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Sodium‐ion capacitors (SICs), designed to attain high energy density, rapid energy delivery, and long lifespan, have attracted much attention because of their comparable performance to lithium‐ion capacitors (LICs), alongside abundant sodium resources. Conventional SIC design is based on battery‐like anodes and capacitive cathodes, in which the battery‐like anode materials involve various reactions, such as insertion, alloying, and conversion reactions, and the capacitive cathode materials usually depend on activated carbon (AC). However, researchers have attempted to construct SICs based on battery‐like cathodes and capacitive anodes or a combination of both in recent years. In this Minireview, charge storage mechanisms and material design strategies for SICs are summarized, with a focus on the battery‐like anode materials from both inorganic and organic sources. Additionally, the challenges in the fabrication of SICs and future research directions are discussed. [ABSTRACT FROM AUTHOR]

Nanocomposites with a well-defined sandwich-like nanostructure were prepared via in situ growing NiCo-layered double hydroxide nanosheets with tunable Ni/Co ratios on reduced graphene oxide (rGO). Electrochemical impedance spectra and N2 adsorption/desorption isotherms confirmed that these sandwich nanostructures effectively promoted charge transport and enlarged the specific surface area. The nanocomposites with Ni : Co = 2 : 1 exhibited a maximum specific capacitance of 2130 F g−1 at 2 A g−1, excellent rate capability (72.7% retention at 15 A g−1), and cycling stability. Asymmetric supercapacitors were assembled with these nanocomposite cathodes and rGO as a negative electrode (anode), and demonstrated an energy density of 34.5 W h kg−1 at a power density of 772 W kg−1, while maintaining a capacity retention of 86.7% after 10 000 cycles at 5 A g−1. The robust electrochemical properties indicate the composites as promising electrodes for electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • An operando crystal-amorphous transformation of VOOH is demonstrated via in-situ / ex-situ structural analyses. • The unique crystal-amorphous transformation allows the obtained amorphous V 2 O 5 to achieve the high capacity, superior rate performance, and high energy and power densities. • The potentiality of cathode materials via operando crystal-amorphous transformation to achieve the enhanced zinc storage is confirmed. Aqueous zinc-ion batteries have obtained broad attention due to their high safety, eco-friendliness, and low cost. However, they are still in the developing stage considering the limited candidate of high-performance cathode materials. Furthermore, the intrinsic storage zinc mechanism is also needed to uncover. Here, we propose an operando crystal-amorphous transformation of tunnel-type VOOH and the obtained amorphous V 2 O 5 serves as a high-performance zinc-ion battery cathode. In-situ X-ray diffraction corroborates the unique operando crystal-amorphous transformation of VOOH during the initial charging process. X-ray photoelectron spectroscopy and transmission electron microscopy further demonstrate the element valence evolution and the lattice structure change, respectively. The operando electrochemical crystal-amorphous transformation allows the obtained amorphous V 2 O 5 to achieve the high capacity of ∼ 350.7 mAh g−1, rate performance (151.2 mAh g−1 at 6.4 A g−1), energy and power densities (137 Wh kg−1 at 6831 W kg−1), unveiling a promising approach of cathode materials via operando crystal-amorphous transformation to achieve the enhanced zinc storage. [ABSTRACT FROM AUTHOR]

NiCoAl layered double hydroxides (NiCoAl-LDHs) with different morphology, structure, size and pseudocapacior properties have been prepared by tuning the ratio of metallic elements via a hydrothermal method. The optimized element proportion of 2D NiCo 2 Al-LDH consisting of hexagonal nanosheets delivers a significantly enhanced specific capacitance 2369.4 F g −1 at a current density of 1 A g −1 . A circle-like growth mechanism is proposed to explain the formation of the 2D NiCo 2 Al-LDH structures. Its 2D structure and the synergistic effect of three metallic elements assure its high electrochemical performance. An asymmetric supercapacitor (ASC) based on NiCo 2 Al-LDH exhibits an ultra-high energy density of 91.0 Wh kg −1 at a power density of 758.2 W kg −1 as well as long-term stability (92% of its initial capacitance retention at 8 A g −1 over 5000 cycles), outperforming most of LDH and metal oxides ASCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new operando non-topological conversion strategy of the ZnIn 2 S 4. • The obtained ZnO@In 2 O 3 as the nickel-zinc battery anode exhibits the enhanced performance. • This work provides a novel strategy to construct high-performance electrode materials. Nickel-zinc batteries have obvious advantages such as high safety, environmental friendship, and high energy density, making them as the most promising alternatives to replace the traditional lead-acid batteries. However, the notorious zinc dendrite issue seriously hinders the development of the nickel-zinc battery. Considering In 2 O 3 can inhibit zinc dendrite effectively, hence it is important to obtain the zinc electrode with uniformly dispersed In 2 O 3. Here, via applying an operando non-topological conversion reaction of ZnIn 2 S 4 , the zinc oxide composite anode with evenly distributed In 2 O 3 can be constructed. Through a series of characterizations such as X-ray diffraction, scanning/transmission electron microscopes, and X-ray photoelectron spectroscopy, the operando non-topological conversion reaction from ZnIn 2 S 4 precursor to ZnO@In 2 O 3 can be directly demonstrated. Meanwhile, as the nickel-zinc battery anode, the obtained ZnO@In 2 O 3 can achieve the high specific capacity (520 mAh g−1), high rate performance, and long cycle stability. This operando non-topological conversion strategy provides a new approach for designing the high-performance electrode materials. [ABSTRACT FROM AUTHOR]

In this work, hierarchical core-shell hollow iron-cobalt sulfides nanoarrays supported on conductive nickel foam (Fe-Co-S/NF) were fabricated using metal-organic frameworks (MOFs) as the sacrificial templates. Delicately manipulating the etching/ion-exchange reaction between Co-MOF and FeSO 4 and the subsequent solvothermal sulfurization led to the formation of hierarchical core-shell hollow nanostructure with FeCo 2 S 4 -nanosheets shell assembled on the Co 3 S 4 hollow nanoarrays. Owing to the complex composition and unique structure, the obtained Fe-Co-S/NF possessed abundant electroactive sites, short charge/ion diffusion path, rich redox reactions and good structural robustness, contributing to the boosted electrochemical performance as supercapacitor electrodes. Consequently, the obtained Fe-Co-S/NF electrode exhibited a specific capacitance of 2695 F g−1 at 1 A g−1, a favorable rate capability with 69.8% capacitance retention at 10 A g−1 (much higher than that of CoS/NF electrode, i.e. , 36.3%), and a retention of 84% over 1000 cycles. Moreover, an asymmetric supercapacitor was assembled by engaging Fe-Co-S/NF and reduced graphene oxide (rGO) as cathode and anode, respectively. The obtained device delivered a high energy density of 43.6 W h kg−1 at a power density of 770 W kg−1, while maintaining a capacity retention of 89.6% after 5000 cycles. The robust electrochemical properties indicate that the Fe-Co-S/NF can be used as promising electrode materials for high performance supercapacitors applications. Image 1 • Unique core-shell hollow iron-cobalt sulfides nanoarrays/nickel foam were fabricated through a novel MOF templated method. • The Fe-Co-S/NF had a high specific capacitance of 2695 F g−1 at a current density of 1 A g−1. • The assembled asymmetric supercapacitor achieved a high energy density of 43.6 W h kg−1 at a power density of 770 W kg−1. • The assembled asymmetric supercapacitor retained 89.6% of its capacitance over 5000 cycles. [ABSTRACT FROM AUTHOR]