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The ever-increasing demand for flexible and portable electronics has stimulated research and development in building advanced electrochemical energy devices which are lightweight, ultrathin, small in size, bendable, foldable, knittable, wearable, and/or stretchable. In such flexible and portable devices, semi-solid/solid electrolytes besides anodes and cathodes are the necessary components determining the energy/power performances. By serving as the ion transport channels, such semi-solid/solid electrolytes may be beneficial to resolving the issues of leakage, electrode corrosion, and metal electrode dendrite growth. In this paper, the fundamentals of semi-solid/solid electrolytes (e.g., chemical composition, ionic conductivity, electrochemical window, mechanical strength, thermal stability, and other attractive features), the electrode-electrolyte interfacial properties, and their relationships with the performance of various energy devices (e.g., supercapacitors, secondary ion batteries, metal-sulfur batteries, and metal-air batteries) are comprehensively reviewed in terms of materials synthesis and/or characterization, functional mechanisms, and device assembling for performance validation. The most recent advancements in improving the performance of electrochemical energy devices are summarized with focuses on analyzing the existing technical challenges (e.g., solid electrolyte interphase formation, metal electrode dendrite growth, polysulfide shuttle issue, electrolyte instability in half-open battery structure) and the strategies for overcoming these challenges through modification of semi-solid/solid electrolyte materials. Several possible directions for future research and development are proposed for going beyond existing technological bottlenecks and achieving desirable flexible and portable electrochemical energy devices to fulfill their practical applications. It is expected that this review may provide the readers with a comprehensive cross-technology understanding of the semi-solid/solid electrolytes for facilitating their current and future researches on the flexible and portable electrochemical energy devices.

Ion exchange membranes (IEMs) play important roles in energy generation and storage field, such as fuel cell, flow battery, however, a major barrier in the way of large-scale application is the high cost of membranes (e.g., Nafion membranes price generally exceeds USD$ 200 m -2 ). The membrane-less technology is one of the promising approaches to solve the problem and thus has attracted much attention and been explored in a variety of research paths. This review introduces one of the representative membrane-less battery types, Biphasic membrane-less redox batteries that eliminate the IEMs according to the principle of solvent immiscibility and realizes the phase splitting in a thermodynamically stable state. It is systematically classified and summarizes their performances as well as the problems they are suffering from, and then several effective solutions are proposed based on the modification of electrodes and electrolytes. Finally, special attention is given to the challenges and prospects of Biphasic membrane-less redox batteries, which could contribute to the development of membrane-less batteries., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

The catalyst‐reconstruction makes it challenging to clarify the practical active sites and unveil the actual reaction mechanism during the CO2 electroreduction reaction (CO2RR). However, currently the impact of the electrolyte microenvironment in which the electrolyte is in contact with the catalyst is overlooked and might induce a chemical evolution, thus confusing the reconstruction process and mechanism. In this work, the carbonate adsorption properties of metal oxides were investigated, and the mechanism of how the electrolyte carbonate affect the chemical evolution of catalysts were discussed. Notably, Bi2O3 with weak carbonate adsorption underwent a chemical reconstruction to form the Bi2O2CO3/Bi2O3 heterostructure. Furthermore, in situ and ex situ characterizations unveiled the formation mechanism of the heterostructure. The in situ formed Bi2O2CO3/Bi2O3 heterostructure with strong electron interaction served as the highly active structure for CO2RR, achieving a formate Faradaic efficiency of 98.1 % at −0.8 Vvs RHE. Theoretical calculations demonstrate that the significantly tuned p‐orbit electrons of the Bi sites in Bi2O2CO3/Bi2O3 optimized the adsorption of the intermediate and lowered the energy barrier for the formation of *OCHO. This work elucidates the mechanism of electrolyte microenvironment for affecting catalyst reconstruction, which contributes to the understanding of reconstruction process and clarification of the actual catalytic structure. [ABSTRACT FROM AUTHOR]

