An important trend in electronics involves the development of materials, mechanical designs and manufacturing strategies that enable the use of unconventional substrates, such as polymer films, metal foils, paper sheets or rubber slabs. The last possibility is particularly challenging because the systems must accommodate not only bending but also stretching. Although several approaches are available for the electronics, a persistent difficulty is in power supplies that have similar mechanical properties, to allow their co-integration with the electronics. Here we introduce a set of materials and design concepts for a rechargeable lithium ion battery technology that exploits thin, low modulus silicone elastomers as substrates, with a segmented design in the active materials, and unusual 'self-similar' interconnect structures between them. The result enables reversible levels of stretchability up to 300%, while maintaining capacity densities of B1.1 mAh cm À 2 . Stretchable wireless power transmission systems provide the means to charge these types of batteries, without direct physical contact.

A protective polydopamine (PDA) coating is applied to core-shell microcapsule surfaces by the polymerization of dopamine monomers. A neutral aqueous solution and the addition of an oxidant (i.e., ammonium persulfate) are crucial for microcapsule survival and the initiation of PDA polymerization, respectively. The resulting PDA coating is a dense and uniform layer approximately 50 nm thick. The PDA protective coating significantly increases capsule stability at an elevated temperature (180 °C) and in a variety of organic solvents and acidic/basic solutions that otherwise lead to deflation and loss of the core content of uncoated microcapsules.

Silicon (Si) composite electrodes are developed with increased cycle lifetimes and reliability through dynamic ionic bonding between active Si nanoparticles and a polymer binder. Amine groups are covalently attached to Si nanoparticles via surface functionalization. Si composite electrodes are fabricated by combining the Si nanoparticles with a poly(acrylic acid) (PAA) binder. The formation of ionic bonds between amine groups on Si particles and carboxylic acid groups on the PAA binder is characterized by X‐ray photoelectron spectroscopy and Raman spectroscopy. Si composite anodes with ionic bonding demonstrate long term cycling stability with capacity retention of 80% at 400 cycles at a current density of 2.1 A g−1 and good rate capability. The dynamic ionic bonds effectively mitigate the deterioration of electrical interfaces in the composite anodes as suggested by stable impedance over 300 cycles.

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Robust microcapsules are prepared with carbon black suspensions high in solids loading (up to 0.2 g/mL) for electrical conductivity restoration. Oxidized carbon black is rendered more hydrophobic through surface functionalization with octadecylamine by two different methods. Functionalization significantly improves dispersability and suspension stability of carbon black in hydrophobic solvents such as o‐dichlorobenzene (o‐DCB), enabling encapsulation by in situ emulsion polymerization. Upon crushing, microcapsules containing functionalized carbon black (FCB) suspensions exhibit significant particle release relative to microcapsules filled with unfunctionalized carbon black. Release of carbon black is further enhanced by the addition of two types of core thickeners, epoxy resin or poly 3‐hexylthiophene (P3HT). Full conductivity restoration (100% restoration efficiency) of damaged silicon anodes is achieved by crushing microcapsules containing FCB suspensions with P3HT. Hydrophobic surface functionalization of carbon black and the addition of core thickeners are both critical for achieving stable microcapsules capable of significant particle release and efficient conductivity restoration.

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