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

Lithium-ion batteries have been widely used in all aspects of life, such as mobile phones, cars or household energy storage, etc. Therefore, it is particularly important to evaluate various performances of lithium-ion batteries. We know that lithium batteries will expand or shrink during charging and discharging, so when designing lithium battery modules, the swelling parameter is one of the important parameters that must be considered. In addition, with the emergence of a new generation of negative electrodes with high specific capacity (such as silicon-based negative electrodes or lithium metal negative electrodes), their structural swelling is much more obvious than that of traditional graphite negative electrodes ^[1,2], Therefore, more and more companies are focusing on the evaluation of the swelling performance of lithium batteries.

Usually, researchers have to prepare electrode into single-layer or multi-layer finished batteries to evaluate the swelling. This method has a long testing cycle, low evaluation efficiency, and consumes a lot of resources, which seriously affects the development process of new materials. IEST has recently innovatively used the model coin cell to evaluate the swelling behavior of the battery electrode, which greatly shortens the evaluation cycle of the material swelling performance, and can save a lot of manpower and material resources for preparing batteries for universities or enterprises. For this model coin cell battery, users are most concerned about whether its cycle efficiency is comparable to that of a traditional steel shell battery pack, and whether the swelling thickness change measured by the model coin cell battery is comparable to that of the finished battery. For this concern, this article provides corresponding comparison data based on these two aspects, which is convenient for users to evaluate and choose.

1.Testing Condition

1.1 Testing Equipment: This article uses the model button battery of IEST and cooperates with the silicon-based negative electrode swelling in-situ fast screening system (RSS1400, IEST) to carry out the charging and discharging test and swelling test of modern coin cell and pouch cell batteries.

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

1.2 Charge and Discharge Test Conditions

①Use IEST's model coin cell battery to assemble NCM//Li coin cell half-cell and NCM//SiC coin cell full battery, and perform 3-cycle charge and discharge at a rate of 01C, which is convenient for subsequent comparison between commercial steel shell button batteries and Performance of single-layer pouch cell stacked batteries.

②Use the commercial 2032 steel shell to assemble the button half battery of NCM//Li, and perform 3 rounds of cycle charge and discharge at the rate of 01C.

③Assemble NCM//SiC single-layer pouch cell laminated batteries, and perform 3 cycles of charge and discharge at a rate of 01C.

1.3 Cell Swelling Test Conditions

The NCM//SiC model Button-type full battery and single-layer pouch cell laminated battery are placed in the silicon-based anode swelling in-situ fast screening system (RSS1400, IEST). After applying an initial preload of 5 kg, the swelling thickness changes of the two were monitored in real time during the charge and discharge process of 01C.

2.Result Analysis

2.1 Comparison of charging and discharging efficiency between the IEST model coin cell battery and the commercial 2032 steel shell coin cell battery. 

The left picture of Figure 2 is the IEST model coin cell, and the right picture is the commercial 2032 steel shell coin cell. We used ternary positive electrodes of the same size and composition to assemble a pair of lithium-sheet coin half-cells, and compared the Coulombic efficiencies of the two at 01C charge and discharge rates, the results are shown in Table 1. It can be seen from the figure that the first effect of the model coin cell is about 89.13%, which is only about 0.718% lower than the commercial steel coin cell, the maximum cycle efficiency of the second and third laps is only about 1.28% lower than that of the commercial steel shell button. In addition, the maximum cycle efficiency COV of the model button and the steel case button for three cycles is only 0.65% (where COV=standard deviation/average*100, in general, if COV<5%, it indicates the repeatability of the two The reproducibility is relatively good), so it can be considered that the IEST model coin cell battery has similar cycle charge and discharge performance to the commercial steel shell coin cell battery!

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

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

2.2 Comparison of the swelling thickness of the IEST model coin cell battery and pouch battery

The left picture of Figure 3 is the IEST model coin cell battery, and the right picture is a single-layer pouch cell laminated battery. The two use the same composition of ternary positive electrode and silicon carbon negative electrode to assemble a full battery, and monitor the swelling thickness change of the two during the charge and discharge process of 01C in real time. The voltage curve and thickness swelling curve of the two are shown in Figure 4, the specific full battery cycle efficiency and swelling thickness comparison are shown in Table 2 and Table 3, respectively. It can be seen from Figure 4 that, whether it is the voltage curve during the charge and discharge process or the thickness swelling curve, the model coin cell battery and the pouch cell laminated battery all show good consistency. It can be seen from Table 2 that, the first efficiency of the model coin cell battery and the pouch cell laminated battery are 41.82% and 42.42%, respectively, and the cycle efficiency of the last two cycles is only 0.12% different; However, it can be seen from Table 3 that the thickness swelling rate COV of the two circles is also within 3.5%, indicating that the thickness swelling rate of the two also has a good consistency.

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

Figure 4. The blue dotted and solid lines are the voltage curve and thickness swelling curve of the model button respectively;

The orange dotted and solid lines are the voltage curve and thickness swelling curve of the single-layer pouch laminated battery respectively.

Table 2. Comparison of cycle efficiency between NCM//SiC model button-type full battery and single-layer pouch laminate battery

Table 3. Comparison of swelling thickness of NCM//SiC model button full battery and single-layer pouch laminate battery

3.Summary

This paper evaluates the charge and discharge performance and swelling thickness of the IEST model coin cell. It can be seen from the results that the cycle charge and discharge efficiency of the model coin cell is basically the same as that of the commercial 2032 steel shell coin cell, the thickness swelling rate during the 3-cycle cycle is also basically consistent with the test results of the single-layer pouch cell laminated battery, indicating that the IEST model coin cell battery has a good cycle charge-discharge efficiency and swelling evaluation effect. This article recommends the use of a silicon-based negative electrode swelling in-situ fast screening C system (RSS1400, IEST) for use with this model, and its thickness swelling test accuracy is 0.1 μm, the resolution can reach 0.01μm, and it has good detection and resolution capabilities for the subtle thickness changes caused by the phase transition of intercalation and deintercalation of lithium, which will help the development of new low-swelling, high-capacity anode materials!

4.Reference Materials

[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.