Potassium‐based energy storage devices (PESDs) are promising candidates for large‐scale energy storage applications owing to potassiums abundant in nature, the low standard redox potential (−2.93 V for K/K+ vs the standard hydrogen electrode) of potassium (K), and high ionic conductivity of K‐ion based electrolytes. However, lack of proper cathode and anode materials hinder practical applications of PESDs. In this work, carbon nanosheets doped with an ultrahigh content of nitrogen (22.7 at%) are successfully synthesized as an anode material for a K‐ion battery, which delivers a high capacity of 410 mAh g−1 at a current density of 500 mA g−1, which is the best result among the carbon based anodes for PESDs. Moreover, the battery exhibits an excellent cycling performance with a capacity retention of 70% after 3000 cycles at a high current density of 5 A g−1. In situ Raman, galvanostatic intermittent titration, and density functional theory calculations reveal that the ultrahigh N‐doped carbon nanosheet (UNCN) simultaneously combines the diffusion and pseudocapacitive mechanisms together, which remarkably improves its electrochemical performances in K‐ion storage. These results demonstrate the good potential of UNCNs as a high‐performance anode for PESDs.

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a b s t r a c tThe theoretical model on the size-dependent thermal conductivity of the nanograins and the composites, based on the phonon confinement and the boundary scattering effects, was developed to predict the 68% reduced thermal conductivity of the nanostructured ceramic coatings made of grains of 40-100 nm compared with the conventional ceramic coatings with micron-scale grains. In order to validate the model, the nanostructured zirconia layers and the corresponding conventional layers were sprayed on the same alloy matrixes, and the insulation temperatures were measured at different temperatures up to 1273 K. It was found that insulation temperature of the nanostructured ceramic systems enhanced about 200 K at most compared with that of the conventional ones. And the average enhancement of the insulation effect is in agreement with the theoretical prediction. The nanostructured ceramic coated systems provide the extending application in thermal barrier engineering, thermoelectric devices and other related applications.