Abstract
This comprehensive study examines the thermal runaway behavior of high-capacity (120 Ah) lithium iron phosphate (LFP) batteries under various test atmospheres. The experiments were conducted in sealed pressure chambers filled with either inert gas (nitrogen) or air. Key parameters, including battery and ambient temperatures, gas production components, and explosion limits, were recorded and analyzed. Results show that compared to an inert atmosphere, the air atmosphere led to a 17.6% increase in battery temperature, a 14% extension in thermal runaway duration, and an 8.2% rise in gas production. This research provides valuable insights into the thermal runaway characteristics of LFP batteries and their behavior under different environmental conditions.
Keywords: lithium iron battery, LFP battery, thermal runaway, test atmosphere, gas production, explosion limit
1. Introduction
Lithium-ion batteries (LIBs) have become prevalent in various applications, including electric vehicles, energy storage systems, and portable electronic devices, due to their high energy density and long cycle life. However, safety concerns persist, particularly regarding thermal runaway incidents, which can lead to catastrophic fires and explosions.
Thermal runaway in LIBs occurs when internal temperatures rise above a critical threshold, triggering rapid exothermic reactions that generate large amounts of heat and flammable gases. Understanding the factors that contribute to thermal runaway and the influence of different test atmospheres is crucial for developing safer battery systems.
This study focuses on the thermal runaway behavior of high-capacity LFP batteries under both inert and air atmospheres. The objectives are to:
- Analyze the thermal runaway characteristics of 120 Ah LFP batteries.
- Investigate the effect of different test atmospheres on battery temperatures, gas production, and explosion limits.
- Provide recommendations for improving the safety of LIB systems.
2. Literature Review
Several studies have examined the thermal runaway behavior of LIBs under various conditions. Wang et al. (2018) investigated the thermal runaway mechanism of LIBs for electric vehicles, highlighting the complexity of the underlying chemical reactions. Other research has focused on specific battery. Other research has focused on specific battery chemistries and configurations. For instance, Jia et al. (2023) compared the thermal runaway and gas venting behaviors of LFP and NCM (nickel-cobalt-manganese) batteries under overcharging and overheating conditions.
While previous studies have provided.
While previous studies have provided valuable insights, there is a lack of comprehensive research on the influence of test atmospheres on the thermal runaway behavior of high-capacity LFP battery. This study aims to fill this gap by investigating the behavior of 120 Ah LFP battery under both inert and air atmospheres.
3. Materials and Methods
3.1 Battery Sample and Preparation
The study used commercial 120 Ah LFP battery with the following specifications:
- Chemistry: Lithium iron phosphate (LFP)
- Capacity: 120 Ah
- Dimensions: 174 mm × 170 mm × 48 mm
- Initial Mass: 2860 g
- Nominal Voltage: 3.20 V
- Cutoff Voltages: 2.50 V (lower) and 3.65 V (upper)
Batteries were fully charged to 100% state of charge (SOC) using a battery cycler before each experiment.
3.2 Experimental Setup
The experiments were conducted in a sealed pressure chamber with a volume of 82 liters. To simulate real-world conditions, batteries were subjected to lateral heating using a 952 W heating plate. Temperature sensors (K-type thermocouples) were placed on various points on the battery surface and in the surrounding environment to monitor temperature changes.
3.2.1 Sensor Placement
- Battery Surface Sensors (T1-T6): Placed on the heating face center, back face center, side face center, positive and negative tabs, and the vent valve.
- Ambient Sensors (T7-T11): Placed 20 cm and 30 cm above the vent valve and 20 cm on both sides of the battery to monitor horizontal and vertical temperature propagation.
A pressure sensor (LFT2800) was also installed to monitor changes in the chamber’s internal pressure during thermal runaway.
3.2.2 Experimental Procedures
Each battery was subjected to two sets of experiments: one in an inert (nitrogen) atmosphere and another in an air atmosphere. The procedures for both sets were identical, except for the chamber’s filling gas.
- Preparation: The battery was fully charged and placed in the pressure chamber.
- Filling: The chamber was filled with either nitrogen or air and sealed.
- Heating: The heating plate was activated, and temperature and pressure sensors began recording data.
- Monitoring: The battery’s voltage was monitored, and the heating plate was turned off when the voltage dropped to zero.
