The impact of oxygen evolution and cation migration on the cycling stability of a Li-rich Li[Li0.2Mn0.6Ni0.1Co0.1]O2 positive electrode

Abstract

New generation cathode materials from the Li-rich NMC group are under constant investigation due to their extremely high energy densities. However, the exact mechanism of lithium (de)insertion in those materials, especially the reactions involving the redox of lattice oxygen, is still elusive. In this paper the structural and electrochemical properties of a high performance cathode material (Li[Li_0.2Mn_0.6Ni_0.1Co_0.1]O₂) are investigated with special attention focused on the TM and oxygen ion contributions in electrochemical processes. The detailed description of the structural, electronic and electrochemical properties of nano-Li[Li_0.2Mn_0.6Ni_0.1Co_0.1]O₂ during lithium (de)insertion are determined by means of electrochemical investigation as well as ex situ XAFS and operando XRD measurements. The obtained results show the correlation of the changes in the electronic structure of the materials with specific structural rearrangements and C2/m → Rm ↔ Fdm phase transitions. This paper shows the detailed analysis of the origins of the high capacity and low capacity fade of Li-rich layered oxides conditioned by the reversibility of the Li ion removal thanks to oxygen redox reactions as well as the migration of transition metal ions in the Li sublattice.