With more renewable energy developed to satisfy the human need in the energy crisis, electricity storage is critical in power utilization and storage. Due to its high safety, high nature reserve, and high energy density, the zinc‐based battery is drawing increasing attention. Together with the expansion of human activities, the low‐temperature battery is developed to satisfy the power demand in extreme environments, and as a critical component, electrolytes shall have a low freezing point and satisfying electrochemical properties in cold conditions. In this review, the development of low‐temperature electrolytes for zinc‐based batteries will be comprehensively introduced. First, the failure mechanism of zinc‐based battery at low temperature will be illustrated. Second, five main types of low‐temperature electrolytes will be introduced in detail. Finally, the regulation of electrolyte/electrode surface at low temperature will be discussed. This review aims to provide a guideline for low‐temperature electrolyte design from the perspective of molecular behavior regulation. [ABSTRACT FROM AUTHOR]

The electrolyte carbonation and the resulting air electrode plugging are the primary factors limiting the cycle life of aqueous alkaline zinc–air batteries (ZABs). In this work, calcium ion (Ca2+) additives were introduced into the electrolyte and the separator to resolve the above issues. Galvanostatic charge–discharge cycle tests were carried out to verify the effect of Ca2+ on electrolyte carbonation. With the modified electrolyte and separator, the cycle life of ZABs was improved by 22.2% and 24.7%, respectively. Ca2+ was introduced into the ZAB system to preferentially react with CO32− rather than K+ and then precipitated granular CaCO3 prior to K2CO3, which was deposited on the surface of the Zn anode and air cathode to form a flower-like CaCO3 layer, thereby prolonging its cycle life. [ABSTRACT FROM AUTHOR]

The advent of wearable electronics has strongly stimulated advanced research into the exploration of flexible zinc−air batteries (ZABs) with high theoretical energy density, high inherent safety, and low cost. However, the half‐open battery structure and the high concentration of alkaline aqueous environment pose great challenges on the electrolyte retention capability and the zinc anode stability. Herein, a starch‐based superabsorbent hydrogel polymer electrolyte (SSHPE) with high ionic conductivity, electrolyte absorption and retention capabilities, strong alkaline resistance and high zinc anode stability has been designed and applied in ZABs. Experimental and calculational analyses probe into the root of the superiority of SSHPEs, confirming the significance of the carboxyl functional groups along their polymer chains. These features endow the as‐fabricated ZAB a long cycle life of 300 h, much longer than that with commonly used poly(vinyl alcohol)‐based electrolyte. [ABSTRACT FROM AUTHOR]

Hydrogen evolution reaction and dendrite growth seriously break the Zn plating/stripping process at the electrolyte/electrode interface, causing the instability of the Zn anode of aqueous zinc ion batteries. To improve the Zn anode stability and reversibility, we report a new electrolyte additive of aqueous electrolyte with the hydrophobic group. This interfacial hydrophobicity maximises the exclusion of free water from the Zn anode surface, which blocks water erosion and reduces interfacial side reactions. Thus, in an optimal 2 M ZnSO4 electrolyte with 2 g·L−1 Tween-85, the hydrogen evolution reaction and other water-induced undesired reactions can be suppressed, which greatly improves the cycling stability and Coulombic efficiency (CE) of Zn plating/stripping process. The stable cycle time of the Zn//Zn symmetric battery reaches over 1300 h, especially at a high current density and a high areal capacity (more than 650 h at 5 mA·cm−2, 5 mAh·cm−2). The average Coulomb efficiency (CE) of Zn//Ti asymmetric cell achieves 98.11% after 300 cycles. The capacity retention rate of Zn//MnO2 full battery is up to 88.6% after 1000 cycles. [ABSTRACT FROM AUTHOR]

