Abstract:
Lithium iron phosphate (LFP) batteries are widely used in energy storage systems due to their high safety, long cycle life, and environmental friendliness. However, LFP battery is prone to thermal runaway under abusive conditions, posing a significant safety risk. The early detection of thermal runaway in LFP battery storage compartments is crucial to prevent accidents. This paper evaluates the effectiveness of various sensors for monitoring the early signs of thermal runaway in LFP battery storage compartments. Five types of multi-function sensors with different detection principles were developed and tested in a 40-foot prototype energy storage container. The sensors monitored parameters such as hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), volatile organic compounds (VOCs), smoke concentration, temperature, and pressure. The results show that catalytic combustion-based H2 sensors and photoionization-based VOC sensors are more effective for early detection of thermal runaway. The paper also proposes a detection strategy for thermal runaway in LFP battery storage compartments based on the sensor evaluation results.
1. Introduction
With the rapid development of renewable energy sources such as wind and solar, energy storage systems have become essential for ensuring the stability and reliability of the power grid. Lithium-ion batteries, especially those using lithium iron phosphate (LFP) as the cathode material, have gained popularity in energy storage applications due to their high safety, long cycle life, and environmental friendliness. However, under certain conditions, such as overcharging, external heating, or internal short circuits, LFP battery can undergo thermal runaway, resulting in fire or explosion. Therefore, effective monitoring and early detection of thermal runaway are critical for ensuring the safety of LFP battery storage compartments.
This paper evaluates the effectiveness of various sensors for monitoring the early signs of thermal runaway in LFP battery storage compartments. The sensors detect parameters such as H2, CO, CO2, VOCs, smoke concentration, temperature, and pressure, which are known indicators of thermal runaway in lithium-ion batteries. The evaluation is conducted using a 40-foot prototype energy storage container equipped with the developed sensors. Based on the evaluation results, a detection strategy for thermal runaway in LFP battery storage compartments is proposed.
2. Background and Related Work
2.1 Thermal Runaway in LFP Battery
LFP battery can undergo thermal runaway due to various factors such as internal short circuits, overcharging, and external heating. During thermal runaway, the battery generates a large amount of heat, leading to the decomposition of the electrolyte and the release of flammable gases such as H2, CO, and VOCs. If left unchecked, thermal runaway can escalate into a fire or explosion.
2.2 Monitoring Parameters for Thermal Runaway Detection
Several parameters have been identified as indicators of thermal runaway in lithium-ion batteries:
- Gases: H2, CO, CO2, and VOCs are released during thermal runaway.
- Smoke: Smoke is generated as the battery casing ruptures and electrolyte vapors ignite.
- Temperature: A rapid increase in battery temperature is an early sign of thermal runaway.
- Pressure: Internal pressure rises as gases are generated within the battery during thermal runaway.
2.3 Sensor Technologies for Thermal Runaway Detection
Various sensor technologies have been developed for detecting the parameters mentioned above. These include:
- Electrochemical sensors: Sensitive to specific gases through electrochemical reactions.
- Semiconductor sensors: Utilize changes in electrical conductivity to detect gases.
- Catalytic combustion sensors: Detect flammable gases by oxidizing them on a heated catalyst.
- Photoionization detectors (PIDs): Detect VOCs by ionizing them with ultraviolet light.
- Thermocouples and resistance temperature detectors (RTDs): Measure temperature.
- Pressure transducers: Measure pressure changes.
3. Experimental Setup
3.1 Test Battery and Container
A 280 Ah LFP battery (lithium iron phosphate battery, LFP, Yilong Energy Co., Ltd.) with dimensions of 204.6 mm × 173.7 mm × 71.7 mm and a rated voltage of 3.2 V was used for the tests. The battery was placed in a 40-foot prototype energy storage container with dimensions of 12.2 m × 2.4 m × 2.6 m (length × width × height).
3.2 Sensor Development
Five types of multi-function sensors were developed, each integrating multiple detection principles into a single unit. The sensors were labeled A to E and are summarized in Table 1.
