Facile charge transport by a hydrophilic organic radical-substituted polymer and the 3D current collection by a self-assembled mesh of single-walled carbon nanotube bundles lead to the operation of an ultrahigh-output rechargeable electrode. Exceptionally large current density beyond 1 A cm and high areal capacity around 3 mAh cm are achieved, which are 10 times larger than those of the previously reported so-called "ultrafast electrodes." A sub-millimeter-thick, flexible, highly safe organic redox polymer-based rechargeable device with an aqueous sodium chloride electrolyte is fabricated to demonstrate the superior performance.

are too thick (>1 mm) to attach skin surface intimately. [18][19][20] Emerging micro norder printing techniques of electrode active materials enabled the fabrication of submillimeterthick batteries. [21] However, the intrinsic brittleness of the conventional inorganic electrodeactive materials and "harsh" electrolytes (e.g., flammable and toxic organic solvents for LIBs and alka line for Nihydrogen, zinc-air, and NiCd batteries) should be problematic for safety. The sealing must also be sufficiently thick and strict to prevent the flammable and toxic materials from exposure. Another major drawback of the conventional inorganic electrodeactive materials is the rather low rate performance. In the case of conventional electrodeactive materials in LIBs, only small current density around 1 µA cm −2 is obtained with a submicron thick electrode according to the limited current rate of ≈70 mA g −1 (assuming the condition of 100 nm thickness, 0.5 C, 140 mAh g −1 , and a tap density of 2.6 g cm −3 , where x C rate corresponds to the full charge/discharge in 1/x h). [22] The output is not enough for powerconsuming applications such as electromagnetic wave emission and biomonitoring display.Design of stretchable batteries is also required for the con formable attaching to skin. Applying zigzag, helix, buckled, mesh, and porous electrodes in geometry are typical approaches to provide stretchability with the inorganic electrodeactive Ultrathin flexible electronic devices have been attracting substantial attention for biomonitoring, display, wireless communication, and many other ubiquitous applications. In this article, organic robust redox-active polymer/carbon nanotube hybrid nanosheets with thickness of just 100 nm are reported as power sources for ultrathin devices conformable to skin. Regardless of the extreme thinness of the electrodes, a moderately large current density of 0.4 mA cm −2 is achieved due to the high output of the polymers (>10 A g −1 ). For the first time, the use of mechanically robust yet intrinsically soft electrodes and polymer nanosheet sealing leads to the fabrication of rechargeable devices with only 1-µm thickness and even with stretchable properties.

A poly(ethylene sulfide) backbone is introduced as the main chain of a radical polymer. Anionic ring‐opening polymerization of an episulfide monomer substituted with 2,2,6,6tetramethylpiperidin1oxyl (TEMPO), a robust nitroxide radical, yields the corresponding polythioether. Compared to the traditional poly(ethylene oxide) backbone, the new polymer shows a lower glass transition temperature (−10 °C), and about threefold higher solid‐state ionic conductivity. The polythioether is also shown to improve the charge/discharge properties of a cathode in solid‐state lithium‐ion batteries.

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In article number https://doi.org/10.1002/smll.201805296, Kenichi Oyaizu, Hiroyuki Nishide, and co‐workers report 100 nmthick, organic robust redox‐active polymer/carbon nanotube hybrid nanosheets as rechargeable power sources. The use of the mechanically robust yet intrinsically soft nanosheets enable the fabrication of organic polymer‐based batteries with only 1 μm thickness and stretchable properties. The devices are highly conformable to skin surfaces.