Vertically aligned nickel-cobalt oxide (NCO) nanosheets with porous structure were successfully synthesized on FTO substrates by a simple electrochemical method without any templates. Cyclic voltammetry (CV) and galvanostatic charge/discharge measurements show that the porous NCO nanosheets have an ideal capacitive performance and long-term stability. With an optimum amount of Ni, the specific capacitance for the NCOs could reach as high as 453 F g À1 at a scan rate of 5 mV s À1 and 506 F g À1 at a current density of 1 A g À1 , showing an improvement of around 50% compared with cobalt oxide. Furthermore, a symmetric supercapacitor based on two NCO electrodes exhibits a maximum specific capacitance of 89.2 F g À1 at 0.17 A g À1 .

Vanadium oxides (VOx) have been intensely investigated as cathode materials for SCs due to the multiple stable oxidation states (III–V) of vanadium in its oxides and typical layered structure. Nevertheless, fast capacity fading is always observed for VOx upon cycling in aqueous electrolyte. Developing an efficient strategy to essentially promote the durability of VOx in mild aqueous electrolyte remains a crucial challenge. Here, an innovative and effective method is reported to significantly boost the durability and capacitance of VOx through tuning the valence state of vanadium. The valence state of vanadium is optimized through a very facile electrochemical oxidation method. A superior electrochemical performance and an ultralong cyclic stability of 100 000 cycles are obtained for these electrodes. An in‐depth study on the variation for the valence state of vanadium during the oxidation process and the cyclic stability test indicates that the long cyclic stability has an important relationship with the distribution of the valence state of vanadium.

The use of electrode materials in their powdery form requires binders and conductive additives for the fabrication of the cells, which leads to unsatisfactory energy storage performance. Recently, a new strategy to design flexible, binder-, and additive-free three-dimensional electrodes with nanoscale surface engineering has been exploited in boosting the storage performance of electrode materials. In this paper, we design a new type of free-standing carbon quantum dot coated VO2 interwoven nanowires through a simple fabrication process and demonstrate its potential to be used as cathode material for lithium and sodium ion batteries. The versatile carbon quantum dots that are vastly flexible for surface engineering serve the function of protecting the nanowire surface and play an important role in the diffusion of electrons. Also, the three-dimensional carbon cloth coated with VO2 interwoven nanowires assisted in the diffusion of ions through the inner and the outer surface. With this unique architecture, the carbon quantum dot nanosurface engineered VO2 electrode exhibited capacities of 420 and 328 mAh g(-1) at current density rate of 0.3 C for lithium and sodium storage, respectively. This work serves as a milestone for the potential replacement of lithium ion batteries and next generation postbatteries.

Employing high-rate ion-intercalation electrodes represents a feasible way to mitigate the inherent trade-off between energy density and power density for electrochemical energy storage devices, but efficient approaches to boost the charge-storage kinetics of electrodes are still needed. Here, we demonstrate a water-incorporation strategy to expand the interlayer gap of α-MoO 3 , in which water molecules take the place of lattice oxygen of α-MoO 3 . Accordingly, the modified α-MoO 3 electrode exhibits theoretical-value-close specific capacity (963 C g −1 at 0.1 mV s −1 ), greatly improved rate capability (from 4.4% to 40.2% at 100 mV s −1 ) and boosted cycling stability (from 21 to 71% over 600 cycles). A fast-kinetics dual-ion-intercalation energy storage device is further assembled by combining the modified α-MoO 3 anode with an anion-intercalation graphite cathode, operating well over a wide discharge rate range. Our study sheds light on a promising design strategy of layered materials for high-kinetics charge storage.

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