In this study, a one-step process to fabricate "Janus"-structured nanocomposites with iron oxide (Fe 3 O 4 ) nanoparticles (Fe 3 O 4 NPs) and polydopamine (PDA) on each side of a graphene oxide (GO) nanosheet using the Langmuir−Schaefer technique has been proposed. The Fe 3 O 4 NPs−GO hybrid is used as a high-capacity active material, while PDA is added as a binder due to its unique wet-resistant adhesive property. The transmission electron microscopy image shows a superlattice-like out-of-plane section of the multilayered nanocomposite, which maximizes the density of the composite materials. Grazing-incidence small-angle X-ray scattering results combined with scanning electron microscopy images confirm that the multilayered Janus composite exhibits an in-plane hexagonal array structure of closely packed Fe 3 O 4 NPs. This Janus multilayered structure is expected to maximize the amount of active material in a specific volume and reduce volume changes caused by the conversion reaction of Fe 3 O 4 NPs. According to the electrochemical results, the Janus multilayer electrode delivers an excellent capacity of ∼903 mAh g −1 at a current density of 200 mA g −1 and a reversible capacity of ∼639 mAh g −1 at 1 A g −1 up to the 1800th cycle, indicating that this Janus composite can be a promising anode for Li-ion batteries.
high-voltage requirements. [1][2][3][4] However, the advancements of cathode active materials are overshadowed by the slow development of cathode binders, which should not be underestimated in terms of enabling practical cathode sheets. This issue becomes more stringent for the development of high-mass-loading cathode sheets, which have garnered considerable attention as a facile and scalable way to construct high-energy-density Li-ion batteries. [5][6][7] Major challenges facing the high-massloading cathode sheets include nonuniform electron/ion conduction networks in their through-thickness direction, [8][9][10][11][12] insufficient adhesion (between electrode active layers and current collectors) under electrolyte-soaked states, [13][14][15] and dissolution of transition metal (TM) ions from cathode active materials. [8,16,17] Notably, these challenges are closely dependent on cathode binders. Several previous studies on cathode binders have focused on the synthesis and engineering of new materials, with particular attention to replacing polyvinylidene fluoride (PVdF) binders that have been predominantly used in commercial cathodes. For example, gum materials [18,19] such as xanthan and guar gums with hydroxyl groups enhance the structural stability and electrochemical performance of overlithiated layered oxide (OLO) cathodes by chelating the dissolved TM ions. Carboxymethyl cellulose (CMC) exerted a strong binding force on OLO and mitigated the phase transition of OLO during cycling. [20,21] Owing to its hydroxyl groups, lignin enhanced the adhesion between LiNi 0.5 Mn 1.5 O 4 (LNMO) active materials and current collectors, and contributed to the formation of uniform cathode-electrolyte interphase (CEI). [22] In addition to these biomaterials, polyacrylic acid (PAA) [23] and Li-PAA [24] were explored as binders for the OLO and LNMO cathodes, which formed stable CEI layers and suppressed the dissolution of TM ions.However, these cathode binders were only suitable for aqueous slurry-based cathode fabrication processes due to their hydrophilic functional groups. More notably, these aqueous binders were not suitable for moisture-sensitive Ni-rich cathode active materials, which have gained considerable attention for high-energy-density Li-batteries used in long-range electric vehicles. The Ni-rich cathode active materials often undergo structural disruption when exposed to water molecules, [25] thus generating unwanted residual Li compounds such as LiOH and In contrast to noteworthy advancements in cathode active materials for lithium-ion batteries, the development of cathode binders has been relatively slow. This issue is more serious for high-mass-loading cathodes, which are preferentially used as a facile approach to enable high-energy-density Li-ion batteries. Here, amphiphilic bottlebrush polymers (BBPs) are designed as a new class of cathode binder material. Using poly (acrylic acid) (PAA) as a sidechain, BBPs are synthesized through ring-opening metathesis polymerization. The BBPs are amphiphilic in nature...
Herein we designed bottlebrush copolymers for use as a neutral additive to block copolymer (BCP) thin films in which they are segregated to the interfaces via architectural effects and produce nonpreferential interfaces to induce perpendicular orientation of BCP microdomains. Two BCP systems were employed, a conventional poly(styrene-b-methyl methacrylate) (PS-b-PMMA) with relatively low χ and similar surface energies between blocks, and a high χ poly(styrene-b-methacrylic acid) (PS-b-PMAA) with distinct surface energies. The bottlebrushes, with either short side-chains of PS-r-PMMA or PS-r-PMAA random copolymers, were synthesized via ring-opening metathesis polymerization (ROMP). Remarkably, it was observed that the top and bottom interfaces of both BCP films were enriched with bottlebrush copolymers, regardless of the surface energy difference between blocks, hence, vertically oriented microdomains were achieved for both BCP systems. This can be attributed to the screening of polymer interactions by a good solvent during the spin-casting process, allowing architectural effects to play a role in surface segregation of bottlebrush copolymers, as confirmed by contact angle measurements and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). We believe that this concept can be further extended to various applications that require polymer films with functional surfaces.
Bottlebrush polymers (BBPs) are three‐dimensional polymers with great academic and industrial potential owing to their highly tunable and intricate architecture. The most popular method to synthesize BBPs is ring‐opening metathesis polymerization (ROMP) with Grubbs' catalyst, allowing living grafting‐through polymerization of macromonomers of up to ultrahigh molecular weights with narrow molecular weight distribution. In this case, it has been well recognized that the purity of macromonomers (MMs) is critical for a successful ROMP reaction. For MMs synthesized from reversible‐deactivation radical polymerization, Grubbs and Xia demonstrated that the better control of ROMP reaction can be achieved when they are prepared via “growth‐then‐coupling” method that is coupling a norbornenyl group to end‐functionalized prepolymers. However, these MMs can also contain various residual impurities from previous synthetic steps, which can potentially poison the catalyst and hamper the ROMP reaction. Herein, we intentionally doped possible impurities into purified MMs to identify the most poisoning species. As a result, it was found that alkyne‐functionalized norbornene most significantly retarded the ROMP reaction due to a formation of Ru‐vinyl‐carbene intermediates having low catalytic reactivity, whereas the other reagents such as solvent, Cu‐catalyst, ligands, and azido‐terminated prepolymers were relatively inert. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 726–737
Herein, we designed a catechol-based compound, 4allyl pyrocatechol (APC), which contains catechol and alkene groups capable of interacting with various metal oxide substrates and being chemically incorporated into a polydimethylsiloxane (PDMS) matrix, respectively. Due to the specific interactions between the catechol and metal oxide surface, this compound incorporated in PDMS can act as a surface "active" additive that effectively enriches the adhesion interface, leading to the improvement of adhesion between PDMS and the substrate. The adhesion property was evaluated by measuring the lap shear strength on various metal substrates, such as aluminum (Al), stainless steel (SUS), and copper (Cu) (each with an oxide skin layer), and compared with that of the commercial additive, 3-glycidoxypropyltrimethoxysilane (GPTMS). Remarkably, APC-incorporated PDMS adhered to metal oxide substrates exhibited the maximum shear strength at a lower loading than GPTMS, suggesting that APC enhances the adhesion of PDMS onto metal oxide surfaces more significantly than GPTMS. For example, it was observed that even 0.3 wt % APC improves the strength on SUS substrates by 1200%, demonstrating that APC is a very effective additive. This improved adhesion behavior is considered to be the consequence of surface segregation of APC groups, as corroborated by surface analysis and molecular dynamics simulations.
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