Boosting the Ionic Conductivity of Pyrrolidinium-Based Ionic Plastic Crystals by LLZO Fillers.

Organic ionic plastic crystals (OIPCs) have attracted attention as novel organic solid electrolyte materials, but their insufficient mechanical strength and ionic conductivity have prevented their application. In this study, a lithium salt, lithium bis(fluorosulfonyl)amide (LiFSA), and an inorganic solid electrolyte, Li7La3Zr2O12 (LLZO), were added to an OIPC, N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide ([C2epyr][FSA]). The fabricated organic-inorganic hybrid solid electrolytes were evaluated thermally, mechanically, and electrochemically to reveal which factors affect the properties of the electrolytes. All samples showed excellent thermal stability regardless of LiFSA or LLZO concentration, and they were found to be highly plastic and ion-conductive solids at a wide range of temperatures. It was also revealed that the addition of LLZO raised the nanoindentation stiffness (HIT) of the [C2epyr][FSA]/LiFSA composites. The ionic conductivity of the hybrid electrolytes was higher than that of the pristine OIPC, reaching a value of 2.1 × 10-4 S cm-1 at 25 °C upon addition of appropriate amounts of LiFSA and LLZO. Overall, samples with higher LiFSA concentration and moderate LLZO concentration exhibited higher ionic conductivity. Cyclic voltammetry results showed that the [C2epyr][FSA]/LiFSA/LLZO composites were lithium-ion conductors. These findings indicate that by optimizing the concentrations of lithium salt and LLZO, it would be possible to realize their applications as solid electrolytes.

Near Elimination of In Vitro Predicted Extrathoracic Aerosol Deposition in Children Using a Spray-Dried Antibiotic Formulation and Pediatric Air-Jet DPI.

PURPOSE: This study evaluated the in vitro aerosol performance of a dry powder antibiotic product that combined a highly dispersible tobramycin powder with a previously optimized pediatric air-jet dry powder inhaler (DPI) across a subject age range of 2-10 years. METHODS: An excipient enhanced growth (EEG) formulation of the antibiotic tobramycin (Tobi) was prepared using a small particle spray drying technique that included mannitol as the hygroscopic excipient and trileucine as the dispersion enhancer. The Tobi-EEG formulation was aerosolized using a positive-pressure pediatric air-jet DPI that included a 3D rod array. Realistic in vitro experiments were conducted in representative airway models consistent with children in the age ranges of 2-3, 5-6 and 9-10 years using oral or nose-to-lung administration, non-humidified or humidified airway conditions, and constant or age-specific air volumes. RESULTS: Across all conditions tested, mouth-throat depositional loss was < 1% and nose-throat depositional loss was < 3% of loaded dose. Lung delivery efficiency was in the range of 77.3-85.1% of loaded dose with minor variations based on subject age (~ 8% absolute difference), oral or nasal administration (< 2%), and delivered air volume (< 2%). Humidified airway conditions had an insignificant impact on extrathoracic depositional loss and significantly increased aerosol size at the exit of a representative lung chamber. CONCLUSIONS: In conclusion, the inhaled antibiotic product nearly eliminated extrathoracic depositional loss, demonstrated high efficiency nose-to-lung antibiotic aerosol delivery in pediatric airway models for the first time, and provided ~ 80% lung delivery efficiency with little variability across subject age and administered air volume.

Evaluation of the Polyhedral Mesh Style for Predicting Aerosol Deposition in Representative Models of the Conducting Airways.

