Pressure-Assisted Synthesis of Highly Crystalline 1T''-Lix MoS2

Lix MoS2 is not only a lithium battery material, but is also an important precursor for the synthesis of MoS2 nanomaterials. Current syntheses of MoS2 , such as in n-butyllithium/LiBH4 or electrochemically, are not satisfying in terms of defined stoichiometry and crystallinity, so an accurate experimental crystal structure determination of this important and widely used material has been long awaited. A high-pressure/high-temperature synthesis yielded highly crystalline 1T''-Lix MoS2 (x=1, 1.333). 1T''-LiMoS2 crystallizes in the space group P1 ‾ $\bar 1$ with a=6.2482(3) Å, b=6.6336(3) Å, c=6.7480(3) Å, α=119.321(2)°, β=90.010(2)° and γ=90.077(2)°. The arrangement of Mo atoms within the b-c-plane confirmed a predicted Peierls distortion. A similar atom distribution pattern to that of Mo is also observed for the lithium atoms. Calculation of bond valence site energies gave an activation barrier of 1.244 eV for 2D lithium-ion migration. For x=1.333, a phase-pure synthesis was achieved.

Bilayer Zwitterionic Metal-Organic Framework for Selective All-Solid-State Superionic Conduction in Lithium Metal Batteries

Solid-state batteries (SSBs) hold immense potential for improved energy density and safety compared to traditional batteries. However, existing solid-state electrolytes (SSEs) face challenges in meeting the complex operational requirements of SSBs. This study introduces a novel approach to address this issue by developing a metal-organic framework (MOF) with customized bilayer zwitterionic nanochannels (MOF-BZN) as high-performance SSEs. The BZN consist of a rigid anionic MOF channel with chemically grafted soft multicationic oligomers (MCOs) on the pore wall. This design enables selective superionic conduction, with MCOs restricting the movement of anions while coulombic interaction between MCOs and anionic framework promoting the dissociation of Li+ . MOF-BZN exhibits remarkable Li+ conductivity (8.76 × 10-4 S cm-1 ), high Li+ transference number (0.75), and a wide electrochemical window of up to 4.9 V at 30 °C. Ultimately, the SSB utilizing flame retarded MOF-BZN achieves an impressive specific energy of 419.6 Wh kganode+cathode+electrolyte -1 under constrained conditions of high cathode loading (20.1 mg cm-2 ) and limited lithium metal source. The constructed bilayer zwitterionic MOFs present a pioneering strategy for developing advanced SSEs for highly efficient SSBs.

Ion Conduction in Composite Polymer Electrolytes: Potential Electrolytes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are expected to become alternatives to lithium-ion batteries (LIBs) as next-generation rechargeable batteries, owing to abundant sodium sources and low cost. However, SIBs still use liquid organic electrolytes (LOEs), which are highly flammable and have the tendency to leak. Although inorganic solid electrolytes (ISEs) and solid polymer electrolytes (SPEs) have been investigated for many years, given their higher safety level, neither of them is likely to be commercialized because of the rigidity of ISEs and the low room-temperature ionic conductivity of SPEs. During the last decade, composite polymer electrolytes (CPEs), composed of ISEs and SPEs, exhibiting both relatively high ionic conductivity and flexibility, have gained much attention and are considered as promising electrolytes. However, the ionic conductivities of CPEs are still unsatisfactory for practical application. Hence, this Review focuses on the principle of sodium ion conductors and particularly on recent investigations and development of CPEs.

Ion Transport in 2D Nanostructured π-Conjugated Thieno[3,2-b]thiophene-Based Liquid Crystal

Leveraging the self-assembling behavior of liquid crystals designed for controlling ion transport is of both fundamental and technological significance. Here, we have designed and prepared a liquid crystal that contains 2,5-bis(thien-2-yl)thieno[3,2-b]thiophene (BTTT) as mesogenic core and conjugated segment and symmetric tetra(ethylene oxide) (EO4) as polar side chains for ion-conducting regions. Driven by the crystallization of the BTTT cores, BTTT/dEO4 exhibits well-ordered smectic phases below 71.5 °C as confirmed by differential scanning calorimetry, polarized optical microscopy, temperature-dependent wide-angle X-ray scattering, and grazing incidence wide-angle X-ray scattering (GIWAXS). We adopted a combination of experimental GIWAXS and molecular dynamics (MD) simulations to better understand the molecular packing of BTTT/dEO4 films, particularly when loaded with the ion-conducting salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Ionic conduction of BTTT/dEO4 is realized by the addition of LiTFSI, with the material able to maintain smectic phases up to r = [Li⁺]/[EO] = 0.1. The highest ionic conductivity of 8 × 10^-3 S/cm was attained at an intermedium salt concentration of r = 0.05. It was also found that ion conduction in BTTT/dEO4 is enhanced by forming a smectic layered structure with irregular interfaces between the BTTT and EO4 layers and by the lateral film expansion upon salt addition. This can be explained by the enhancement of the misalignment and configurational entropy of the side chains, which increase their local mobility and that of the solvated ions. Our molecular design thus illustrates how, beyond the favorable energetic interactions that drive the assembly of ion solvating domains, modulation of entropic effects can also be favorably harnessed to improve ion conduction.

