Research on Constitutive Models of Electro-Mechanical Coupling of Electrode Materials
Silicon-based, tin-based electrode materials are ideal electrode materials for lithium-ion batteries due to their high capacitance density. However, mechanically this type of material is often accompanied by large volume deformation during charging and discharging, resulting in a high stress state and causing problems such as fracture and destruction of the electrode structure, which seriously affects the service life of the lithium-ion battery.
In order to reasonably design the electrode structure and avoid the mechanical damage that may occur in the structure, it is necessary to establish the force-electro-chemical coupling constitutive relation of the electrode material during charge and discharge. The usual practice is to use the in-situ measurement experiment and the Stoney formula to obtain the evolution of the stress during charge and discharge of the electrode material. However, this method must rely on three assumptions that the thickness of the thin film is much smaller than the thickness of the substrate, the thickness of the thin film is negligible in the deformation process, and the adhesion between the thin film and the substrate is good. The time high performance battery is usually difficult to meet these conditions.
In order to solve this problem, the research team of the State Key Laboratory of Nonlinear Mechanics at the Institute of Mechanics, Chinese Academy of Sciences, developed a set of finite element calculation methods based on the force-electro-chemical coupling theory, which can accurately characterize the charge of the electrode material during charge and discharge. Plastic deformation and intrinsic stress evolution. This method was used for finite element simulation. The error analysis of Stoney's formula caused by large elastic-plastic deformation of electrode film was described. The large deformation of the electrode film, elasto-plastic constitutive relation and interfacial material properties versus stress-charge-discharge curve The influence, as well as the correspondence between the electrode material parameters and the characteristics of stress-charge-discharge state curves. This work helps to study the force-electro-chemical coupling constitutive relation of electrode materials during charge and discharge.
Related research results have been published in the International Journal of power sources (Wen, J., Wei, Y., Cheng, YT, 2018. Examining the validity of Stoney-equation for in-situ stress measurements in thin film electrodes using large -deformation finite-element procedure. J.Power Sources, 387,126-134.) and Journal of the Mechanics and Physics of Solids (Wen, J., Wei, Y., Cheng, YT, 2018. Strength evolution in elastic plastic During electrochemical processes: A numerical method and its applications. J. Mech. Phys. Solids, 116, 403-415.). The study 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.
Figure: Typical layered battery structure and its deformation. (a) Electrode thin film-adhesive-substrate structure; (b) Comparing the numerical model with the experimental results, showing stress changes in the electrode film during charge and discharge processes; (c) Elasto-plasticity of electrode materials and interface failure Internal film shear stress profile.
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