N‐alkyl‐N‐alkyl pyrrolidinium‐based ionic liquids (ILs) are promising candidates as non‐flammable plasticizers for lowering the operation temperature of poly(ethylene oxide) (PEO)‐based solid polymer ...electrolytes (SPEs), but they present limitations in terms of lithium‐ion transport, such as a much lower lithium transference number. Thus, a pyrrolidinium cation was prepared with an oligo(ethylene oxide) substituent with seven repeating units. We show, by a combination of experimental characterizations and simulations, that the cation's solvating properties allow faster lithium‐ion transport than alkyl‐substituted analogues when incorporated in SPEs. This proceeds not only by accelerating the conduction modes of PEO, but also by enabling new conduction modes linked to the solvation of lithium by a single IL cation. This, combined with favorable interfacial properties versus lithium metal, leads to significantly improved performance on lithium‐metal polymer batteries.
Ionic liquids (ILs) allow improvement of the ionic conductivity of ternary PEO‐based solid polymer electrolytes. However, the lack of Li‐ion coordination of these plasticizers and the addition of extra ions results in a low Li‐ion conductivity. An oligo(ethylene oxide)‐based IL was synthesized to overcome these limitations and enable additional transport modes, resulting in a high Li‐ion conductivity.
Dual-ion batteries (DIBs) and dual-graphite batteries (DGBs) attract increasing attention as an alternative approach for stationary energy storage due to their environmental, cost and safety benefits ...over other state-of-the-art battery technologies. In order to realize an extraordinary cell performance of DGBs, it is of particular importance to stabilize the interphases between electrolyte and electrode, for both the negative and positive electrodes. In this work, we present the implementation of highly concentrated electrolytes (HCEs) in DIBs and DGBs, i.e. electrolyte formulations based on either LiPF6 or LiTFSI in dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC). A reversible cycling stability of the graphitic negative electrode is proven as well as the stability of the HCEs against oxidative decomposition at the positive electrode at a cathode potential of 5V vs. Li/Li+. Additionally, we demonstrate that the anodic dissolution of the aluminum (Al) current collector is successfully suppressed by using LiTFSI-based HCEs, which show a comparable resistivity against Al dissolution as LiPF6-based electrolytes. Furthermore, a strong dependence of concentration and onset potential of anion intercalation is observed and comprehensively discussed with respect to the thermodynamic environment of the electrolyte. Overall, the use of HCEs enables a highly reversible cycling stability, providing extraordinary high specific discharge capacities of 80–100 mAh g−1 for lithium metal-based DIBs and DGBs. The evaluation of voltage efficiency (VE) and energy efficiency (EE) reveals the highest values for the EMC/LiPF6-based electrolyte, i.e. 96% (VE) and 95% (EE). In summary, the use of HCEs is a promising strategy to further optimize the electrochemical performance of DIBs and DGBs in terms of high reversible capacity and cycling stability and decreased parasitic side reactions.
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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 (S BET). Similar S 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.
Two‐dimensional (2D) transition‐metal dichalcogenides (TMDs) have drawn much attention due to their unique physical and chemical properties. Using TMDs as templates for the generation of 2D ...sandwich‐like materials with remarkable properties still remains a great challenge due to their poor solvent processability. Herein, MoS2‐coupled sandwich‐like conjugated microporous polymers (M‐CMPs) with high specific surface area were successfully developed by using functionalized MoS2 nanosheets as template. As‐prepared M‐CMPs were further used as precursors for preparation of MoS2‐embedded nitrogen‐doped porous carbon nanosheets, which were revealed as novel electrocatalysts for oxygen reduction reaction with mainly four‐electron transfer mechanism and ultralow half‐wave potential in comparison with commercial Pt/C catalyst. Our strategy to core–shelled sandwich‐like hybrids paves a way for a new class of 2D hybrids for energy conversion and storage.
Hierarchically porous MoS2/N‐doped carbon hybrids were fabricated by pyrolysis of MoS2‐templated microporous polymer sandwiches. The hybrids are characterized by high specific surface areas and aspect ratios and show promising oxygen reduction reaction and supercapacitor performances.
Microporous, pillared graphene‐based frameworks are generated in a simple functionalization/coupling procedure starting from reduced graphene oxide. They are used for the fabrication of ...high‐performance supercapacitor devices.
pH-Switchable Ampholytic Supramolecular Copolymers Frisch, Hendrik; Unsleber, Jan Patrick; Lüdeker, David ...
Angewandte Chemie (International ed.),
September 16, 2013, Letnik:
52, Številka:
38
Journal Article
Recenzirano
β‐sheet‐encoded anionic and cationic dendritic peptide amphiphiles form supramolecular copolymers when self‐assembled in a 1:1 feed ratio of the monomers. These ampholytic materials have been ...designed for on‐off polymerization in response to pH triggers. The cooperative supramolecular self‐assembly process is switched on at a physiologically relevant pH value and can be switched off by increasing or decreasing the pH value.