Fast Hydroxide Conduction via Hydrogen-Bonding Network Confined in Benzimidazolium-Functionalized Covalent Organic Frameworks

In both hydrophobic and hydrophilic nanochannels, confined water clusters spontaneously form dense internal hydrogen bond networks and hence exhibit fast mass-transfer kinetics. Covalent organic frameworks (COFs), a porous polymer, enables one-dimensional open channels to achieve ordered assembly guided by synthetic techniques and allows the accommodation of a large number of water molecules within the nanochannels. In the field of alkaline anion exchange membrane fuel cells, it has been a long-term pursuit of scientists to build abundant hydrogen bonds around hydrogen oxides (OH^-) to improve the conduction of OH^- by increasing the water content. Here, we designed and synthesized a OH^- conductor by assembling benzimidazolium into COFs, and a significantly high conductivity of 10^-1 S cm^-1 was achieved at 353 K. Theoretical calculations showed that the water clusters confined in the pores of COFs and the regularly arranged hydroxides cooperatively formed a dense hydrogen bond network and OH^- conducted diffusive conduction through the Grotthuss hopping of protons in this hydrogen bond network.

Incorporation of Poly(Ionic Liquid) with PVDF-HFP-Based Polymer Electrolyte for All-Solid-State Lithium-Ion Batteries

A solid-state polymer electrolyte membrane is formed by blending poly(vinylidene fluoride-co-hexafluoropropylene) with the synthesized copolymer of poly(methyl methacrylate-co-1-vinyl-3-butyl-imidazolium bis(trifluoromethanesulfonyl)imide, in which lithium bis(trifluoromethane)sulfonimide molecules are applied as the source of lithium ions. The accordingly formed membrane that contains 14 wt.% of P(MMA-co-VBIm-TFSI), 56 wt.% of PVDF-HFP, and 30 wt.% of LiTFSI manifests the best electrochemical properties, achieving an ionic conductivity of 1.11 × 10⁻⁴ S·cm⁻¹ at 30 °C and 4.26 × 10⁻⁴ S·cm⁻¹ at 80 °C, a Li-ion transference number of 0.36, and a wide electrochemical stability window of 4.7 V (vs. Li/Li⁺). The thus-assembled all-solid-state lithium-ion battery of LiFePO₄/SPE/Li delivers a discharge specific capacity of 148 mAh·g⁻¹ in the initial charge–discharge cycle at 0.1 C under 60 °C. The capacity retention of the cell is 95.2% after 50 cycles at 0.1 C and the Coulombic efficiency remains close to 100% during the cycling process.

In Situ TEM Study of Structural Changes in Na-β″-Alumina Using Electron Beam Irradiation

Real-time structural changes in Na-β″-alumina were observed in situ using transmission electron microscopy (TEM) with electron beam irradiation. Na-β″-alumina has been widely investigated as a solid electrolyte material for sodium–sulfur secondary batteries owing to its high ionic conductivity. This high conductivity is known to be due to the Na⁺ ions on the loosely packed conduction planes of Na-β″-alumina. In the present study, we acquired real-time videos of the generation of spinel blocks caused by the conduction of Na⁺ ions. In addition, by observing Na extraction during electron beam irradiation, we experimentally confirmed that spinel block generation originates from the Na⁺ ion conduction, which has been a subject of recent debate.

Structural Plasticity of the Selectivity Filter in Cation Channels

Ion channels allow for the passage of ions across biological membranes, which is essential for the functioning of a cell. In pore loop channels the selectivity filter (SF) is a conserved sequence that forms a constriction with multiple ion binding sites. It is becoming increasingly clear that there are several conformations and dynamic states of the SF in cation channels. Here we outline specific modes of structural plasticity observed in the SFs of various pore loop channels: disorder, asymmetry, and collapse. We summarize the multiple atomic structures with varying SF conformations as well as asymmetric and more dynamic states that were discovered recently using structural biology, spectroscopic, and computational methods. Overall, we discuss here that structural plasticity within the SF is a key molecular determinant of ion channel gating behavior.

