Analysis Of Electrochemical Diffusion Induced Stress Relaxation Mechanism Of The Electrode

The development of Li-ion battery with high voltage,high energy density,non-memory effect long cycle life and environmental friendliness,is of major importance for a wide applied to portable electronic,electric vehicles,large-scale stationary energy storage systems in renewable energy plants.However,the manufacture technology of Li-ion battery is still faced with some problems,such as ageing.After many years of use,Li-ion repeatedly insert and extract from the electrode,leading to phase transformation,volume variation and large stress,which results in the electrode mechanics performance degradation.It is necessary to quantitatively research on the chemical response mechanism and mechanical properties of electrode materials caused by lithation.In the framework of continuum mechanics,a general theory is proposed to describe the failure process induced by electro-chemo-mechanisms in amorphous electrodes.The theory considers mass transport through the system,deformation in electrodes.The chemical concentration and the displacement fields are introduced as independent variables for the formulation diffusion-mechanics coupling.we forformulate a unified framework of balance laws and thermodynamically-consistent constitutive equations which couple Cahn-Hilliard-type species diffusion with large elastic deformations of body.The model together with the numerical method is supplemented into commercial finite element software ABAQUS.The approach is used to analyze the combined effects of diffusion and stress on the lithiation of LiFePO4 electrodes.Two types of electrodes are investigated which are square planar electrodes and circle electrodes.It is found that the geometry of electrodes has important effects on the stress level and capacity of electrodes.On the basis of the ideas in optimizing the structure of the silicon thin film electrode,dig a small hole at the center of the circular planar electrode for structural optimization,aiming at reducing the electrode deformation and stress concentration.The analytic result show that the optimized electrode can reduce stress,nodal displacement and high charge speed,which proves that the structure optimize battery performance.In addition,in order to verify the validity of the method,This paper completed numerical simulation of the cycle of lithiation and delithiation.The coupled chemo-mechanics model together with the numerical techniques developed here provides an efficient simulation tools to predict various chemical mechanical behaviour happened in electrodes.