Thiophene-Based Microporous Polymer Networks via Chemical or Electrochemical Oxidative Coupling

Four thiophene-based monomers have been synthesized by Stille- or Suzuki-type couplings followed by chemical or electrochemical polymerization into microporous polymer networks (MPNs) with high BET surface areas (<i>S</i>_BET). Similar <i>S</i>_BET values of up to 2020 and 2135 m² g^–1 have been determined for tetraphenyl­methane-cored bulk MPN powders and thin films, respectively. Electrochemical polymerization in boron trifluoride diethyl etherate (BFEE)/dichloromethane (DCM) mixtures allows for the generation of MPN films with optimized porosity. Moreover, an interesting effect of boron trifluoride on the connectivity of the monomeric units during electropolymerization is observed for 3-thienyl-based monomers. Finally, the electrochemical reduction of 1,3,5-trinitro­benzene at MPN-modified glassy carbon (GC) electrodes shows increased cathodic responses compared to nonmodified GC electrodes due to interaction between electron-deficient nitroaromatic analyte and electron-rich MPN film. The influence of the specific surface area of MPNs on the electrochemical response is also studied for this class of materials

New Phosphonate-Based Additives for Fortification in Model Epoxies

The bulk properties of polymers are often adjusted via addition of a complex blend of compounds collectively known as additives, where so-called molecular fortifiers (or antiplasticizers) may improve the mechanical properties. On the basis of our previous work, we have further explored the potential of reactive phosphonate based additives for enhancement of mechanical and thermal properties of an amine-cured model epoxy resin. In particular, successful fortification based on “ionic bond” formation was achieved for a series of novel custom-made compounds with systematic variation of side groups. Both cure temperature and chemical structure of the fortifier have significant impact on the epoxy’s properties as well as aging behavior. Long-term storage of the epoxies resulted in partial loss of initially achieved fortification. Bifunctional fortifiers revealed particularly robust and much superior performance compared to the previously recommended fortifier dimethyl methylphosphonate (DMMP), rendering them most promising for potential application

Crystal Engineering of Pharmaceutical Co-crystals: “NMR Crystallography” of Niclosamide Co-crystals

Niclosamide is a Biopharmaceutics Classification System (BCS) class II taeniacide currently reconsidered for new promising applications including treatment of rheumatoid arthritis, prevention of protein degeneration in neurodegenerative diseases, or even multi-targeted therapy of cancer and cancer stem cells. Its efficacy in medical treatments, however, is currently limited by its insufficient solubility or bioavailability. Thus, we have further explored the potential of hydrogen-bond-mediated co-crystal formation of niclosamide with suitable co-formers selected from either the “Generally Regarded as Safe” (GRAS) or United States Food and Drug Administration (U.S. FDA) “Everything Added to Food in the United States” (EAFUS) list, respectively. Solvent-assisted solid grinding and/or slow solvent evaporation yielded four new co-crystals: (i) niclosamide–2-aminothiazole (NCL-AT), (ii) niclosamide–benzamide (NCL-BA), (iii) niclosamide–isoniazide (NCL-IN), and (iv) niclosamide–acetamide I and II (NCL-AA-I/NCL-AA-II). The crystal structures of NCL-AA-I/II, NCL-AT were solved from white microcrystalline powder samples on the basis of the combined application of powder X-ray diffraction (PXRD), solid-state NMR, and Density Functional Theory (DFT) chemical shift computation. In addition, the crystal structure of the monohydrate NCL-H_A was reconsidered for comparison. Finally an improvement of the equilibrium solubility of the 1:1 co-crystal NCL-AT could be determined (2.8 times that of pristine NCL and 1.4 times that of NCL-UREA co-crystal), suggesting NCL-AT as a candidate for future medical treatment

Supramolecular Self-Assembly of Methylated Rotaxanes for Solid Polymer Electrolyte Application

Li⁺-conducting solid polymer electrolytes (SPEs) obtained from supramolecular self-assembly of trimethylated cyclodextrin (TMCD), poly­(ethylene oxide) (PEO), and lithium salt are investigated for application in lithium-metal batteries (LMBs) and lithium-ion batteries (LIBs). The considered electrolytes comprise nanochannels for fast lithium-ion transport formed by CD threaded on PEO chains. It is demonstrated that tailored modification of CD beneficially influences the structure and transport properties of solid polymer electrolytes, thereby enabling their application in LMBs. Molecular dynamics (MD) simulation and experimental data reveal that modification of CDs shifts the steady state between lithium ions inside and outside the channels, in this way improving the achievable ionic conductivity. Notably, the designed SPEs facilitated galvanostatic cycling in LMBs at fast charging and discharging rates for more than 200 cycles and high Coulombic efficiency

