In Operando Visualization of the Electrochemical Formation of Liquid Polybromide Microdroplets

Scientific issues of zinc-bromine flow batteries and mitigation strategies

Zinc-bromine flow batteries (ZBFBs) are promising candidates for the large-scale stationary energy storage application due to their inherent scalability and flexibility, low cost, green, and environmentally friendly characteristics. ZBFBs have been commercially available for several years in both grid scale and residential energy storage applications. Nevertheless, their continued development still presents challenges associated with electrodes, separators, electrolyte, as well as their operational chemistry. Therefore, rational design of these components in ZBFBs is of utmost importance to further improve the overall device performance. In this review, the focus is on the scientific understanding of the fundamental electrochemistry and functional components of ZBFBs, with an emphasis on the technical challenges of reaction chemistry, development of functional materials, and their application in ZBFBs. Current limitations of ZBFBs with future research directions in the development of high performance ZBFBs are suggested.

Iodine Redox Chemistry in Rechargeable Batteries

Halogens have been coupled with metal anodes in a single cell to develop novel rechargeable batteries based on extrinsic redox reactions. Since the commercial introduction of lithium-iodine batteries in 1972, they have shown great potential to match the high-rate performance, large energy density, and good safety of advanced batteries. With the development of metal anodes (e.g. Li, Zn), one of the actual challenges lies in the preparation of electrochemically active and reliable iodine-based cathodes to prevent self-discharge and capacity decay of the rechargeable batteries. Understanding the fundamental reactions of iodine/polyiodide and their underlying mechanisms is still highly desirable to promote the rational design of advanced cathodes for high-performance rechargeable batteries. In this Minireview, recent advances in the development of iodine-based cathodes to fabricate rechargeable batteries are summarized, with a special focus on the basic principles of iodine redox chemistry to correlate with structure-function relationships.

Side-View Operando Optical Microscopy Analysis of a Graphite Anode to Study Its Kinetic Hysteresis

Operando analyses have provided several breakthroughs in the construction of high-performance materials and devices, including energy storage systems. However, despite the advances in electrode engineering, the formidable issues of lithium intercalation and deintercalation kinetics cannot be investigated by using planar observations. This study concerns side-view operando observation by optical microscopy of a graphite anode based on its color changes during electrochemical lithiation. Since the graphite color varies according to the optical energy gap during lithiation and delithiation, this technique can be used to study the corresponding charge-discharge kinetics. In addition, the cell configuration uses liquid electrolytes similar to commercial cells, allowing practical application. Furthermore, this side-view observation has shown that microscale spatial variations in rate and composition control the insertion and deinsertion, revealing the kinetics throughout the whole electrode. The results of this study could enhance the fundamental understanding of the kinetics of battery materials.