Dense‐Stacking Porous Conjugated Polymer as Reactive‐Type Host for High‐Performance Lithium Sulfur Batteries
Xiaowei WangYangyuchen YangChen LaiRunlai LiHaomin XuDarren H. S. TanKun ZhangWei YuØeystein FjeldbergMing LinWei TangYing Shirley MengKian Ping Loh
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Abstract Commercialization of the lithium‐sulfur battery is hampered by bottlenecks like low sulfur loading, high cathode porosity, uncontrollable Li 2 S x deposition and sluggish kinetics of Li 2 S activation. Herein, we developed a densely stacked redox‐active hexaazatrinaphthylene (HATN) polymer with a surface area of 302 m 2 g −1 and a very high bulk density of ca. 1.60 g cm −3 . Uniquely, HATN polymer has a similar redox potential window to S, which facilitates the binding of Li 2 S x and its transformation chemistry within the bulky polymer host, leading to fast Li 2 S/S kinetics. The compact polymer/S electrode presents a high sulfur loading of ca. 15 mg s cm −2 (200‐μm thickness) with a low cathode porosity of 41 %. It delivers a high areal capacity of ca. 14 mAh cm −2 and good cycling stability (200 cycles) at electrolyte–sulfur (E/S) ratio of 5 μL mg s −1 . The assembled pouch cell delivers a cell‐level high energy density of 303 Wh kg −1 and 392 Wh L −1 .π-Conjugated molecules and polymers are expected to have a variety of applications in organic electronics. Control over how these π-conjugated systems stack in the solid state is crucial for utilization of their desirable photophysical and electrical properties. Some molecules need to be designed with enhanced π-stacking abilities, whereas others might display novel properties as a result of restricting their π-stacking abilities. Furthermore, π-conjugated molecules or polymers that display partial π-stacking are of interest for potential new applications because of the synergy of the contrasting properties of stacked and isolated π-conjugated systems. Here, we highlight recent progress in molecular design to control π-stacking, with a particularly focus on the redox properties of these unique molecular systems.
Organic Electronics
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The stacking of layers forming three-dimensional periodic structures is explored in the general case, where neither the layers nor the stacking need to be close-packed, and the connectivity number for the system may be either two or four. Procedures are described whereby all possible stacking variants can be systematically derived for a given number of layers, and for a given number of possible stacking positions. The latter depends on the structure of the layer and on the stacking vector.
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A series of structural polytypes formed in an Mg-1at.%Zn-2at.%Y alloy has been identified, which are reasonably viewed as long-period stacking derivatives of the hcp Mg structure with alternate AB stacking of the close-packed atomic layers. Atomic-resolution Z-contrast imaging clearly revealed that the structures are long-period chemical-ordered as well as stacking-ordered; unique chemical order along the stacking direction occurs as being synchronized with a local faulted stacking of AB'C'A, where B' and C' layers are commonly enriched by Zn/Y atoms.
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Modulating the Interlayer Stacking of Covalent Organic Frameworks for Efficient Acetylene Separation
Controllable modulation of the stacking modes of 2D (two-dimensional) materials can significantly influence their properties and functionalities but remains a formidable synthetic challenge. Here, an effective strategy is proposed to control the layer stacking of imide-linked 2D covalent organic frameworks (COFs) by altering the synthetic methods. Specifically, a modulator-assisted method can afford a COF with rare ABC stacking without the need for any additives, while solvothermal synthesis leads to AA stacking. The variation of interlayer stacking significantly influences their chemical and physical properties, including morphology, porosity, and gas adsorption performance. The resultant COF with ABC stacking shows much higher C2 H2 capacity and selectivity over CO2 and C2 H4 than the COF with AA stacking, which is not demonstrated in the COF field yet. Furthermore, the outstanding practical separation ability of ABC stacking COF is confirmed by breakthrough experiments of C2 H2 /CO2 (50/50, v/v) and C2 H2 /C2 H4 (1/99, v/v), which can selectively remove C2 H2 with good recyclability. This work provides a new direction to produce COFs with controllable interlayer stacking modes.
