| Lithium-ion batteries(LIBs) have been widely used because of its numerous excellent properties, such as the high voltage platform, high energy density, low self-discharge rate, long cycle life, no memory effect and environmental-friendly, etc. The electrode materials are the important component of LIBs and directly determine the level of electrochemical performance of LIBs. Currently, the theoretical specific capacity of the commercialized electrode materials is relatively low, which cannot meet the increasing demand for the application in the high specific capacity needs field such as electric vehicles. Therefore, the high-capacity electrode materials are critical for the development of a new generation of high-performance LIBs. However, the volume deformations of these electrode materials are serious during the process of charging-discharging, and the associated large lithiated stress will simultaneously generated. This will lead to the damage or even pulverization of the electrode active materials, and directly result in the fading of capacity and the decrease of cycle performance.In order to solve the problem of the lithiation deformation and failure of high-capacity electrode materials for LIBs, by the theoretical analysis and finite element numerical simulation, we have established the phase-transition lithiation models and stress failure models of electrode materials with different structures in this paper. We aim to clarify the stress evolution of electrode materials in the lithiation process, obtain the lithiation failure phase diagram between the critical failure state and its structural dimensions and basic mechanical properties. In addition, we have further verified the theoretical results by experiment. The main research work of this paper includes the following aspects:(1) We established a phase-transition lithiation model based on the elastic-perfectly plastic deformation, and simulated the phase-transition lithiation process of electrode materials of the film and sphere structures(including the solid sphere, hollow sphere and hollow core-shell structures) by the finite element software of ABAQUS. In addition, we also analyzed the dynamic evolution of the concentration field and stress field in the lithiation process, and founded that there is a mutation of the lithiation stress in the phase boundary. The main reason for the materials failure is the tensile stress, which increases continuously in the surface and interfacial of electrode materials. The hollow structure can not only accelerate the lithiation rate, but also alleviate the outward lithiation expansion to a certain extent, and the hollow core-shell structure can control the outward lithiation deformation of the electrode material effectively.(2) On the basis of the phase-transition lithiation model and the energy failure criteria, we established the fracture and debonding models of the film and hollow core-shell structures. According to the dimensional analysis and finite element simulation, through the function fitting, we also determined the non-dimensional function between the critical failure SOC of electrode materials and its structural dimensions and basic mechanical properties, and obtained the corresponding lithiation failure phase diagram, which provided the theoretical basis for the safety properties analyzing of high-capacity electrode materials in the lithiation process.(3) We electrodeposited Sn films with different thicknesses by electroplating, which were assembled into button cells and the charging-discharging experiments were conducted. We obtained the critical failure SOC of Sn film with different thicknesses in the lithiation process by SEM. Results show that for film thicknesses of 10 ?m, 18 ?m, 26 ?m and 35 ?m, the critical fracture were SOC = 1, SOC = 0.72, SOC = 0.5 and SOC = 0.36, respectively. The experimental values are basically consistent with theoretical prediction, which proved the accuracy of the lithiation failure phase diagram. |
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