First-Principles Study On The Effect Of Electron Doping On The Mechanical Properties Of Lithium Ion Battery Electrode Materials

Efficient and reasonable transformation,storage and rational use of clean and renewable energy,such as natural solar energy,are the key and fundamental to human protection and governance of today's environment,a shortcut to promote human society and economy out of the development bottleneck,and also a necessary path.At present,the use of lithium-ion batteries is an important way to realize the conversion,storage and utilization of clean energy.With the increasing demand for high-power,large capacity and long cycle life lithium-ion batteries,people began to seek a new generation of electrode materials,and the mechanical stability of the electrode materials plays an important role in the safe use of lithium batteries.In this paper,the first principle method is used to study the mechanical stability of new lithium electrode materials,including IVA materials?Si,Ge and Sn?and two-dimensional materials?graphene,silicene and 2H-MoS₂?in the process of lithium intercalation,and the micro mechanism of the change of mechanical properties is revealed.The main research contents and results are as follows:1.The density functional theory is used to study the mechanical stability of the IVA material after lithium ion embedding.It is found that the elastic constants of C₁₁ and C₄₄decrease with the increase of lithium embedding concentration,and there are obvious volume expansion and elastic softening phenomenon,and the mechanical stability of the material also decreases.Through further study of the effect of electron doping on the mechanical stability of IVA materials,we found that the same results with lithium ion embedding.The results show that the electron doping effect is the mechanism that leads to the decrease of the mechanical stability of group IV materials in the process of lithium doping.2.We studied the changes in the basic structure and mechanical constants of graphene,silicene and MoS₂ during lithium insertion,and revealed the microscopic mechanism of these changes from the perspective of mechanical properties.For graphene,Li-doping has little effect on the mechanical properties of it,which further proves the potential of graphene as a LIBs material.For silicene,it is indicated that the embedding of Li atoms has no substantial change on the mechanical properties of silicene,ie.,silicene has strong mechanical stability in the process of adsorbing Li atoms,and it is an excellent electrode alternative for LIBs.For 2H-MoS₂,we found that both lithium atoms and electron doping can soften the 2H-MoS₂ material.Since each lithium atom has a valence electron,which will contribute electron to the crystalline lattice when a lithium atom is doped onto the surface of MoS₂.The electron will occupy the 4d² orbit of Mo atoms,which leads to the loss of charge between Mo-S bonds and the instability resulting in the structural transformation of 2H-MoS₂.These results show that the mechanism of the decrease of mechanical stability of 2H-MoS₂ is due to the electron doping effect.