Charge/Discharge Efficiency and Expansion Thickness of Model Coin Cell Performance Evaluation

1. Background

1. Background

Lithium-ion electrodes undergo repeated volume changes during lithiation and delithiation. Emerging high-capacity anodes — such as silicon-based and lithium-metal anodes — exhibit much larger dimensional changes than graphite, making swelling evaluation a critical part of material screening and module design. [1,2].

Typically, researchers evaluate electrode swelling by building single-layer or multi-layer finished cells. However, this process is time-consuming, inefficient, and resource-intensive, often slowing down the development of new materials. In response, IEST has introduced an innovative approach using a model coin cell to efficiently evaluate electrode expansion. This method significantly shortens testing cycles and reduces the material and manpower required for full-cell assembly, making it ideal for both academic and industrial applications.

A common concern among users is whether this model coin cell can deliver cycling efficiency comparable to traditional steel-case batteries, and whether its expansion measurements align with those of finished batteries. This article addresses these concerns by presenting comparative data in both areas, helping users make informed decisions.

2. Testing Condition

2.1 Testing Equipment

This study uses the model coin cell of IEST and cooperates with the Silicon-Based Anode Swelling In-Situ Screening System(RSS1400, IEST) to carry out the charging and discharging test and expansion test of model coin cell and pouch cells. The RSS1400 system is specifically designed for high-precision thickness monitoring, making it ideal for in-situ expansion analysis.

Figure 1. Silicon-based anode swelling in-situ rapid screening system (RSS1400)

2.2 Charge and Discharge Test Conditions

• IEST’s Model Coin Cell was used to assemble NCM/Li half-cells and NCM/SiC full cells. These were subjected to three charge–discharge cycles at 0.1C to facilitate comparison with commercial steel-case coin cells and single-layer pouch cell stacked batteries.

• A commercial 2032 steel-case coin cell was assembled into an NCM/Li half-cell configuration and cycled under the same conditions.

• A single-layer pouch cell laminated battery (NCM/SiC) was also assembled and cycled three times at 0.1C.

2.3 Cell Expansion Test Conditions

The NCM/SiC Model Coin Cell full battery and the single-layer pouch cell laminated battery were placed in the RSS1400 system. An initial preload force of 5 kg was applied, and real-time thickness changes were monitored during 0.1C charge–discharge cycles.

3. Result Analysis

3.1 Cycling Efficiency: IEST Model Coin Cell vs. Commercial Steel-Case Coin Cell

The left image in Figure 2 shows IEST’s model coin cell, while the right shows a commercial 2032 steel-case coin cell. Both were assembled into NCM/Li half-cells using identical ternary cathodes and cycled at 0.1C. Table 1 compares their Coulombic efficiencies.

The first-cycle efficiency of the model coin cell was approximately 89.13%, only about 0.72% lower than that of the steel-case cell. The difference in maximum efficiency over the next two cycles was within 1.28%. The coefficient of variation (COV) for efficiency over three cycles was only 0.65% (where COV < 5% indicates good reproducibility). These results confirm that the model coin cell offers cycling performance comparable to conventional steel-case coin cells.

Figure 2. The left picture is the model coin cell of IEST; the right picture is the commercial 2032 steel shell cell.

Table 1. Comparison of cycle efficiency between NCM/Li model coin half-cells and commercial steel-shell cells

3.2 Expansion Thickness: IEST Model Coin Cell vs. Single-Layer Pouch Cell

The left side of Figure 3 shows IEST’s model coin cell, and the right shows the single-layer pouch cell stacked battery. Both were assembled into NCM/SiC full cells using the same electrode materials. Their voltage and thickness expansion profiles during 0.1C cycling are shown in Figure 4.

As illustrated, both the voltage and expansion curves align closely between the two cell types. Table 2 indicates that the first-cycle efficiency was 41.82% for the model coin cell and 42.42% for the single-layer pouch cell, with a mere 0.12% difference in efficiency in subsequent cycles. Table 3 shows that the thickness expansion COV remained below 3.5%, confirming that the model coin cell effectively replicates the expansion behavior of pouch-type full cells.

Figure 3. The left picture is the IEST model button battery; the right picture is the single-layer pouch stacked cell.

Figure 4. The blue dashed and solid lines are the voltage profile and thickness expansion profile of the model coin cell, respectively;
Orange dashed and solid lines are the voltage profile and thickness expansion curve of single-layer pouch cell, respectively

Table 2. Comparison of cycle efficiency between NCM/SiC model coin cell and single-layer stacked stacked pouch cell

Table 3. Comparison of expansion thickness of NCM/SiC model coin cell y and single-layer stacked pouch cell

4. Discussion & practical benefits

Why the model coin cell works: the IEST model coin cell preserves critical stack architecture and electrode-to-electrode pressure conditions that determine thickness changes during cycling. When tested under a controlled preload in RSS1400, the model format captures the same deformation trends observed in single-layer pouch assemblies.

Key advantages for R&D:

• Faster screening: dramatically shortens evaluation cycles compared with full pouch builds.

• Lower resource use: reduces electrode and cell component consumption for early material triage.

• High sensitivity: RSS1400’s sub-micron resolution enables detection of minute reversible and irreversible expansions tied to phase changes or mechanical degradation.

• Good predictive power: close correlation with single-layer pouch results supports confident down-selection for scale-up.

Recommended use case: use the IEST Model Coin Cell together with RSS1400 for early-stage evaluation of high-expansion anode materials (e.g., silicon composites) to rapidly compare formulations, coating thicknesses, and pre-treatment strategies before committing to larger pouch or cylindrical prototypes.

4. Summary

This study demonstrates that IEST’s model coin cell delivers cycling efficiency on par with commercial steel-case coin cells and accurately reflects the expansion characteristics of single-layer pouch cell configurations. The results confirm that the model coin cell is a reliable, efficient, and resource-saving solution for evaluating electrode materials, particularly for swelling analysis.

For optimal results in silicon-based anode expansion tests, we recommend using the model coin cell with the Silicon-Based Anode Swelling In-Situ Screening System (RSS1400). This system offers exceptional precision, with thickness measurement accuracy of 0.1 μm and resolution up to 0.01 μm, enabling detection of subtle phase-change-induced expansion—making it an essential tool for developing next-generation, low-expansion, high-capacity anode materials.

5. References

[1] J. Lin, L. Wang, Q.S. Xie, Q. Luo, D.L. Peng, C. B. Mullins and A. Heller, Stainless Steel-Like Passivation Inspires Persistent Silicon Anodes for Lithium-Ion Batteries. Angew. Chem. 135 (2023) e202216557.

[2] M. Ashuri, Q.R. He and L.L. Shaw, Silicon as a potential anode material for Li-ion batteries: where size, geometry and structure matter. Nanoscale 8 (2016) 74–103.