Influence of Cationic Poly(ionic liquid) Architecture on the Ion Dynamics in Polymer Gel Electrolytes

Brinkkötter, Marc; Lozinskaya, Elena I.; Ponkratov, Denis O.; Vygodskii, Yakov S.; Schmidt, Daniel F.; Shaplov, Alexander S.; Schönhoff, Monika

doi:10.1021/acs.jpcc.9b03089

Cited by 20 publications

(21 citation statements)

References 56 publications

(130 reference statements)

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“…Motivated by the desire to transition polyILs toward electrochemical applications, interest has arisen in the properties of lithium salt-doped polyILs. − In such a context, experiments have demonstrated that the dynamics of the free ion species (lithium ions and the counteranion of the polyIL) become faster with an increase in the concentration of lithium salt c Li . Such trends are opposite the results noted in monomeric IL systems, in which the mobility of both lithium and anions decrease with an increase in the concentration of salt.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of Ion Transport in Lithium Salt-Doped Polymeric Ionic Liquid Electrolytes

et al. 2020

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Recent experimental results have demonstrated that polymeric ionic liquids doped with Li salts exhibit enhanced ionic mobilities and lithium ion transference numbers with increasing salt concentrations. In this study, we used atomistic molecular dynamics simulations on a model system of lithium salt-doped 1-butyl-3-methyl-imidazolium bistriflimide ionic liquids and poly(1-butyl-3-methyl-imidazolium bistriflimide) electrolytes to identify the molecular mechanisms underlying such findings. Our results mirror qualitatively the experimental results on the influence of salt doping on the ion mobilities. Further, a surprisingly stronger dependence (coupling) between the lithium ion mobilities and polymer segmental dynamics is observed relative to the coupling between the anion diffusivities and polymer dynamics. We present results for ion coordination and hopping characteristics to rationalize such behaviors and identify the mechanistic origins of the properties of this emerging class of polymer electrolytes.

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Section: Introductionmentioning

confidence: 99%

Mechanisms of Ion Transport in Lithium Salt-Doped Polymeric Ionic Liquid Electrolytes

et al. 2020

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“…Concerning an optimization of ion transport, the interplay of coexisting phases is not necessarily a drawback, as it might even be exploited in a material with a polymer-enriched phase enhancing mechanical stability, while ion transport is enhanced in IL-rich domains. This is reminiscent of ternary gels of cationic polyionic liquid (PIL) in Li-salt/IL, 55 where optimized ion transport was found for those polymeric structures, which promote a phase separation into IL-enriched and polymerenriched domains.…”

Section: ■ Conclusionmentioning

confidence: 99%

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

et al. 2020

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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.

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“…However, as a result of tethering the counterion to the polymer backbone, polyILs exhibit lower ionic conductivities even relative to other salt‐doped SPEs 1,9–20 . Hence, a number of efforts have been exploring strategies such as block copolymer polyILs, 21–31 plasticizing polyILs using ILs, 32,33 salt doping polyILs 31,34–42 etc. as means to enhance the conductivity of polyIL based systems.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of ion transport in lithium salt‐doped polymeric ionic liquid electrolytes at higher salt concentrations

Zhang

Lin

Ganesan

2021

Journal of Polymer Science

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We used atomistic simulations to study the mechanisms of ion transport in salt‐doped polymeric ionic liquid systems at higher salt concentrations. Consistent with the experimental observations, our simulations indicate that at higher salt concentrations, the anion mobilities become lower than that of the lithium cations. Further, the anion mobilities become relatively insensitive to the salt concentration, while the mobilities of lithium increase with increasing salt concentration. We rationalize the results for the anion mobilities by considering the fractions of anions which are exclusively coordinated with the polycations (Type1); co‐coordinated with cations and lithium (Type2); and those exclusively coordinated with lithium (Type3). By considering the coordination characteristics of the different types of anions and their hopping motions, we demonstrate that the net anion mobilities results from a compensation effect of the salt concentration dependence of the mobilities of the different anions. With respect to the mobilities of the lithium ions, we demonstrate that the latter moves primarily by a structural diffusion mechanism involving refreshing of the solvation shell during hopping. Further, for the majority of the lithium ions, the solvation shell is shown to be comprised of co‐coordinated Type2 anions, and that the number of polycations and the unique polymer chains involved in such coordination decreases with increasing salt concentration. Such changes are shown to weaken the solvation shell around the lithium, thereby facilitating faster ion motion. Together, our results suggest that systems in which the anion which exhibits a stronger coordination to the polycation in comparison to that of the lithium can facilitate higher transference numbers without a concomitant reduction in the mechanical strength.

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Influence of Cationic Poly(ionic liquid) Architecture on the Ion Dynamics in Polymer Gel Electrolytes

Cited by 20 publications

References 56 publications

Mechanisms of Ion Transport in Lithium Salt-Doped Polymeric Ionic Liquid Electrolytes

Mechanisms of Ion Transport in Lithium Salt-Doped Polymeric Ionic Liquid Electrolytes

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

Mechanisms of ion transport in lithium salt‐doped polymeric ionic liquid electrolytes at higher salt concentrations

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