A New In-situ Analysis Technology For Battery Gas Composition Of Lithium-ion Pouch Cells

 1. Author Information and Article Summary

In 2020, Jan-Patrick Schmiegel et al. installed a a gas sampling port (GSP) on the lithium-ion pouch cell, in-situ to realize the battery gas composition analysis of different charging times, different voltage states, different SOC, etc.

Figure 1. Schematic illustration of the gas sampling process and the corresponding voltage-dependent gas chromatograms.

2. Sample Preparation and Testing Device

2.1 Cell Information

NCM-811 / Artificial Graphite System, Add GSP Device in the Aluminum-plastic Film Packaging, As Shown in Figure 2.

Figure 2. Schematic diagram of the battery pack mounting flow

2.2 Electrochemical Test Process

The battery is first placed at 1.5V constant pressure for 20h, and then the transformation step, the gas in the gas bag is recycled and then a cycle, the gas composition will be analyzed regularly throughout the whole process.

2.3 Introduction of the In-situ Gas Sampling Port

As shown in Figure 3, the gas sampling port (GSP) device is sealed by thermal pressure at the edge of the aluminum-plastic film bag on the side of the battery.

Figure 3. Schematic diagram of the gas sampling port device

2.4 In-situ Battery Gassing Composition Analysis

GC-BID equipment is mixed with 200L high pure argon, and 5L of gas is removed at each CV step for component analysis. The schematic diagram of the gas extraction process is shown in Figure 4.

Figure 4. Schematic diagram of the gas extraction process

2.5 In-situ Cell Volume Measurement

Monitor the volume changes of the battery in real time by measuring the pull of the cell in the liquid.

2.6 Gas tightness verification of soft pack battery with gas sampling port

As shown in Figure 5, the cycle capacity monitoring of GSP battery and blank control group was carried out, and it was found that the capacity curve of the two was only 1 mAh, which shows that the gas tightness of GSP battery is good.

Figure 5. Cycle capacity comparison of the two batteries

3. Interpretation of Result

3.1 Electrochemical Performance Analysis

Figure 6 compares the differential capacity curves of both battery cycles with a reaction peak at about 3V, the reaction of EC reducing energy SEI on the negative electrode surface. Figure 7 monitors the volume change of the initially filled 1mL argon cell for four consecutive days and finds only about 22L error, which may originate from the noise signal rather than the volume change, indicating the good gas tightness of the cell.

Figure 6. Differential capacity curves during a cycle of two battery cycles

Figure 7. Cell volume changes during four-day storage process with GSP

3.2 Analysis of the Gas Production Mechanism in the Transformation Capacity Stage

The comparison of whether the electrolyte system cells containing FEC additives into the gas components at different voltage positions in the capacity, as shown in Figure 8, the gas corresponding to the dashed line is analyzed, and the differential capacity curve can be found that after FEC addition, the reaction peak of the battery at another 3V decreases, and comparing the gas components at different voltages in the charging process CO, C₂H₄ and C₂H₆ decreases in the battery after FEC addition, And compared with the gas volume, FEC-containing cells have less gas production.

Figure 8. Cell voltage vs cell capacity plot for the modified formation cycle of NCM-811

Figure 9. Differential cell capacity vs cell voltage for the first formation cycle for NCM-811

Figure 10. Gas production volume comparison of battery charging with different voltages of the two electrolyte systems

4. Summary

In this paper, GPS gas extraction device is assembled in lithium-ion pouch cell to realize in-situ battery gas composition analysis, which can monitor real-time gas production components at different voltage positions in the capacity process and be used to guide the in-depth analysis of battery gas production mechanism.

5. IEST Related Test Equipment Recommendation

In-situ Gas Production Volume Monitoring Instrument: Model GVM2200, test temperature range of 20℃ ~85℃, support dual-channel (2 cells) synchronous test, 1L resolution, good long-term stability, can synchronously monitor the gas production volume change of cells under circulation, storage, overcharge and discharge and other conditions, to help the research and development of materials and cells.

6. Original Paper

Jan-Patrick Schmiegel, Marco Leißing, et al. Novel In Situ Gas Formation Analysis Technique Using a Multilayer Pouch Bag Lithium Ion Cell Equipped with Gas Sampling Port.Journal of The Electrochemical Society, 2020 167 060516.