Tae-woo Kwon

Hyperbranched β-Cyclodextrin Polymer as an Effective Multidimensional Binder for Silicon Anodes in Lithium Rechargeable Batteries

Polymeric binders play an important role in electrochemical performance of high-capacity silicon (Si) anodes that usually suffer from severe capacity fading due to unparalleled volume change of Si during cycling. In an effort to find efficient polymeric binders that could mitigate such capacity fading, herein, we introduce polymerized β-cyclodextrin (β-CDp) binder for Si nanoparticle anodes. Unlike one-dimensional binders, hyperbranched network structure of β-CDp presents multidimensional hydrogen-bonding interactions with Si particles and therefore offers robust contacts between both components. Even the Si nanoparticles that lost the original contacts with the binder during cycling recover within the multidimensional binder network, thus creating a self-healing effect. Utilizing these advantageous features, β-CDp-based Si electrode shows markedly improved cycling performance compared to those of other well-known binder cases, especially when combined with linear polymers at an appropriate ratio to form hybrid binders.

Highly elastic binders integrating polyrotaxanes for silicon microparticle anodes in lithium ion batteries

A stretchy binder protects the silicon A challenge in using silicon particles for lithium batteries is that the large volume changes during charge-discharge cycling cause the particles to fracture, which builds up an insulating interface layer. Choi et al. show that traditional binder materials used to cushion the silicon particles can be improved by adding small amounts of polyrotaxanes (see the Perspective by Ryu and Park). The molecules consist of multiple rings that are strung along a linear segment and stoppered at each end. Some of the rings are anchored to the polymer binder, whereas others float freely, yielding a highly mobile but connected network that anchors the binder, and thus the silicon particles, together. Science, this issue p. 279; see also p. 250 The stability of silicon microparticle anodes is enhanced by highly elastic binders incorporating polyrotaxanes. Lithium-ion batteries with ever-increasing energy densities are needed for batteries for advanced devices and all-electric vehicles. Silicon has been highlighted as a promising anode material because of its superior specific capacity. During repeated charge-discharge cycles, silicon undergoes huge volume changes. This limits cycle life via particle pulverization and an unstable electrode-electrolyte interface, especially when the particle sizes are in the micrometer range. We show that the incorporation of 5 weight % polyrotaxane to conventional polyacrylic acid binder imparts extraordinary elasticity to the polymer network originating from the ring sliding motion of polyrotaxane. This binder combination keeps even pulverized silicon particles coalesced without disintegration, enabling stable cycle life for silicon microparticle anodes at commercial-level areal capacities.

Millipede-inspired structural design principle for high performance polysaccharide binders in silicon anodes

We systematically investigate polysaccharide binders for high-capacity silicon anodes in lithium ion batteries to find critical factors for the binder function. Analogous to the millipedes strong adhesion based on adhesive pads located on each leg, xanthan gum exhibits the best performance by utilizing its double helical superstructure with side chains and ion–dipole interactions, revealing the great importance of the superstructure and charge interactions in the Si binder design.

Systematic Molecular-Level Design of Binders Incorporating Meldrum's Acid for Silicon Anodes in Lithium Rechargeable Batteries

Covalent or Noncovalent? Systematic investigation of polymeric binders incorporating Meldrums acid reveals most critical binder properties for silicon -anodes in lithium ion batteries, that is self-healing effect facilitated by a series of noncovalent interactions.

Dynamic Cross-Linking of Polymeric Binders Based on Host–Guest Interactions for Silicon Anodes in Lithium Ion Batteries

We report supramolecular cross-linking of polymer binders via dynamic host-guest interactions between hyperbranched β-cyclodextrin polymer and a dendritic gallic acid cross-linker incorporating six adamantane units for high-capacity silicon anodes. Calorimetric analysis in the solution phase indicates that the given host-guest complexation is a highly spontaneous and enthalpically driven process. These findings are further verified by carrying out gelation experiments in both aqueous and organic media. The dynamic cross-linking process enables intimate silicon-binder interaction, structural stability of electrode film, and controlled electrode-electrolyte interface, yielding enhanced cycling performance. Control experiments using both α, γ-CDp with different cavity sizes and a guest molecule incorporating a single adamantane unit verified that the enhanced cycle life originates from the host-guest interaction between β-cyclodextrin and adamantane. The impact of the dynamic cross-linking is maximized at an optimal stoichiometry between the two components. Importantly, the present investigation proves that the molecular-level tuning of the host-guest interactions can be translated directly to the cycling performance of silicon anodes.

Self-assembled Micelle Interfering RNA for Effective and Safe Targeting of Dysregulated Genes in Pulmonary Fibrosis.

The siRNA silencing approach has long been used as a method to regulate the expression of specific target genes in vitro and in vivo. However, the effectiveness of delivery and the nonspecific immune-stimulatory function of siRNA are the limiting factors for therapeutic applications of siRNAs. To overcome these limitations, we developed self-assembled micelle inhibitory RNA (SAMiRNA) nanoparticles made of individually biconjugated siRNAs with a hydrophilic polymer and lipid on their ends and characterized their stability, immune-stimulatory function, and in vivo silencing efficacy. SAMiRNAs form very stable nanoparticles with no significant degradation in size distribution and polydispersity index over 1 year. Overnight incubation of SAMiRNAs (3 μm) on murine peripheral blood mononuclear cells did not cause any significant elaboration of innate immune cytokines such as TNF-α, IL-12, or IL-6, whereas unmodified siRNAs or liposomes or liposome complexes significantly stimulated the expression of these cytokines. Last, the in vivo silencing efficacy of SAMiRNAs was evaluated by targeting amphiregulin and connective tissue growth factor in bleomycin or TGF-β transgenic animal models of pulmonary fibrosis. Intratracheal or intravenous delivery two or three times of amphiregulin or connective tissue growth factor SAMiRNAs significantly reduced the bleomycin- or TGF-β-stimulated collagen accumulation in the lung and substantially restored the lung function of TGF-β transgenic mice. This study demonstrates that SAMiRNA nanoparticle is a less toxic, stable siRNA silencing platform for efficient in vivo targeting of genes implicated in the pathogenesis of pulmonary fibrosis.

Energy Band-Gap Engineering of Conjugated Microporous Polymers via Acidity-Dependent in Situ Cyclization

Conjugated microporous polymers (CMPs) offer a unique structure integrating π-conjugated backbone into a porous network for the simultaneous transport of charges and materials. However, tuning electronic properties of CMPs so far has been limited to an approach of varying the monomers, and the precious metal catalysts are inevitably needed for the C-C coupling reaction. Here, we present a powerful strategy to synthesize CMPs and precisely tune their optical band gap and surface area through metal-free in situ cyclization reaction controlled by the acid strength of acid catalysts. Notably, the optical band gap of CMPs showed a linear relationship with the p Ka of acid catalysts, which provides us with the ability to obtain the desired band gap between 2.07 and 3.35 eV, falling in the range of the visible solar spectrum. Moreover, CMPs exhibited excellent textural properties such as microporosity and high specific surface area.