A critical factor affecting the accuracy of Computational Fluid Dynamic (CFD) simulations and the time required to conduct them is construction of the computational mesh. This study aimed to evaluate the relatively new polyhedral mesh style for simulating aerosol deposition in the upper conducting airways compared with established meshing techniques and experimental data. Hexahedral and polyhedral mesh solutions were compared in two benchmark geometries: 1) a 90°-bend with flow characteristics similar to the extrathoracic airways of an adolescent child, and 2) a double bifurcation representing bifurcations B3-B5 in an adult. Both 4-block and 5-block hexahedral meshes were used in the 90°-bend to capture the potential of fully-structured hexahedral meshes. In the 90°-bend, polyhedral elements matched polydisperse in vitro deposition data with 20% relative error (RE; averaged across the particle sizes considered), which is an improvement on the accuracy of the 4-block hexahedral mesh (35% RE) and is similar to the accuracy of the 5-block hexahedral mesh (19% RE). In the double bifurcation, deposition fraction relative differences evaluated between polyhedral and hexahedral meshes ranged from 0.3% to 28.6% for the different particle sizes assessed, which is an order of magnitude improvement compared with previous studies that considered hexahedral vs. hybrid tetrahedral-prism meshes for the same flow field. Solution convergence time with polyhedral elements was found to be 50% to 140% higher than with hexahedral meshes of comparable size. While application dependent, the increase in simulation time observed with polyhedral meshes will likely be outweighed by the ease and convenience of polyhedral mesh construction. It was concluded that the polyhedral mesh style, with sufficient resolution especially near the walls, is an excellent alternative to the highly regarded hexahedral mesh style for predicting upper airway aerosol transport and deposition and provides a powerful new tool in the assessment of respiratory aerosol dosimetry.

Determining the efficacy of camera traps, live capture traps, and detection dogs for locating cryptic small mammal species.

Metal box (e.g., Elliott, Sherman) traps and remote cameras are two of the most commonly employed methods presently used to survey terrestrial mammals. However, their relative efficacy at accurately detecting cryptic small mammals has not been adequately assessed. The present study therefore compared the effectiveness of metal box (Elliott) traps and vertically oriented, close range, white flash camera traps in detecting small mammals occurring in the Scenic Rim of eastern Australia. We also conducted a preliminary survey to determine effectiveness of a conservation detection dog (CDD) for identifying presence of a threatened carnivorous marsupial, Antechinus arktos, in present-day and historical locations, using camera traps to corroborate detections. 200 Elliott traps and 20 white flash camera traps were set for four deployments per method, across a site where the target small mammals, including A. arktos, are known to occur. Camera traps produced higher detection probabilities than Elliott traps for all four species. Thus, vertically mounted white flash cameras were preferable for detecting the presence of cryptic small mammals in our survey. The CDD, which had been trained to detect A. arktos scat, indicated in total 31 times when deployed in the field survey area, with subsequent camera trap deployments specifically corroborating A. arktos presence at 100% (3) indication locations. Importantly, the dog indicated twice within Border Ranges National Park, where historical (1980s-1990s) specimen-based records indicate the species was present, but extensive Elliott and camera trapping over the last 5-10 years have resulted in zero A. arktos captures. Camera traps subsequently corroborated A. arktos presence at these sites. This demonstrates that detection dogs can be a highly effective means of locating threatened, cryptic species, especially when traditional methods are unable to detect low-density mammal populations.

Rheological and Ionic Transport Properties of Nanocomposite Electrolytes Based on Protic Ionic Liquids and Silica Nanoparticles.

In this study, the effect of hydrophilic silica nanoparticle (AEROSIL 200) addition on the rheological and transport properties of several protic ionic liquids (PILs) consisting of protonated 1,8-diazabicyclo[5.4.0]undec-7-ene cation (DBU) was studied. Interactions between the surface silanol groups of the silica nanoparticles and the ions of these PILs affected the nature of particle aggregation and the hydrogen bonding environment, which was reflected in the nonlinear rheological behaviors and transport properties of their colloidal suspensions. In contrast to shear-thinning gels formed by colloidal suspensions of the silica nanoparticles in [DBU][TFSA] ([TFSA] = [N(SO2CF3)2]), [DBU][TfO] ([TfO] = [CF3SO3]), and [DBU][TFA] ([TFA] = [CF3CO2]), a shear-thickening stable suspension was formed in the [DBU][MSA] ([MSA] = [CH3SO3]) system. A relatively strong interaction between the silanol groups and the ions of [DBU][MSA] and the ability of this PIL to form a thicker solvation layer through hydrogen bonding were assumed to be responsible for this unique behavior. Moreover, the [DBU][MSA]-silica system showed a large enhancement in the conductivity at a certain silica concentration. This enhancement was not observed in the other PIL-silica composites that exhibited shear-thinning behavior. Even though diffusion of ions was found to be restricted in the presence of silica, a preferentially stronger interaction between [MSA] anions and the silica surface resulted in an increase in the number of charge carriers.

