Charge Storage Mechanism and Structural Evolution of Viologen Crystals as the Cathode of Lithium Batteries

• Published in: Angewandte Chemie International Edition Vol. 59; no. 28; pp. 11533 - 11539
• Main Authors: Ma, Ting, Liu, Luojia, Wang, Jiaqi, Lu, Yong, Chen, Jun
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 06.07.2020
• Edition: International ed. in English
• Subjects: Batteries; Cathodes; charge storage; Conductivity; Crystal structure; Crystals; DFT calculations; Electric vehicles; Electrode materials; Electrodes; Electrolytes; Electron conductivity; Evolution; Iodides; Ionic crystals; Lithium; Lithium batteries; Rechargeable batteries; structural evolution; viologen crystals; viologen crystals; lithium batteries; structural evolution; charge storage; DFT calculations
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202002773

Although organic ionic crystals represent an attractive class of active materials for rechargeable batteries owing to their high capacity and low solubility in electrolytes, they generally suffer from limited electronic conductivity and moderate voltage. Furthermore, the charge storage mechanism and structural evolution during the redox processes are still not clearly understood. Here we describe ethyl viologen iodide (EVI2) and ethyl viologen diperchlorate (EV(ClO4)2) as cathode materials of lithium batteries which crystallize in a monoclinic system with alternating organic EV2+ layers and inorganic I−/ClO4− layers. The EVI2 electrode exhibits a high initial discharge plateau of 3.7 V (vs. Li+/Li) because of its anion storage ability. When I− is replaced by ClO4−, the obtained EV(ClO4)2 electrode displays excellent rate performance with a theoretical capacity of 78 % even at 5 C owing to the good electron conductivity of ClO4− layers. EVI2 and EV(ClO4)2 also show excellent cycling stability (capacity retention >96 % after 200 cycles). Performance enhancers: Ionic crystals of ethyl viologen iodide (EVI2) and ethyl viologen diperchlorate (EV(ClO4)2) have shown excellent electrochemical performance, such as high rate performance and excellent cycling stability, as cathode materials of lithium batteries. The good electron conduction of ClO4− layers results in EV(ClO4)2 having a theoretical capacity of 78 % even at 5 C.