NMR studies of polymeric sodium ion conductors-a brief review.

Sodium has long been considered an alternative active battery cation to lithium because of the chemical similarity and the overwhelming natural abundance of Na compared to Li. In the "early days" of poly (ethylene oxide) (PEO) and alkali metal salt complexes proposed as polymer electrolytes, studies of Na-salt/PEO materials were nearly as prevalent as those of lithium analogues. Fast forwarding to the present day, there is growing interest in sodium battery chemistry spurred by the challenges of continued advancement in lithium-based batteries. This article reviews the progress made in sodium-based polymer electrolytes from the early days of PEO to the present time. Other polymeric electrolytes such as gel polymer electrolytes (GPE), including formulations based on ionic liquids (ILs), are also discussed.

Sodium Rich Vanadium Oxy-Fluorophosphate - Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O - as Advanced Cathode for Sodium Ion Batteries.

Conventional sodium-based layered oxide cathodes are extremely air sensitive and possess poor electrochemical performance along with safety concerns when operating at high voltage. The polyanion phosphate, Na3 V2 (PO4 )3 stands out as an excellent candidate due to its high nominal voltage, ambient air stability, and long cycle life. The caveat is that Na3 V2 (PO4 )3 can only exhibit reversible capacities in the range of 100 mAh g-1 , 20% below its theoretical capacity. Here, the synthesis and characterizations are reported for the first time of the sodium-rich vanadium oxyfluorophosphate, Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O, a tailored derivative compound of Na3 V2 (PO4 )3 , with extensive electrochemical and structural analyses. Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O delivers an initial reversible capacity of 117 mAh g-1 between 2.5 and 4.5 V under the 1C rate at room temperature, with 85% capacity retention after 900 cycles. The cycling stability is further improved when the material is cycled at 50 °C within 2.8-4.3 V for 100 cycles. When paired with a presodiated hard carbon, Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O cycled with a capacity retention of 85% after 500 cycles. Cosubstitution of the transition metal and fluorine in Na3.2 Ni0.2 V1.8 (PO4 )2 F2 O as well as the sodium-rich structure are the major factors behind the improvement of specific capacity and cycling stability, which paves the way for this cathode in sodium-ion batteries.

Broadband NMR Relaxometry as a Powerful Technique to Study Molecular Dynamics of Ionic Liquids.

Fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry technique has been demonstrated to be a useful analytical tool to investigate molecular dynamics in very diverse systems during the last decades. Of particular importance has been its application in studying ionic liquids, upon which this review article is based. Some of the research carried out on ionic liquids during the last ten years using this technique is highlighted in this article with the aim of promoting the favorable features of FFC NMR applied toward understanding dynamics of complex systems.

Acid-in-Clay Electrolyte for Wide-Temperature-Range and Long-Cycle Proton Batteries.

Proton conduction underlies many important electrochemical technologies. A family of new proton electrolytes is reported: acid-in-clay electrolyte (AiCE) prepared by integrating fast proton carriers in a natural phyllosilicate clay network, which can be made into thin-film (tens of micrometers) fluid-impervious membranes. The chosen example systems (sepiolite-phosphoric acid) rank top among the solid proton conductors in terms of proton conductivities (15 mS cm-1 at 25 °C, 0.023 mS cm-1 at -82 °C), electrochemical stability window (3.35 V), and reduced chemical reactivity. A proton battery is assembled using AiCE as the solid electrolyte membrane. Benefitting from the wider electrochemical stability window, reduced corrosivity, and excellent ionic selectivity of AiCE, the two main problems (gassing and cyclability) of proton batteries are successfully solved. This work draws attention to the element cross-over problem in proton batteries and the generic "acid-in-clay" solid electrolyte approach with superfast proton transport, outstanding selectivity, and improved stability for room- to cryogenic-temperature protonic applications.

A high-performance hydroxide exchange membrane enabled by Cu2+-crosslinked chitosan.