Li-ion hopping conduction in highly concentrated lithium bis(fluorosulfonyl)amide/dinitrile liquid electrolytes.

Li+ ion hopping conduction in highly concentrated solutions of lithium bis(fluorosulfonyl)amide (LiFSA) dissolved in dinitrile solvents, namely succinonitrile, glutaronitrile, and adiponitrile, was investigated. Phase behaviors of the LiFSA/dinitrile binary mixtures assessed by differential scanning calorimetry suggested that LiFSA and the dinitriles form stable solvates in a molar ratio of 1 : 2. For succinonitrile, a glass forming room temperature liquid is formed when [LiFSA]/[succinonitrile] > 1. The corresponding glutaronitrile and adiponitrile mixtures have melting points below 60 °C. The self-diffusion coefficients of Li+, FSA-, and dinitrile measured with pulsed field gradient NMR suggested that Li+ ion diffuses faster than anion and dinitrile in the liquids of composition [LiFSA]/[dinitrile] = 1/0.8, indicating emergence of Li+ ion hopping conduction. X-ray crystallography for the LiFSA-(dinitrile)2 solvates and Raman spectroscopy for the liquids with composition [LiFSA]/[dinitrile] > 1 revealed that the two cyano groups of the dinitrile coordinate to two different Li+ ions and form solvent-bridged structures of (Li+-dinitrile-Li+). In addition, the Raman spectra suggested that ionic aggregates (Li+-FSA--Li+) are formed in the liquids with composition [LiFSA]/[dinitrile] > 1. Although there is frequent ligand (dinitrile and/or anion) exchange for each Li+ ion in the liquid state, the polymeric network structures (solvent-bridged structure and ionic aggregates) restrict the facile motion of ligands because each ligand is interacting with multiple Li+ ions in the highly concentrated electrolytes. This induces the faster diffusion of the Li+ ion than that of the ligands, i.e., hopping conduction of Li+ through ligand exchange. Electrochemical measurements clarified that the [LiFSA]/[succinonitrile] = 1/0.8 electrolyte possesses a relatively high Li+ transport ability (limiting current density > 7 mA cm-2) thanks to the Li+ hopping conduction, regardless of its extremely high viscosity (3142 mPa s) and relatively low conductivity (0.26 mS cm-1) at room temperature. Furthermore, this electrolyte was shown to have a high Li+ transference number (>0.6), exhibited reversible Li metal deposition/dissolution i.e. suppression of reductive decomposition of the solvent, and could be successfully applied to graphite and LiNi1/3Mn1/3Co1/3O2 half-cells.

Ionic transport in highly concentrated lithium bis(fluorosulfonyl)amide electrolytes with keto ester solvents: structural implications for ion hopping conduction in liquid electrolytes.

