Literature Interpretation: Gas Composition Analysis and Detection of In-situ Gas Production of Lithium Batteries.
Jan-Patrick Schmiegel et al. from the Battery Research Center of the Institute of Physical Chemistry of the University of Munich, Germany, published a study on the analysis and detection of gas composition of in-situ gas production of lithium batteries in the journal Electrochemical Society, which studied the analysis of gas composition of batteries under different charging times, different voltage states and different SOC conditions through a gas sampling device (GSP, gas sampling port) installed on lithium-ion pouch batteries. The following are the specific research protocols:
Samples and testing equipment
1. Cell information: GSP device is added when the aluminum-plastic film is packaged. Battery assembly process using NCM-811 synthetic graphite system
2. Electrochemical test steps
Perform 20 hours on the battery (15V constant voltage) and then start to enter the formation step.
When the formation is finished, the gas in the air pocket is extracted and resealed, and then recycled. Throughout the process, the composition of the gas is analyzed periodically.
3. Introduction of in-situ gas extraction device
The GSP in-situ air extraction device is adopted, and the edge of the aluminum-plastic film bag on the side of the battery is sealed by hot pressing.
4. In-situ gas composition analysis
In the study, 5 L of gas was removed for gas composition analysis at each CV step in the cell (Analytical Equipment: GC-BID).
5. Volume measurement of in-situ batteries: Monitor the volume change of the battery throughout the formation process in real time by measuring the buoyancy of the battery in the liquid.
6. Verification of air tightness of pouch batteries: By monitoring the cyclic capacity comparison between the GSP battery and the blank control group, it was found that the capacity curve of the two was 1 mAh different, which fully indicated the good air tightness of the GSP battery.
Analysis of results:
During the cycle of the two batteries, a reaction peak will appear around 3V:
EC reactions on the surface of the negative electrode to reduce performance SEI.
Through four consecutive days of monitoring and experimental maps, the error between the two is only about 22 l, which may come from external noise, i.e., environmental influence, rather than the change in its own volume, which once again verifies the good air tightness of the battery.
a.Differential capacity curve b. for one cycle of two batteriesThe change in the volume of the GSP cell during the four-day storage period.
c.The difference between the formation capacity curves of the two types of batteries with or without FEC and the corresponding gas outlet voltage and differential capacity curves.
The gas composition was analyzed at the position corresponding to the dotted line, and compared with the differential capacity curve, it was found that the reaction peak of the battery at about 3V was reduced after the addition of FEC, and compared with the gas composition at different voltages during the charging process, it was found that the content of CO, C2H4 and C2H6 in the gas produced by the battery after adding FEC was significantly reduced, and the gas production of cells containing FEC was also less compared with the volume of gas production.
Gas composition curves of different voltages for battery charging of two electrolyte systems.
Comparison of the gas production volume of two electrolyte system batteries at different voltages.
Summary
In this study, the analysis of gas components of in-situ gas production is realized through the GSP gas production device in lithium-ion pouch batteries, and the specific components of gas production at different voltage positions in the formation process can be monitored in real time, which has an important reference role for further understanding and analysis of the gas production mechanism.
Electro-Relaxed DC GPT Solution
The testing methods used in the institute cannot really realize the linkage test of gas production volume measurement and composition analysis, so as to achieve the purpose of real-time in-situ measurement. Moreover, it is necessary to preset the pipeline in the pouch battery packaging stage, which cannot realize the gas production failure analysis of the packaged pouch battery or even the hard-shell battery. Therefore, it has certain limitations.
The DC GPT solution of the Relaxation In-situ Gas Production Tester can directly feed the battery gas production from pouch cells, square shell batteries, and cylindrical batteries into the gas production volume measurement device through a specially designed GSP gas recovery device. The gas production volume measurement device adopts the patented technology of ultra-trace gas flow measurement, and can monitor the gas production behavior of the battery in real time, continuously, in-situ, real-time, and continuously through the GSP gas production device, including parameters such as gas production volume and gas production rate. Compared with the instrument measuring device based on the traditional Archimedes buoyancy method, ideal gas calculation method and other methods, this equipment can directly measure the volume data (l) of the micro-produced gas without data conversion or conversion, and the data can directly monitor the trace volume change of the gas, and the results are accurate and reliable, and the repeatability is high. At the same time, the equipment can be connected in series with GC-MS, DEMS and other gas composition analysis equipment to realize the linkage test and detection means of gas production volume measurement and component analysis, which provides real and reliable data support for material research and development and the analysis and research of the gas production mechanism of lithium battery cells.
References
jan-patrick schmiegel, marco leißing, et al. novelin situ gas formation analysis technique using a multilayer pouch bag lithiumion cell equipped with gas sampling port. journal of the electrochemicalsociety, 2020 167 060516.