Recently, several groups have identified that this “extra” capacity is resulting from a reversible oxygen redox process2-7. In this work, we examine in detail the charging process in Li[Li0.2Ni0.2Mn0.6]O2 with direct experimental evidence of a dominant O redox process, accompanied by a minor contribution from oxygen loss, when the material is charged beyond 4.4 V. The formation of hole states around the oxygen during charging was probed using soft x-ray absorption spectroscopy (SAXS), as shown in Figure 1. Additionally, recent results that underpin the oxygen redox process in a number of closely related Li-rich compositions will be discussed, as well as the requirements necessary to form holes on the oxygen in these compounds. The conclusions of this work, and that of other researchers working to understand anion redox, provide us with a guidance which can be used to discover future high energy density cathode materials.
1. Goodenough, J. B.; Kim, Y. Chem Mater 2010, 22, (3), 587-603.
2. Luo, K.; Roberts, M. R.; Hao, R.; Guerrini, N.; Pickup, D. M.; Liu, Y. S.; Edstrom, K.; Guo, J. H.; Chadwick, A. V.; Duda, L. C.; Bruce, P. G. Nat Chem 2016, 8, (7), 684-691.
3. Luo, K.; Roberts, M. R.; Guerrini, N.; Tapia-Ruiz, N.; Hao, R.; Massel, F.; Pickup, D. M.; Ramos, S.; Liu, Y. S.; Guo, J.; Chadwick, A. V.; Duda, L. C.; Bruce, P. G. J Am Chem Soc 2016, 138, (35), 11211-8.
4. Koga, H.; Croguennec, L.; Menetrier, M.; Mannessiez, P.; Weill, F.; Delmas, C. J Power Sources 2013, 236, 250-258.
5. Koga, H.; Croguennec, L.; Menetrier, M.; Mannessiez, P.; Weill, F.; Delmas, C.; Belin, S. J Phys Chem C 2014, 118, (11), 5700-5709.
6. Sathiya, M.; Rousse, G.; Ramesha, K.; Laisa, C. P.; Vezin, H.; Sougrati, M. T.; Doublet, M. L.; Foix, D.; Gonbeau, D.; Walker, W.; Prakash, A. S.; Ben Hassine, M.; Dupont, L.; Tarascon, J. M. Nat Mater 2013, 12, (9), 827-835.