Tremendous efforts have been dedicated into the development of high‐performance energy storage devices with nanoscale design and hybrid approaches. The boundary between the electrochemical capacitors and batteries becomes less distinctive. The same material may display capacitive or battery‐like behavior depending on the electrode design and the charge storage guest ions. Therefore, the underlying mechanisms and the electrochemical processes occurring upon charge storage may be confusing for researchers who are new to the field as well as some of the chemists and material scientists already in the field. This review provides fundamentals of the similarities and differences between electrochemical capacitors and batteries from kinetic and material point of view. Basic techniques and analysis methods to distinguish the capacitive and battery‐like behavior are discussed. Furthermore, guidelines for material selection, the state‐of‐the‐art materials, and the electrode design rules to advanced electrode are proposed.

the LIBs. Considerable improvements in the design and optimization of anode composition and structure are still required.This note reports our design and implementation of a SnS 2based nanocomposite anode for the NIBs. SnS 2 has a CdI 2 -type of layered structure (a = 0.3648 nm, c = 0.5899 nm, space group P3m1) consisting of a layer of tin atoms sandwiched between two layers of hexagonally close packed sulfur atoms. This layered structure with a large interlayer spacing (c = 0.5899 nm) should easy the insertion and extraction of guest species and adapt more easily to the volume changes in the host during cycling. This has been confi rmed by the performance of SnS 2 as a reversible lithium storage host in several studies. [ 17 ] The electrochemical properties of layered sulfi des (SnS 2 , MoS 2 , WS 2 ) were further improved by integration with graphene. The structural compatibility between the two layered compounds and the good electronic properties of graphene led to very stable composites (i.e. long cycle-life) with high reversible capacity and good rate performance in LIB applications. [ 18 ] The SnS 2 layer structure should also be viable for reversible Na + storage since, in comparison with tin and other tin-based materials, it has the largest buffer for the volume changes in Na-Sn reactions. The LIB developmental efforts also suggest layer-structured SnS 2reduced graphene oxide (SnS 2 -RGO) nanocomposites as an improved version of the SnS 2 anode.The design of the SnS 2 -RGO hybrid structure for reversible storage of Na + was based on the following materials principles: 1) a large interlayer spacing in the SnS 2 structure benefi ting Na + intercalation and diffusion, and more buffering space for benefi cial adjustment the volume changes in the host during cycling; 2) fast collection and conduction of electrons through a highly conductive RGO network; and 3) inhibition of Sn (Na x Sn) aggregation during cycling by RGO after material hybridization. The experimental results validated the expectations: the SnS 2 -RGO anode delivered a high charge (desodiation) specifi c capacity of 630 mAh g −1 at 0.2 A g −1 , and more impressively, 544 mAh g −1 after a ten-fold increase in current density to 2 A g −1 . The electrode was also very stable to cycling; providing a nearly unvarying capacity of 500 mAh g −1 at 1 A g −1 even after 400 charge-discharge cycles.The SnS 2 -RGO nanocomposite was produced by a facile hydrothermal route from a mixture of tin (IV) chloride, thioacetamide (TAA) and graphene oxide (GO) (details in the Experimental Section). In the comparison of the X-ray diffraction (XRD) patterns of the SnS 2 -RGO composite, SnS 2 and GO in Figure 1 a, GO only displayed a single diffraction peak at 10.9° from the (002) planes. [ 19 ] The powder XRD patterns of SnS 2 and The idea of sodium-ion batteries (NIBs) as a substitute of lithium-ion batteries (LIBs) for grid-scale energy storage was initially driven by cost considerations. [ 1 ] Research in the last several years has shown that NIBs are not necessar...

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Water splitting is one of the ideal technologies to meet the ever increasing demands of energy. Many materials have aroused great attention in this field. The family of nickel-based sulfides is one of the examples that possesses interesting properties in water-splitting fields. In this paper, a controllable and simple strategy to synthesize nickel sulfides was proposed. First, we fabricated NiS hollow microspheres via a hydrothermal process. After a precise heat control in a specific atmosphere, NiS porous hollow microspheres were prepared. NiS was applied in hydrogen evolution reaction (HER) and shows a marvelous performance both in acid medium (an overpotential of 174 mV to achieve a current density of 10 mA/cm and the Tafel slope is only 63 mV/dec) and in alkaline medium (an overpotential of 148 mV to afford a current density of 10 mA/cm and the Tafel slope is 79 mV/dec). NiS was used in oxygen evolution reaction (OER) showing a low overpotential of 320 mV to deliver a current density of 10 mA/cm, which is meritorious. These results enlighten us to make an efficient water-splitting system, including NiS as HER catalyst in a cathode and NiS as OER catalyst in an anode. The system shows high activity and good stabilization. Specifically, it displays a stable current density of 10 mA/cm with the applying voltage of 1.58 V, which is a considerable electrolyzer for water splitting.

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Nonaqueous rechargeable lithium–oxygen batteries (LOBs) are one of the most promising candidates for future electric vehicles and wearable/flexible electronics. However, their development is severely hindered by the sluggish kinetics of the ORR and OER during the discharge and charge processes. Here, we employ MOF-assisted spatial confinement and ionic substitution strategies to synthesize Ru single atoms riveted with nitrogen-doped porous carbon (Ru SAs-NC) as the electrocatalytic material. By using the optimized Ru0.3 SAs-NC as electrocatalyst in the oxygen-breathing electrodes, the developed LOB can deliver the lowest overpotential of only 0.55 V at 0.02 mA cm–2. Moreover, in-situ DEMS results quantify that the e–/O2 ratio of LOBs in a full cycle is only 2.14, indicating a superior electrocatalytic performance in LOB applications. Theoretical calculations reveal that the Ru–N4 serves as the driving force center, and the amount of this configuration can significantly affect the internal affinity of intermediate species. The rate-limiting step of the ORR on the catalyst surface is the occurrence of 2e– reactions to generate Li2O2, while that of the OER pathway is the oxidation of Li2O2. This work broadens the field of vision for the design of single-site high-efficiency catalysts with maximum atomic utilization efficiency for LOBs.

Conductive polymer hydrogels are receiving considerable attention in applications such as soft robots and human-machine interfaces. Herein, a transparent and highly ionically conductive hydrogel that integrates sensing, UV-filtering, water-retaining, and anti-freezing performances is achieved by the organic combination of tannic acid-coated hydroxyapatite nanowires (TA@HAP NWs), polyvinyl alcohol (PVA) chains, ethylene glycol (EG), and metal ions. The highly ionic conductivity of the hydrogel enables tensile strain, pressure, and temperature sensing capabilities. In particular, in terms of the hydrogel strain sensors based on ionic conduction, it has high sensitivity (GF = 2.84) within a wide strain range (350%), high linearity (R 2 = 0.99003), fast response (≈50 ms) and excellent cycle stability. In addition, the incorporated TA@HAP NWs act as a nano-reinforced filler to improve the mechanical properties and confer a UV-shielding ability upon the hydrogel due to its size effect and the characteristics of absorbing ultraviolet light waves, which can reflect and absorb short ultraviolet rays and transmit visible light. Meanwhile, owing to the water-locking effect between EG and water molecules, the hydrogel exhibits freezing resistance at low temperatures and moisture retention at high temperatures. This biocompatible and multifunctional conductive hydrogel provides new ideas for the design of novel ionic skin devices.

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