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Studies have found that electrochromic electron acceptor materials - polychalcone viologen compounds

2019-05-13 来源:转载自第三方
Recently, the He Gang research team of Xi'an Jiaotong University published an article entitled “Electrochromic Poly(chalcogenoviologens) as Anode Materials for High-Performance Organic Radical Li-Ion Batteries” in the internationally renowned journal Angewandte Chemie International Edition. The article reports a series of electrochromic electron acceptor materials with a number of stable reversible redox centers, and is used as a negative electrode for organic radical lithium-ion batteries (ORLIBs).
A viologen compound is a cationic organic molecule having excellent redox properties. Under the application of voltage or illumination, a two-step reversible single-electron oxidation reduction can be performed to generate a free radical cation state and a neutral molecular state accompanied by a distinct color change. The unique redox properties of the viologen molecule make it widely used in the field of energy storage materials, such as inorganic/organic lithium/sodium/magnesium ion batteries, water-based organic liquid flow batteries, organic radical batteries, and lithium-oxygen batteries. As a new type of energy storage device, organic radical batteries have the advantages of no rare metals, adjustable redox properties, and flexible design at the molecular level. However, these batteries also have less redox states, low capacity and stability. Defects such as poor performance greatly limit its application.
Viologen (RV2+) is an organic molecule based on a double-quaternized 4,4'-bipyridyl electron acceptor. Using an applied voltage or direct illumination, Viologen can undergo two steps of reversible single-electron reduction with significant discoloration. This phenomenon is very common in free radical type of viologen compounds (RV2+ + e- ↔ RV+•; RV+• + e– ↔ RV), which has been used in electrochromic devices (ECD), molecular machines and organic batteries. Investigated. Due to the versatility of its synthesis and the susceptibility of redox characteristics, the development of energy storage devices based on viologen has increased significantly over the past few decades. The excellent redox properties and unique free radical state of the viologen make it a candidate for special electrodes in the new generation of energy storage devices, such as inorganic/organic Li/Na/Mg ion batteries, aqueous organic redox flow batteries, Organic radical batteries, lithium oxygen batteries, etc. As a promising emerging energy storage technology, organic radical lithium-ion batteries (ORBS) show some advantages over previously reported inorganic and polymeric materials, such as the need for rare metals, redox characteristics are easy to adjust, It is safer at the molecular level and more flexible in design, but the development of this battery is still limited. For example, battery capacity and stability are low due to less redox states and lower specific energy. Therefore, the development of novel viologen derivatives with multiple stable redox centers and higher specific energy can significantly improve performance and expand the range of ORBs.
Previous research work has shown that the introduction of chalcogen elements into the organic conjugated system can greatly improve the redox characteristics of the materials. The organic lithium sodium ion batteries prepared based on such electrode materials have a large specific capacity. The previous research of Professor He Gang of Xi'an Jiaotong University found that the introduction of chalcogen elements into the derivative of viologen and the introduction of more redox centers on the basis of the viologen molecule further improved the redox characteristic of the derivative of the viologen. It is not difficult to imagine that the application of chalcogen-containing viologen compound to organic radical lithium-ion batteries can not only greatly improve the performance of free radical batteries, but also combine the discoloration properties of such molecules with battery performance to develop new organic Color changing battery.
Based on the above considerations, Professor He Gang's research group successfully prepared the chalcogen-containing viologen polymer based on the previous study of chalcogen-containing viologen, and applied it as an electrode material to organic radical lithium-ion batteries. The study found that with the introduction of sulfur/selenium/bismuth, battery capacity and cycle stability have increased significantly. Among them, the strontium-containing viologen polymer showed the best performance, and the capacity reached 502 mAh g-1 when the coulombic efficiency reached 100%. Related mechanism studies show that the introduction of ruthenium atoms greatly increases the conductivity of the electrode material and increases the lithiation site. On this basis, a new type of flexible color-changing battery was prepared by combining the electrochromic properties of the strontium-containing viologen polymer with the battery application, which was accompanied by obvious color change during the charging and discharging process of the battery. This research work not only developed a new class of organic radical batteries, but also provided new ideas for the research in the field of color-changing batteries.
Edited by Suzhou Yacoo Science Co., Ltd.