An “acetonitrile/water in salt” electrolyte with non-flammability, high conductivity, a high stability window and a wide applicable temperature range enables high-performance supercapacitors.

Water-in-salt" (WIS) electrolytes with wide electrochemical stability windows (ESWs) have made a breakthrough in energy density of aqueous batteries and supercapacitors (SCs), but the sluggish ion diffusion limits their widespread application. Although the ion diffusion of WIS electrolytes can be improved by the addition of organic co-solvents, the effects of types and amounts of added organic solvents on the physicochemical properties of hybrid electrolytes are not clear. Here, the conductivity, ESW, and flammability of a series of hybrid electrolytes prepared by adding different organic solvents to a typical lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-based WIS electrolyte are systematically studied. The results show that acetonitrile (ACN) is the best one to improve ion diffusion while maintaining high-level safety and wide ESW. Furthermore, a ternary phase diagram of LiTFSI/H 2 O/ACN is drawn to comprehensively show the relationship among the conductivity, flammability, and solubility of the hybrid electrolytes. According to the guidance of this phase diagram, an optimal hybrid electrolyte (LiTFSI/H 2 O/(ACN) 3.5 ) is obtained, and the carbon-based symmetric SC using such hybrid electrolyte is able to fully work at 2.4 V with superior rate capability and excellent cycling stability over 40 000 cycles.

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Anion exchange membrane fuel cells (AEMFCs) performance have significantly improved in the last decade (>1 W cm−2), and is now comparable with that of proton exchange membrane fuel cells (PEMFCs). At high current densities, issues in the catalyst layer (CL, composed of catalyst and ionomer), like oxygen transfer, water balance, and microstructural evolution, play important roles in the performance. In addition, CLs for AEMFCs have different requirements than for PEMFCs, such as chemical/physical stability, reaction mechanism, and mass transfer, because of different conductive media and pH environment. The anion exchange ionomer (AEI), which is the soluble or dispersed analogue of the anion exchange membrane (AEM), is required for hydroxide transport in the CL and is normally handled separately with the electrocatalyst during the electrode fabrication process. The importance of the AEI–catalyst interface in maximizing the utilization of electrocatalyst and fuel/oxygen transfer process must be carefully investigated. This review briefly covers new concepts in the complex AEMFC catalyst layer, before a detailed discussion on advances in CLs based on the design of AEIs and electrocatalysts. The importance of the structure–function relationship is highlighted with the aim of directing the further development of CLs for high‐performance AEMFC.

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Electrochemical quartz crystal microbalance (EQCM) can be used to study the charge storage mechanisms of supercapacitors because of its excellent accuracy in mass change, and a homogeneous and ultrathin sample coating is strongly required for accurate measurement. However, it is difficult to obtain such a coating by the frequently used methods. Here a vacuum filtration‐and‐transfer (VFT) technique is reported to achieve this target. To prove the universality of this method, six materials with different dimensions are selected as research objects, and they are prepared into test films on quartz by VFT method and well‐used spray method for EQCM measurements, respectively. The results show that the VFT method can eliminate the influence caused by inhomogeneity of the films, which is beneficial for clearly distinguishing the rigid model from the viscoelastic model. This method helps EQCM to reflect more precise quality change as well as deformation of the material itself. Consequently, it makes EQCM more reliable to describe the energy storage mechanisms of various electrode materials.

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The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201905838. Recently, a new class of aqueous electrolytes named "waterin-salt (WiS)" formulated with superconcentrated lithium salts Dual ion batteries (DIBs) have recently attracted ever-increasing attention owing to the potential advantages of low material cost and good environmental friendliness. However, the potential safety hazards, cost, and environmental concerns mainly resulted from the commonly used nonaqueous organic solvents severely hinder the practical application of DIBs. Herein, a hybrid aqueous/nonaqueous water-in-bisalt electrolyte with both broad electrochemical stability window and excellent safety performance is developed. The lithium-based DIB assembled using KS6 graphite and niobium pentoxide as the active materials in the cathode and anode exhibits good comprehensive performance including capacity, cycling stability, rate performance, and medium discharge voltage. Initial capacities of ≈47.6 and 29.6 mAh g −1 retention after 300 cycles can be delivered with a medium discharge voltage of around 2.2 V in the voltage window of 0-3.2 V at the current density of 200 mA g −1 . Good rate performance for the battery can be indicated by 29.7 mAh g −1 discharge capacity retention at 400 mA g −1 . It is noteworthy that the coulombic efficiency of the battery can reach as high as 93.9%, which is comparable to that of the corresponding DIBs using nonaqueous organic electrolytes.www.advancedsciencenews.com