Session: 03-13-01: Multifunctional Electronics and Energy Devices

Paper Number: 95397

95397 - Three-Dimensional Finite Element Analysis of Microstructural Deformation of Anode Sheet in Lithium-Ion Battery (Lib) 

(Abstracts)

Anode of a lithium-ion battery has a layered structure consisting of active material layer (consisting of binder and active material) and foil layer of current collector (copper foil). Since flexible batteries are used in wearable devices and IoT devices, various deformation (various loads) is often experienced in their practical use. Since the performance of the copper foil itself cannot be significantly changed, the deformability and reliability of the active material layer is important for improving their flexibility and ensuring electrical properties. To achieve higher performance of LiB, micromechanical design of the active material layer is strongly necessary. This study thus established a method for creating a three-dimensional model with microstructure that enables micromechanical design of the active material layer using the finite element method (FEM). The validity of the model and the deformation mechanism were discussed by comparing the results with uniaxial tensile tests of anode sheet.

(Method)

Since the active material layer is a brittle material, which is coated on copper foil, it is not possible to make a free-standing layer (as a single active material layer). Therefore, uniaxial tensile tests were conducted for the entire anode sheet, and the nominal stress-strain curve of the active material layer was computationally obtained by using the superposition principle. In addition, nominal stress-strain curves were obtained for the bulk binder material using the same method. Subsequently, to create the FEM model, cross-sectional observation was performed using scanning electron microscope (SEM). Distribution of the particle size and volume ratio of the Si content were obtained from the SEM images, and those are reproduced in the FEM model. The nominal stress - strain curve of the binder obtained previously was input as the binder properties, and compute uni-axial deformation of active material layer. The computed stress-strain curve was compared with that obtained from experimental tensile test. Deformation mechanism in microstructure was elucidated.

(Result and discussion)

It is found that the nominal stress- strain curves from the experiments showed similar trend with that of FEM computation. Therefore, it can be said that this model is a sufficiently reproducible three-dimensional model with a relatively simple creation method. At the microstructural point of view, the deformation was mainly caused by the binder, and stress concentration occurs between the particle-binder interface, resulting in microcracks around the stress concentration. This trend was very similar with experimental microstructure of SEM images.

(Conclusion)

This study developed an FEM model of the active material layer in the anode sheet of lithium-ion battery. Since the active material consists of Si particles and polymeric binder, such a microstructure was mimicked in our three dimensional FEM model. Uni-axial deformation behavior was computed, and their deformation behavior was compared with experiments. Furthermore, deformation mechanism of microstructure was elucidated. At large deformation, the binder was a critical, and it is found that crack nucleation and interface delamination caused by stress concentration between the particle and binder interface. These are considered to be the cause of battery short circuits.

Presenting Author: Kazuma Ogata Chuo University

Presenting Author Biography: I'm a graduate student at Chuo university.

Authors:

Kazuma Ogata Chuo University
Yoshinori Takano Chuo University
Akio Yonezu Chuo University