| Lithium-ion battery is a rechargeable battery, which works based on lithium-ion diffusion moving between positive and negative polars. During charge-discharge process, a lithium-ion repeatedly infiltrate and precipitate into battery electrode, which will results in a dramatic change of the volume of the electrodes. Due to the inconsistency of the deformation happened on electrodes, the electrode itself will produce stresses, and the electrode will be damaged by such large amount of stresses.To study the special mechanical properties of lithium-ion-battery electrode generated by the coupling of structure deformation and ion diffusion, especially the influence of various cracks in battery electrodes material on its internal stress distributions upon the charging and discharging processes, this paper established a theoretical model of a lithium-ion battery electrodes in the charge-discharge process describes the coupling between electrode structure deformation and diffusion behavior within the electrode structure of the lithium ion. This paper also quantitatively calculated and simulated the model via the commercial Finite Element Analysis (FEA) software "COMSOL Multiphysics", systematically studied the effect of a variety of factors, such as charge and discharge rate, internal cracks or holes inside the electrode structure, etc. upon the electrode structure mechanical behavior and diffusion field.Scholars from Brown University firstly proposed the quantitative dependencies between the ion diffusion coefficient and the influence of the internal stress. They also established the elastic-diffuse coupling model specifically to the round sheet shaped electrode material under constant current charging condition.Based on the model stated above, a quantitative simulation with respect to the cracked or hole-insided electrode structure was presented in this paper through the commercial FEA software "COMSOL Multiphysics". While the crack is located in the center of the circular electrode structure, the effects of round, oval, rectangular or other shapes and geometric dimensions had on the stress distribution of the electrode plate was explored. And we found that the slenderness ratio and dimention of elliptical cracks may also strongly impact the degree of electrode plate internal stress concentration.After comparing different shapes of cracks, we also found the shape of cracks are significantly influencing the degree of stress concentration as well. While the scale of cracks are identical, rectangular shaped crack generates the most severe stress concentration, elliptical shaped follows and then round hole effects the smallest.Secondly, this work also studied the effect of crack position in round shaped electrode upon the stress distribution inside the material. Found that the deviation from the center also closely related to the stress distribution within electrode sheet. To elliptical and round cracks, when its position deviates towards the outside of the center, the degree of stress distribution will firstly increase then drop down regarding the increasing distance of deviation. This reveals that for a certain crack, we can always find a position that will results in the largest degree of stress concentration.Finally, this paper studied the effects of the charge and discharge rate on the stress distribution in the electrode, meanwhile, a horizontal comparison of the effects of charging and discharging conditions on stress distribution was carried out. The result is that for stress concentration and ion distribution condition inside the electrode plate, different rate of charge-discharge could give out an entirely different behavior. Upon the same current intensity, the degree of electrode plate stress concentration during charging procedure is way higher than discharge process. |
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