Effect of Ni Content on Anionic Redox Activity in Ru-Containing Li-Rich Cathode Material

The high energy density of Li-rich layered oxides is associated with anionic redox reaction as it can deliver extra capacity. Herein, using first-principles calculations, we do a contrastive study of anionic redox mechanism in two Li-rich layered oxides, i.e., Li1.167Ni0.167Ru0.667O2 (Li7NiRu4O12) and Li1.167Ni0.333Ru0.5O2 (Li7Ni2Ru3O12), which are marked as LNR4O and LN2R3O, respectively. Our results reveal that the anionic oxidation potential is observed at around 3.95 V in LN2R3O, while, at around 4.31 V, oxygen oxidation reaction can only be achieved in LNR4O. The difference of anionic redox activity can be attributed to the different local oxygen environments between these two materials. Due to the relatively higher content of Ni in the LN2R3O, there are two additional local environments around oxygen (O-Li4NiRu and O-Li3Ni2Ru). Lattice oxygen is more easily oxidized in these two oxygen configurations, which explains the lower anionic oxidation potential in the LN2R3O. In addition, despite not containing linear Li-O-Li configuration, oxygen in the O-Li3Ni2Ru can still have anionic redox activity upon delithiation, which indicates that the anionic redox may not be only determined by linear Li-O-Li configuration. Our finding broadens the fundamental understanding of anionic redox mechanism in Li-rich oxides.