Mg‐air batteries are a promising new generation of batteries because they can operate in neutral electrolytes that are safe and nontoxic. However, the high corrosion and low utilization of Mg anodes in Mg‐air batteries result in low specific capacity and severe self‐discharge. In this study, an Mg(OTf)2‐based aqueous electrolyte is developed, which addresses these issues by reducing the contact of the Mg anode with water molecules from the hydrophobic −CF3 groups and forming an MgF2 protective layer. The assembled Mg‐air batteries exhibit specific capacities of up to 1920 mAh g−1Mg (87.32 % utilization based on the Mg anode). In addition, the resting time of the corresponding Mg‐air batteries was 123 times longer than that of Mg‐air batteries with pure NaCl electrolytes under the same conditions. [ABSTRACT FROM AUTHOR]

The application of NaCl-based aluminum-air batteries is limited due to the passivation of the aluminum anode. In an effort to solve this problem, this work studied the influence of different concentrations of Ga3+ additives on the discharge behavior of Al in the NaCl electrolyte. The results of both experiments and theoretical calculations have shown that commercial purity aluminum could be significantly activated by Ga3+. Based on microstructure observations and electrochemical impedance spectroscopy, the influence activation mechanism of Ga3+ on the discharge behavior of commercial purity Al is clarified. The addition of Ga3+ biased the surface charge of aluminum along the activation direction, forming activation sites, and then destroyed the surface passivation film. Due to the formation of a gallium–aluminum amalgam, the Al-air battery had the best discharge characteristics in the electrolyte with 0.2 M Ga3+, and its discharge voltage reached 0.9734 V with a remarkable increase compared with that of NaCl solution (0.4228 V). Therefore, Ga3+ additive is a promising choice for NaCl-based Al-air batteries to improve their discharge voltage. [ABSTRACT FROM AUTHOR]

The development of flexible zinc–air battery (ZAB) is highly desirable in achieving superior and stable electrochemical/mechanical properties. Herein, we developed a Zn‐coated foam anode with three‐dimensional (3D) architecture, obtained by electroplating Zn on Cu foam substrate. The compact outer surface and sufficient amount of metallic Zn could be controlled accurately by selecting appropriate porous substrate and electroplating time on Cu foam. Moreover, adding tetraethylammonium hydroxide (TEAOH) to conventional polyvinyl alcohol (PVA)–KOH hydrogel electrolyte effectively improved the water retention of the semi‐solid electrolyte with stable ionic conductivity. The electrolyte precursor fluid was poured on the uneven outer surface of Zn‐coated foam anode and then frozen crosslinked to increase contact between the 3D anode and the electrolyte. A flexible semi‐solid‐state ZAB based on the 3D Zn‐coated foam anode and the hydrogel electrolyte was assembled and exhibited good discharge performance, high energy density (586.5 Wh kgZn−1) and long cycling life. Benefiting from the flexibility of all components, the resultant ZAB performed stable charge and discharge under bending conditions, indicating its promising potential application for flexible and portable energy storage devices. [ABSTRACT FROM AUTHOR]

Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references). [ABSTRACT FROM AUTHOR]

Abstract: Submicron-sized cuprous oxide crystallites was prepared by electrodeposition, and polyethylene glycol (PEG) was introduced to improve the dispersity of crystallites. Transmission electron microscopy (TEM) and scanning electronic microscopy (SEM) were applied to characterize its crystal structure and morphology. Based on the analysis, it was found that PEG can affect the growth mode of cuprous oxide crystallites, which improves of the dispersity of the crystallites. The growth of cuprous oxide crystallites without PEG presents obvious aggregation dominant, while diffusion becomes the dominant mechanism when PEG is introduced into the electrolyte. The photo transmission character of cuprous oxide crystallites was measured by UV–vis spectrophotometer, and the calculated band gap energy of which is approximately 2.17eV. The photoelectrochemical property of the crystallites was also characterized with the current–potential responses to a linear potentiodynamic scan under chopped illumination, and it is found that the photocurrent of the cuprous oxide crystallites electrodeposited with PEG is obviously larger than the one without PEG. [Copyright &y& Elsevier]

Keywords: characterization methods; electrolytes; in situ; lithium-ion batteries; silicon-based anodes The development of characterization methods is anticipated to greatly promote the upgrade of high-performance lithium-ion batteries (LIB) based on silicon (Si)-based anodes. Characterization methods, electrolytes, in situ, lithium-ion batteries, silicon-based anodes. [Extracted from the article]

