Unraveling the Enhanced Cycling Performance of Lithium–Oxygen Batteries Based on Metal Organic Frameworks
Authors: Zhang Xiahui , Dong Panpan , Gray Jake T. , Cha Younghwan , Ha Su , Song Min-Kyu 
Published: February 2020

Owing to their five times higher energy density (~3500 Wh/kg) than that of lithium-ion batteries, lithium–oxygen (Li–O2 or Li­–air) batteries have been considered as one of the most promising next-generation energy storage devices.1 However, Li–O2 batteries still suffer from several challenges that hinder their practical applications, including low energy efficiency and short cycle life. It has been well-documented that such challenges are mainly caused by the parasitic reactions between cell components (e.g., cathodes and electrolytes) and aggressively reactive oxygen species (e.g., singlet O2 and superoxide radicals), which result in the repaid passivation and failure of Li–O2 batteries.2,3 Therefore, the cycling performance of Li–O2 batteries can be significantly improved by suppressing those parasitic reactions.
Metal–organic frameworks (MOFs), an emerging type of crystalline microporous materials, have been widely studied as cathodes, separators, and electrolytes for high-energy Li batteries due to their large surface area, high porosity, and chemically unsaturated metal sites.4 For example, our group recently reported a MOF/CNT cathode for Li–O2 batteries with enhanced cycling performance via the formation and decomposition of less-reactive LiOH compared to Li2O2.5 Besides, MOF-modified separators have also been reported as molecular/ionic sieves to mitigate the shuttling effect of polysulfides in lithium–sulfur batteries and redox mediators in Li–O2 batteries.6,7 Herein, we present our mechanistic study on the enhanced performance of MOF-based Li–O2 batteries. Operando characterization techniques including Raman and mass spectrometry and ex-situ quantitative techniques including NMR and titration were carried out to comprehensively understand the reaction mechanism and the reversibility of Li­–O2 chemistry. The enhanced battery performance and reaction mechanism will be discussed in this presentation.

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