Elucidating Effect of Transition Metal on Anionic Oxygen Activity in High-Energy Li-Rich Layered Oxides

Abstract

In commercial Li-ion batteries, well-ordered close-packed oxides, particularly, layered lithium transition metal oxides, LiTMO2 (TM = Ni, Mn, Co, Al), are widely used. Despite the high theoretical capacity of these layered oxides (> 270 mAh/g), they are typically operated to deliver a capacity of less than 200 mAh/g to attain good cycling and safety attributes.1-6 Nowadays, strategies to push the capacity limit of such materials have led to the development of Li-rich layered oxides7, 8, which can consistently deliver a reversible capacity approaching 300 mAh/g. This exceptionally high capacity is far beyond the theoretical capacity from Ni and Co redox, for example, Ni redox (Ni2+/4+) can only account for a theoretical capacity of 127 mAh/g in a Co-free compound, Li1.2Ni0.2Mn0.6O2. This has been clearly directed to the participation of oxygen redox in the electrochemical reaction.9-14 In our work, we aimed to probe the electrochemical activity of anionic oxygen in Li-rich layered oxides from material perspective via tackling the effect of transition metal species. We have successfully synthesized a series of Li-rich layered oxides, Li2-x-yNixTmyO2 (TM is transition metal). Compounds with designed transition metals possess a similar crystal structure and enable a similar amount of Li removal and uptake during charge-discharge processes, but with a significantly different charge profile, characterized by the voltage plateau around 4.55 V. We performed a systematic study to capture the oxygen activity ranging from O2- in the lattice to O0 in gaseous phase in the as-produced compounds by combining a suite of advanced characterization techniques with in-situ differential electrochemical spectrometry (DEMS). We have observed completely different oxygen behaviors in such compounds with varied transition metals. We will present our experimental evidence on a reversible participation of electrons from oxygen in Li-, Mn-rich layered oxide. We hope these findings will provide additional insights into the complex mechanism of oxygen redox and the development of advanced high-capacity Li-ion cathodes. Reference 1. J. B. Goodenough and Y. Kim, Chem. Mater., 2010, 22, 587-603. 2. J. B. Goodenough and K.-S. Park, J. Am. Chem. Soc., 2013, 135, 1167-1176. 3. M. S. Whittingham, Chemical Reviews, 2004, 104, 4271-4301. 4. B. L. Ellis, K. T. Lee and L. F. Nazar, Chemistry of Materials, 2010, 22, 691-714. 5. M. S. Whittingham, Chemical Reviews, 2014, 114, 11414-11443. 6. J. Xu, F. Lin, M. M. Doeff and W. Tong, Journal of Materials Chemistry A, 2017, 5, 874-901. 7. S.-H. Kang, Y. K. Sun and K. Amine, Electrochemical and Solid-State Letters, 2003, 6, A183-A186. 8. Z. Lu, D. D. MacNeil and J. R. Dahn, Electrochemical and Solid-State Letters, 2001, 4, A191-A194. 9. C. Delmas, Nat Chem, 2016, 8, 641-643. 10. A. Grimaud, W. T. Hong, Y. Shao-Horn and J. M. Tarascon, Nat Mater, 2016, 15, 121-126. 11. K. Luo, M. R. Roberts, R. Hao, N. Guerrini, D. M. Pickup, Y.-S. Liu, K. Edström, J. Guo, A. V. Chadwick, L. C. Duda and P. G. Bruce, Nat Chem, 2016, 8, 684-691. 12. D.-H. Seo, J. Lee, A. Urban, R. Malik, S. Kang and G. Ceder, Nat Chem, 2016, 8, 692-697. 13. Z. Chenglong, W. Qidi, L. Yaxiang, H. Yong-Sheng, L. Baohua and C. Liquan, Journal of Physics D: Applied Physics, 2017, 50, 183001. 14. B. Qiu, M. Zhang, Y. Xia, Z. Liu and Y. S. Meng, Chemistry of Materials, 2017, 29, 908-915.