1. Author Information and Article Abstract

Recently, Peng Tan’s group (first author Zhiyuan Zhang) at the University of Science and Technology of China (USTC) investigated the effects of external pressure on the polarization and cycling performance of silicon-based anode battery, and found that the appropriate external pressure can reduce the polarization of the cell during the cycling process, and that applying a stepped external pressure during the battery cycling process can significantly enhance the cycle life. The results of this study can be used as an effective strategy for capacity enhancement of silicon-based anode battery to guide the process design of battery packs.

2. Experimental Plan

2.1. Battery cell design system and charge and discharge conditions:

as shown in the table below：

2.2 High-precision In-situ Swelling Characterization Equipment: IEST-SWE2100 in-situ swelling equipment is used to apply precise external pressure to the cell and detect thickness swelling.

Visual and Textual Analysis

The author explored the impact of polarization on the charge and discharge process by changing the external pressure exerted on the surface of the cell. It was found that as the pressure increased, the peak position of the differential capacity curve first moved to the left and then to the right, among them, the cell corresponding to 0.02MPa has the smallest polarization, indicating that this pressure is the most suitable test condition.

Continue to explore the cycle life of the cell under the external pressure of 0.02MPa. As the cycle progresses, the swelling thickness trend of the cell has three stages: rapid growth, slow growth, and rapid growth. This phenomenon corresponds to the capacity attenuation trend.

Combining CT and SEM to analyze the thickness difference of the cell before and after aging, it was found that due to different binding forces, the thickness expansion of different locations of the cell will also be different, after the battery core ages, the electrolyte dries up, the contact between particles deteriorates, and side reactions increase, etc. These will cause the polarization of the cell to increase and the capacity to lose.

Based on the above analysis, the author developed a way to improve the cycle life of the cell. During the cycle process of the cell, the external pressure is continuously increased, which can make the cell capacity rebound to a certain extent. As the cycle progresses, the electrolyte decomposes to produce serious gas, the particle expansion gap increases, and side reactions increase. Capacity loss can be slowed down by loading increasing pressure, compared with applying a fixed 0.02MPa pressure, the stepped force method increases the capacity retention rate of the cell from 80% to 85%.

3. Summary

By exploring the impact of external pressure on the polarization and cycle performance of silicon-based anode battery, it was found that appropriate external pressure can reduce the polarization of the cell during cycling, and applying stepped external pressure during the battery cycle can significantly Improve cycle life. The research results can be used as an effective strategy to increase the capacity of silicon-based anode battery and guide the process design of battery packs.

4. Original Article

Performance of Lithium-Ion Pouch Cells with Silicon Composite Anodes under External Mechanical Pressure

5. Recommended Test Equipment Related to IEST

SWE series in-situ swelling analysis system (IEST): Utilizing a highly stable and reliable automation platform, equipped with a high-precision thickness measurement sensor, it can measure the thickness change amount and change rate of the cell during the entire charge and discharge process, and can achieve the following functions:

• Test battery swelling thickness curve under constant pressure condition.
• Test battery swelling force curve under constant gap condition.
• Battery compression performance test: stress strain curve – compression modulus.
• Step-by-step test of battery swelling force.
• Different temperature controls: -20~80°C.