Ion exchange membranes are widely used to selectively transport ions in various electrochemical devices. Hydroxide exchange membranes (HEMs) are promising to couple with lower cost platinum-free electrocatalysts used in alkaline conditions, but are not stable enough in strong alkaline solutions. Herein, we present a Cu2+-crosslinked chitosan (chitosan-Cu) material as a stable and high-performance HEM. The Cu2+ ions are coordinated with the amino and hydroxyl groups of chitosan to crosslink the chitosan chains, forming hexagonal nanochannels (~1 nm in diameter) that can accommodate water diffusion and facilitate fast ion transport, with a high hydroxide conductivity of 67 mS cm-1 at room temperature. The Cu2+ coordination also enhances the mechanical strength of the membrane, reduces its permeability and, most importantly, improves its stability in alkaline solution (only 5% conductivity loss at 80 °C after 1,000 h). These advantages make chitosan-Cu an outstanding HEM, which we demonstrate in a direct methanol fuel cell that exhibits a high power density of 305 mW cm-2. The design principle of the chitosan-Cu HEM, in which ion transport channels are generated in the polymer through metal-crosslinking of polar functional groups, could inspire the synthesis of many ion exchange membranes for ion transport, ion sieving, ion filtration and more.

Nanoscale Hybrid Electrolytes with Viscosity Controlled Using Ionic Stimulus for Electrochemical Energy Conversion and Storage.

As renewable energy is rapidly integrated into the grid, the challenge has become storing intermittent renewable electricity. Technologies including flow batteries and CO2 conversion to dense energy carriers are promising storage options for renewable electricity. To achieve this technological advancement, the development of next generation electrolyte materials that can increase the energy density of flow batteries and combine CO2 capture and conversion is desired. Liquid-like nanoparticle organic hybrid materials (NOHMs) composed of an inorganic core with a tethered polymeric canopy (e.g., polyetheramine (HPE)) have a capability to bind chemical species of interest including CO2 and redox-active species. In this study, the unique response of NOHM-I-HPE-based electrolytes to salt addition was investigated, including the effects on solution viscosity and structural configurations of the polymeric canopy, impacting transport behaviors. The addition of 0.1 M NaCl drastically lowered the viscosity of NOHM-based electrolytes by up to 90%, reduced the hydrodynamic diameter of NOHM-I-HPE, and increased its self-diffusion coefficient, while the ionic strength did not alter the behaviors of untethered HPE. This study is the first to fundamentally discern the changes in polymer configurations of NOHMs induced by salt addition and provides a comprehensive understanding of the effect of ionic stimulus on their bulk transport properties and local dynamics. These insights could be ultimately employed to tailor transport properties for a range of electrochemical applications.

Dynamics of Glyceline and Interactions of Constituents: A Multitechnique NMR Study.

The dynamics of the organic components of the deep eutectic solvent (DES) glyceline are analyzed using an array of complementary nuclear magnetic resonance (NMR) methods. Fast-field cycling 1H relaxometry, pulsed field gradient diffusion, nuclear overhauser effect spectroscopy (NOESY), 13C NMR relaxation, and pressure-dependent NMR experiments are deployed to sample a range of frequencies and modes of motion of the glycerol and choline components of the DES. Generally, translational and rotational diffusion of glycerol are more rapid than those of choline while short-range rotational motions observed from 13C relaxation indicate slow local motion of glycerol at low choline chloride (ChCl) content. The rates of glycerol and choline local motions become more similar at higher ChCl. This result taken together with pressure-dependent NMR studies show that the addition of ChCl makes it easier to disrupt glycerol packing. Finally, a relatively slow hydroxyl H-exchange process between glycerol and choline protons is deduced from the data. Consistent with this, NOESY results indicate relatively little direct H-bonding between glycerol and choline. These results suggest that the glycerol H-bonding network is disrupted as choline is added, but primarily in regions where there is intimate mixing of the two components. Thus, the local dynamics of most of the glycerol resembles that of pure glycerol until substantial choline chloride is present.

CO2 utilization in built environment via the PCO2 swing carbonation of alkaline solid wastes with different mineralogy.

