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Downsizing the cell size of honeycomb monoliths to nanoscale would offer high freedom of nanostructure design beyond their capability for broad applications in different fields. However, the microminiaturization of honeycomb monoliths remains a challenge. Here, we report the fabrication of microminiaturized honeycomb monoliths-honeycomb alumina nanoscaffold-and thus as a robust nanostructuring platform to assemble active materials for microsupercapacitors. The representative honeycomb alumina nanoscaffold with hexagonal cell arrangement and 400 nm inter-cell spacing has an ultrathin but stiff nanoscaffold with only 16 ± 2 nm cell-wall-thickness, resulting in a cell density of 4.65 × 10 9 cells per square inch, a surface area enhancement factor of 240, and a relative density of 0.0784. These features allow nanoelectrodes based on honeycomb alumina nanoscaffold synergizing both effective ion migration and ample electroactive surface area within limited footprint. A microsupercapacitor is finally constructed and exhibits record high performance, suggesting the feasibility of the current design for energy storage devices.

Rechargeable Na-air batteries are the subject of great interest because of their high theoretical specific energy density, lower cost, and lower charge potential compared with Li-air batteries. However, high purity O 2 as a working environment is required to achieve high-performance Na-air batteries, which obstructs their application as a high-energy-density battery. Although aqueous Na-air batteries can operate in ambient air, long cycle and high safety remain challenges for aqueous Na-air batteries because the aqueous electrolyte is volatile. Here, a quasi-solid-state Na-air battery is reported by utilizing a gel cathode, which is composed of single-walled carbon nanotubes and roomtemperature ionic liquids, achieving high safety and long cycling life of 125 cycles (528 h) at a current density of 0.1 mA cm −2 , which is surprisingly better than that of quasi-solid-state NaO 2 batteries. In situ XRD characterizations reveal that water in ambient air is gradually deposited on the surface of the gel cathode to form a water layer, which facilitates the generation of soluble discharge product of NaOH thermodynamically with high conductivity. This work shall be critical to develop and promote the practical application of Na-air batteries, opening a new way to the design of solid-state metal-air batteries.

As an attractive cathode candidate for sodium-ion batteries, P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 is famous for its high stability in humid air, attractive capacity, and high operating voltage. However, the low Na + transport kinetics, oxygen-redox reactions, and irreversible structural evolution at high-voltage areas hinder its practical application. Herein, a comprehensive study of a microbar P2-type Ni 2/3 Ni 1/4 Mg 1/12 Mn 2/3 O 2 material with {010} facets is presented, which exhibits high reversibility of structural evolution and anionic redox activity, leading to outstanding rate capability and cyclability. The notable rate performance (53 mA h g −1 at 20 C, 2.0− 4.3 V) contributed to the high exposure of {010} facets via controlling the growth orientation of the precursor, which is certified by density functional theory calculation and lattice structural analysis. Mg substitution strengthens the reversibility of anionic oxygen redox and structural evolution in high-voltage areas that was confirmed by the in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy tests, leading to outstanding cyclic reversibility (68.9% after 1000 cycles at 5 C) and slowing down the voltage fading. This work provides new insights into constructing electrochemically active planes combined with heteroatom substitution to improve the Na + transport kinetics and structural stability of layered oxide cathodes for sodium storage.

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