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	Molecular dynamics study on the Li diffusion mechanism and delithiation process of Li2MnO3
	Huang, Yang1,2; Liu, Long3; Gao, Min2,4
	2020-03-01
摘要	Li2MnO3 is critical component in the well-studied Li-excess cathode materials xLi(2)MnO(3)center dot(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 Li2-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 Li2-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 spinet-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 Li0.8MnO3, 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 Li2-xMnO3. Other charge compensation mechanism should be considered in this high delithiation stage, eg. oxygen release.
关键词	Li2MnO3 Molecular dynamics Diffusion Delithiation
DOI	10.1016/j.ssi.2019.115195
发表期刊	SOLID STATE IONICS
ISSN	0167-2738
卷号	346页码:8
通讯作者	Huang, Yang(huangyang@ihep.ac.cn) ; Gao, Min(gao.l.min@gmail.com)
收录类别	SCI
WOS记录号	WOS:000517851600008
语种	英语