Carbon mineralization to solid carbonates is one of the reaction pathways that can not only utilize captured CO2 but also potentially store it in the long term. In this study, the dissolution and carbonation behaviors of alkaline solid wastes (i.e., waste concrete) was investigated. Concrete is one of the main contributors to a large carbon emission in the built environment. Thus, the upcycling of waste concrete via CO2 utilization has multifaceted environmental benefits including CO2 emission reduction, waste management and reduced mining. Unlike natural silicate minerals such as olivine and serpentine, alkaline solid wastes including waste concrete are highly reactive, and thus, their dissolution and carbonation behaviors vary significantly. Here, both conventional acid (e.g., hydrochloric acid) and less studied carbonic acid (i.e., CO2 saturated water) solvent systems were explored to extract Ca from concrete. Non-stoichiometric dissolution behaviors between Ca and Si were confirmed under far-from-equilibrium conditions (0.1 wt% slurry density), and the re-precipitation of the extracted Si was observed at near-equilibrium conditions (5 wt% slurry density), when the Ca extraction was performed at a controlled pH of 3. These experiments, with a wide range of slurry densities, provided valuable insight into Si re-precipitation phenomena and its effect on the mass transfer limitation during concrete dissolution. Next, the use of the partial pressure of CO2 for the pH swing carbon mineralization process was investigated for concrete, and the results were compared to those of Mg-bearing silicate minerals. In the PCO2 swing process, the extraction of Ca was significantly limited by the precipitation of the carbonate phase (i.e., calcite), since CO2 bubbling could not provide a low enough pH condition for concrete-water-CO2 systems. Thus, this study showed that the two-step carbon mineralization via PCO2 swing, that has been developed for Mg-bearing silicate minerals, may not be viable for highly reactive Ca-bearing silicate materials (e.g., concrete). The precipitated calcium carbonate (PCC) derived from waste concrete via a pH swing process showed very promising results with a high CO2 utilization potential as an upcycled construction material.

Li-Ion Diffusion in Nanoconfined LiBH4-LiI/Al2O3: From 2D Bulk Transport to 3D Long-Range Interfacial Dynamics.

Solid electrolytes based on LiBH4 receive much attention because of their high ionic conductivity, electrochemical robustness, and low interfacial resistance against Li metal. The highly conductive hexagonal modification of LiBH4 can be stabilized via the incorporation of LiI. If the resulting LiBH4-LiI is confined to the nanopores of an oxide, such as Al2O3, interface-engineered LiBH4-LiI/Al2O3 is obtained that revealed promising properties as a solid electrolyte. The underlying principles of Li+ conduction in such a nanocomposite are, however, far from being understood completely. Here, we used broadband conductivity spectroscopy and 1H, 6Li, 7Li, 11B, and 27Al nuclear magnetic resonance (NMR) to study structural and dynamic features of nanoconfined LiBH4-LiI/Al2O3. In particular, diffusion-induced 1H, 7Li, and 11B NMR spin-lattice relaxation measurements and 7Li-pulsed field gradient (PFG) NMR experiments were used to extract activation energies and diffusion coefficients. 27Al magic angle spinning NMR revealed surface interactions of LiBH4-LiI with pentacoordinated Al sites, and two-component 1H NMR line shapes clearly revealed heterogeneous dynamic processes. These results show that interfacial regions have a determining influence on overall ionic transport (0.1 mS cm-1 at 293 K). Importantly, electrical relaxation in the LiBH4-LiI regions turned out to be fully homogenous. This view is supported by 7Li NMR results, which can be interpreted with an overall (averaged) spin ensemble subjected to uniform dipolar magnetic and quadrupolar electric interactions. Finally, broadband conductivity spectroscopy gives strong evidence for 2D ionic transport in the LiBH4-LiI bulk regions which we observed over a dynamic range of 8 orders of magnitude. Macroscopic diffusion coefficients from PFG NMR agree with those estimated from measurements of ionic conductivity and nuclear spin relaxation. The resulting 3D ionic transport in nanoconfined LiBH4-LiI/Al2O3 is characterized by an activation energy of 0.43 eV.

