Accurate and imperceptible monitoring of electrophysiological signals is of primary importance for wearable healthcare. Stiff and bulky pregelled electrodes are now commonly used in clinical diagnosis, causing severe discomfort to users for long-time using as well as artifact signals in motion. Here, we report a ~100 nm ultra-thin dry epidermal electrode that is able to conformably adhere to skin and accurately measure electrophysiological signals. It showed low sheet resistance (~24 Ω/sq, 4142 S/cm), high transparency, and mechano-electrical stability. The enhanced optoelectronic performance was due to the synergistic effect between graphene and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which induced a high degree of molecular ordering on PEDOT and charge transfer on graphene by strong π-π interaction. Together with ultra-thin nature, this dry epidermal electrode is able to accurately monitor electrophysiological signals such as facial skin and brain activity with low-motion artifact, enabling human-machine interfacing and long-time mental/physical health monitoring.

Graphene, with its properties of intrinsic flexibility, reliable electrical performance, and high chemical stability, is highly desirable as bioelectrodes for detecting electrophysiological signals. However, its mechanical properties limit its application to a great extentenergy dissipation mechanisms are not provided by the carbon network for external strain and it easily cracks. Herein, inspired by the very structure of the avian nest, we report a durable and nondisposable transparent graphene skin electrode for detecting electrophysiological signals, which was fabricated by semi-embedding highly graphitized electrospun fiber/monolayer graphene (GFG) into soft elastomer. Because of the semi-embedded structure and strong interaction between annealed electrospun fiber and graphene through graphitization, as-fabricated conductive film demonstrated high conductivity and transparency (∼150 Ω/□ at 83% transmittance), as well as a stable electrical performance under mechanical vibrations (strain, peel-off, stir, etc.). It can be used to reliably collect vital biometric signals, such as electrocardiogram (ECG), surface electromyogram (sEMG), and electroencephalogram (EEG). Furthermore, the semi-embedded GFG in the elastomer demonstrated excellent washability (rinsing/stirring in water) and repeatability (∼10 repeats) with high signal-to-noise ratio (up to 30 dB) while detecting sEMG. This is the first report of durable and transparent graphene skin electrode for biometric signals detection, revealing potential opportunities in wearable healthcare applications.

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Great efforts have been made to build integrated devices to enable future wearable electronics; however, safe, disposable, and cost-effective power sources still remain a challenge. In this paper, an all-solid-state power source was developed by using graphene materials and can be printed directly on an insulating substrate such as paper. The design of the power source was inspired by electric eels to produce programmable voltage and current by converting the chemical potential energy of the ion gradient to electric energy in the presence of moisture. An ultrahigh voltage of 192 V with 175 cells in series printed on a strip of paper was realized under ambient conditions. For the planar cell, the mathematical fractal design concept was adapted as printed patterns, improving the output power density to 2.5 mW cm−3, comparable to that of lithium thin-film batteries. A foldable three-dimensional (3D) cell was also achieved by employing an origami strategy, demonstrating a versatile design to provide green electric energy. Unlike typical batteries, this power source printed on flexible paper substrate does not require liquid electrolytes, hazardous components, or complicated fabrication processes and is highly customizable to meet the demands of wearable electronics and Internet of Things applications.

Solid polymer electrolytes (SPEs) of superior ionic conductivity, long-term cycling stability, and good interface compatibility are regarded as promising candidates to enable the practical applications of solid lithium metal batteries (SLMBs). Here, a mixed-matrix SPE (MMSE) with incorporated metal–organic frameworks (MOFs) and ionic liquid is prepared. The dissociation of Li salt in MMSE can be promoted effectively due to the introduction of MOF via the Fourier-transform infrared spectroscopy (FT-IR) analysis, density functional theory calculation, and molecular dynamics simulation. The as-formed MMSE exhibits an ultralow thickness of 20 μm with a satisfactory ionic conductivity and lithium-ion transference number (1.1 mS cm–1 at 30 °C, 0.72). The optimized SLMBs with high-voltage LiMn0.75Fe0.25PO4 (LMFP) exhibit an excellent cyclability at 4.2 V under room temperature. Moreover, Li/MMSE/LiFePO4 cells have desirable cycle performance from −20 to 100 °C, and their capacity remains 143.3 mA h g–1 after being cycled 300 times at 10 C at 100 °C. The Li/LiFePO4 pouch cells also show excellent safety under extreme conditions. The Li symmetric cells can work steadily even at a supreme current density of 4 mA cm–2 at 100 °C. From the above analysis, these MMSEs present new opportunities for the development of SLMBs with good electrochemical properties.