Aqueous rechargeable batteries (ARBs) have become a lively research theme due to their advantages of low cost, safety, environmental friendliness, and easy manufacturing. However, since its inception, the aqueous solution energy storage system has always faced some problems, which hinders its development, such as the narrow electrochemical stability window of water, poor percolation of electrode materials, and low energy density. In recent years, to overcome the shortcomings of the aqueous solution-based energy storage system, some very pioneering work has been done, which also provides a great inspiration for further research and development of future high-performance aqueous energy storage systems. In this paper, the latest advances in various ARBs with high voltage and high energy density are reviewed. These include aqueous rechargeable lithium, sodium, potassium, ammonium, zinc, magnesium, calcium, and aluminum batteries. Further challenges are pointed out.
Aqueous can be better in terms of safety, friendliness, and energy density.
To address increasing energy supply challenges and allow for the effective utilization of renewable energy sources, transformational and reliable battery chemistry are critically needed to obtain higher energy densities. Here, significant progress has been made in the past few decades in energetic battery systems based on the concept of multi-electron reactions to overcome existing barriers in conventional battery research and application. As a result, a systematic understanding of multi-electron chemistry is essential for the design of novel multi-electron reaction materials and the enhancement of corresponding battery performances. Based on this, this review will briefly present the advancements of multi-electron reaction materials from their evolutionary discovery from lightweight elements to the more recent multi-ion effect. In addition, this review will discuss representative multi-electron reaction chemistry and materials, including ferrates, metal borides, metal oxides, metal fluorides, lithium transition metal oxides, silicon, sulfur and oxygen. Furthermore, insertion-type, alloy-type and conversion-type multi-electron chemistry involving monovalent Li+ and Na+ cations, polyvalent Mg2+ and Al3+ cations beyond those of alkali metals as well as activated S2− and O2− anions are introduced in the enrichment and development of multi-electron reactions for electrochemical energy storage applications. Finally, this review will present the ongoing challenges and underpinning mechanisms limiting the performance of multi-electron reaction materials and corresponding battery systems.
Typical catalyst inks in proton exchange membrane fuel cells (PEMFCs) are composed of a catalyst, its support, an ionomer and a solvent and are used with solution processing approaches to manufacture conventional catalyst layers (CLs). Because of this, catalyst ink formulation and deposition processes are closely related to CL structure and performance. However, catalyst inks with ideal rheology and optimized electrochemical performances remain lacking in the large-scale application of PEMFCs. To address this, this review will summarize current progress in the formulation, characterization, modeling and deposition of catalyst inks. In addition, this review will highlight recent advancements in catalyst ink materials and discuss corresponding complex interactions. This review will also present various catalyst ink dispersion methods with insights into their stability and introduce the application of small-angle scattering and cryogenic transmission electron microscopy (cryo-TEM) technologies in the characterization of catalyst ink microstructures. Finally, recent studies in the kinetic modeling and deposition of catalyst inks will be analyzed.
The formulation and the deposition process of catalyst inks determine the formation of catalyst. The interaction between the components of the catalyst ink governs the microstructure and processability of the ink, thereby affecting the microstructure and performance of the CL.
All-solid-state lithium batteries (ASSLBs) have attracted increasing attention due to their high safety and energy density. Among all corresponding solid electrolytes, sulfide electrolytes are considered to be the most promising ion conductors due to high ionic conductivities. Despite this, many challenges remain in the application of ASSLBs, including the stability of sulfide electrolytes, complex interfacial issues between sulfide electrolytes and oxide electrodes as well as unstable anodic interfaces. Although oxide cathodes remain the most viable electrode materials due to high stability and industrialization degrees, the matching of sulfide electrolytes with oxide cathodes is challenging for commercial use in ASSLBs. Based on this, this review will present an overview of emerging ASSLBs based on sulfide electrolytes and oxide cathodes and highlight critical properties such as compatible electrolyte/electrode interfaces. And by considering the current challenges and opportunities of sulfide electrolyte-based ASSLBs, possible research directions and perspectives are discussed.
The oxygen evolution reaction (OER) with its intractably high overpotentials is the rate-limiting step in many devices, including rechargeable metal–air batteries, water electrolysis systems and solar fuel devices. Correspondingly, spin state transitions from spin singlet OH–/H2O reactants to spin triplet O2 product have not yet received enough attention. In view of this, this article will discuss electron behaviours during OER by taking into consideration of spin attribute. The main conclusion is that, regardless of the possible adopted mechanisms (the adsorbate evolution mechanism or the lattice oxygen mechanism), the underlying rationale of OER is that three in four electrons being extracted from adsorbates should be in the same spin direction before O=O formation, superimposing high requirements on the spin structure of electrocatalysts. Therefore, upon fully understanding of the OER mechanism with considerations of spin, the awareness of the coupling between spin, charge, orbital and lattice parameters is necessary in the optimization of geometric and electronic structures in transition metal systems. Based on this, this article will discuss the possible dependency of OER efficiency on the electrocatalyst spin configuration, and the relevance of well-recognized factors with spin, including the crystal field, coordination, oxidation, bonding, the e g electron number, conductivity and magnetism. It is hoped that this article will clarify the underlying physics of OER to provide rational guidance for more effective design of energy conversion electrocatalysts.