NMR Relaxometry and Diffusometry Analysis of Dynamics in Ionic Liquids and Ionogels for Use in Lithium-Ion Batteries.

We have investigated the charge transport dynamics of a novel solid-like electrolyte material based on mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM] TFSI) and various concentrations of lithium salt bis(trifluoromethylsulfonyl)imide (LiTFSI) confined within a SiO2 matrix, prepared via a sol-gel method. The translational diffusion coefficients of BMIM+, TFSI-, and Li+ in ILs and confined ILs (ionogels, IGs) with different concentrations of lithium salt have been measured at variable temperatures, covering the 20-100 °C range, using nuclear magnetic resonance (NMR) pulsed field gradient diffusion spectroscopy. The mobility of BMIM+, TFSI-, and Li+ was found to increase with the [BMIM] TFSI/LiTFSI ratio, exhibiting an almost liquid-like mobility in IGs. Additionally, the effect of confinement on IL rotational dynamics has been analyzed by measuring 1H, 19F, and 7Li spin-lattice relaxation rate dispersions of IGs at different temperatures, using fast field-cycling NMR relaxometry. The analysis of the experimental data was performed assuming the existence of two fractions of the liquid: a bulk fraction (at least several ionic radii from the silica particles) and a surface fraction (close to the silica particles) and using two different models based on translational and rotational diffusion and reorientation mediated by translational displacements. The existence and weighting of these two fractions of ions were obtained from the direct diffusion measurements. The results show that the ion dynamics slowed only modestly under confinement, which evidences that IGs preserve IL transport properties, and this behavior is an encouraging indication for using IGs as a solid electrolyte for Li+ batteries.

Polymer Capacitor Dielectrics for High Temperature Applications.

Much effort has been invested for nearly five decades to identify and develop new polymer capacitor dielectrics for higher than ambient temperature applications. Simultaneous demands of processability, dielectric permittivity, thermal conductivity, and dielectric breakdown strength dictated by increasing high power performance criteria limit the number of available materials. The present review first explains the advantages of metallized polymer film capacitors over the film-foil, ceramic, and electrolytic counterparts and then presents a comprehensive review on both past developmental effort of commercial resins and recent research progress on new polymers targeted for operating temperature above 150 °C. Some historical background and discussion on the limitation of the commercially available polymer film dielectrics for high temperature applications are also given. In many cases, further development of promising polymers that appear to possess all or most of the important criteria is limited by lack of large scale market incentives but could be of great value to niche applications in the military or aerospace realm.

Enhanced Lithium Oxygen Battery Using a Glyme Electrolyte and Carbon Nanotubes.

The lithium oxygen battery has a theoretical energy density potentially meeting the challenging requirements of electric vehicles. However, safety concerns and short lifespan hinder its application in practical systems. In this work, we show a cell configuration, including a multiwalled carbon nanotube electrode and a low flammability glyme electrolyte, capable of hundreds of cycles without signs of decay. Nuclear magnetic resonance and electrochemical tests confirm the suitability of the electrolyte in a practical battery, whereas morphological and structural aspects revealed by electron microscopy and X-ray diffraction demonstrate the reversible formation and dissolution of lithium peroxide during the electrochemical process. The enhanced cycle life of the cell and the high safety of the electrolyte suggest the lithium oxygen battery herein reported as a viable system for the next generation of high-energy applications.

Correlating Li+-Solvation Structure and its Electrochemical Reaction Kinetics with Sulfur in Subnano Confinement.

Combining theoretical and experimental approaches, we investigate the solvation properties of Li+ ions in a series of ether solvents (dimethoxyethane, diglyme, triglyme, tetraglyme, and 15-crown-5) and their subsequent effects on the solid-state lithium-sulfur reactions in subnano confinement. The ab initio and classical molecular dynamics (MD) simulations predict Li+ ion solvation structures within ether solvents in excellent agreement with experimental evidence from electrospray ionization-mass spectroscopy. An excellent correlation is also established between the Li+-solvation binding energies from the ab initio MD simulations and the lithiation overpotentials obtained from galvanostatic intermittent titration techniques (GITT). These findings convincingly indicate that a stronger solvation binding energy imposes a higher lithiation overpotential of sulfur in subnano confinement. The mechanistic understanding achieved at the electronic and atomistic level of how Li+-solvation dictates its electrochemical reactions with sulfur in subnano confinement provides invaluable guidance in designing future electrolytes and electrodes for Li-sulfur chemistry.

