Battery systems have been evolving rapidly, with new battery technologies being developed each passing day. These new battery systems are developed after rigorous testing and analysis and are proving to be much more efficient than their traditional counterparts.
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Importance of Gas Analysis for Battery Systems
Battery gases are byproducts of internal chemical reactions occurring within batteries. The analysis of these gases can offer valuable insights into the battery's condition, aiding in the detection of potential issues and enhancing overall safety.
Gas analysis plays a crucial role in identifying early faults or abnormalities in batteries. Specific gas emissions during normal operation can signal problems like overheating, internal shorts, or other malfunctions.
Moreover, it serves as a tool to assess the battery's overall health. Variations in the types and amounts of emitted gases over time can signify battery degradation. It is an integral part of the research and development of new battery technologies, offering insights into battery chemistry and behavior under diverse conditions and contributing to the fabrication of safer and more efficient energy storage systems.
Gas Analysis during Thermal Runaway Mechanism
Thermal runaway (TR) in a lithium-ion battery (LIB) is a sequence of various chemical reactions. During TR, the battery cell temperature can rapidly rise, releasing toxic reaction gases. This can lead to an uncontrolled battery fire and the emission of toxic fire fumes, potentially resulting in an explosion. TR can be initiated by external factors like heat, mechanical damage such as penetration, short circuits, or overcharging of the battery.
To investigate the thermal runaway (TR) reaction in lithium-ion batteries (LIB), studies focus on quantifying the release of various gases under different conditions. Measurements are usually conducted near the TR source, where high concentrations of flue gases and elevated temperatures are observed. Gas and emission detectors are used for this purpose.
Commonly monitored gases during thermal runaway events in lithium-ion batteries include inorganic compounds like carbon monoxide (CO), carbonates such as dimethyl carbonate, acids like hydrofluoric acid (HF), and volatile organic compounds (VOCs) such as methane.
Research studies also often focus on battery off-gassing, which serves as an early indicator of an impending thermal runaway (TR) and can be detected minutes before full TR occurs. Detecting the initiation of a TR reaction is crucial for safety. Gases like hydrofluoric acid (HF) and various carbonates are commonly used as indicators, with a 1 ppm level of HF sometimes employed as a threshold.
Direct High Efficiency Gas Analysis of Li-ion Batteries
Significant efforts have been directed toward enhancing the energy density of lithium-ion batteries for wider applications in electric vehicles and grid energy storage. High concentrations of nickel, manganese, and cobalt in layered oxides on the cathode side show promise for the next generation of Li-ion batteries.
In the Journal of Power Sources, researchers have identified that some Ni-rich NMC cathodes, like NMC811, are already in use, offering higher capacities. However, a drawback is that increasing Ni content compromises the stability of NMC cathodes.
The article also states that gas generation is a significant side effect during the formation cycling process and repetitive charge and discharge of lithium-ion batteries. Gases formed at the interfaces between the electrode and electrolyte have been observed to migrate between the anode and cathode, initiating intricate local reactions with other gaseous species.
This, in turn, triggers additional side reactions at the interfaces. Gas generation and consumption have been identified as contributors to the degradation of material surfaces and increased anode interfacial resistance, and it negatively affects the long-term cycling performance of cells.
The researchers devised an innovative experimental setup to analyze gas generation in prismatic pouch cells in real time. A lithium-ion pouch cell was directly linked to a quadruple mass spectrometer via a glass capillary. The pressure difference facilitated the movement of generated gases to the mass spectrometer column for comprehensive analysis. Gaseous species were examined during both the formation cycle and aging cycles in Li-ion pouch cells.
In the formation cycle, the dominant species among the generated gases was C2H4 from the decomposition of Ethylene carbonate (EC), constituting nearly 90% of all generated gases. During the aging cycles, the hydrocarbons were identified as originating from the reduction of electrolyte at the anode side as the SEI layer progressed toward its complete formation.
Case Study: Gas Analysis of 21700 Li(Ni0.8Co0.1Mn0.1O2) Cell
The failure of lithium-ion batteries (LIBs) is associated with the release of toxic and flammable gases. The type and amount of these gases depend on factors such as cell type, failure mechanism, state of charge (SoC), and environmental oxygen (O2) levels. This understanding is crucial for battery pack manufacturers who rely on real-time monitoring to assess the state of health (SoH) of a LIB. It also has implications for emergency responders dealing with thermal runaway (TR) events.
In the study published in the Journal of Power Sources, researchers used a Hiden HPR-20 mass spectrometer for real-time analysis of battery vent gas from a commercially available NMC-811 21700 cell.
NMC chemistry was chosen due to its prevalence in high-performance applications. Real-time results indicated that safety venting produced mostly methane, with methane concentration positively correlated with state of charge (SoC). In contrast, during thermal runaway (TR), the gas mixture included hydrogen (H2), carbon dioxide (CO2), and carbon monoxide (CO). This real-time gas analysis is useful for studying the chemical stability of batteries while also having concrete information about their degradation.
In short, gas analysis is essential to ensure the durability and safe operation of battery systems, especially Lithium-ion batteries.
More from AZoM: The Importance of Gas Analysis in Hydrogen Fuel Cells
References and Further Reading
Gasmet: A Nederman Company, 2023. Gas Analysis – the Cornerstone of Battery Safety Testing. [Online]
Available at: https://www.gasmet.com/blog/gas-analysis-the-cornerstone-of-battery-safety-testing/
Abbott, K. et. al. (2022). Comprehensive gas analysis of a 21700 Li (Ni0. 8Co0. 1Mn0. 1O2) cell using mass spectrometry. Journal of Power Sources, 539, 231585. Available at: https://doi.org/10.1016/j.jpowsour.2022.231585
Hiden Analytical (2023). Real-Time Gas Analysis of Li-ion Battery Failure [Online]
Available at: https://www.hidenanalytical.com/research/real-time-gas-analysis-of-li-ion-battery-failure/
Geng, L. et. al. (2020). High accuracy in-situ direct gas analysis of Li-ion batteries. Journal of Power Sources, 466, 228211. Available at: https://doi.org/10.1016/j.jpowsour.2020.22821
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