Relation between Ionic Conductivity and Solubility of CO2 in Pressurized Solid Polymer Electrolytes

• Published in: Macromolecules Vol. 40; no. 9; pp. 3348 - 3354
• Main Authors: Tominaga, Yoichi, Asai, Shigeo, Sumita, Masao
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.05.2007
• Subjects: Applied sciences; Electrical, magnetic and optical properties; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Pressure effect; Electrical properties; Graft copolymer; Carbon dioxide; Ionic conductivity; Polymer solid electrolyte; Lithium compound; Methacrylate copolymer; Ethylene oxide copolymer; Experimental study; Amorphous copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma0624402

The isothermal conductivity and solubility of CO2 in amorphous poly(oligo-oxyethylene glycol methacrylate) (PMEO)−LiX (X = N(SO2CF3)2, CF3SO3, LiClO4, BF4, and Br) electrolytes at CO2 pressures between 0.1 and 20 MPa were measured by an in-situ impedance unit consisting of a supercritical CO2 extraction system and an original high-pressure reactor. Solubility was estimated from the gravimetric change at desorption procedure (CO2-out), which is based on the Fickian diffusion of CO2 molecules in polymer. The relation between the conductivity in CO2 and q t = 0 (the amount of saturated CO2 in 1 g of a sample) is discussed as a function of pressure. The conductivity in pressurized CO2 increases linearly with increasing q t = 0 due to the decrease in T g and the effect on q t = 0 of fluorine atoms in the anion; there is the Lewis acid−base interaction between CO2 molecules and dissociated anions. The LiTFSI electrolyte had the highest q t = 0, more than 0.35, and the conductivity at 20 MPa was 17 times higher than that at 0.1 MPa. In-situ FT-IR measurements revealed that the CO2 molecules absorbed into the PMEO matrix weaken the original CO/OH hydrogen bonds and enhance the flexible ether side chains leading to fast ionic transport. Studies on solid polymer electrolytes (SPEs) such as PMEO using pressurized CO2 fluid as a treatment medium have a possibility to realize excellent ionic conductivity even in the dry state. We expect that a novel preparation process for SPEs can be established using the CO2 as solvent, which leads to an environmentally benign system for sustainable chemistry.