Elucidation of the Effects of Particle Morphology on Stress and Reaction Fields in All-Solid-State Battery Electrode Structures and Structural Design
Authors: Sato Koki , Eto Yuki , Yano Shinichiro , So Magnus , Yano Takeru , Inoue Gen 
Published: December 2024

In recent years, demand for rechargeable batteries for electric vehicles and energy storage systems has been growing. In particular, Lithium-ion Batteries (LiB) have various advantages such as high energy density and output density, high voltage, and excellent cycle characteristics, but they use flammable organic electrolyte, which poses a safety problem due to the risk of ignition. In addition, as demand for LiB increases, there is a need to further improve their performance. Therefore, All-Solid-State Batteries (ASSB) are attracting attention as a next-generation storage battery that can replace LiB. ASSB do not use flammable organic electrolyte, but non-flammable inorganic electrolyte, which is thought to improve safety, enable a layered structure, increase capacity, and solve other issues. In a conventional battery using electrolyte, the active material (AM) is completely covered by the electrolyte, whereas in an ASSB, the AM and solid electrolyte (SE) are solid materials, so it is important to handle the effects of solid-solid interface contact and microstructure, and it is necessary to solve the problem of electrode layer contact area. The particle shape of the AM affects the reaction field area and ionic conduction pathways. From the viewpoint of the reaction area, the gap between the AM and the SE inhibits the insertion and desorption of Li+, and from the viewpoint of the ionic conduction pathway, the gap between the SE inhibits the conduction pathway of Li+. In this study, we elucidated the effect of particle shape on battery performance in the anode of ASSB, and proposed a guideline for the optimal design of new materials.

The discrete element method (DEM) is a time-evolving method for solving the motion of solid particles based on the equations of motion for translation and rotation. It calculates the forces acting on the particles by assuming springs and dashpots that represent elastic and viscous damping between the particles. In addition, plastic deformation is reflected by considering dashpots between particles [1]. After the electrode layer was created by DEM, tortuosity and contact area were obtained. Multi-Network Model (MNM) [2] was used in the electrochemical calculations. In MNM, AM–AM, SE–SE, and AM–SE particle networks were constructed, and electronic conduction, ionic conduction, ion diffusion, and interfacial electrode reactions were calculated. The analytical equations were solved based on Newman's theory of porous electrodes [3] by coupling the Li concentration in AM, AM electronic potential, electrolyte ion potential, and electrochemical reactions. The Li concentration in AM was determined from the diffusion equation, the electron and ionic potentials were determined to satisfy the electroneutrality condition, and the electrochemical reaction was determined from the Butler-Volmer equation.

By changing the particle shapes in the ASSB electrode structure using DEM, contact area and tortuosity of each particle shape were quantitatively evaluated. The results of the electrochemical calculations using the results obtained in this study were reflected in MNM, suggesting that the relationship between contact area and tortuosity of the particle shape influences the battery performance.

Acknowledgment

This study was supported by JST–Mirai Program(JPMJMI24G1), Japan.

References

[1] M. So, G.Inoue et al., J. Electrochem. Soc., 168 030538 (2021).

[2] R. Hirate et al., MATEC Web of Conferences, 333, 17002 (2021).

[3] G. M. Goldin et al., Electrochim. Acta, 64, 118 (2012).