Self-healing chemistry enables the stable operation of silicon microparticle anodes for high-energy lithium-ion batteries

• Chao Wang,
• Hui Wu,
• Zheng Chen,
• Matthew T. McDowell,
• Yi Cui
• & Zhenan Bao

The ability to repair damage spontaneously, which is termed self-healing, is an important survival feature in nature because it increases the lifetime of most living creatures. This feature is highly desirable for rechargeable batteries because the lifetime of high-capacity electrodes, such as silicon anodes, is shortened by mechanical fractures generated during the cycling process. Here, inspired by nature, we apply self-healing chemistry to silicon microparticle (SiMP) anodes to overcome their short cycle-life. We show that anodes made from low-cost SiMPs (~3–8 µm), for which stable deep galvanostatic cycling was previously impossible, can now have an excellent cycle life when coated with a self-healing polymer. We attain a cycle life ten times longer than state-of-art anodes made from SiMPs and still retain a high capacity (up to ~3,000 mA h g⁻¹). Cracks and damage in the coating during cycling can be healed spontaneously by the randomly branched hydrogen-bonding polymer used.

Interfacial assembly of protein–polymer nano-conjugates into stimulus-responsive biomimetic protocells

Xin Huang, Mei Li, David C. Green, David S. Williams, Avinash J. Patil & Stephen Mann

The mechanism of spontaneous assembly of microscale compartments is a central question for the origin of life, and has technological repercussions in diverse areas such as materials science, catalysis, biotechnology and biomedicine. Such compartments need to be semi-permeable, structurally robust and capable of housing assemblages of functional components for internalized chemical transformations. In principle, proteins should be ideal building blocks for the construction of membrane-bound compartments but protein vesicles with cell-like properties are extremely rare. Here we present an approach to the interfacial assembly of protein-based micro-compartments (proteinosomes) that are delineated by a semi-permeable, stimulus-responsive, enzymatically active, elastic membrane consisting of a closely packed monolayer of conjugated protein–polymer building blocks. The proteinosomes can be dispersed in oil or water, thermally cycled to temperatures of 70 °C, and partially dried and re-inflated without loss of structural integrity. As a consequence, they exhibit protocellular properties such as guest molecule encapsulation, selective permeability, gene-directed protein synthesis and membrane-gated internalized enzyme catalysis.

Stress-Responsive Polymers Containing Cyclobutane Core Mechanophores: Reactivity and Mechanistic Insights

Zachary S. Kean †, Zhenbin Niu †, Gihan B. Hewage †, Arnold L. Rheingold ‡, and Stephen L. Craig *†

A primary goal of covalent mechanochemistry is to develop polymer bound mechanophores that undergo constructive transformations in response to otherwise destructive forces. The [2 + 2] cycloreversion of cyclobutane mechanophores has emerged as a versatile framework to develop a wide range of stress-activated functionality. Herein, we report the development of a class of cyclobutane bearing bicyclo[4.2.0]octane mechanophores. Using carbodiimide polyesterification, these stress-responsive units were incorporated into high molecular weight polymers containing up to 700 mechanophores per polymer chain. Under exposure to the otherwise destructive elongational forces of pulsed ultrasound, these mechanophores unravel by 7 Å per monomer unit to form α,β-unsaturated esters that react constructively via thiol–ene conjugate addition to form sulfide functionalized copolymers and cross-linked polymer networks. To probe the dynamics of the mechanochemical ring opening, a series of bicyclo[4.2.0]octane derivatives that varied in stereochemistry, substitution, and symmetry were synthesized and activated. Reactivity and product stereochemistry was analyzed by 1H NMR, which allowed us to interrogate the mechanism of the mechanochemical [2 + 2] cycloreversion. These results support that the ring opening is not concerted but proceeds via a 1,4 diradical intermediate. The bicyclo[4.2.0]octanes hold promise as active functional groups in new classes of stress-responsive polymeric materials.

