Synthesis polyethersulfone-based amphiphilic block copolymers & development of single-ion conductors for lithium ion batteries.

摘要

Polyethersulfone (PES) membranes often foul easily because of their hydrophobicity, and addition of amphiphilic PES block copolymers to membrane formulations may help overcome this problem. This dissertation explores the synthesis and aggregation properties of relevant amphiphilic ABA block copolymers, where PES is the hydrophobic B block and poly(2-hydroxyethyl methacrylate) or poly(2-hydroxypropyl methacrylate) are the hydrophilic A blocks. 1H nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) confirm the block copolymer synthesis, and 1H NMR spectra and TGA also provide consistent data on copolymer compositions. The amphiphilic copolymers aggregate when the amount of water in DMSO reaches 20 vol%, and dynamic light scattering (DLS) shows that aggregates have radii of ∼60 nm at copolymer concentrations from 1 to 30 mg/mL.;Lithium ion batteries are now ubiquitous, but concentration polarization is still a problem in the currently used battery electrolytes, especially in high-current applications. Immobilizing anions and having lithium cations contribute to most of the ionic conductivity is a good solution to address this problem of concentration polarization. This work aims to create nanoparticle-containing electrolytes using silica nanoparticles modified with polyanions that have Li+ as the counterion. Anion mobility is restricted by the polyanion polymer backbones, which is further immobilized by the nanoparticles. The polyelectrolyte-grafted nanoparticles were synthesized by surface atom transfer radical polymerization (ATRP) of monomers from initiator-grafted silica nanoparticles. To prepare a lithium-ion conductor, the polyelectrolyte-grafted nanoparticles were blended with poly(ethyleneglycol) dimethyl ether with Mw of ∼500 (PEGDME-500). Because the anions are immobile, lithium is the only ion that conducts current. Four polyelectrolytes are used to form multilayer-grafted nanoparticles, aiming at improving conductivity of the material. FTIR and TGA are used to prove successful synthesis of the polymer modified particles. AC impedance shows that the best conductivity is from a Bis(trifluoromethanesulfonyl)imide (TFSI) analogue monomer, which is around 10-6 S/cm, which is in the same range as a monolayer-grafted silica nanoparticle system using similar TFSI analogue structure. A proposed model shows that the multilayer-grafted nanoparticles only have outermost layer of lithium cations accessible to the solution, because of the low solubility of polyelectrolytes in the PEGDME-500 solvent.;Direct modifification of poly(ethyleneglycol) via alkyne-azide or thiol-ene click chemistry as single lithium ion conductor. To make sure 1,2,3-triazole or sulfur structure from click chemistry is not impeding lithium transport, we synthesize 1,2,3-triazole and sulfur containing PEGs via step growth polymerization. Conductivity measurement of lithium perchlorate with triazole containing PEG or sulfur containing PEG shows similar data as the pure PEG, which proves that click chemistry could be applied in the development of single ion conductors for Lithium Ion Batteries.