Influence of Li-Salt on the Mesophases of Pluronic Block Copolymers in Ionic Liquid.

Brinkkotter M, Geisler R, Großkopf S, Hellweg T, Schonhoff M. Influence of Li-Salt on the Mesophases of Pluronic Block Copolymers in Ionic Liquid. The journal of physical chemistry. B. 2020;124(42):9464–9474.We study the complex mixture of a polyethylene oxide-b-polypropylene oxide-b-polyethylene oxide triblock copolymer (Pluronic F127) with ionic liquid (IL) and Li-salt, which is potentially interesting as an electrolyte system with decoupled mechanical and ion-transport properties. Small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) are employed to scrutinize the phase structures and elucidate the ternary phase diagram. These data are combined with the ion diffusivities obtained by pulsed field gradient (PFG) nuclear magnetic resonance (NMR). Analyzing the partial ternary phase diagram of F127/LiTFSI/Pyr14TFSI, hexagonal, lamellar, and micellar mesophases are identified, including two-phase coexistence regions. While the PPO block is immiscible with the liquid, and forms the backbone of the mesostructured aggregates, the PEO blocks are not well miscible with the IL. Poorly solvated, the latter may still crystallize. At a higher IL content, PEO is further solvated, but a major solvation effect occurs due to addition of Li-salt. Li ions promote solubilization of the PEO chains in the IL, since they coordinate to the PEO chains. This was identified as the mechanism of a transition of the mesostructures, with increasing Li-salt content changing from a hexagonal to a lamellar and further to a micellar phase. In summary, both, the amount of IL and its compatibility with the PEO block, the latter being controlled by the Li-salt amount, influence the compositions of the formed mesophases and the ion diffusion in their liquid regions

Unveiling the transport properties of protic ionic liquids: Lithium ion dynamics modulated by the anion fluorine reservoir

Protic ionic liquids (PILs) show great potential as electrolyte components for energy storage devices. A comprehensive understanding of their transport properties must be achieved to optimize the design of safer and efficient electrolytes. This study focuses on a series of PILs based on the DBUH+ cation (protonated 1,8-diazabicyclo[ 5,4,0]‑undec-7-ene superbase) and three anions derived from strong acids: TFO- (triflate), IM1- (perfluorobutyl-trifluoromethylsulfonylimide) and TFSI- (bis(trifluoromethylsulfonyl)imide). Neat PILs and PILs doped with LiTFO, LiIM14, and LiTFSI were studied using temperature-dependent NMR diffusion and relaxation techniques. The ionicity of these systems was also evaluated. Results revealed that the dynamic behaviour of lithium ions, as well as ionicity, strongly depend on the structural features of the anions, particularly in the case of IM14- , whose main feature is the uneven distribution of the fluorinated sidegroups. The 19F relaxation rates in IM14 provide insights into the rotational reorientation of that anion. DBUH-IM14 exhibited diffusion coefficients lower than the expected ones on the basis of its viscosity, likely due to fluorophilic intermolecular interactions involving the fluorinated terminal groups. The presence of Li+ in the DBUH-IM14 electrolyte led to unexpected and relatively faster translational mobility of Li+ ions, resulting in a higher lithium apparent transference number. However, the trends observed in ionicity indicate a more complex interplay between intermolecular interactions and ion correlations. While DBUH-TFSI showed minimal effect of Li+ addition, DBUH-TFO and DBUH-IM14 exhibited a significant decrease in ionicity, possibly attributed to strong interactions between ions