In-situ Testing of The Volume, Stress, and Thickness Changes of Different Silicon Anodes in Pouch Cells

1. Author Information and Article Abstract

In 2017, the J.R. Dahn research group investigated silicon anode pouch cells using in-situ characterization methods to measure volume, stress, and thickness changes of electrodes during cycling. By combining experimental data with computational analysis, they quantitatively determined the contribution of each component in silicon-composite electrodes to overall volume expansion, laying a foundation for understanding the expansion mechanisms of silicon anode materials.

2. Experimental Procedure

2.1 Fabrication of Three Types of Pouch Cells:

(A) Li(Ni₁₋ₓ₋ᵧCoₓAlᵧ)O₂ (NCA)/SiO-graphite (Supplier A), fully charged to 4.2 V with a capacity of 260 mAh;

(B) LiCoO₂ (LCO)/Si Alloy-graphite (Supplier B), fully charged to 4.35 V with a capacity of 230 mAh;

(C) Li(Ni₁₋ₓ₋ᵧCoₓAlᵧ)O₂ (NCA)/nano Si-C (Supplier C), fully charged to 4.4 V with a capacity of 165 mAh.

2.2 Testing Equipment and Procedures:

In situ XRD, in situ volume expansion, in-situ stress expansion, and in situ thickness expansion tests were conducted. The setups for stress and thickness measurements are illustrated in Figure 1.

Figure 1. Stress and thickness expansion testing apparatus.

3. Results and Analysis

Figure 2 shows the volume, stress, and thickness expansion curves of the three pouch cell types during charge/discharge. Cells A and B exhibited comparable volume and stress expansion, both significantly larger than Cell C. Cells A and C displayed plateau regions in their expansion curves at high voltages, while Cell B showed steep increases/decreases in the same range. Since these curves reflect combined contributions from both electrodes, isolating the anode’s expansion requires component-specific analysis.

Figure 2. Volume, stress, and thickness expansion curves of the three cell types during charge/discharge.

Figure 3(a)(b) presents volume expansion ratios of pure Si and graphite from literature. Figure 3(c) shows the expansion ratio for the NCA material as determined by the in situ XRD method in this study. The results reveal that silicon and graphite undergo volume expansions of approximately 280% and 10%, respectively, during charging. The expansion curve for silicon increases linearly with state-of-charge (SOC), whereas the graphite expansion curve exhibits a step change during the 2L→stage 2 phase transition, with no significant overall volume expansion in that stage. In contrast, the NCA material exhibits an opposite trend during charge and discharge, contracting by about 4.5% in volume over the entire charging process, with the majority of the contraction occurring in the high-SOC region.

Figure 3. Volume Change Ratio Curves of Three Pure Electrode Materials during Charge/Discharge

Figure 4: By fitting the dV/dQ curves, the influence of each component on the overall voltage–capacity curve for the Si and graphite composite is obtained.

Figure 4. Voltage-capacity curve fitting for Si and graphite composites

Figure 5: This figure presents the decomposition of the component-specific volume expansion curves for the full cell, comparing the SiO/graphite composite electrode with the NCA electrode. The plateau observed in the high-voltage range of Cell A’s expansion curve is attributed to the contraction of the NCA counteracting the expansion of SiO. This results in a net plateau in the overall cell expansion profile.

Figure 5. Decomposed Component Volume Expansion Curves for the Full Cell of the SiO/Graphite Composite Electrode and NCA Electrode

Figure 6: Figure 6 shows the expansion force and capacity change curves over long cycle-life tests for pouch cells B and C. When comparing the cycling and expansion performance between these cells, the cell with LCO/Si alloy-carbon exhibits higher irreversible expansion forces and a faster capacity decay rate than the cell with NCA/Si–C.

Figure 6. Long Cycle-Life Expansion Force and Capacity Change Curves for Pouch Cells B and C

4. Conclusion

The authors applied in-situ characterization methods to measure the volume, stress, and thickness changes of the electrodes. By combining these measurements with computational analysis, they quantitatively determined the volume expansion contribution of each component in the silicon composite electrode. This work lays the foundation for a deeper understanding of the expansion mechanism in silicon anode materials.

5. Original Article

6. IEST Recommended Testing Equipment

6.1 IEST In-Situ Battery Gassing Volume Analyzer(Model GVM2200). Key features include:

• Integrated Force and Electrical Testing System: Capable of long-term in situ online monitoring with high resolution (1 μL).
• Temperature-Controlled Environment: Operates over a temperature range of 20–85°C.
• Dedicated Testing Software: Real-time data acquisition and display for the mechanical testing system, with automatic plotting of volume change curves alongside electrochemical performance curves.

6.2 IEST In-Situ Cell Swelling Testing System(SWE Series)

Utilizing a highly stable and reliable automated platform integrated with a high-precision thickness sensor, this system measures the total thickness changes and rate of change during the entire charge/discharge cycle of the battery. Its capabilities include:

• Measuring the battery’s expansion thickness curve under constant pressure conditions.
• Measuring the battery’s expansion force curve under constant gap conditions.
• Testing the battery’s compression performance: stress–strain curves and compression modulus.
• Stepwise testing of battery expansion force.
• Temperature control over a range of −20 to 80°C.