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This work investigates the effect of zwitterionic molecules on ionic association in ethylene oxide (EO)-based electrolytes using molecular dynamics simulations. Zwitterionic molecules can associate with cations and anions because they possess both positively and negatively charged groups. This unique feature can be leveraged to develop electrolytes with high ionic conductivity if we understand how zwitterionic molecules influence ionic associations. We investigate the ionic associations in the electrolytes composed of oligo(ethylene oxide) (EO) (EO x , x = 2, 3, 4, and 5), LiTFSI and zwitterionic molecules containing cationic imidazole group and anionic sulfonate group using molecular dynamics simulations. The analyzed properties include the radial distribution functions between Li+, [TFSI]-, EO x and zwitterionic molecules, the structures and dynamics of Li+-[TFSI]-, Li+- EO x and Li+-zwitterion associations, and the diffusion coefficients of Li+, [TFSI]-, EO x and zwitterionic molecules. The simulation results show two distinct effects of zwitterionic molecules on ionic associations in the electrolytes. First, they could release Li+ from the trapping effect of EO x chains and accelerate Li+ transport. Second, they can associate with Li+ themselves and slow down the Li+ transport. The competition between these two effects relates to the length of the EO x chains. Our simulations suggest that zwitterionic molecules could help manipulate the ionic conductivity of polyethylene oxide electrolytes. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: The behaviors of the ionic hydration in nanopore are of both biological and chemical interests. Using carbon nanotube (CNT) as the 1-D nanopore model, we investigated the effect of the modified groups (Cing on the pore inner wall on the hydration of Li+, Na+ and K+ with molecular dynamics simulation. The structures of the water molecules around the cations confined in the modified CNTs were compared with their counterparts in the pristine CNTs. Among the three cations, the sequence of the sensitivity for the spatial and orientation distributions of the water molecules in the first coordination shells is: K+ >Na+ >Li+. The same modification results in the opposite effects for the ionic hydration inside the (10, 10) and (8, 8) CNTs. Inside the (10, 10) CNT, the modification enhances the ionic hydration, whereas inside the (8, 8) CNT, the ionic hydration is weakened by the modification of CNT wall. [ABSTRACT FROM AUTHOR]