Exploring the Phase Stability of Li₂Mn1–xTMxO₃ (TM = Ni, Co, Cr, Ru) Cathode Materials in Lithium-Ion Batteries via the Cluster Expansion Method

Li2MnO3 has garnered significant interest as a potential cathode material due to its high electrochemical capacity, cost-effectiveness, and eco-friendliness. Nonetheless, its practical utilization is hindered by structural deterioration, which results in rapid capacity and voltage decay during cycling. To mitigate these challenges, cationic dopants have been incorporated to minimize structural collapse and enhance cathode material performance. Consequently, there is a strong desire to identify novel doped configurations as a remedial strategy for optimizing Li2MnO3 properties. In this study, the stability of the Li2Mn1–xTMxO3 system (TM = Ni, Co, Cr, Ru) was explored using cluster expansion and Monte Carlo simulations. By employing cluster expansion, binary ground state diagrams were generated, revealing 73, 65, 90, and 83 newly stable phases in Li2Mn1–xNixO3, Li2Mn1–xCoxO3, Li2Mn1–xCrxO3, and Li2Mn1–xRuxO3, respectively. The outcomes indicated that Li2Mn0.83Ni0.17O3, Li2Mn0.5Co0.5O3, Li2Mn0.5Cr0.5O3, and Li2Mn0.5Ru0.5O3 represent the most stable doped phases within the Li2MnO3 system. The application of Monte Carlo simulations enabled the assessment of high-temperature characteristics across the entire range of TM concentrations (0 ≤ x ≤ 1), facilitating the construction of phase diagrams. The Li2Mn1–xNixO3, Li2Mn1–xCoxO3, Li2Mn1–xCrxO3, and Li2Mn1–xRuxO3 systems exhibited favorable mixing at temperatures of 850, 700, 1700, and 1300 K, respectively. These discoveries present a clear trajectory for optimizing the properties of Li2MnO3, offering valuable insights into conceptualizing innovative cathode materials characterized by enhanced stability and performance.