Stabilization of Li2MnO3 phase by Mg doping suppressing irreversible oxygen loss and Mn ions migration

Abstract

Li-rich Mn-based oxide cathode material has attracted people’s attention in that their higher specific capacity, which is attributed to their unique biphasic structure. When the voltage is greater than 4.5V, the Li2MnO3 phase is activated to provide a high specific capacity. But during the cycling process, the Li2MnO3 phase is continuously activated. During this process, O2 will be released and transition metal (TM) ions will migrate, leading to structural phase transition, resulting in voltage decay and capacity loss. In this work, 2wt% Mg-doped Li1.18Mg0.02Mn0.54Co0.13Ni0.13O2 exhibits excellent electrochemical performance. After 100 cycles at 1C, the capacity retention rate is 87.83% By introducing Mg at the position of Li in the TM layer, a more stable Mg-O bond is introduced, in which the inert Mg is not involved in the redox reaction but is fixed in the TM layer. The Li2MnO3 phase is optimized by stabilizing the lattice oxygen to make the Li2MnO3 phase more stable, so as to suppress the irreversible oxygen loss and slow down the structural phase transition. Improved the issue of low initial Coulomb efficiency of materials, the voltage attenuation is alleviated, and the cycle stability is improved.