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Modeling of progressive delamination in a thin film electrode driven by diffusion-induced stresses

Yicheng Song (Shanghai University), JunQian Zhang (Shanghai University)

Lithium ion batteries: When Chemistry meets Mechanics

Mon 2:40 - 4:00

Salomon 003

A semi-analytical method based on the cohesive model has been developed to investigate the progressive growth of interface delamination in an axisymmetric thin film electrode driven by diffusion-induced stresses. The key dimensionless parameters that control the interfacial stresses and delamination have been identified. They are the plate thickness h, plate radius R, the elastic modulus ratio E, the Poisson’s ratio of vs and vp, the cohesive strength and the lithiation induced deformation inhomogeneity i. The dependence of delamination on the parameters h, R and i have been discussed. It was found reducing the dimensionless plate thickness h could improve electrode stability. The dimensionless radius R is found to have great impacts on the propagating speed of debonding zone at the beginning of cracking. If R is large, the delamination would occur in a suddenly jumping way. And in all cases, increasing i would result in negative effects, such as larger stresses and faster damages. Evolutions of the cohesive zone and debonding zone during charging process have also been predicted. The cohesive zone propagates in an accelerating manner and the debonding zone advances in a slowing down manner. Shear delamination was found to occur in low rate charging, whereas opening delamintiaon would be induced in high rate cases. In addition, delamination maps which showed the existence conditions of cohesive zone and debonding zone were provided. According to the maps, it is possible to select appropriately thickness and radius of active plate, and charging velocity to avoid delamination during a given charging duration. Finally, it was predicted that the critical radius of an 100nm Si thin film electrode is 0.2 ~ 0.6µm for interfacial fracture energy 1~3 J/m2. This value is significantly smaller than experimental reports. The discrepancy was believed from the assumptions that plastic deformation and stress-assisted diffusion had been neglected in the model.