Natural wood-based materials are directly utilized to construct ultra-thick all-wood-structured supercapacitors with ultra-high capacitance and energy density.

Aerogels can be used in a broad range of applications such as bioscaffolds, energy storage devices, sensors, pollutant treatment, and thermal insulating materials due to their excellent properties including large surface area, low density, low thermal conductivity, and high porosity. Here we report a facile and effective top-down approach to fabricate an anisotropic wood aerogel directly from natural wood by a simple chemical treatment. The wood aerogel has a layered structure with anisotropic structural properties due to the destruction of cell walls by the removal of lignin and hemicellulose. The layered structure results in the anisotropic wood aerogel having good mechanical compressibility and fragility resistance, demonstrated by a high reversible compression of 60% and stress retention of ∼90% after 10 000 compression cycles. Moreover, the anisotropic structure of the wood aerogel with curved layers stacking layer-by-layer and aligned cellulose nanofibers inside each individual layer enables the wood aerogel to have an anisotropic thermal conductivity with an anisotropy factor of ∼4.3. An extremely low thermal conductivity of 0.028 W/m·K perpendicular to the cellulose alignment direction and a thermal conductivity of 0.12 W/m·K along the cellulose alignment direction can be achieved. The thermal conductivity is not only much lower than that of the natural wood material (by ∼3.6 times) but also lower than most of the commercial thermal insulation materials. The top-down approach is low-cost, scalable, simple, yet effective, representing a promising direction for the fabrication of high-quality aerogel materials.

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With high conductivity and stretchable for large cross-sections, liquid metals such as galinstan are promising for creating stretchable devices and interconnects. Creating high resolution features in parallel is challenging, with most techniques limited to a hundred micrometers or more. In this work, multilevel electroplated stencils are investigated for printing liquid metals, with galinstan features as small as ten micrometers printed on soft elastomers, a factor of 10 reduction over past liquid metal stencil printing. Capacitors and resistive strain sensors are also demonstrated, showing the potential for creating stretchable conductors and devices.

Liquid metals are ideally suited for creating low resistance traces able to undergo large mechanical strains. In this work, multilayer fluidic channels in soft silicone are used to create two inductor topologies, a solenoid and a double planar coil, based on the liquid metal galinstan. Electromechanical models were developed for the inductance upon stretching for each inductor, finding that the double planar coil has lower strain sensitivity in each direction than the solenoid. A three turn double planar coil and six turn solenoid, with unstretched inductances of approximately 250 nH and 55 nH respectively, were fabricated and tested using custom tensile and compressive strain testing setups and compared with the analytical model. The double planar coil was found to increase in inductance when stretched in either in-plane axes, with a measured rise of approximately 40% for 100% strain. The solenoid decreased in inductance by 24% for 100% strain along the core direction, and increased by 50% for the same strain along the core width.