Failure Mechanisms at the Interfaces between Lithium Metal Electrodes and a Single-Ion Conducting Polymer Gel Electrolyte

Polymer electrolytes have the potential to enable rechargeable lithium (Li) metal batteries. However, growth of nonuniform high surface area Li still occurs frequently and eventually leads to a short-circuit. In this study, a single-ion conducting polymer gel electrolyte is operated at room temperature in symmetric Li||Li cells. We use X-ray microtomography and electrochemical impedance spectroscopy (EIS) to study the cells. In separate experiments, cells were cycled at current densities of 0.1 and 0.3 mA cm–2 and short-circuits were obtained eventually after an average of approximately 240 cycles and 30 cycles, respectively. EIS reveals an initially decreasing interfacial resistance associated with electrodeposition of nonuniform Li protrusions and the concomitant increase in electrode surface area. X-ray microtomography images show that many of the nonuniform Li deposits at 0.1 mA cm–2 are related to the presence of impurities in both electrolyte and electrode phases. Protrusions are globular when they are close to electrolyte impurities but are moss-like when they appear near the impurities in the lithium metal. At long times, the interfacial resistance increases, perhaps due to additional impedance due to the formation of additional solid electrolyte interface (SEI) at the growing protrusions until the cells short. At 0.3 mA cm–2, large regions of the electrode–electrolyte interface are covered with mossy deposits. EIS reveals a decreasing interfacial resistance due to the increase in interfacial area up to short-circuit; the increase in interfacial impedance observed at the low current density is not observed. The results emphasize the importance of pure surfaces and materials on the microscopic scale and suggest that modification of interfaces and electrolyte may be necessary to enable uniform Li electrodeposition at high current densities

In Situ Diffuse Reflectance Infrared Fourier-Transform Spectroscopy Investigation of Fluoroethylene Carbonate and Lithium Difluorophosphate Dual Additives in SEI Formation over Cu Anode

The synergetic effect of fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2) dual additives on the cycling stability of lithium metal batteries has been previously reported. This study applies in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) to examine the impact of these two additives on SEI species formation over Cu anode using a base electrolyte of LiPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC). The results indicate that all electrolyte components and additives can be electrochemically reduced over the Cu anode following a potential sequence of LiPO2F2 > FEC > EC > DEC. The results illustrate that LiPF6 likely interacts with the Cu anode upon contact, resulting in LixPFy, which can lead to a reduction peak at ∼1.44 V in CV. With the base electrolyte, reduced species from LixPFy lead to the formation of alkyl phosphorus fluorides (RPF), which can be suppressed by the presence of FEC and/or LiPO2F2. Similar to previous reports, FEC reduction in the 1st lithiation cycle leads to the continuous formation of poly(FEC), while EC is electrochemically reduced to (CH2OCO2Li)2 and Li2CO3 and DEC is reduced to CH3CH2OCO2Li and Li2CO3. With only the LiPO2F2 additive, the redox of LiPO2F2 can be found in CV with LixPOy as the possible reduced product. In addition, Li2CO3 formation from EC and DEC reduction was relatively suppressed by the presence of LiPO2F2. The simultaneous presence of the FEC additive can suppress the redox of LiPO2F2 and partly the decomposition of LiPF6 likely via the preferential adsorption of FEC on Cu. Similar DRIFTS observations are found over the Li anode. The electrolyte with dual additives demonstrates a possible advantage from poly(FEC) and LixPOy species formation, suppressing the reduction of LixPFy, EC, and DEC though not completely