Ionic Covalent Organic Frameworks for Energy Devices

Covalent organic frameworks (COFs) are a class of porous crystalline materials whose facile preparation, functionality, and modularity have led to their becoming powerful platforms for the development of molecular devices in many fields of (bio)engineering, such as energy storage, environmental remediation, drug delivery, and catalysis. In particular, ionic COFs (iCOFs) are highly useful for constructing energy devices, as their ionic functional groups can transport ions efficiently, and the nonlabile and highly ordered all-covalent pore structures of their backbones provide ideal pathways for long-term ionic transport under harsh electrochemical conditions. Here, current research progress on the use of iCOFs for energy devices, specifically lithium-based batteries and fuel cells, is reviewed in terms of iCOF backbone-design strategies, synthetic approaches, properties, engineering techniques, and applications. iCOFs are categorized as anionic COFs or cationic COFs, and how each of these types of iCOFs transport lithium ions, protons, or hydroxides is illustrated. Finally, the current challenges to and future opportunities for the utilization of iCOFs in energy devices are described. This review will therefore serve as a useful reference on state-of-the-art iCOF design and application strategies focusing on energy devices.

Modified Li7P3S11 Glass-Ceramic Electrolyte and Its Characterization

Li₇P₃S₁₁ glass ceramics have high conductivities competitive with liquid electrolytes, making them good candidates as solid-state electrolytes for all-solid-state lithium-ion batteries. However, the metastable nature and performance of Li₇P₃S₁₁ glass ceramics remain mysterious. Herein, modified Li₇P₃S₁₁ glass ceramics with compositions of 70Li₂S-30P₂S₅ were prepared via two-step mechanical milling and thermal annealing. Li₇P₃S₁₁ glass ceramics synthesized using the conventional method (mechanical milling and thermal annealing) were again ball-milled to obtain amorphous 70Li₂S-30P₂S₅ with a peculiar glass structure. Further thermal annealing was carried out to crystallize the glass. The obtained crystalline phase was analogous to the original Li₇P₃S₁₁ phase, but the conductivity was enhanced by a factor of 1.7. Based on ³¹P solid-state nuclear magnetic resonance (NMR) spectroscopy, the Li₇P₃S₁₁ phase contained an additional PS₄^3- unit. A rational deconvolution procedure for the ³¹P solid-state NMR spectra based on crystalline Li₇P₃S₁₁ was developed and applied to the samples. The analysis can resolve the additional crystalline PS₄^3- unit in the Li₇P₃S₁₁ structure. Based on two-dimensional double-quantum ³¹P NMR spectroscopy, the additional PS₄^3- unit is located adjacent to the P₂S₇^4- unit, suggesting that P₂S₇^4- is divided into two PS₄^3- units in the Li₇P₃S₁₁ phase. The flip motion of Li⁺ was also investigated based on the ⁷Li spin-lattice relaxation time. The independent activation energy of spin-lattice relaxation with respect to temperature in the Li₇P₃S₁₁ phase was attributed to a conduction path between the two PS₄^3- units. The findings provide a synthetic route that can be used to develop metastable solid-state electrolytes.

Charge Carrier Transport Behavior and Dielectric Properties of BaF2:Tb3+ Nanocrystals

The charge carrier behavior and dielectric properties of BaF₂:Tb³⁺ nanocrystals have been studied by alternating current (AC) impedance spectroscopy. The electron and ion coexist in the transport process. The F^- ion's contribution to the total conduction increases with the doping concentration up to 4% and then decreases. Tb doping leads to the increase of defect quantities and a variation of charge carrier transport paths, which causes the increase of the ion diffusion coefficient and the decreases of bulk and grain boundary resistance. When the Tb-doped concentration is higher than 4%, the effect of deformation potential scattering variation on the transport property is dominant, which results in the decrease of the ion diffusion coefficient and increases of bulk and grain boundary resistance. The conduction properties of our BaF₂:Tb³⁺ nanocrystals are compared with previous results that were found for the single crystals of rare earth-doped BaF₂. Tb doping causes increases of both the quantity and the probability of carrier hopping, and it finally leads to increases of BaF₂ nanocrystals' permittivity in the low frequency region.

