7Li nuclear magnetic resonance studies of dynamics in a ternary gel polymer electrolyte based on polymeric ionic liquids

Recent Advancements in Gel Polymer Electrolytes for Flexible Energy Storage Applications

Since the last decade, the need for deformable electronics exponentially increased, requiring adaptive energy storage systems, especially batteries and supercapacitors. Thus, the conception and elaboration of new deformable electrolytes becomes more crucial than ever. Among diverse materials, gel polymer electrolytes (hydrogels, organogels, and ionogels) remain the most studied thanks to the ability to tune the physicochemical and mechanical properties by changing the nature of the precursors, the type of interactions, and the formulation. Nevertheless, the exploitation of this category of electrolyte as a possible commercial product is still restrained, due to different issues related to the nature of the gels (ionic conductivity, evaporation of filling solvent, toxicity, etc.). Therefore, this review aims to resume different strategies to tailor the properties of the gel polymer electrolytes as well as to provide recent advancements in the field toward the elaboration of deformable batteries and supercapacitors.

Nuclear Magnetic Resonance Relaxation Pathways in Electrolytes for Energy Storage

Nuclear Magnetic Resonance (NMR) spin relaxation times have been an instrumental tool in deciphering the local environment of ionic species, the various interactions they engender and the effect of these interactions on their dynamics in conducting media. Of particular importance has been their application in studying the wide range of electrolytes for energy storage, on which this review is based. Here we highlight some of the research carried out on electrolytes in recent years using NMR relaxometry techniques. Specifically, we highlight studies on liquid electrolytes, such as ionic liquids and organic solvents; on semi-solid-state electrolytes, such as ionogels and polymer gels; and on solid electrolytes such as glasses, glass ceramics and polymers. Although this review focuses on a small selection of materials, we believe they demonstrate the breadth of application and the invaluable nature of NMR relaxometry.

Versatile Copolymer for Stretchable and Self-healable Liquid-free Ionic Conductive Elastomers

To facilitate the practical use of ionic conductive materials for flexible electronics, the issues existing in hydrogels and ionogels, such as low thermostability and possible solvent leakage, need to be resolved but are inevitable. Liquid-free ionic elastomers (ICEs) as an alternative option are free of such concerns but have been facing the drawbacks of low conductivity and less satisfying mechanical properties. Here, a versatile copolymer with π-π stacking and cation-π interactions for high-performance ICE is proposed. The ICEs presented tunable mechanical and electrical properties by varying the feed ratio of the ternary monomers. The optimized ICE possessed high stretchability and strength, fast shape-recovery, self-healing, decent conductivity, and desirable stability against heat and under ambient conditions. The use of virgin and self-healed ICEs as the conductors for dielectric elastomer actuators (DEA) is demonstrated and exhibits comparable actuating performance to the reported DEA employing organogels and ionogels. The work provides a facile approach for fabricating ICEs with versatile properties that can be used for flexible electronics.

Li+ Dynamics of Liquid Electrolytes Nanoconfined in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are excellent platforms to design hybrid electrolytes for Li batteries with liquid-like transport and stability against lithium dendrites. We report on Li⁺ dynamics in quasi-solid electrolytes consisting in Mg-MOF-74 soaked with LiClO₄-propylene carbonate (PC) and LiClO₄-ethylene carbonate (EC)/dimethyl carbonate (DMC) solutions by combining studies of ion conductivity, nuclear magnetic resonance (NMR) characterization, and spin relaxometry. We investigate nanoconfinement of liquid inside MOFs to characterize the adsorption/solvation mechanism at the basis of Li⁺ migration in these materials. NMR supports that the liquid is nanoconfined in framework micropores, strongly interacting with their walls and that the nature of the solvent affects Li⁺ migration in MOFs. Contrary to the "free'' liquid electrolytes, faster ion dynamics and higher Li⁺ mobility take place in LiClO₄-PC electrolytes when nanoconfined in MOFs demonstrating superionic conductor behavior (conductivity σ_rt > 0.1 mS cm^-1, transport number t_Li⁺ > 0.7). Such properties, including a more stable Li electrodeposition, make MOF-hybrid electrolytes promising for high-power and safer lithium-ion batteries.

