivity of the as-prepared CPEs, in which the ionic conductivity and lithium ion transference number at room temperature are up to 3.263 mS cm⁻¹ and 0.4292, respectively, and the reciprocal temperature dependence of ionic conductivity follows Vogel-Tamman-Fulcher relation. Furthermore, the anti-shrinkage rate of the as-prepared CPE membrane distinctly outperforms the commercial polyolefin membrane at 120 °C about 2 h. The interfacial resistance of the assembled Li/CPE/Li simulated cell can rapidly increase to a steady value about 548 Ω from the initial value about 362 Ω at 30 °C during 5 days storage, and the assembled Li/CPE/LiCoO₂ coin cell with the electrolyte also show excellent rate and cycle performance, which indicates that this kind of CPE is an exciting potential candidate as polymer electrolyte for the lithium ion battery.