Anisotropic Ion Diffusion and Electrochemically Driven Transport in Nanostructured Block Copolymer Electrolytes.

Nanostructured block copolymer electrolytes have the potential to enable solid-state batteries with lithium metal anodes. We present complete continuum characterization of ion transport in a lamellar polystyrene-b-poly(ethylene oxide) copolymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte as a function of salt concentration. Electrochemical measurements are used to determine the Stefan-Maxwell salt diffusion coefficients [Formula: see text], [Formula: see text], and [Formula: see text]. Individual self-diffusion coefficients of the lithium- and TFSI-containing species were measured by pulsed-field gradient NMR (PFG-NMR). The NMR data indicate that salt diffusion is locally anisotropic, and this enables determination of a diffusion coefficient parallel to the lamellae, D∥, and a diffusion coefficient through defects in the lamellae, D⊥. We quantify anisotropic diffusion by defining an NMR morphology factor and demonstrate that it is correlated to defect density seen by transmission electron microscopy. We find agreement between the electrochemically determined Stefan-Maxwell diffusion coefficients and the diffusion coefficient D⊥ determined by PFG-NMR. Our work indicates that the performance of nanostructured block copolymer electrolytes in batteries is strongly influenced by ion transport through defects.

Improved Anisotropic Thermoelectric Behavior of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) via Magnetophoresis.

There is strong demand for achieving morphological control of conducting polymers in its many potential applications, from energy harvesting to spintronics. Here, the static magnetic-field-induced alignment of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) particles is demonstrated. PEDOT:PSS thin films cast under modest mT-level magnetic fields exhibit a fourfold increase in the Seebeck coefficient and doubled electrical conductivity. Atomic force microscopy measurements confirm the presence of conducting islands that exhibit a 10-fold increase in the local charge carrier mobility and threshold behavior that is associated with phase separation. High-resolution scanning electron microscopy identifies a consistent structural coil-to-rod transition, and three-dimensional time-of-flight secondary-ion mass spectrometry imaging shows that the rodlike structures coincide with PEDOT domains that generally align with the magnetic field and cluster on the outer surface. Grazing-incidence small-angle X-ray scattering, Raman spectra, electron paramagnetic resonance, and circular dichroism spectroscopy point to the physical nature of the magnetophoretic alignment, which is expected to occur via magnetic coupling of PEDOT domains with polaron modes. Because casting under mT-level magnetic fields increases the electrical conductivity and Seebeck coefficient of PEDOT:PSS thin films without additional dopants that commonly limit the thermoelectric performance, our research reveals that low-field magnetophoresis significantly influences the structure and corresponding physical properties of PEDOT:PSS. Our results also point to concerns that the presence of small external magnetic fields in laboratory settings may appreciably and inadvertently influence the PEDOT:PSS morphology during settling, drying, or annealing processes.

Defect chemistry and electrical properties of garnet-type Li7La3Zr2O12.

Garnet-type cubic Li7La3Zr2O12 exhibits one of the highest lithium-ion conductivity values amongst oxides (up to ∼2 mS cm-1 at room temperature). This compound has also emerged as a promising candidate for solid electrolytes in all-solid-state lithium batteries, due to its high ionic conductivity, good chemical stability against lithium metal, and wide electrochemical stability window. Defect chemistry of this class of materials, although less studied, is critical to the understanding of the nature of ionic conductivity and predicting the properties of grain boundaries and heterogeneous solid interfaces. In this study, the electrical properties of nominally undoped cubic Li7La3Zr2O12 are characterized as a function of temperature and pO2 using a suite of AC impedance and DC polarization techniques. The formation of ionic defects and defect pairs as well as their impact on the transport properties are discussed, and a Brouwer-type diagram is constructed.