Recent studies have suggested that a Li ion hopping or ligand- or anion-exchange mechanism is largely involved in Li ion conduction of highly concentrated liquid electrolytes. To understand the determining factors for the Li ion hopping/exchange dominant conduction in such liquid systems, ionic diffusion behavior and Li ion coordination structures of concentrated liquid electrolytes composed of lithium bis(fluorosulfonyl)amide (Li[FSA]) and keto ester solvents with two carbonyl coordinating sites of increasing intramolecular distance (methyl pyruvate (MP), methyl acetoacetate (MA), and methyl levulinate (ML)) were studied. Diffusivity measurements of MP- and MA-based concentrated electrolytes showed faster Li ion diffusion than the solvent and FSA anion, demonstrating that Li ion diffusion was dominated by the Li ion hopping/exchange mechanism. A solvent-bridged, chain-like Li ion coordination structure and highly aggregated ion pairs (AGGs) or ionic clusters e.g. Lix[FSA]y(y-x)- forming in the electrolytes were shown to contribute to Li ion hopping conduction. By contrast, ML, with greater intramolecular distance between the carbonyl moieties, is more prone to form a bidentate complex with a Li cation, which increased the contribution of the vehicle mechanism to Li ion diffusion even though similar AGGs and ionic clusters were also observed. The clear correlation between the unusual Li ion diffusion and the solvent-bridged, chain-like structure provides an important insight into the design principles for fast Li ion conducting liquid electrolytes that would enable Li ion transport decoupled from viscosity-controlled mass transfer processes.

Use of computational fluid dynamics deposition modeling in respiratory drug delivery.

INTRODUCTION: Respiratory drug delivery is a surprisingly complex process with a number of physical and biological challenges. Computational fluid dynamics (CFD) is a scientific simulation technique that is capable of providing spatially and temporally resolved predictions of many aspects related to respiratory drug delivery from initial aerosol formation through respiratory cellular drug absorption. AREAS COVERED: This review article focuses on CFD-based deposition modeling applied to pharmaceutical aerosols. Areas covered include the development of new complete-airway CFD deposition models and the application of these models to develop a next-generation of respiratory drug delivery strategies. EXPERT OPINION: Complete-airway deposition modeling is a valuable research tool that can improve our understanding of pharmaceutical aerosol delivery and is already supporting medical hypotheses, such as the expected under-treatment of the small airways in asthma. These complete-airway models are also being used to advance next-generation aerosol delivery strategies, like controlled condensational growth. We envision future applications of CFD deposition modeling to reduce the need for human subject testing in developing new devices and formulations, to help establish bioequivalence for the accelerated approval of generic inhalers, and to provide valuable new insights related to drug dissolution and clearance leading to microdosimetry maps of drug absorption.

Direct Evidence for Li Ion Hopping Conduction in Highly Concentrated Sulfolane-Based Liquid Electrolytes.

We demonstrate that Li+ hopping conduction, which cannot be explained by conventional models i.e., Onsager's theory and Stokes' law, emerges in highly concentrated liquid electrolytes composed of LiBF4 and sulfolane (SL). Self-diffusion coefficients of Li+ ( DLi), BF4- ( DBF4), and SL ( DSL) were measured with pulsed-field gradient NMR. In the concentrated electrolytes with molar ratios of SL/LiBF4 ≤ 3, the ratios DSL/ DLi and DBF4/ DLi become lower than 1, suggesting faster diffusion of Li+ than SL and BF4-, and thus the evolution of Li+ hopping conduction. X-ray crystallographic analysis of the LiBF4/SL (1:1) solvate revealed that the two oxygen atoms of the sulfone group are involved in the bridging coordination of two different Li+ ions. In addition, the BF4- anion also participates in the bridging coordination of Li+. The Raman spectra of the highly concentrated LiBF4-SL solution suggested that Li+ ions are bridged by SL and BF4- even in the liquid state. Moreover, detailed investigation along with molecular dynamics simulations suggests that Li+ exchanges ligands (SL and BF4-) dynamically in the highly concentrated electrolytes, and Li+ hops from one coordination site to another. The spatial proximity of coordination sites, along with the possible domain structure, is assumed to enable Li+ hopping conduction. Finally, we demonstrate that Li+ hopping suppresses concentration polarization in Li batteries, leading to increased limiting current density and improved rate capability compared to the conventional concentration electrolyte. Identification and rationalization of Li+ ion hopping in concentrated SL electrolytes is expected to trigger a new paradigm of understanding for such unconventional electrolyte systems.

