Limitation of Redox Mediator in Li-O2 Batteries: Indecomposable By-Products

Abstract

Redox mediators have been studied passionately to improve energy efficiency and cycle life of lithium-oxygen batteries by facilitating decomposition of the discharge product (lithium peroxide) and, thus, reducing the side reactions at high potential during charging. Nevertheless, the cycling performance of lithium-oxygen batteries with redox mediators is still unsatisfactory; this problem must be verified and resolved for the successful application of redox mediators. In this study, we confirmed that widely used redox mediators cannot decompose by-products on the cathode, leading to passivation of the cathode surface despite the successful decomposition of lithium peroxide. By schematizing the routes for by-products formation, we described the processes by which by-products are accumulated on the cathode in the absence and presence of a redox mediator. Based on the intuitive verification of the unproven relationship between a redox mediator and by-products, we proposed a complementary strategy to overcome the limitations of redox mediator and prevent the accumulation of by-products, which is essential for improvement of lithium-oxygen batteries.References W.-J. Kwak, H. Kim, Y. K. Petit, C. Leypold, T. T. Nguyen, N. Mahne, P. Redfern, L. A. Curtiss, H.-G. Jung, S. M. Borisov, S. A. Freunberger and Y.-K. Sun, Nat. Commun., 2019, 10, 1380. W.-J. Kwak , R. Sharma , D. Sharon , C. Xia , H. Kim , L. R. Johnson , P. G. Bruce , L. F. Nazar , Y.-K. Sun , A. A. Frimer , M. Noked , S. A. Freunberger and D. Aurbach, Chem. Rev., 2020, just accepted. https://doi.org/10.1021/acs.chemrev.9b00609 M. M. Ottakam Thotiyl, S. A. Freunberger, Z. Peng and P. G. Bruce, J. Am. Chem. Soc., 2013, 135, 494.