With the remarkably large theoretical specific capacity of silicon (Si), Si‐based rechargeable lithium‐ion batteries (LIBs) have attracted great interest, as they are expected to meet the growing demand for large‐scale energy storage devices, electric vehicles, and portable electronic devices with high energy density. However, the Si‐based LIB faces great challenges due to the cyclic volume changes induced by Si, which lead to considerable capacity fading. To facilitate the use of high‐performance LIBs enabled by Si‐based anodes, understanding the fading mechanism is necessary. In this regard, various advanced characterization methods have been developed to reveal the fading mechanism and to develop a modification strategy associated with compositional and structural evolution. In this review, the general understanding of the fading mechanism and the technical specifications of Si‐based LIBs are discussed. The recent progress in advanced characterization methods for Si‐based LIBs is summarized with respect to the achievements in compositional and structural interpretation. Several possible future research directions for Si‐based LIBs and the expected development trends in relevant characterization methods are also discussed. [ABSTRACT FROM AUTHOR]

Flexible Zn‐based batteries are emerging candidates for wearable electronics owing to the natural merits of zinc, such as environmental friendliness and low cost. In article number 1802605 by Cheng Zhong, Jun Lu, and co‐workers, the challenges of developing flexible Li‐ion batteries are presented. Thereafter, a brief overview of recent progress in the development of flexible Zn‐based rechargeable batteries from the perspective of energy density, rechargeability, flexible electrolytes, and some other issues that remain to be addressed, are highlighted. [ABSTRACT FROM AUTHOR]

Aluminum-air battery (AAB) with NaCl-based electrolyte exhibits great application potential owing to wide source, high safety, and low cost of the electrolyte. However, the passivation film generated on Al anode surface restricts its continuous dissolution during discharge process. Herein, oxidant additives (FeCl 3 or KMnO 4) are introduced into NaCl-based electrolyte to enhance activity of Al anode as well as the discharge performance of the battery. A significant increase in the discharge voltage is observed, reaching 1.18V with FeCl 3 and 1.15V with KMnO 4 , considerably higher than the voltage of 0.56V observed in electrolytes without additives. The strong oxidizing properties of these additives promote the dissolution reaction of the Al anode through substitution reactions, resulting in the rupture of the passivation film. In addition, MnO 2 is also generated in the case with KMnO 4 , and then gathers on the surface of Al anode to hinder the discharge reaction, especially for the case with excessive additive. This work explores the effect of oxidant additive on enhancing activation property of Al anode, and provides a guidance of additive choosing in near-neutral electrolyte for AAB. [Display omitted] • The discharge voltage was improved up to 1.18V in the case with FeCl 3. • The dissolution reaction of Al anode was promoted owing to the oxidizing property. • Discharge process was hindered due to enriched by-product in the case with KMnO 4. [ABSTRACT FROM AUTHOR]

Aqueous secondary Zn–Ni batteries have attracted extensive attention as a potential candidate to meet the increasing demand for energy storage device since they are environmental friendly and can provide inherent safety, high energy density and power density. However, the uneven deposition, passivation and corrosion of ZnO anode severely reduce the cycling life of the battery. Herein, tetraethylammonium bromide (TEAB) and polyethylene oxide (PEO) are introduced into the battery as electrolyte additives. The Zn–Ni battery achieves an excellent cycling life of 450 h since the additives provide more reduction sites and hinder the formation of dead zinc. In addition, the electrolyte additives can also reduce the corrosion current density of the anode and maintain the stable cycle of the battery under floating charge mode for more than 40 days. These results confirm the great practical application potential of aqueous Zn–Ni battery. • Tetraethylammonium bromide and polyethylene oxide are used as electrolyte additives. • The electrolyte additives effectively increase the reduction sites of zinc. • The batteries exhibit better cyclic stability and floating charge performance. [ABSTRACT FROM AUTHOR]

Review: 507 refs. [ABSTRACT FROM AUTHOR]