First-principles Research On The Lithium Storage Mechanism Of Anode Materials For Lithium Ion Batteries

The rapid development of the electronic market reveals a breakthrough in terms of electrode materials in recent years. Lithium-ion batteries(LIBs) with high reversible capacity, high energy density, and good cycle life, are widely used as potable power sources in the diverse electronic devices. Because of its flexibility, high surface area and ultra-short ion transport distance, two dimensional materials are one of the best choices for construction of high performance lithium ion battery. Recently, a single layered two dimensional graphite-like structure, named phosphorene, was successfully separated from the black phosphorus. Due to its proper band gap width(0.5 eV ~ 1.5 eV), high carrier mobility(5000 cm-1V-1s-1), phosphorene has attracted wide attention. In this paper, a new type of negative electrode material, phosphorene, is selected as the research object. On the one hand, the characteristics of structural transformation, the diffusion of lithium ion, and the mechanism of lithium ion insertion and extraction were studied. On the other hand,we reveals the influence of the construction of the heterojunction on its conductivity, capacity and cycle performance. These studies provide theoretical guidance for the design and optimization of electrode materials for lithium ion batteries.Moreover, we studied the adsorption and diffusion properties of lithium in the pristine and single vacancy defects phosphorene. The pristine phosphorene shows a high capacity(432.79 mAhg-1), low diffusion barrier(0.09 eV), and the volume change is negligible during the charge/discharge process. However, the weak binding with Li limit the application of phosphorene in LIBs. Interestingly, the introduction of defects can greatly improve the binding strength and diffusion properties of lithium ion. Compared to the pristine phosphorene, the binding energy of lithium in the vicinity of the vacancy increased by about 1 eV. More importantly, the introduction of vacancy opens a new channel for the diffusion of Li between two different grooves(with an energy barrier of 0.13 eV), which will significantly improve the fast charge/discharge capacity of the battery.Besides, we studied the improvement of electrochemical properties of phosphorene-graphene heterostructure compared with pristine phosphorene which with poor conductivity, relatively low capacity and weak Li binding strength. The calculated result show that the phosphorene/graphene heterostructure(P/G) can greatly improve the binding energy without affecting the high mobility of Li within the layers. Besides, the band structure of the phosphorene-graphene show that the conductivity of the heterostructure improved significantly(Eg= 0.03 eV) compared to pristine phosphorene. Interestingly, the P/G also displays the ultrahigh stiffness(Cac = 350 N/m, Czz = 464 N/m), which can effectively avoid the distortion of the pristine phosphorene after the insertion of lithium.