- Gas Collection and Analysis: After thermal runaway, the produced gases were collected and analyzed using gas chromatography.
3.3 Data Analysis
Data collected during the experiments were analyzed to determine:
- Temperature Profiles: Battery surface and ambient temperatures during thermal runaway.
- Gas Production: Volume and composition of gases produced during thermal runaway.
- Explosion Limits: Calculated using Le Chatelier’s law to assess the flammability of the produced gases.
4. Results
4.1 Battery Temperature Profiles
4.1.1 Inert Atmosphere
Under inert conditions, the battery’s thermal runaway process exhibited distinct stages:
- Heating Stage (0-904 s): Battery temperatures increased steadily.
- Venting Stage (904-1290 s): The vent valve opened, releasing gases and causing a slight temperature drop.
- Thermal Runaway Stage (1290-1750 s): Internal reactions intensified, causing a rapid temperature rise and voltage drop.
- Cooling Stage: After thermal runaway, temperatures gradually decreased.
4.1.2 Air Atmosphere
In the air atmosphere, similar stages were observed, but with notable differences in temperatures and durations (Table 1):
Table 1: Comparison of key temperature parameters in inert and air atmospheres.
| Test Atmosphere | Peak Temperature (°C) | Max Temperature Rate (°C/s) | Thermal Runaway Duration (s) |
|---|---|---|---|
| Inert | 218.0 | 3.9 | 460 |
| Air | 256.3 (+17.6%) | 4.1 (+5.1%) | 524 (+14%) |
4.2 Gas Production and Composition
4.2.1 Gas Production Volume
The volume of gases produced during thermal runaway was significantly higher in the air atmosphere.
4.2.2 Gas Composition
The major gas components in both atmospheres were similar (Table 2), but their proportions varied.
Table 2: Gas composition during thermal runaway in inert and air atmospheres.
| Gas Component | Inert Atmosphere (%) | Air Atmosphere (%) |
|---|---|---|
| H₂ | 52.8 | 49.5 |
| CO₂ | 26.5 | 28.0 |
| CO | 7.4 | 8.0 |
| CH₄ | 6.2 | 8.5 |
| C₂H₄ | 5.0 | 6.0 |
In the air atmosphere, H₂ proportions decreased slightly, while CH₄ and C₂H₄ increased. This suggests more intense reactions between battery materials and atmospheric oxygen.
4.3 Explosion Limits
Using Le Chatelier’s law, the explosion limits of the produced gases were calculated. The results show that both atmospheres produced gases with high explosion potential (Table 3).
Table 3: Explosion limits of produced gases in inert and air atmospheres.
| Atmosphere | Lower Explosion Limit (%) | Upper Explosion Limit (%) |
|---|---|---|
| Inert | 6.3 | 67.9 |
| Air | 5.9 | 62.7 |
5. Discussion
5.1 Temperature Differences
The air atmosphere significantly affected battery temperatures during thermal runaway. The higher peak temperature and longer duration can be attributed to additional exothermic reactions between battery materials and atmospheric oxygen.
5.2 Gas Production and Composition
The increased gas production in the air atmosphere can also be explained by enhanced chemical reactions with oxygen. The shift in gas composition, particularly the decrease in H₂ and increase in CH₄ and C₂H₄, supports this hypothesis.
5.3 Safety Implications
These findings have important implications for battery safety. The increased temperatures, gas production, and explosion potential in the air atmosphere highlight the need for robust venting and cooling systems in battery packs exposed to ambient air.
6. Conclusion
This study comprehensively examined the thermal runaway behavior of 120 Ah LFP battery under both inert and air atmospheres. Key findings include:
- The thermal runaway process exhibits distinct stages of heating, venting, runaway, and cooling.
- The air atmosphere leads to significantly higher battery temperatures (+17.6%), longer thermal runaway durations (+14%), and increased gas production (+8.2%) compared to an inert atmosphere.
- The produced gases have high explosion potential in both atmospheres.
The results provide valuable insights into the thermal runaway characteristics of high-capacity LFP battery and their behavior under different test atmospheres. Future research should focus on developing more effective venting and cooling strategies to mitigate the risks associated with thermal runaway in LIB systems.