Efforts to create block-polymer-based templates with ultrasmall domain sizes has stimulated integrated experimental and theoretical work in an effort to design and prepare self-assembled systems that can achieve unprecedented domain sizes. We recently reported the utilization of molecular dynamics simulations with transferable force fields to identify amphiphilic oligomers capable of self-assembling into ordered layered and cylindrical morphologies with sub-3 nm domain sizes. Motivated by these predictions, we prepared a sugar-based amphiphile with a hydrocarbon tail that shows thermotropic self-assembly to give a lamellar mesophase with a 3.5 nm pitch and sub-2 nm nanodomains above the melting temperature and below the liquid-crystalline clearing temperature. Complementary atomistic simulations of the molecular assemblies gave morphologies and spacings that were in near-perfect agreement with the experimental results. The effective combination of molecular design, simulation, synthesis, and structural characterization demonstrates the power of this integrated approach for next-generation templating technologies.
The coupling of lithium metal (Li), an ester electrolyte, and high voltage cathode materials is expected to realize rechargeable batteries with high energy densities. Herein, a "cationic size effect" is first demonstrated to promote the dissolution of NO 3 − in an ester electrolyte and a SEI layer containing Li 3 N is constructed. By adjusting the size of quaternary ammonium (R 4 N + ), the charge localization state of R 4 N + and the binding energy between R 4 N + and NO 3 − are regulated, achieving a high solubility (1.8 M) of tetraethylammonium nitrate (TEAN) in ethylene carbonate. Using TEAN as an ester electrolyte additive, the Li/Cu batteries can stably run over 1000 h with an average CE of 98.6%, 8 times longer than that of a conventional ester electrolyte. Moreover, the cyclic life of assembled Li/LiFePO 4 and Li/NCM811 batteries can also be increased by 3−4 times.
Using molecular dynamics simulations and transferable force fields, we designed a series of symmetric triblock amphiphiles (or high-χ block oligomers) comprising incompatible sugar-based (A) and hydrocarbon (B) blocks that can selfassemble into ordered nanostructures with sub-1 nm domains and full domain pitches as small as 1.2 nm. Depending on the chain length and block sequence, the ordered morphologies include lamellae, perforated lamellae, and hexagonally perforated lamellae. The self-assembly of these amphiphiles bears some similarities, but also some differences, to those formed by symmetric triblock polymers. In lamellae formed by ABA amphiphiles, the fraction of B blocks "bridging" adjacent polar domains is nearly unity, much higher than that found for symmetric triblock polymers, and the bridging molecules adopt elongated conformations. In contrast, "looping" conformations are prevalent for A blocks of BAB amphiphiles. Above the order−disorder transition temperature, the disordered states are locally well-segregated yet the B blocks of ABA amphiphiles are significantly less stretched than in the lamellar phases. Analysis of both hydrogen-bonded and nonpolar clusters reveals the bicontinuous nature of these network phases. This simulation study furnishes detailed insights into structure− property relationships for mesophase formation on the 1 nm length scale that will aid further miniaturization for numerous applications.
Molecular dynamics simulations are used to study binary blends of an AB-type diblock and an AB 2 -type miktoarm triblock amphiphiles (also known as high-χ block oligomers) consisting of sugar-based (A) and hydrocarbon (B) blocks. In their pure form, the AB diblock and AB 2 triblock amphiphiles self-assemble into ordered lamellar (LAM) and cylindrical (CYL) structures, respectively. At intermediate compositions, however, the AB 2 -rich blend (0.2 ≤ x AB ≤ 0.4) forms a double gyroid (DG) network, whereas perforated lamellae (PL) are observed in the AB-rich blend (0.5 ≤ x AB ≤ 0.8). All of the ordered mesophases present domain pitches under 3 nm, with 1 nm feature sizes for the polar domains. Structural analyses reveal that the nonuniform interfacial curvatures of DG and PL structures are supported by local composition variations of the LAM- and CYL-forming amphiphiles. Self-consistent mean field theory calculations for blends of related AB and AB 2 block polymers also show the DG network at intermediate compositions, when A is the minority block, but PL is not stable. This work provides molecular-level insights into how blending of shape-filling molecular architectures enables network phase formation with extremely small feature sizes over a wide composition range.
The construction of high sulfur (S) loading cathode is one of the critical parameters to obtain lithium–sulfur (Li–S) batteries with high energy density, but the slow redox reaction rate of high S loading cathode limits the development process. In this paper, a metal coordinated polymer‐based three‐dimensional network binder, which can improve the reaction rate and stability of S electrode. Compared with traditional linear polymer binders, the metal coordinated polymer binder can not only increase the load amount of S through the three‐dimensional cross‐linking, but also promote the interconversion reactions between S and lithium sulfide (Li2S), avoiding the passivation of electrode and improving the stability of the positive electrode. At an S load of 4–5 mg cm−2 and an E/S ratio of 5.5 µL mg−1, the discharged voltage in the second platform is 2.04 V and the initial capacity is 938 mA h g−1 with metal coordinated polymer binder. Moreover, the capacity retention rate approaches 87% after 100 cycles. In comparison, the discharged voltage in the second platform is lost and the initial capacity is 347 mA h g−1 with PVDF binder. It demonstrates the advanced properties of metal‐coordinated polymer binders for improving the performance of Li–S batteries.
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