Comparison of the Electrical Response of Cu and Ag Ion-Conducting SDC Memristors Over the Temperature Range 6 K to 300 K

Electrical performance of self-directed channel (SDC) ion-conducting memristors which use Ag and Cu as the mobile ion source are compared over the temperature range of 6 K to 300 K. The Cu-based SDC memristors operate at temperatures as low as 6 K, whereas Ag-based SDC memristors are damaged if operated below 125 K. It is also observed that Cu reversibly diffuses into the active Ge2Se3 layer during normal device shelf-life, thus changing the state of a Cu-based memristor over time. This was not observed for the Ag-based SDC devices. The response of each device type to sinusoidal excitation is provided and shows that the Cu-based devices exhibit hysteresis lobe collapse at lower frequencies than the Ag-based devices. In addition, the pulsed response of the device types is presented.

One-Dimensional Cuprous Selenide Nanostructures with Switchable Plasmonic and Super-ionic Phase Attributes

Cuprous selenide nanocrystals have hallmark attributes, especially tunable localized surface plasmon resonances (LSPRs) and super-ionic behavior. These attributes of cuprous selenide are now integrated with a one-dimensional morphology. Essentially, Cu₂ Se nanowires (NWs) of micrometer-scale lengths and about 10 nm diameter are prepared. The NWs exhibit a super-ionic phase that is stable at temperatures lower than in the bulk, owing to compressive lattice strain along the radial dimension of the NWs. The NWs can be switched between oxidized and reduced forms, which have contrasting phase transition and LSPR characteristics. This work thus makes available switchable, one-dimensional waveguides and ion-conducting channels.

Cryo-EM structures and functional characterization of the murine lipid scramblase TMEM16F

The lipid scramblase TMEM16F initiates blood coagulation by catalyzing the exposure of phosphatidylserine in platelets. The protein is part of a family of membrane proteins, which encompasses calcium-activated channels for ions and lipids. Here, we reveal features of murine TMEM16F (mTMEM16F) that underlie its function as a lipid scramblase and an ion channel. The cryo-EM data of mTMEM16F in absence and presence of Ca²⁺ define the ligand-free closed conformation of the protein and the structure of a Ca²⁺-bound intermediate. Both conformations resemble their counterparts of the scrambling-incompetent anion channel mTMEM16A, yet with distinct differences in the region of ion and lipid permeation. In conjunction with functional data, we demonstrate the relationship between ion conduction and lipid scrambling. Although activated by a common mechanism, both functions appear to be mediated by alternate protein conformations that are at equilibrium in the ligand-bound state.

Calcium-dependent electrostatic control of anion access to the pore of the calcium-activated chloride channel TMEM16A

TMEM16A is a ligand-gated anion channel that is activated by intracellular Ca²⁺. This channel comprises two independent pores and closely apposed Ca²⁺ binding sites that are contained within each subunit of a homodimeric protein. Previously we characterized the influence of positively charged pore-lining residues on anion conduction (Paulino et al., 2017a). Here, we demonstrate the electrostatic control of permeation by the bound calcium ions in mouse TMEM16A using electrophysiology and Poisson-Boltzmann calculations. The currents of constitutively active mutants lose their outward rectification as a function of Ca²⁺ concentration due to the alleviation of energy barriers for anion conduction. This phenomenon originates from Coulombic interactions between the bound Ca²⁺ and permeating anions and thus demonstrates that an electrostatic gate imposed by the vacant binding site present in the sterically open pore, is released by Ca²⁺ binding to enable an otherwise sub-conductive pore to conduct with full capacity.

Anion Conductive Triblock Copolymer Membranes with Flexible Multication Side Chain

To achieve highly conductive and stable anion exchange membranes (AEMs) for fuel cells, novel triblock copolymer AEMs bearing flexible side chain were synthesized. The triblock structure and flexible side chain are responsible for the developed hydrophilic/hydrophobic phase separated morphology and well-connected ion conducting channels, as confirmed by transmission electron microscopy. As a result, the triblock copolymer AEMs with flexible side chain (ABA-TQA- x) demonstrated considerably higher conductivities, up to 130.5 mS cm^-1 at 80 °C, than the AEMs with monocation side chain (ABA-MQA). Furthermore, the long alkyl spacer between the backbone and quaternary ammonium groups, as well as long intercation spacer limits the water swelling of the membranes to some degree, resulting in good alkaline stability. The ABA-TQA-44 membrane retained 84.7% and 83.1% of its original conductivity and ionic exchange capacity, respectively, after immersed in a 1 M aqueous KOH solution at 80 °C for 480 h. Furthermore, the peak power density of a H₂/O₂ single cell using ABA-TQA-44 is 204.6 mW cm^-2 at a current density of 500 mA cm^-2 at 80 °C.

