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Bimetallic sulfides offer high theoretical specific capacitance and good stability as electrode materials due to their diverse redox reactions, larger specific surface areas, and better conductivity. The morphology of the electrode material is an important influencing factor for the electrochemical properties. Herein, a series of ZnCoS electrode materials with different morphologies were prepared by varying the solvent in the solvothermal reaction, and the effects of different microstructures on the electrochemical properties of ZnCoS were investigated. The ratio of water and ethanol in the solvent was controlled to modulate the microstructure of the as-prepared ZnCoS materials. XRD and XPS revealed the physical and chemical structure of the ZnCoS materials. SEM and TEM observations showed that the microstructure of ZnCoS transformed from one-dimensional wires to two-dimensional sheets with increasing amounts of ethanol. The maximum specific capacitance of the as-prepared ZnCoS materials is 6.22 F cm−2 at a current density of 5 mA cm−2, which is superior to that of most previously reported bimetallic sulfides. The enhanced electrochemical performance could be ascribed to its sheet-assembled spherical structure, which not only shortens the path of ion diffusion but also increases the contact between surface active sites and the electrolyte. Moreover, the spherical structure provides numerous void spaces for buffering the volume expansion and penetration of the electrolyte, which would be favorable for electrochemical reactions. Furthermore, the ZnCoS electrodes were coupled with activated carbon (AC) electrodes to build asymmetric supercapacitors (ASCs). The ASC device exhibits a maximum energy density of 0.124 mWh cm−2 under a power density of 2.1 mW cm−2. Moreover, even under a high-power density of 21 mW cm−2, the energy density can still reach 0.055 mWh cm−2. [ABSTRACT FROM AUTHOR]

Improving zinc metal (Zn0) reversibility and minimizing the N/P ratio are critical to boosting the energy density of Zn0 batteries. However, in reality, an excess Zn source is usually adopted to offset the irreversible zinc loss and guarantee sufficient zinc cycling, which sacrifices the energy density and leads to poor practicability of Zn0 batteries. To address the above conundrum, here, we report a lean‐Zn and hierarchical anode based on metal–organic framework (MOF)‐derived carbon, where trace Zn0 is pre‐reserved within the anode structure to make up for any irreversible zinc source loss. This allows us to construct low N/P ratio Zn0 full cells when coupling the lean‐Zn anode with Zn‐containing cathodes. Impressively, high Zn0 reversibility (average Coulombic efficiency of 99.4% for 3000 cycles) and long full‐cell lifetime (92% capacity retention after 900 cycles) were realized even under the harsh lean‐Zn condition (N/P ratio: 1.34). The excellent Zn reversibility is attributed to the hierarchy structure that homogenizes zinc ion flux and electric field distribution, as confirmed by theoretical simulations, which therefore stabilizes Zn0 evolution. The lean‐Zn anode design strategy will provide new insights into construction of high‐energy Zn0 batteries for practical applications. [ABSTRACT FROM AUTHOR]

To construct high–energy‐density supercapacitors, an electrode material with high conductivity needs to be compounded with an electrode material with high capacitive properties. Herein, NiCo2S4‐β‐cyclodextrin graphene (CDG) composite material formed by growing NiCo2S4 nanoparticles on graphene oxide (GO) modified with β‐Cyclodextrin (β‐CD) is reported. The modification of β‐CD can tackle the problem of agglomeration of GO and acts as a bridge to increase the binding force between NiCo2S4 nanoparticles and substrates. Combining the benefits of the modified GO and NiCo2S4, the synthesized composite electrode exhibits excellent electrochemical properties of 1325.9 F g−1 at 1 A g−1 and rate capability of 55.5% as current density increases from 1 to 7 A g−1. Moreover, the asymmetric device, fabricated with NiCo2S4‐β‐CDG as the positive electrode and active carbon as the negative electrode, exhibits a maximum energy of 30.72 Wh kg−1 at 1.28 kW kg−1 power density. [ABSTRACT FROM AUTHOR]

The commercialization of potassium‐ion batteries requires promising anodes with excellent reversible capacity and cycle stability. Graphite anodes have attracted extensive research owing to the formation of stable intercalation compounds, which also helps to focus attention on low‐cost carbon‐based anodes. However, the slow diffusion of potassium ion (K+) and structural damage of graphite caused by large size may lead to capacity decay. Herein, the modification strategies have been summarized, including microstructure regulation, heteroatom doping and building stable solid electrolyte interphase. And the opportunities and challenges faced by these improvement methods are proposed. Meanwhile, carbon‐based materials used as hosts or conductive carriers to improve the performance of other anodes are also summarized. [ABSTRACT FROM AUTHOR]

Highlights: The traditional and novel etching methods are summarized and compared, especially fluorine-free method. The methods for accelerating exfoliation of Ti3C2Tx are classified. The energy storage mechanisms of Ti3C2Tx in different electrolytes are compared. Based on energy storage mechanisms, the influencing factors of morphology and surface functional groups are discussed. In response to the problems of the Ti3C2Tx, strategies for improving capacitance from structure modulation to composite structure construction are summarized and compared.Ti3C2Tx, a novel two-dimensional layer material, is widely used as electrode materials of supercapacitor due to its good metal conductivity, redox reaction active surface, and so on. However, there are many challenges to be addressed which impede Ti3C2Tx obtaining the ideal specific capacitance, such as restacking, re-crushing, and oxidation of titanium. Recently, many advances have been proposed to enhance capacitance performance of Ti3C2Tx. In this review, recent strategies for improving specific capacitance are summarized and compared, for example, film formation, surface modification, and composite method. Furthermore, in order to comprehend the mechanism of those efforts, this review analyzes the energy storage performance in different electrolytes and influencing factors. This review is expected to predict redouble research direction of Ti3C2Tx materials in supercapacitors. [ABSTRACT FROM AUTHOR]