For the coming full-fledged xEV era, rechargeable lithium ion batteries with higher capacities are strongly desired. However, the current commercial cathode materials, such as layered-rocksalt oxide, are reaching the limit of their theoretical capacities.

Li-rich oxide cathode materials, which can access not only to transition metal redox reactions but also to redox reactions during the Li insertion/de-insertion, are expected as candidates for the next generation high capacity cathode materials as they can store much more Li ions than the current commercial cathode materials. However, one of the main drawback of these materials are voltage-fading with structural transition upon electrochemical cycling. It is considered due to oxygen loss at surface and transition metal rearrangement ^[1][2].

To suppress the oxygen loss without decreasing capacity, we focused on the oxyfluoride cathode material. Especially, we confirmed that disordered Rocksalt type-Li₂MnO₂F synthesized by mechanochemical process exhibit a discharge capacity of 330mAh/g with both transition metal and oxygen redox reaction, which is much higher than conventional cathode materials (200mAh/g) ^[3]. Recently, Bruce et al, disclosed that the Li_1.9Mn_0.95O_2.05F_0.95 does not exhibit oxygen loss from the lattice. This indicates that the Li-rich oxyfluoride is one of the noteworthy material for the high capacity cathode materials.

In this study, we will discuss the possibility of the oxyfluoride materials for the next-generation high capacity cathode material from the view point of structures and compositions by comparing with some other oxide cathode materials without fluorine doping.

[1] N. Yabuuchi et al, J. Am. Chem. Soc. 133 (2011) 4404

[2] Y. S. Meng et al, Energy Environ. Sci., 4 (2011) 2223

[3] R. Natsui, K Nakura, POSITIVE ELECTRODE ACTIVE MATERIAL AND BATTERY, WO2017/013848

[4] P. G. Bruce et al, Energy Environ. Sci., (2018) Advanced Article