Ceramic-in-Polymer Hybrid Electrolytes with Enhanced Electrochemical Performance

Polymer electrolytes are attractive candidates to boost the application of rechargeable lithium metal batteries. Single-ion conducting polymers may reduce polarization and lithium dendrite growth, though these materials could be mechanically overly rigid, thus requiring ion mobilizers such as organic solvents to foster transport of Li ions. An inhomogeneous mobilizer distribution and occurrence of preferential Li transport pathways eventually yield favored spots for Li plating, thereby imposing additional mechanical stress and even premature cell short circuits. In this work, we explored ceramic-in-polymer hybrid electrolytes consisting of polymer blends of single-ion conducting polymer and PVdF-HFP, including EC/PC as swelling agents and silane-functionalized LATP particles. The hybrid electrolyte features an oxide-rich layer that notably stabilizes the interphase toward Li metal, enabling single-side lithium deposition for over 700 h at a current density of 0.1 mA cm–2. The incorporated oxide particles significantly reduce the natural solvent uptake from 140 to 38 wt % despite maintaining reasonably high ionic conductivities. Its electrochemical performance was evaluated in LiNi0.6Co0.2Mn0.2O2 (NMC622)||Li metal cells, exhibiting impressive capacity retention over 300 cycles. Notably, very thin LiNbO3 coating of the cathode material further boosts the cycling stability, resulting in an overall capacity retention of 78% over more than 600 cycles, clearly highlighting the potential of hybrid electrolyte concepts

Indirect “No-Bond” ³¹P···³¹P Spin–Spin Couplings in <i>P</i>,<i>P</i>‑[3]Ferrocenophanes: Insights from Solid-State NMR Spectroscopy and DFT Calculations

No-bond ³¹P–³¹P indirect dipolar couplings, which arise from the transmission of nuclear spin polarization through interaction of proximal nonbonded electron pairs have been investigated in the solid state for a series of closely related substituted <i>P</i>,<i>P</i>-[3]­ferrocenophanes and model systems. Through variation and combination of ligands (phenyl, cyclohexyl, isopropyl) at the two phosphorus sites, the P···P distances in these compounds can be varied from 3.49 to 4.06 Å. Thus, the distance dependence of the indirect no-bond coupling constant <i>J</i>_nb can be studied in a series of closely related compounds. One- and two-dimensional solid-state NMR experiments serve to establish the character of these couplings and to measure the isotropic coupling constants <i>J</i>_iso, which were found to range between 12 and 250 Hz. To develop an understanding of the magnitude of <i>J</i>_nb in terms of molecular structure, their dependences on intramolecular internuclear distances and relative orbital orientations is discussed by DFT-calculations on suitable models. In agreement with the literature the dependence of <i>J</i>_nb on the P···P distance is found to be exponential; however, the steepness of this curve is highly dependent on the internuclear equilibrium distance. For a quantitative description, the off-diagonal elements of the expectation value of the Kohn–Sham–Fock operator in the LMO basis for the LMOs of the two phosphorus lone-pairs is proposed. This parameter correlates linearly with the calculated <i>J</i>_nb values and possesses the same distance-dependence. In addition, the simulations indicate a distinct dependence of <i>J</i>_nb on the dihedral angle defined by the two C–P bonds providing ligation to the molecular backbone. For disordered materials or those featuring multiple sites, conformers, and/or polymorphism, a new double-quantum NMR method termed DQ-DRENAR can be used to conveniently measure internuclear ³¹P–³¹P distances. If conducted on compounds with known P···P distances, such measurements can also serve to estimate the magnitude of the anisotropy Δ<i>J</i> of these no-bond indirect spin–spin couplings. The DFT results suggest that in the present series of compounds the magnitude of Δ<i>J</i> is strongly correlated with that of the isotropic component, as both parameters have analogous distance dependences. While our studies indicate a sizable <i>J</i>-anisotropy for the model compound 1,8-bis­(diphenylphosphino)­napthalene (Δ<i>J</i> ∼ −70 Hz), the corresponding values for the <i>P</i>,<i>P</i>-[3]­ferrocenophanes are significantly smaller, affecting their DQ-DRENAR curves only in a minor way. Based on the above insights, the structural aspects of conformational disorder and polymorphism observed in some of the <i>P</i>,<i>P</i>-[3]­ferrocenophanes are discussed

Concerted Effect of Ion- and Electron-Conductive Additives on the Electrochemical and Thermal Performances of the LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material Synthesized by a Taylor-Flow Reactor for Lithium-Ion Batteries