Connection between Lithium Coordination and Lithium Diffusion in [Pyr12O1 ][FTFSI] Ionic Liquid Electrolytes.

The use of highly concentrated ionic liquid-based electrolytes results in improved rate capability and capacity retention at 20 °C compared to Li+ -dilute systems in Li-metal and Li-ion cells. This work explores the connection between the bulk electrolyte properties and the molecular organization to provide insight into the concentration dependence of the Li+ transport mechanisms. Below 30 mol %, the Li+ -containing species are primarily smaller complexes (one Li+ cation) and the Li+ ion transport is mostly derived from the vehicular transport. Above 30 mol %, where the viscosity is substantially higher and the conductivity lower, the Li+ -containing species are a mix of small and large complexes (one and more than one Li+ cation, respectively). The overall conduction mechanism likely changes to favor structural diffusion through the exchange of anions in the first Li+ solvation shell. The good rate performance is likely directly influenced by the presence of larger Li+ complexes, which promote Li+ -ion transport (as opposed to Li+ -complex transport) and increase the Li+ availability at the electrode.

Polymeric peptide pigments with sequence-encoded properties.

Melanins are a family of heterogeneous polymeric pigments that provide ultraviolet (UV) light protection, structural support, coloration, and free radical scavenging. Formed by oxidative oligomerization of catecholic small molecules, the physical properties of melanins are influenced by covalent and noncovalent disorder. We report the use of tyrosine-containing tripeptides as tunable precursors for polymeric pigments. In these structures, phenols are presented in a (supra-)molecular context dictated by the positions of the amino acids in the peptide sequence. Oxidative polymerization can be tuned in a sequence-dependent manner, resulting in peptide sequence-encoded properties such as UV absorbance, morphology, coloration, and electrochemical properties over a considerable range. Short peptides have low barriers to application and can be easily scaled, suggesting near-term applications in cosmetics and biomedicine.

Solvation behavior of carbonate-based electrolytes in sodium ion batteries.

Sodium ion batteries are on the cusp of being a commercially available technology. Compared to lithium ion batteries, sodium ion batteries can potentially offer an attractive dollar-per-kilowatt-hour value, though at the penalty of reduced energy density. As a materials system, sodium ion batteries present a unique opportunity to apply lessons learned in the study of electrolytes for lithium ion batteries; specifically, the behavior of the sodium ion in an organic carbonate solution and the relationship of ion solvation with electrode surface passivation. In this work the Li+ and Na+-based solvates were characterized using electrospray mass spectrometry, infrared and Raman spectroscopy, 17O, 23Na and pulse field gradient double-stimulated-echo pulse sequence nuclear magnetic resonance (NMR), and conductivity measurements. Spectroscopic evidence demonstrate that the Li+ and Na+ cations share a number of similar ion-solvent interaction trends, such as a preference in the gas and liquid phase for a solvation shell rich in cyclic carbonates over linear carbonates and fluorinated carbonates. However, quite different IR spectra due to the PF6- anion interactions with the Na+ and Li+ cations were observed and were rationalized with the help of density functional theory (DFT) calculations that were also used to examine the relative free energies of solvates using cluster - continuum models. Ion-solvent distances for Na+ were longer than Li+, and Na+ had a greater tendency towards forming contact pairs compared to Li+ in linear carbonate solvents. In tests of hard carbon Na-ion batteries, performance was not well correlated to Na+ solvent preference, leading to the possibility that Na+ solvent preference may play a reduced role in the passivation of anode surfaces and overall Na-ion battery performance.

NMR Studies of Solvent-Free Ceramic Composite Polymer Electrolytes-A Brief Review.

Polyether-based polymer electrolytes containing ceramic inorganic oxide fillers often exhibit improved mechanical and ion transport properties compared to their filler-free counterparts. The nature of local scale interactions that give rise to these enhanced properties is explored by nuclear magnetic resonance measurements.