Enhanced Electrochemical Stability of Molten Li Salt Hydrate Electrolytes by the Addition of Divalent Cations.

Water can be an attractive solvent for Li-ion battery electrolytes owing to numerous advantages such as high polarity, nonflammability, environmental benignity, and abundance, provided that its narrow electrochemical potential window can be enhanced to a similar level to that of typical nonaqueous electrolytes. In recent years, significant improvements in the electrochemical stability of aqueous electrolytes have been achieved with molten salt hydrate electrolytes containing extremely high concentrations of Li salt. In this study, we investigated the effect of divalent salt additives (magnesium and calcium bis(trifluoromethanesulfonyl)amides) in a molten salt hydrate electrolyte (21 mol kg-1 lithium bis(trifluoromethanesulfonyl)amide) on the electrochemical stability and aqueous lithium secondary battery performance. We found that the electrochemical stability was further enhanced by the addition of the divalent salt. In particular, the reductive stability was increased by more than 1 V on the Al electrode in the presence of either of the divalent cations. Surface characterization with X-ray photoelectron spectroscopy suggests that a passivation layer formed on the Al electrode consists of inorganic salts (most notably fluorides) of the divalent cations and the less-soluble solid electrolyte interphase mitigated the reductive decomposition of water effectively. The enhanced electrochemical stability in the presence of the divalent salts resulted in a more-stable charge-discharge cycling of LiCoO2 and Li4Ti5O12 electrodes.

Magnesium bis(trifluoromethanesulfonyl)amide complexes with triglyme and asymmetric homologues: phase behavior, coordination structures and melting point reduction.

The phase behavior of binary mixtures of triglyme (G3) and Mg[TFSA]2 (TFSA: bis(trifluoromethanesulfonyl)amide) was investigated, towards the development of a Mg2+-based room-temperature solvate ionic liquid (SIL) electrolyte. In a 1 : 1 molar ratio, G3 and Mg[TFSA]2 form a thermally stable complex (decomposition temperature, Td: 240 °C) with a melting point (Tm) of 70 °C, which is considerably lower than that of the analogous tetraglyme (G4) system (137 °C). X-ray crystallography of a single crystal of [Mg(G3)][TFSA]2 revealed that a single Mg2+ cation is coordinated by a single, distorted, tetradentate G3 molecule from one side, and two monodentate [TFSA]- anions, with transoid conformation, from the reverse side to form an ion pair. Raman spectra of [Mg(G3)][TFSA]2 in the molten state revealed the presence of different coordination structures, as the liquid exhibits changes in the vibrational modes corresponding to G3 and the [TFSA]- anion compared to those observed for the solid. Investigation of the ion pair stabilization energies by DFT calculations suggests that higher stability cation complexes and ion pairs co-exist in the molten state than those observed in the crystalline state. These results imply that the coordination structures of the ion pairs play a key role in providing SILs with low Tm. To decrease the Tm further, several asymmetric homologues of G3, which have higher conformational flexibility than G3, were investigated. Notably, a 1 : 1 mixture of Mg[TFSA]2 with G3Bu (where one of the terminal methyl groups of G3 is substituted for a butyl group) formed a thermally stable complex (Td: 251 °C) without any distinct Tm and showed reasonable ionic conductivity at room-temperature, indicating partial dissociation of ions. In this electrolyte, which showed high oxidative stability, quasi-reversible Mg deposition/dissolution was achieved, indicating that Mg2+-based room-temperature SILs can be utilized as a new class of Mg electrolyte.

Protic ionic liquids with primary alkylamine-derived cations: the dominance of hydrogen bonding on observed physicochemical properties.

Novel protic ionic liquids (PILs) were synthesized by neutralization of primary alkylamines with bis(trifluoromethanesulfonyl)amide acid. An extensive hydrogen bonding network in these PILs was observed via lower thermal stability, temperature dependent inversion from non-Newtonian to Newtonian fluidic behavior, and lower ionicity compared to their secondary and tertiary analogues.

