A constitutive model for force-electro-chemical coupling of lithium ion battery electrode materials

Silicon-based and tin-based electrode materials have become ideal electrode materials for lithium-ion batteries due to their high capacitance density. However, in mechanics, this type of material is often accompanied by large volume deformation during the process of charging and discharging, resulting in high-stress conditions and causing problems such as fracture and destruction of electrode structures, which seriously affect the service life of lithium-ion batteries.

In order to design the electrode structure reasonably and avoid the mechanical damage caused by the structure, it is necessary to establish the force-electricity-chemical coupling constitutive relationship of the electrode material in the process of charging and discharging. The usual approach is the stress evolution during the charging and discharging of electrode materials obtained by in-situ measurement experiments and Stoney formulas. However, this method must rely on three assumptions: the thickness of the film is much smaller than the thickness of the substrate, the thickness of the film is negligible during the deformation process, and the adhesion between the film and the substrate is good. Time high-performance batteries are usually difficult to meet. These conditions.

In order to solve this problem, the research team of the State Key Laboratory of Nonlinear Mechanics of the Institute of Mechanics of the Chinese Academy of Sciences developed a set of finite element calculation methods based on the force-electric-chemical coupling theory, which can accurately describe the bombs of the electrode materials during charge and discharge. Large plastic deformation and inherent stress evolution. The finite element simulation is carried out by this method. The error analysis of the Stoney formula caused by the large elastic-plastic deformation of the electrode film is described. The large deformation, elastoplastic constitutive relation of the electrode film and the property of the interface material on the stress-charge-discharge state curve Influence, and the correspondence between electrode material parameters and stress-charge-discharge state curve characteristics. This work has helped to study the force-electro-chemical coupling constitutive relationship of electrode materials during charge and discharge.

Related research results have been published in the international journal Journalofpowersources (Wen, J., Wei, Y., Cheng, YT, 2018. Examining the validity of Stoney-equation for in-situ stress measures in thin film electrode susinga large-deformation finite-element procedure. J. PowerSources, 387, 126-134.) and Journal of the Mechanics and Physics of Solids (Wen, J., Wei, Y., Cheng, YT, 2018. Stress evolution inelastic-plastic electrodes during electrochemical processes: Anumerical method and its applications. J. Mech. Phys. Solids, 116, 403-415.). The research was supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences Class B Pilot Project, and the National Science Foundation of the United States.

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