Modeling the Interfacial Chemistry of Graphene-Based Composite Electrode Materials for Lithium Ion Battery

摘要

High volumetric expansions, large compressive stresses, and subsequent interfacial debonding are largely associated with high energy density materials such as Silicon (Si). Incorporation of additional materials such as Graphene provides Si anode a porous skeleton, allowing Si to expand/contract easily with low mechanical stresses and continuous electrical contact with added advantages of flexibility, good conductivity, lightweight, and high surface Li diffusivity. The interface between Si and Graphene has been extensively studied computationally, and effects of its attributes on battery performance have been determined via experimental investigation of Si-Graphene based composite electrodes. Graphene significantly lowers the stresses in expanding Si, thus increasing its cycle life. In this study, specific interfacial attributes, which directly or indirectly contribute towards the strain accommodation in expanding electrodes have been analyzed, with the aim to create a model that will help in understanding and predicting the performance of graphene provided-interface in Lithium ion batteries. For this purpose, First Principle calculations are carried out using VASP to examine the interfacial chemistry of Si-Graphene system. Produced results are then further compared with additional electrode models: Tin(Sn) and Selenium(Se). While Sn is another high energy density material, which holds promise as anode for ion batteries beyond LIB, Se is a cathode material with superior electrical conductivity and lithiation rates. Both materials undergo strenuous phase changes during battery performance. Changes in interface characteristics post phase change of electrode have also been emphasized. It was understood that interfacial cohesive energy is not merely dependent upon the atomic attributes and type of bonding with the Graphene surface as mostly highlighted, but also on unaccounted for lattice mismatch between the crystalline electrode and Graphene. With changing phases and deviation in lattice constants, interface adhesion changes even though bonding between electrode and Graphene remains unchanged.