Application of Ionic Liquids to Energy Storage and Conversion Materials and Devices.

Ionic liquids (ILs) are liquids consisting entirely of ions and can be further defined as molten salts having melting points lower than 100 °C. One of the most important research areas for IL utilization is undoubtedly their energy application, especially for energy storage and conversion materials and devices, because there is a continuously increasing demand for clean and sustainable energy. In this article, various application of ILs are reviewed by focusing on their use as electrolyte materials for Li/Na ion batteries, Li-sulfur batteries, Li-oxygen batteries, and nonhumidified fuel cells and as carbon precursors for electrode catalysts of fuel cells and electrode materials for batteries and supercapacitors. Due to their characteristic properties such as nonvolatility, high thermal stability, and high ionic conductivity, ILs appear to meet the rigorous demands/criteria of these various applications. However, for further development, specific applications for which these characteristic properties become unique (i.e., not easily achieved by other materials) must be explored. Thus, through strong demands for research and consideration of ILs unique properties, we will be able to identify indispensable applications for ILs.

Stability of Glyme Solvate Ionic Liquid as an Electrolyte for Rechargeable Li-O2 Batteries.

A solvate ionic liquid (SIL) was compared with a conventional organic solvent for the electrolyte of the Li-O2 battery. An equimolar mixture of triglyme (G3) and lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]), and a G3/Li[TFSA] mixture containing excess glyme were chosen as the SIL and the conventional electrolyte, respectively. Charge behavior and accompanying gas evolution of the two electrolytes was investigated by electrochemical mass spectrometry (ECMS). From the linear sweep voltammetry performed on an as-prepared cell, we demonstrate that the SIL has a higher oxidative stability than the conventional electrolyte and, furthermore, offers the advantage of lower volatility, which would benefit an open-type lithium-O2 cell design. Moreover, CO2 evolution during galvanostatic charge was less in the SIL, which implies less side reaction. However, O2 evolution during charge did not reach the theoretical value in either of the two electrolytes. Several mass spectral fragments were generated during the charge process, which provided evidence for side reactions of glyme-based electrolytes. We further relate the difference in observed discharge product morphology for these electrolytes to the solubility of the superoxide intermediate, determined by rotating ring disk electrode (RRDE) measurements.

A perfluorinated moiety-grafted carbon nanotube electrode for the non-aqueous lithium-oxygen battery.

A perfluorinated alkyl chain grafted to carbon nanotubes is employed in the lithium-oxygen (Li-O2) cell. We demonstrate a highly localized Li-O2 electrochemical reaction in close proximity to the perfluorinated moiety owing to its high O2 affinity. This hydrophobic modification can provide an enhancement in capacity for a very thin microbattery system.

A structured three-dimensional polymer electrolyte with enlarged active reaction zone for Li-O2 batteries.

The application of conventional solid polymer electrolyte (SPE) to lithium-oxygen (Li-O2) batteries has suffered from a limited active reaction zone due to thick SPE and subsequent lack of O2 gas diffusion route in the positive electrode. Here we present a new design for a three-dimensional (3-D) SPE structure, incorporating a carbon nanotube (CNT) electrode, adapted for a gas-based energy storage system. The void spaces in the porous CNT/SPE film allow an increased depth of diffusion of O2 gas, providing an enlarged active reaction zone where Li(+) ions, O2 gas, and electrons can interact. Furthermore, the thin SPE layer along the CNT, forming the core/shell nanostructure, aids in the smooth electron transfer when O2 gas approaches the CNT surface. Therefore, the 3-D CNT/SPE electrode structure enhances the capacity in the SPE-based Li-O2 cell. However, intrinsic instability of poly(ethylene oxide) (PEO) of the SPE matrix to superoxide (O2(·-)) and high voltage gives rise to severe side reactions, convincing us of the need for development of a more stable electrolyte for use in this CNT/SPE design.