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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Effect of Ionic Liquid Components on the Coil Dimensions of PEO

Here, small-angle neutron scattering is used to measure the infinite dilution radius of gyration ($R_{g,0}$) for a range of molecular weights (10–250 kg/mol) of perdeuterated poly(ethylene oxide) (d-PEO) in various imidazolium-based ILs at 80 °C. The Flory exponents ($\nu$) evaluated in the ILs studied (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6 ]), and 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM][BF 4 ])) lie between 0.58 and 0.60, indicating good solvent behavior. The coil dimensions of d-PEO increase on increasing the alkyl chain length of the cation and on decreasing the anion basicity. A more pronounced effect on coil dimensions is observed upon altering the anion, compared to the dependence on cation alkyl chain length. The temperature dependence of $R_{g,0}$ is found to be moderate in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF 4 ]), where the coil size decreases upon increasing the temperature from 80 to 135 °C. Addition of up to 10 wt % of a salt, lithium bis(trifluoromethylsulfonyl)imide, to mixtures of d-PEO and [BMIM][TFSI] has no significant effect on $R_{g,0}$. These results are discussed in terms of the relative interactions among PEO, the cation, and the anion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Electrochemical and Chemical Reactivities of Titanium Oxide-Based Materials with a Chloroaluminate Ionic Liquid Electrolyte for Aluminum Batteries

Here, by selecting three different types of electrode materials, we intended to better understand the Al 3+ intercalation chemistry of titanium oxide-based frameworks with an acidic chloroaluminate electrolyte. In agreement with previous reports, we confirmed that the native interstitial sites of anatase TiO 2 are less prone to accommodate Al 3 + than Li + or Na + ions, while introducing cationic vacancies largely increases the electrochemical storage capacity. Upon the first cycle, the highest reversible capacity, up to 277 mAh/g, was obtained for a hydrated layered structure featuring cationic vacancies. Total scattering data showed that the insertion of Al 3+ ions induced a strong distortion of the framework. In addition, combined 27 Al MAS NMR and DFT calculations revealed that in oxy-hydroxylated vacant sites, the coordination mode of Al 3+ ions depends on the arrangement of anions around vacancies inducing the occurrence of 4-, 5-, and 6-fold coordination modes. Further cycling experiments revealed a progressive capacity fading for all electrode materials. Using cyclic voltammetry on the used electrolyte, we evidenced that a partial dissolution has occurred, which is more pronounced for the layered hydrate compound, and that solubilized species are electrochemically active, giving rise to specific signatures in both CVs and galvanostatic experiments. Raman spectroscopy enabled us to characterize these species, which are derived from the Ti-Cl system. The solubilized species, however, eventually precipitated, as shown by a purple deposit observed on the separator and tentatively assigned to TiCl 3 , known to be insoluble in this medium. By providing further information on the Al 3+ intercalation chemistry and a better understanding of the electrochemical and chemical reactivities of electrode materials, this work will enable progress to be made in the development of aluminum-ion batteries.

Al3+-ion insertion chemistry↗