Inhomogeneous lithium deposition or dendrite formation and occurrence of “dead lithium” fractions are challenging issues, hampering the commercial application of lithium metal batteries. Conditions ...and strategies for minimizing potential failure of lithium metal anodes are currently not fully understood, despite recent progress. We report a protocol utilizing in situ and ex situ7Li solid-state NMR spectroscopy to quantify irreversible lithium losses in batteries, clearly distinguishing losses due to SEI formation and fractions of “dead lithium,” revealing a distribution of different lithium metal microstructures on both working and counter electrodes upon plating and stripping. Estimates of dead lithium fractions of 3.3% ± 0.6% (with 5% FEC) and 9.4% ± 0.6% (without 5% FEC) are determined. The proposed protocol affords benchmarking of commercial cells, including future design of suitable strategies for effective development and tailoring of electrolyte formulations, fostering further advancement of high-performance energy storage applications.
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Fractions of dead lithium and lithium ions consumed by SEI formation are quantifiedCombining in situ, ex situ NMR and gas chromatography data is a versatile approachReduction of dead lithium fractions is achieved by addition of 5% of additive FEC
Lithium metal is an attractive anode material that is prone to the formation of inhomogeneous deposits and “dead lithium” fractions, limiting specific cell capacities. Hsieh et al. propose a protocol to quantify fractions of dead lithium, based on in situ/ex situ7Li NMR and gas chromatography data. By demonstrating the relation of Li deposition homogeneity, SEI stability, and dead lithium fractions, relevant individual contributions to observable lithium losses are revealed.
Organic radical batteries (ORBs) represent a viable pathway to a more sustainable energy storage technology compared to conventional Li-ion batteries. For further materials and cell development ...towards competitive energy and power densities, a deeper understanding of electron transport and conductivity in organic radical polymer cathodes is required. Such electron transport is characterised by electron hopping processes, which depend on the presence of closely spaced hopping sites. Using a combination of electrochemical, electron paramagnetic resonance (EPR) spectroscopic, and theoretical molecular dynamics as well as density functional theory modelling techniques, we explored how compositional characteristics of cross-linked poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymers govern electron hopping and rationalise their impact on ORB performance. Electrochemistry and EPR spectroscopy not only show a correlation between capacity and the total number of radicals in an ORB using a PTMA cathode, but also indicates that the state-of-health degrades about twice as fast if the amount of radical is reduced by 15%. The presence of up to 3% free monomer radicals did not improve fast charging capabilities. Pulsed EPR indicated that these radicals readily dissolve into the electrolyte but a direct effect on battery degradation could not be shown. However, a qualitative impact cannot be excluded either. The work further illustrates that nitroxide units have a high affinity to the carbon black conductive additive, indicating the possibility of its participation in electron hopping. At the same time, the polymers attempt to adopt a compact conformation to increase radical-radical contact. Hence, a kinetic competition exists, which might gradually be altered towards a thermodynamically more stable configuration by repeated cycling, yet further investigations are required for its characterisation.
Slow diffusion reactions of the pentaphosphaferrocene Cp*Fe(η5‐P5) (Cp*=η5‐C5Me5 (1)) with CuX (X=Cl, Br, I) in different stoichiometric ratios and solvent mixtures result in the formation of one‐ ...and two‐dimensional polymeric compounds 2–6 with molecular formula {Cu(μ‐X)}{Cp*Fe(μ3,η5:η1:η1‐P5)}n (X=Cl (2 a), I (2′c)), {Cu(μ‐I)}{Cp*Fe(μ3,η5:η1:η1‐P5)}n (3), {CuX}{Cp*Fe(μ4,η5:η1:η1:η1‐P5)}n (X=Cl (4 a), Br (4 b), I (4 c), Br (4′b), I (4′c)), {Cu3(μ‐I)2(μ3‐I)}{Cp*Fe(μ5,η5:η1:η1:η1:η1‐P5)}n (5) and {Cu4(μ‐X)4(CH3CN)}{Cp*Fe(μ7,η5:η2:η1:η1:η1:η1:η1‐P5)}n (X=Cl (6 a), Br (6 b)), respectively. The polymeric compounds have been characterised by single‐crystal X‐ray diffraction analyses and, for selected examples, by magic angle spinning (MAS) NMR spectroscopy. The solid‐state structures demonstrate the versatile coordination modes of the cyclo‐P5 ligand of 1, extending from two to five coordinating phosphorus atoms in either σ or σ‐and‐π fashion. In compounds 2 a, 2′c and 3, two phosphorus atoms of 1 coordinate to copper atoms in a 1,2 coordination mode (2 a, 2′c) and an unprecedented 1,3 coordination mode (3) to form one‐dimensional polymers. Compounds 4 a–c, 4′b, 4′c and 5 represent two‐dimensional coordination polymers. In compounds 4, three phosphorus atoms coordinate to copper atoms in a 1,2,4 coordination mode, whereas in 5 the cyclo‐P5 ligand binds in an unprecedented 1,2,3,4 coordination mode. The crystal structures of 6 a,b display a tilted tube, in which all P atoms of the cyclo‐P5 ligand are coordinated to copper atoms in σ‐ and π‐bonding modes.
The right tool for the job: Small changes in the reaction conditions of pentaphosphaferrocene with Cu halides have a decisive impact on the supramolecular self‐assembly process to form 1D and 2D polymers. The novel products have been systematically investigated using single‐crystal X‐ray structure analyses and high‐resolution 31P solid‐state NMR techniques including R‐TOBSY experiments (see figure).
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