Pouch Cell In-Situ Gas Volume Analyzer

MSE Supplies offers a Pouch Cell In-Situ Gas Volume Analyzer. It adopts high accuracy monitoring system, which can measure in-situ cells' volume changes in the entire charge-discharge process, obtain cells' gassing volume and the volume change rate during each stage. The analyzer can be used for improving efficiency, cost down, optimize cell design, etc.

Lithium-ion Battery Gassing Behavior

Formation gas production: The formation process of lithium-ion batteries will produce a large amount of gas. The amount of gas is closely related to the cell chemical system, anode and cathode materials, electrolyte components, and formation conditions. The formation conditions (such as current, cut-off voltage, temperature, pressure, etc.) affect the time of the formation step. We can improve the production efficiency of the battery by effectively shortening the formation cycle.

Gas production during overcharge: Lithium-ion batteries will have serious side reactions during the overcharging process. It causes a large amount of gas generation, which makes the battery volume or internal pressure increase rapidly (increase the risk of thermal runaway). It is a significant safety issue in actual use of lithium-ion batteries.

Gas production during storage or cycle: During long-term storage or cycling, lithium-ion batteries will undergo side reactions and produce gas (especially under high temperature), which is a very critical reliability issue for lithium-ion batteries.

Typical Testing (Ex-Situ) V.S Our Testing (In-Situ)

Typical testing (ex-situ): 

The method of displacement volume has been widely used to measure
cells volume after gassing. It is easy to operate but provides limited information:
1. Single point measuring: can only acquire partial data of volume change and gassing rate of the cells.

2. Non-in-situ measuring: easily interfered by external environment during the transfer-measurement process.

3. Weighed by general balance: unable to achieve an online, long-term, stable, and high accuracy measurement.

4. High waste of cells: unable to remove the influence of cell consistency.

5. Internal Pressure Measurement: It is also a widely used method, which monitors the internal pressure change of cells by implanting a pressure sensor into the cell. This method can only be applied on the prismatic cells, and needs to prepare special cell sample. In conclusion, it is complicated to operate and and has really high cost. 

Our testing (in-situ): 

Our system can monitor the gassing process continuously with high stability. It applied high accuracy ADC data acquisition module and multi-functional in-situ gas volume monitor software MISG. These help to monitor the volume changes during the charge-discharge process in real-time, and present the swelling and shrinkage level of battery online. 

Features:

• High-energy learning test system: long-term in-situ monitoring and meeting the accuracy requirements
• Dedicated test software: real-time display of mechanical test data and automatically draw the volume change curves
• Auxiliary system: special structure design convenient to intervene in supporting auxiliary system, realizing test temperature adjustment control

Applications:

• Gas Formation Analysis
• Gas Overcharge Analysis
• Gas Cycle Analysis
• Gas Storage Analysis
• Others

Technical Specifications：

Examples: 

1. Different materials’ formation gassing application

The modified material A has a smaller particle size than the conventional material B, and the SEI film formation reaction is more sufficient during formation, and the gas production is larger. With the same design parameters, only the modification and surface modification of the material are performed. By comparing the gas production and gas production rate of the cell formation, the effect of the processed material on the cell formation can be quickly and intuitively obtained, helping the development and improvement of new materials.

2. Different electrolyte's formation gassing application

In the same electrolyte, the cell formation gas production and its rate for electrolyte B with a certain additive is greater than electrolyte A without additives. This additive can make the cell film to form more completely. The additives in the electrolyte have a great influence on the SEI film formation reaction of the cell formation stage. By comparing the changes in the gas production volume and rate of the cell formation for the electrolyte with different additives, the effects of the additive on the cell formation can be evaluated. The influence of the formation process with the three electrode formation curves help improve the electrolyte formulation.

3. Different temperature and rate of formation conditions

The setting of the cell formation condition affects the cell formation time and the film quality. We can improve the cell production efficiency by shortening the cell formation time. By setting different formation conditions, the starting point of the gas production voltage of the cell and the gas production rate at each stage of the formation are obtained quantitatively, which helps to guide the improvement of the cell formation process and improves the production efficiency.

4. Different NCM materials' overcharge-gassing application

The above graphs are the cell's SOC comparison during gas production. We can see that the high nickel cell produces gas earlier. By monitoring the normal charging process of the battery cell, volume, temperature of overcharged to 200% SOC, three-electrode curve, the potential and reaction rate of a large number of side reactions, the overcharged lithium potential, and the positive electrode material decomposition potential, we can accurately obtained various information quantitatively

In the normal voltage range, the volume change of the cell is less than 1.2%, which is basically due to the structural swelling caused by lithium intercalation. When the SOC of high Ni-2 is greater than 40%, the structural swelling of high Ni-1 is slightly greater than that of high Ni-2. After overcharging to 5V, the SOC of high Ni-2 material is later than that of high Ni-1 material, which indicates that high Ni-2 material can adapt to higher charging voltage, release more capacity and improve the energy density of the cell while maintaining stable structure.

5. Types and contents of electrolyte additives

By comparing the overcharge gassing behavior of lithium-ion cells with two different types of additives, we can see the reaction potential of Additive A is lower than Additive B, and the total gassing is lower, which means it is a better overcharge protection additive.

6. Different NCM materials cycle-gassing application

The red line in the first graph is cell A and the black line is cell B. They used different ternary materials. Cell B's volume increased more than cell A and the irreversible volume increased from 0.01ml to 0.04ml.

7. Comparing NCM811 modified conditions

The above result shows that the voltage drop of NCM811 is larger in Method-1 and also more gas production. The in-situ method can be used to compare the advantages of different modification methods of different materials.

8. Comparing different types of electrode

The two cells above adopt different electrolyte systems. We can determine that EL-A cells produce more gas than EL-B cells by using the cell volume change curve. This result indicates that the electrolyte system is more likely to produce gas under high temperature and high pressure.

9. Comparing different storage temperature

From the above graph, we can see that the cell has good storage performance at 70°C and high gas production at 85°C. By using in-situ method, we can monitor the storage gas production behavior continuously and acquiring the data for gas production at starting point and maximum point.