Hybrid supercapacitors are considered the next-generation energy storage equipment due to their superior performance. In hybrid supercapacitors, battery electrodes need to have large absolute capacities while displaying high cycling stability. However, enhancing areal capacity via decreasing the size of electrode materials results in reductions in cycling stability. To balance the capacity–stability trade-off, rationally designed proper electrode structures are in urgent need and still of great challenge. Here we report a high-capacity and high cycling stability electrode material by developing a nickel phosphate lamination structure with ultrathin nanosheets as building blocks. The nickel phosphate lamination electrode material exhibits a large specific capacity of 473.9 C g–1 (131.6 mAh g–1, 1053 F g–1) at 2.0 A g–1 and only about 21% capacity loss at 15 A g–1 (375 C g–1, 104.2 mAh g–1, 833.3 F g–1) in 6.0 M KOH. Furthermore, hybrid supercapacitors are constructed with nickel phosphate lamination and activated carbon (AC), possessing high energy density (42.1 Wh kg–1 at 160 W kg–1) as well as long cycle life (almost 100% capacity retention after 1000 cycles and 94% retention after 8000 cycles). The electrochemical performance of the nickel phosphate lamination structure not only is commensurate with the nanostructure or ultrathin materials carefully designed in supercapacitors but also has a longer cycling lifespan than them. The encouraging results show the great potential of this material for energy storage device applications.

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Manganese oxides composed of various valence states Mn x+ (x = 2, 3, and 4) have attracted wide attention as promising electrode materials for asymmetric supercapacitor. However, the poor electrical conductivity limited their performance and application. Appropriate regulation content of Mn x+ in mixed-valent manganese oxide can tune the electronic structure and further improve their conductivity and performance. Herein, we prepared manganese oxides with different Mn2+/Mn3+ ratios through an over-reduction (OR) strategy for tuning the internal electron structure of mixed-valent manganese, which could make these material oxides a good platform for researching the structure–property relationships. The Mn2+/Mn3+ ratio of manganese oxide could be precisely tuned from 0.6 to 1.7 by controlling the amount of reducing agent for manipulating the redox processes, where the manganese oxide electrode with the most appropriate Mn2+/Mn3+ ratio, as 1.65 (OR4) exhibits large capacitance (274 F g–1) and the assembling asymmetric supercapacitors by combining OR4 (positive) and the commercial activated carbon (as negative) achieved large 2.0 V voltage window and high energy density of 27.7 Wh kg–1 (power density of 500 W kg–1). The cycle lifespan of the OR4//AC could keep about 92.9% after 10 000-cycle tests owing to the Jahn–Teller distortion of the Mn­(III)­O6 octahedron, which is more competitive compared to other work. Moreover, a red-light-emitting diode (LED) can easily be lit for 15 min by two all-solid supercapacitor devices in a series.

Intrinsically poor conductivity and sluggish ion-transfer kinetics limit the further development of electrochemical storage of mesoporous manganese dioxide. In order to overcome the challenge, defect engineering is an effective way to improve electrochemical capability by regulating electronic configuration at the atomic level of manganese dioxide. Herein, we demonstrate effective construction of defects on mesoporous α-MnO2 through simply controlling the degree of redox reaction process, which could obtain a balance between Mn3+/Mn4+ ratio and oxygen vacancy concentration for efficient supercapacitors. The different structures of α-MnO2 including the morphology, specific surface area, and composition are successfully constructed by tuning the mole ratio of KMnO4 to Na2SO3. The electrode materials of α-MnO2-0.25 with an appropriate Mn3+/Mn4+ ratio and abundant oxygen vacancy showed an outstanding specific capacitance of 324 F g–1 at 0.5 A g–1, beyond most reported MnO2-based materials. The asymmetric supercapacitors formed from α-MnO2-0.25 and activated carbon can present an energy density as high as of 36.33 W h kg–1 at 200 W kg–1 and also exhibited good cycle stability over a wide voltage range from 0 to 2.0 voltage (kept at approximately 98% after 10 000 cycles in galvanostatic cycling tests) and nearly 100% Coulombic efficiency. Our strategy lays a foundation for fine regulation of defects to improve charge-transfer kinetics.

Colorless‐to‐black switching has attracted widespread attention for smart windows and multifunctional displays because they are more useful to control solar energy. However, it still remains a challenge owing to the tremendous difficulties in the design of completely reverse absorptions in transmissive and colored states. Herein, we report on an electrochemical device that can switch between colorless and black by using the electrochemical process of hybrid organic–inorganic perovskite MAPbBr3, which shows a high integrated contrast ratio of up to 73% from 400 to 800 nm. The perovskite solution can be used as the active layer to assemble the device, showing superior transmittance over the entire visible region in neutral states. By applying an appropriate voltage, the device undergoes reversible switching between colorless and black, which is attributed to the formation of lead and Br2 in the redox reaction induced by the electron transfer process in MAPbBr3. In addition, the contrast ratio can be modulated over the entire visible region by changing the concentration and the applied voltage. These results contribute toward gaining an insightful understanding of the electrochemical process of perovskites and greatly promoting the development of switchable devices.