image: Catalytic mechanism during oxygen reduction reaction and oxygen evolution reaction, unique advantages and corresponding screening criteria of redox mediators for lithium-oxygen batteries. view more
Credit: ©Science China Press
The development of aprotic lithium-oxygen (Li-O2) batteries with ultra-high theoretical specific energies has been severely hindered by sluggish reaction kinetics and undesired parasitic reactions. Molecular catalysts, i.e., redox mediators (RMs), have been explored to catalyze the oxygen electrochemistry in Li-O2 batteries, and are considered as a promising strategy. Recently, Dr. Yaying Dou (Zhengzhou University), Dr. Zhaojun Xie (Nankai University), Prof. Zhen Zhou (Zhengzhou University), Prof. Yingjin Wei (Jilin University), and Prof. Zhangquan Peng (Dalian Institute of Chemistry, Chinese Academy of Sciences) systematically and comprehensively summarize the development and application of the recently updated RMs in Li-O2 batteries.
Specifically, Dou et al. highlight the working principles, unique advantages and selection criteria of RMs in Li-O2 batteries (see below). When summarizing recent advances related to RMs, they classify RMs into organic, organometallic, and inorganic compounds based on their chemical composition. Meanwhile, they also classify the catalytic functions of RMs according to the catalyzed electrode reactions, including ORR RMs, OER RMs, and bifunctional RMs. On this basis, they discuss in depth the catalytic processes and corresponding optimization strategies for RMs.
“To be objective, although RMs provide new prospects for Li-O2 batteries, the scientific issues and technical challenges raised cannot be ignored,” Dou et al. say. For example, the suitability of RMs with other battery components (electrode materials, solvents, salts, etc.) is unclear. Besides, the redox shuttle of RMs leads to the corrosion of Li anodes and loss of the catalytic activity of RMs. Moreover, some organic RMs may suffer from decomposition similar to that of electrolytes or carbon. Most importantly, there is no consensus on the factors of the dynamics of the reaction between RMs and reactants.
Finally, under the dual background of academic exploration and practical application, Dou et al. make suggestions for future research of RMs, including understanding the oxidation kinetics of Li2O2 with RMs, regulating the molecular structure of RMs, optimizing the components of RMs-assisted Li-O2 batteries, analyzing the catalytic efficiency of RMs, and exploring the guidelines for seeking new RMs. Besides, they also indicate that the research directions of practical Li-O2 batteries mainly focus on three aspects: fundamental mechanisms underpinning Li-O2 electrochemistry, further optimization of battery components, and realizing the operation of Li-O2 batteries under ambient conditions. “More advanced experimental, computational, and applied investigations are needed to advance practical development of RM-assisted Li-O2 batteries.” said Dou et al.
See the article:
Redox Mediators for High-Performance Lithium-Oxygen Batteries
https://doi.org/10.1093/nsr/nwac040
Journal
National Science Review