Mechanochemical strengthening of a synthetic polymer in response to typically destructive shear forces

• Ashley L. Black Ramirez,
• Zachary S. Kean,
• Joshua A. Orlicki,
• Mangesh Champhekar,
• Sarah M. Elsakr,
• Wendy E. Krause
• & Stephen L. Craig

Abstract: High shear stresses are known to trigger destructive bond-scission reactions in polymers. Recent work has shown that the same shear forces can be used to accelerate non-destructive reactions in mechanophores along polymer backbones, and it is demonstrated here that such mechanochemical reactions can be used to strengthen a polymer subjected to otherwise destructive shear forces. Polybutadiene was functionalized with dibromocyclopropane mechanophores, whose mechanical activation generates allylic bromides that are crosslinked in situ by nucleophilic substitution reactions with carboxylates. The crosslinking is activated efficiently by shear forces both in solvated systems and in bulk materials, and the resulting covalent polymer networks possess moduli that are orders-of-magnitude greater than those of the unactivated polymers. These molecular-level responses and their impact on polymer properties have implications for the design of materials that, like biological materials, actively remodel locally as a function of their physical environment.

A general approach to DNA-programmable atom equivalents

Chuan Zhang,Robert J. Macfarlane,Kaylie L. Young,Chung Hang J. Choi,Liangliang Hao,Evelyn Auyeung,Guoliang Liu,Xiaozhu Zhou& Chad A. Mirkin

Nanoparticles can be combined with nucleic acids to programme the formation of three-dimensional colloidal crystals where the particles’ size, shape, composition and position can be independently controlled1, 2, 3, 4, 5, 6, 7. However, the diversity of the types of material that can be used is limited by the lack of a general method for preparing the basic DNA-functionalized building blocks needed to bond nanoparticles of different chemical compositions into lattices in a controllable manner. Here we show that by coating nanoparticles protected with aliphatic ligands with an azide-bearing amphiphilic polymer, followed by the coupling of DNA to the polymer using strain-promoted azide–alkyne cycloaddition⁸ (also known as copper-free azide–alkyne click chemistry), nanoparticles bearing a high-density shell of nucleic acids can be created regardless of nanoparticle composition. This method provides a route to a virtually endless class of programmable atom equivalents for DNA-based colloidal crystallization.

Preorganized Hydrogel: Self-Healing Properties of Supramolecular Hydrogels Formed by Polymerization of Host–Guest-Monomers that Contain Cyclodextrins and Hydrophobic Guest Groups

Takahiro Kakuta¹, Yoshinori Takashima¹, Masaki Nakahata¹, Miyuki Otsubo¹, Hiroyasu  Yamaguchi¹, Akira Harada^1,2,*

 

Supramolecular hydrogels formed by a host-guest interaction show self-healing properties. The cube-shaped hydrogels with β-cyclodextrin and adamantane guest molecules mend after being broken. The hydrogels sufficiently heal to form a single gel, and the initial strength is restored. Although contact between a freshly cut and uncut surface does not mend the gels, two freshly cut surfaces selectively mend.
 

“Flex-Activated” Mechanophores: Using Polymer Mechanochemistry To Direct Bond Bending Activation

Michael B. Larsen and Andrew J. Boydston *

We describe studies in mechanochemical transduction that probe the activation of bonds orthogonal to an elongated polymer main chain. Compression of mechanophore-cross-linked materials resulted in the release of small molecules via cleavage of covalent bonds that were not integral components of the elongated polymer segments. The reactivity is proposed to arise from the distribution of force through the cross-linking units of the polymer network and subsequent bond bending motions that are consistent with the geometric changes in the overall reaction. This departure from contemporary polymer mechanochemistry, in which activation is achieved primarily by force-induced bond elongation, is a first step toward mechanophores capable of releasing side-chain functionalities without inherently compromising the overall macromolecular architecture.