Li₂MnO₃ is critical component in the well-studied Li-excess cathode materials xLi₂MnO₃·(1- x)LiMO₂ for achieving high lithium storage capacity. In this article, the diffusion of Li ions in Li₂MnO₃ is studied using molecular dynamics (MD) simulation with well-behaved empirical force fields obtained by fitting against the crystal structure from experiment and phonons calculated using Density Function Theory (DFT). We have found two possible tetrahedral hopping channels, 0-TM and 1-TM(Mn⁴⁺) channel, which are differentiated by the face sharing octahedral cations. Simulation results show that the 0-TM channel is active for Li hopping, while 1-TM(Mn⁴⁺) channel is inactive. During the delithiation process, the Li ions in the transition metal (TM) layer are firstly removed, then those in the Li layer. However, the Li ions will be trapped in the tetrahedral 0-TM channels as long as the four face sharing octahedral sites are cleared. Up to x = 1.0 for Li_2-xMnO₃, almost all the Li ions are located at the tetrahedral sites, forming a regular array along a axis. The de-intercalation of tetrahedral Li ions requires a high voltage (>5.2 V vs. Li/Li+), limiting the practical capacities measured in lab. The diffusion of Mn ions into the Li layer is observed in a deeper delithiated structure (x = 1.2 for Li_2-xMnO₃), indicating an initial phase transformation to a spinel-like structure. However, the Mn ions are mainly trapped in the tetrahedral sites in the Li layer, instead of the octahedral sites in spinel-like structure. A few of Mn ions diffusing into the octahedral sites in Li layers have no face sharing tetrahedral Li ions, revealing a further Li de-intercalation is imperative for the complete phase transformation. During the delithation process, the oxygen sublattice shows a strong stability. In the deeply dilithiated structure Li_0.8MnO₃, the local distortion of the oxygen sublattice is observed, which may indicate the oxygen release at this high delithation stage. Our model is not stable for x ≥ 1.4 in Li_2-xMnO₃. Other charge compensation mechanism should be considered in this high delithiation stage, eg. oxygen release.

Li ₂ MnO ₃是经过充分研究的锂过量正极材料xLi ₂ MnO ₃ ·（1- x）LiMO _2的关键成分，以实现高锂存储容量。在本文中，使用分子动力学（MD）模拟研究了锂离子在Li ₂ MnO _3中的扩散，该模拟具有良好的经验力场，该经验力场通过拟合实验所得的晶体结构和使用密度函数理论（DFT）计算的声子而获得。我们发现了两个可能的四面体跳跃通道，0-TM和1-TM（Mn ⁴⁺）通道，通过共享八面体阳离子的面部加以区分。仿真结果表明，0-TM通道对Li跳跃有效，而1-TM（Mn ⁴⁺）通道无效。在脱锂过程中，首先去除过渡金属（TM）层中的Li离子，然后去除Li层中的锂离子。但是，只要清除了四个共享面的八面体位点，锂离子就会被困在四面体0-TM通道中。Li _2-x MnO ₃最高x = 1.0，几乎所有的锂离子都位于四面体位置，沿轴形成规则的阵列。四面体锂离子的去嵌入需要高电压（相对于Li / Li +，> 5.2 V），从而限制了在实验室中测量的实际容量。在更深的去锂化结构中观察到Mn离子扩散到Li层中（对于Li _2-x MnO _3， x = 1.2），表示初始相转变为尖晶石状结构。但是，Mn离子主要被捕获在Li层的四面体部位，而不是尖晶石状结构中的八面体部位。扩散到Li层八面体位置的少数Mn离子没有面共享四面体Li离子，这表明进一步的Li脱嵌对于完整的相变是必不可少的。在脱锂过程中，氧亚晶格表现出很强的稳定性。在深层锂化的结构Li _0.8 MnO _3中，观察到氧亚晶格的局部变形，这可能表明氧在此高脱锂阶段释放。在Li _2-x MnO _3中x≥1.4时我们的模型不稳定。在这种高去磁化阶段，应考虑其他电荷补偿机制，例如。氧气释放。