Research On The Diffusion-induced Stress In A Spherical Electrode Particle

Rechargeable lithium-ion batteries are widely used in the field of electric vehicle and electronics. The development of lithium-ion batteries with high capacity, high rate capability, long-life reliability need to decrease the potential risk of mechanical degradation caused by electrochemical lithiation stress. Deeply understanding the influence factors on the diffusion induced stress (DIS) will facilitate to improve the performance of batteries. In this thesis, we discussed the effects of inhomogeneous initial concentration on the DIS under potentiostatic control. Then by using core-shell model we discussed the influence of lithiation mechanisms transition on the DIS.First, for single-phase case, the initial concentration will influence the DIS significantly. Here, the effect of inhomogeneous initial concentration on the DIS under potentiostatic control was reported. By controlling the remaining amount of lithium ions and the interval time between discharge and charge, various initial concentrations were obtained. Then under variable initial cases the profiles of the concentration and DIS were plotted respectively. We found that the inhomogeneous initial concentration can decrease the DIS greatly. Furthermore, the comparison between inhomogeneous and homogeneous initial concentration shows that the homogeneity hinders the decrease of DIS.Second, for phase-separating electrodes, the change of discharging condition will make the miscibility gap vanish leading to a transition of lithiation mechanisms, which will further cause great difference in concentration and DIS. Spinodal instability analysis was first performed to estimate how the miscibility gap depend on the particle size and the boundary reaction rate,. After that we simulated the concentration and DIS under variable miscibility gap by a core-shell two-phase model and found that the maximum of the DIS significantly depends on the particle size and the boundary reaction rate. Based on the Tresca stress criterion, a map for the electrode failure was constructed. The results indicate that the failure caused by the DIS can be avoided by appropriate selection of the said parameters in such electrodes.