Acetylene
Covalent organic framework
Separation (statistics)
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Predicting the strength of stacking interactions involving heterocycles is vital for several fields, including structure-based drug design. While quantum chemical computations can provide accurate stacking interaction energies, these come at a steep computational cost. To address this challenge, we recently developed quantitative predictive models of stacking interactions between drug-like heterocycles and the aromatic amino acids Phe, Tyr, and Trp (DOI: 10.26434/chemrxiv.7628939.v4). These models depend on heterocycle descriptors derived from electrostatic potentials (ESPs) computed using density functional theory and provide accurate stacking interactions without the need for expensive computations on stacked dimers. Herein, we show that these ESP-based descriptors can be reliably evaluated directly from the atom connectivity of the heterocycle, providing a means of predicting both the descriptors and the potential for a given heterocycle to engage in stacking interactions without resorting to any quantum chemical computations. This enables the conversion of simple molecular representations ( e.g . SMILES) directly into accurate stacking interaction energies using a freely-available online tool, thereby providing a way to rapidly rank the stacking abilities of large sets of heterocycles.
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Quantum chemical
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Stacking vs thickness: Stacking between the metal–organic layers (MOLs) of MOFs determines their thickness: the higher the stacking, the higher the thickness. This thickness plays an important role in controlling the function of the material, hence, regulating the stacking in 2D nano-MOFs might be very important. We tuned the stacking by modulating the chemical structure of the organic linkers in a series of isostructural MOFs. AFM, XRPD, FESEM, etc. showed the chemical functionality of the linkers to play a pivotal role in modulating stacking efficiency. Such an approach might open a new avenue in controlling the thickness of 2D materials. More information can be found in the Research Article by B. Manna, S. Ida et al. (DOI: 10.1002/chem.202201665).
Isostructural
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<p>Predicting the strength of stacking interactions involving heterocycles is vital for several fields, including structure-based drug design. While quantum chemical computations can provide accurate stacking interaction energies, these come at a steep computational cost. To address this challenge, we recently developed quantitative predictive models of stacking interactions between drug-like heterocycles and the aromatic amino acids Phe, Tyr, and Trp (DOI: 10.26434/chemrxiv.7628939.v4). These models depend on heterocycle descriptors derived from electrostatic potentials (ESPs) computed using density functional theory and provide accurate stacking interactions without the need for expensive computations on stacked dimers. Herein, we show that these ESP-based descriptors can be reliably evaluated directly from the atom connectivity of the heterocycle, providing a means of predicting both the descriptors and the potential for a given heterocycle to engage in stacking interactions without resorting to any quantum chemical computations. This enables the conversion of simple molecular representations (<i>e.g</i>. SMILES) directly into accurate<i> </i>stacking interaction energies using a freely-available online tool, thereby providing a way to rapidly rank the stacking abilities of large sets of heterocycles.</p> <p> </p>
Quantum chemical
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Stacking vs thickness: Stacking between the metal–organic layers (MOLs) of MOFs determines their thickness: the higher the stacking, the higher the thickness. This thickness plays an important role in controlling the function of the material, hence, regulating the stacking in 2D nano-MOFs might be very important. We tuned the stacking by modulating the chemical structure of the organic linkers in a series of isostructural MOFs. AFM, XRPD, FESEM, etc. showed the chemical functionality of the linkers to play a pivotal role in modulating stacking efficiency. Such an approach might open a new avenue in controlling the thickness of 2D materials. More information can be found in the Research Article by B. Manna, S. Ida et al. (DOI: 10.1002/chem.202201665).
Isostructural
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As an extension of Table 7.1.5B of International Tables for X-ray Crystallography [(1967), Vol. II. Birmingham: Kynoch Press], the possible stacking variants up to ten layers are arranged according to the percentage of hexagonal stacking. A method is given which allows one to calculate the number of possible stacking variants for any number of layers.
Table (database)
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Predicting the strength of stacking interactions involving heterocycles is vital for several fields, including structure-based drug design. While quantum chemical computations can provide accurate stacking interaction energies, these come at a steep computational cost. To address this challenge, we recently developed quantitative predictive models of stacking interactions between druglike heterocycles and the aromatic amino acids Phe, Tyr, and Trp (DOI: 10.1021/jacs.9b00936 ). These models depend on heterocycle descriptors derived from electrostatic potentials (ESPs) computed using density functional theory and provide accurate stacking interactions without the need for expensive computations on stacked dimers. Herein, we show that these ESP-based descriptors can be reliably evaluated directly from the atom connectivity of the heterocycle, providing a means of predicting both the descriptors and the potential for a given heterocycle to engage in stacking interactions without resorting to any quantum chemical computations. This enables the rapid conversion of simple molecular representations (e.g., SMILES) directly into accurate stacking interaction energies using a freely available online tool, thereby providing a way to rank the stacking abilities of large sets of heterocycles.
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