Effect of PAMAM Dendrimers on Interactions and Transport of LiTFSI and NaTFSI in Propylene Carbonate-Based Electrolytes

Poly(amidoamine) (PAMAM)-based electrolytes are prepared by dissolving the PAMAM half-generations G1.5 or G2.5 in propylene carbonate (PC), either with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) or sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) salts. The solutions, designed for ion battery applications, are studied in terms of ions transport properties. Raman Spectroscopy reveals information about the interactions between cations and PAMAM dendrimers as well as full dissociation of the salts in all solutions. Pulsed-field gradient Nuclear Magnetic Resonance (PFG NMR), measured as a function of both temperature and PAMAM concentration, are obtained for the cation, anion, solvent, and dendrimer molecules using lithium (7Li), sodium (23Na), fluorine (19F), and hydrogen (1H) NMR, respectively. It was found that lithium diffusion is slow compared to the larger TFSI anion and decreases with PAMAM concentration due to interactions between cation and dendrimer. Comparison of conductivities calculated from diffusion coefficients using the Nernst-Einstein equation, with conductivity measurements obtained from Impedance Spectroscopy (IS), shows slightly higher IS conductivities, caused among others by PAMAM conductivity.

Toward High-Energy-Density Lithium Metal Batteries: Opportunities and Challenges for Solid Organic Electrolytes

With increasing demands for safe, high capacity energy storage to support personal electronics, newer devices such as unmanned aerial vehicles, as well as the commercialization of electric vehicles, current energy storage technologies are facing increased challenges. Although alternative batteries have been intensively investigated, lithium (Li) batteries are still recognized as the preferred energy storage solution for the consumer electronics markets and next generation automobiles. However, the commercialized Li batteries still have disadvantages, such as low capacities, potential safety issues, and unfavorable cycling life. Therefore, the design and development of electromaterials toward high-energy-density, long-life-span Li batteries with improved safety is a focus for researchers in the field of energy materials. Herein, recent advances in the development of novel organic electrolytes are summarized toward solid-state Li batteries with higher energy density and improved safety. On the basis of new insights into ionic conduction and design principles of organic-based solid-state electrolytes, specific strategies toward developing these electrolytes for Li metal anodes, high-energy-density cathode materials (e.g., high voltage materials), as well as the optimization of cathode formulations are outlined. Finally, prospects for next generation solid-state electrolytes are also proposed.

A review of NMR methods used in the study of the structure and dynamics of ionic liquids

Recently, NMR spectroscopy has been emerging out as a powerful tool to study the structure and dynamics of ionic liquids (ILs) and ILs-Li⁺ salt mixtures. This mini-review primarily focuses on the applications of various NMR spectroscopic techniques such as self-diffusion measurements, NMR relaxometry, two-dimensional NMR, and other novel NMR approaches to study the structure and dynamics of ILs and its mixtures with lithium salts. Copyright © 2017 John Wiley & Sons, Ltd.

Spin relaxation studies of Li+ ion dynamics in polymer gel electrolytes

Two ternary polymer gel electrolyte systems are compared, containing either polyethylene oxide (PEO) or the poly-ionic liquid poly(diallyldimethylammonium) bis(trifluoromethyl sulfonyl)imide (PDADMA-TFSI). Both gel types are based on the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl sulfonyl)imide (P₁₄TFSI) and LiTFSI. We study the influence of the polymers on the local lithium ion dynamics at different polymer concentrations using ⁷Li spin-lattice relaxation data in dependence on frequency and temperature. In all cases the relaxation rates are well described by the Cole-Davidson motional model with Arrhenius dependence of the correlation time and a temperature dependent quadrupole coupling constant. For both polymers the correlation times are found to increase with polymer concentration. The activation energy of local motions slightly increases with increasing PEO concentration, and slightly decreases with increasing PDADMA-TFSI concentration. Thus the local Li⁺ motion is reduced by the presence of either polymer; however, the reduction is less effective in the PDADMA⁺ samples. We thus conclude that mechanical stabilization of a liquid electrolyte by a polymer can be achieved at a lower decrease of Li⁺ motion when a cationic polymer is used instead of PEO.

Direct determination of ionic transference numbers in ionic liquids by electrophoretic NMR

Transference numbers of ions in a series of ionic liquids are obtained from electrophoretic mobilities by eNMR.