To address the issue that a single coating agent cannot simultaneously enhance Li+-ion transport and electronic conductivity of Ni-rich cathode materials with surface modification, in the present study, we first successfully synthesized a LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material by a Taylor-flow reactor followed by surface coating with Li-BTJ and dispersion of vapor-grown carbon fibers treated with polydopamine (PDA-VGCF) filler in the composite slurry. The Li-BTJ hybrid oligomer coating can suppress side reactions and enhance ionic conductivity, and the PDA-VGCFs filler can increase electronic conductivity. As a result of the synergistic effect of the dual conducting agents, the cells based on the modified NCM811 electrodes deliver superior cycling stability and rate capability, as compared to the bare NCM811 electrode. The CR2032 coin-type cells with the NCM811@Li-BTJ + PDA-VGCF electrode retain a discharge specific capacity of ∼92.2% at 1C after 200 cycles between 2.8 and 4.3 V (vs Li/Li+), while bare NCM811 retains only 84.0%. Moreover, the NCM811@Li-BTJ + PDA-VGCF electrode-based cells reduced the total heat (Qt) by ca. 7.0% at 35 °C over the bare electrode. Remarkably, the Li-BTJ hybrid oligomer coating on the surface of the NCM811 active particles acts as an artificial cathode electrolyte interphase (ACEI) layer, mitigating irreversible surface phase transformation of the layered NCM811 cathode and facilitating Li+ ion transport. Meanwhile, the fiber-shaped PDA-VGCF filler significantly reduced microcrack propagation during cycling and promoted the electronic conductance of the NCM811-based electrode. Generally, enlightened with the current experimental findings, the concerted ion and electron conductive agents significantly enhanced the Ni-rich cathode-based cell performance, which is a promising strategy to apply to other Ni-rich cathode materials for lithium-ion batteries

Indirect “No-Bond” ³¹P···³¹P Spin–Spin Couplings in <i>P</i>,<i>P</i>‑[3]Ferrocenophanes: Insights from Solid-State NMR Spectroscopy and DFT Calculations

No-bond ³¹P–³¹P indirect dipolar couplings, which arise from the transmission of nuclear spin polarization through interaction of proximal nonbonded electron pairs have been investigated in the solid state for a series of closely related substituted <i>P</i>,<i>P</i>-[3]­ferrocenophanes and model systems. Through variation and combination of ligands (phenyl, cyclohexyl, isopropyl) at the two phosphorus sites, the P···P distances in these compounds can be varied from 3.49 to 4.06 Å. Thus, the distance dependence of the indirect no-bond coupling constant <i>J</i>_nb can be studied in a series of closely related compounds. One- and two-dimensional solid-state NMR experiments serve to establish the character of these couplings and to measure the isotropic coupling constants <i>J</i>_iso, which were found to range between 12 and 250 Hz. To develop an understanding of the magnitude of <i>J</i>_nb in terms of molecular structure, their dependences on intramolecular internuclear distances and relative orbital orientations is discussed by DFT-calculations on suitable models. In agreement with the literature the dependence of <i>J</i>_nb on the P···P distance is found to be exponential; however, the steepness of this curve is highly dependent on the internuclear equilibrium distance. For a quantitative description, the off-diagonal elements of the expectation value of the Kohn–Sham–Fock operator in the LMO basis for the LMOs of the two phosphorus lone-pairs is proposed. This parameter correlates linearly with the calculated <i>J</i>_nb values and possesses the same distance-dependence. In addition, the simulations indicate a distinct dependence of <i>J</i>_nb on the dihedral angle defined by the two C–P bonds providing ligation to the molecular backbone. For disordered materials or those featuring multiple sites, conformers, and/or polymorphism, a new double-quantum NMR method termed DQ-DRENAR can be used to conveniently measure internuclear ³¹P–³¹P distances. If conducted on compounds with known P···P distances, such measurements can also serve to estimate the magnitude of the anisotropy Δ<i>J</i> of these no-bond indirect spin–spin couplings. The DFT results suggest that in the present series of compounds the magnitude of Δ<i>J</i> is strongly correlated with that of the isotropic component, as both parameters have analogous distance dependences. While our studies indicate a sizable <i>J</i>-anisotropy for the model compound 1,8-bis­(diphenylphosphino)­napthalene (Δ<i>J</i> ∼ −70 Hz), the corresponding values for the <i>P</i>,<i>P</i>-[3]­ferrocenophanes are significantly smaller, affecting their DQ-DRENAR curves only in a minor way. Based on the above insights, the structural aspects of conformational disorder and polymorphism observed in some of the <i>P</i>,<i>P</i>-[3]­ferrocenophanes are discussed