Two-dimensional (2D) hydroxide nanosheets can exhibit exceptional electrochemical performance owing to their shortened ion diffusion distances, abundant active sites, and various valence states. Herein, we report ZnCo(OH)Cl·0.45HO nanosheets (thickness ∼30 nm) which crystallize in a layered structure and exhibit a high specific capacitance of 3946.5 F g at 3 A g for an electrochemical pseudocapacitor. ZnCo(OH)Cl·0.45HO was synthesized by a homogeneous precipitation method and spontaneously crystallized into 2D nanosheets in well-defined hexagonal morphology with crystal structure revealed by synchrotron X-ray powder diffraction data analysis. In situ growth of ZnCo(OH)Cl·0.45HO nanosheet arrays on conductive Ni foam substrate was successfully realized. Asymmetric supercapacitors based on ZnCo(OH)Cl·0.45HO nanosheets @Ni foam// PVA, KOH//reduced graphene oxide exhibits a high energy density of 114.8 Wh kg at an average power density of 643.8 W kg, which surpasses most of the reported all-solid-state supercapacitors based on carbonaceous materials, transition metal oxides/hydroxides, and MXenes. Furthermore, a supercapacitor constructed from ZnCo(OH)Cl·0.45HO nanosheets@PET substrate shows excellent flexibility and mechanical stability. This study provides layered bimetallic hydroxide nanosheets as promising electroactive materials for flexible, solid-state energy storage devices, presenting the best reported performance to date.

Hierarchical nanostructures with highly exposed active surfaces for high‐performance pseudocapacitors have attracted considerable attention. Herein, a one‐step growth of (Ni xCo1−x)9Se8 solid solution series in various conductive substrates as advanced electrodes for flexible, foldable supercapacitors is developed. The formation of (NixCo1−x)9Se8 solid solution is confirmed by Vegard's law. Interestingly, the as‐grown (NixCo1−x)9Se8 solid solution series spontaneously crystallized into nanodendrite arrays with hierarchical morphology and fractal feature. The optimized (Ni0.1Co0.9)9Se8 nanodendrites deliver a specific capacitance of 3762 F g−1 at a current density of 5 A g−1 and remains 94.8% of the initial capacitance after 5000 cycles, owing to the advantage from fractal feature with numerous exposed () surface as well as fast ion diffusion. The as‐assembled flexible (Ni0.1Co0.9)9Se8@carbon fiber cloth (CFC)//PVA/KOH//reduced graphene oxide@CFC device exhibits an ultrahigh energy density of 17.0 Wh kg−1@ 3.1 kW kg−1, outperforming recently reported pseudocapacitors based on nickel‐cobalt sulfide and selenide counterparts. This study provides rational guidance toward the design of fractal feature with superior electrochemical performances due to the significantly increased electrochemical active sites. The resulting device can be easily folded, pulled, and twisted, enabling potential applications in high‐performance wearable and gadget devices.

Two-dimensional LDH nanosheets recently have generated considerable interest in various promising applications because of their intriguing properties. Herein, we report a facile in situ nucleation strategy toward in situ decorating monodispersed Ni-Fe LDH ultrafine nanosheets (UNs) on graphene oxide template based on the precise control and manipulation of LDH UNs anchored, nucleated, grown, and crystallized. Anion-exchange behavior was observed in this Ni-Fe LDH UNs@rGO composite. The Ni-Fe LDH UNs@rGO electrodes displayed a significantly enhanced specific capacitance (2715F g at 3 A g) and energy density (82.3 Wh kg at 661 W kg), which exceeds the energy densities of most previously reported nickel iron oxide/hydroxides. Moreover, the asymmetric supercapacitor, with the Ni-Fe LDH UNs @rGO composite as the positive electrode material and reduced graphene oxide (rGO) as the negative electrode material, exhibited a high energy density (120 Wh kg ) at an average power density of 1.3 kW kg. A charge transfer from LDH layer to graphene layer, which means a built in electric field directed from LDH to graphene can be established by DFT calculations, which can significantly accelerate reaction kinetics and effectively optimize the capacitive energy storage performance.

The realization of high-performance anode materials with high capacity at fast lithiation kinetics and excellent cycle stability remains a significant but critical challenge for high-power applications such as electric vehicles. Two-dimensional nanostructures have attracted considerable research interest in electrochemical energy storage devices owing to their intriguing surface effect and significantly decreased ion-diffusion pathway. Here we describe rationally designed metastable CoSeO·HO nanosheets synthesized by a facile hydrothermal method for use as a Li ion battery anode. This crystalline nanosheet can be steadily converted into amorphous phase at the beginning of the first Li discharge cycling, leading to ultrahigh reversible capacities of 1100 and 515 mAh g after 1000 cycles at a high rate of 3 and 10 A g, respectively. The as-obtained amorphous structure experiences an isotropic stress, which can significantly reduce the risk of fracture during electrochemical cycling. Our study offers a precious opportunity to reveal the ultrafast lithiation kinetics associated with the rapid amorphization mechanism in layered cobalt selenide nanosheets.

Core-shell structured nanohybrids are currently of significant interest due to their synergetic properties and enhanced performances. However, the restriction of lattice mismatch remains a severe obstacle for heterogrowth of various core-shells with two distinct crystal structures. Herein, a controlled synthesis of lattice-mismatched core-shell TiO2 @MoS2 nano-onion heterostructures is successfully developed, using unilamellar Ti0.87 O2 nanosheets as the starting material and the subsequent epitaxial growth of MoS2 on TiO2 . The formation of these core-shell nano-onions is attributed to an amorphous layer-induced heterogrowth mechanism. The number of MoS2 layers can be well tuned from few to over ten layers, enabling layer-dependent synergistic effects. The core-shell TiO2 @MoS2 nano-onion heterostructures exhibit significantly enhanced energy storage performance as lithium-ion battery anodes. The approach has also been extended to other lattice-mismatched systems such as TiO2 @MoSe2 , thus suggesting a new strategy for the growth of well-designed lattice-mismatched core-shell structures.