Imidazolium-Functionalized Poly(arylene ether sulfone) Anion-Exchange Membranes Densely Grafted with Flexible Side Chains for Fuel Cells

With the intention of optimizing the performance of anion-exchange membranes (AEMs), a set of imidazolium-functionalized poly(arylene ether sulfone)s with densely distributed long flexible aliphatic side chains were synthesized. The membranes made from the as-synthesized polymers are robust, transparent, and endowed with microphase segregation capability. The ionic exchange capacity (IEC), hydroxide conductivity, water uptake, thermal stability, and alkaline resistance of the AEMs were evaluated in detail for fuel cell applications. Morphological observation with the use of atomic force microscopy and small-angle X-ray scattering reveals that the combination of high-local-density-type and side-chain-type architectures induces distinguished nanophase separation in the AEMs. The as-prepared membranes have advantages in effective water management and ionic conductivity over traditional main-chain polymers. Typically, the conductivity and IEC were in the ranges of 57.3-112.5 mS cm(-1) and 1.35-1.84 mequiv g(-1) at 80 °C, respectively. Furthermore, the membranes exhibit good thermal and alkaline stability and achieve a peak power density of 114.5 mW cm(-2) at a current density of 250.1 mA cm(-2). Therefore, the present polymers containing clustered flexible pendent aliphatic imidazolium promise to be attractive AEM materials for fuel cells.

Effect of doping on surface reactivity and conduction mechanism in samarium-doped ceria thin films

A systematic study by reversible and hysteretic electrochemical strain microscopy (ESM) in samples of cerium oxide with different Sm content and in several working conditions allows disclosing the microscopic mechanism underlying the difference in electrical conduction mechanism and related surface activity, such as water adsorption and dissociation with subsequent proton liberation. We have measured the behavior of the reversible hysteresis loops by changing temperature and humidity, both in standard ESM configuration and using the first-order reversal curve method. The measurements have been performed in much smaller temperature ranges with respect to alternative measuring techniques. Complementing our study with hard X-ray photoemission spectroscopy and irreversible scanning probe measurements, we find that water incorporation is favored until the doping with Sm is too high to allow the presence of Ce3+. The influence of doping on the surface reactivity clearly emerges from all of our experimental results. We find that at lower Sm concentration, proton conduction is prevalent, featured by lower activation energy and higher electrical conductivity. Defect concentrations determine the type of the prevalent charge carrier in a doping dependent manner.

Crystal structure and functional mechanism of a human antimicrobial membrane channel

Multicellular organisms fight bacterial and fungal infections by producing peptide-derived broad-spectrum antibiotics. These host-defense peptides compromise the integrity of microbial cell membranes and thus evade pathways by which bacteria develop rapid antibiotic resistance. Although more than 1,700 host-defense peptides have been identified, the structural and mechanistic basis of their action remains speculative. This impedes the desired rational development of these agents into next-generation antibiotics. We present the X-ray crystal structure as well as solid-state NMR spectroscopy, electrophysiology, and MD simulations of human dermcidin in membranes that reveal the antibiotic mechanism of this major human antimicrobial, found to suppress Staphylococcus aureus growth on the epidermal surface. Dermcidin forms an architecture of high-conductance transmembrane channels, composed of zinc-connected trimers of antiparallel helix pairs. Molecular dynamics simulations elucidate the unusual membrane permeation pathway for ions and show adjustment of the pore to various membranes. Our study unravels the comprehensive mechanism for the membrane-disruptive action of this mammalian host-defense peptide at atomistic level. The results may form a foundation for the structure-based design of peptide antibiotics.

The barium site in a potassium channel by x-ray crystallography

X-ray diffraction data were collected from frozen crystals (100 degrees K) of the KcsA K(+) channel equilibrated with solutions containing barium chloride. Difference electron density maps (F(barium) - F(native), 5.0 A resolution) show that Ba(2+) resides at a single location within the selectivity filter. The Ba(2+) blocking site corresponds to the internal aspect (adjacent to the central cavity) of the "inner ion" position where an alkali metal cation is found in the absence of the blocking Ba(2+) ion. The location of Ba(2+) with respect to Rb(+) ions in the pore is in good agreement with the findings on the functional interaction of Ba(2+) with K(+) (and Rb(+)) in Ca(2+)-activated K(+) channels (Neyton, J., and C. Miller. 1988. J. Gen. Physiol. 92:549-567). Taken together, these structural and functional data imply that at physiological ion concentrations a third ion may interact with two ions in the selectivity filter, perhaps by entering from one side and displacing an ion on the opposite side.