Selecting Substituent Elements for Li-Rich Mn-Based Cathode Materials by Density Functional Theory (DFT) Calculations

Abstract

Li₂MnO₃ is known to stabilize the structure of the Li-rich Mn-based cathode materials <i>x</i>Li₂MnO₃·(1 – <i>x</i>)­LiMO₂ (M = Ni, Co, Mn, etc.). However, its presence makes these materials suffer from drawbacks including oxygen release, irreversible structural transition, and discharge potential decay. In order to effectively address these issues by atomic substitution, density function theory (DFT) calculations were performed to select dopants from a series of transition metals including Ti, V, Cr, Fe, Co, Ni, Zr, and Nb. Based on the calculations, Nb is chosen as an dopant, because Nb substitution is predicted to be able to increase the electronic conductivity, donate extra electrons for charge compensation and postpone the oxygen release reaction during delithiation. Moreover, the Nb atoms bind O more strongly and promote Li diffusion as well. Electrochemical evaluation on the Nb-doped Li₂MnO₃ show that Nb doping can indeed improve the performances of Li₂MnO₃ by increasing its electrochemical activity and hindering the decay of its discharge potential