Table 1: Summary of Developed Multi-function Sensors
| Sensor Type | Gas Sensors | Other Sensors |
|---|---|---|
| A | Electrochemical H2, CO, VOC (SP) | Temperature, Smoke |
| B | Semiconductor H2, CO, VOC (SP) | Temperature, Smoke |
| C | Electrochemical H2, CO, VOC (SP), | Temperature, Smoke, |
| (Same as A, without separate listing) | Pressure | |
| D | Catalytic Combustion H2, | Temperature, Smoke, |
| Electrochemical CO, PID VOC | PID VOC, CO2 | |
| E | Semiconductor H2, Electrochemical | Temperature, Smoke, |
| CO, CO2, VOC (SP) | Pressure |
Note: SP stands for Solid Polymer Electrochemical.
3.3 Test Configuration
The sensors were installed at different positions within the container to evaluate their effectiveness in detecting thermal runaway. The positions were labeled 1 to 5, with Sensor 1 located near the battery and Sensor 5 farthest away. The sensors monitored the following parameters:
- Gases (H2, CO, CO2, VOCs): Detected using the respective sensors integrated into the multi-function units.
- Smoke Concentration: Detected using a semiconductor smoke sensor.
- Temperature: Measured using a K-type thermocouple.
- Pressure: Measured using a pressure transducer.
3.4 Test Procedure
The battery was fully charged using a constant current-constant voltage (CC-CV) charging protocol. Once charged, the battery was subjected to thermal abuse by applying external heat using a heating plate. The sensors continuously monitored the parameters mentioned above during the test. The tests were conducted under both ignition and non-ignition conditions to evaluate the sensors’ performance under different scenarios.
4. Experimental Results
4.1 Heating-Induced Thermal Runaway without Ignition
Figure 1 shows the evolution of various parameters during a heating-induced thermal runaway test without ignition.
Figure 1: Evolution of Parameters During Heating-Induced Thermal Runaway without Ignition
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- VOC Detection: VOCs were detected earliest, followed by H2 and CO. This indicates that electrolyte volatilization occurs before significant gas generation.
- H2 and CO Detection: Catalytic combustion-based H2 sensors detected H2 earlier than electrochemical sensors. Similarly, PID-based VOC sensors detected VOCs earlier than solid polymer electrochemical sensors.
- Temperature and Pressure: Temperature rose rapidly during thermal runaway, while pressure changes were not significant for early detection.
- Smoke Detection: Smoke was detected after H2 and CO, consistent with the progression of thermal runaway.
4.2 Comparison of Sensor Types
Table 2: Comparison of Sensor Types for Early Detection of Thermal Runaway
| Sensor Type | Early Detection Parameter | Time to Detection (s) |
|---|---|---|
| A (Electrochemical) | H2, CO (simultaneous) | 1493 |
| B (Semiconductor) | H2, CO (simultaneous) | 1621 |
| C (Combination) | Similar to A | 1495 |
| D (Catalytic + PID) | VOC (earliest), then H2 | VOC: 750, H2: 1462 |
| E (Semiconductor + CO2) | Similar to B | 1619 |
The catalytic combustion-based H2 sensor and PID-based VOC sensor in Sensor D provided the earliest detections, highlighting their effectiveness for early warning of thermal runaway.
4.3 Effect of Ignition
Ignition significantly altered the gas concentrations and temperatures during thermal runaway. Figure 2 shows the comparison between ignition and non-ignition conditions.
Figure 2: Comparison of Parameters During Ignition and Non-Ignition Conditions
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- Gas Concentrations: Ignition increased CO, CO2, and smoke concentrations while decreasing H2 and VOC concentrations due to combustion.
- Temperature: Temperature rose more rapidly during ignition, facilitating earlier detection.
- Pressure: Pressure changes remained insignificant for early detection in both conditions.
5. Detection Strategy
Based on the experimental results, the following detection strategy is proposed for early warning of thermal runaway in LFP battery storage compartments:
- Primary Sensors: Use catalytic combustion-based H2 sensors and PID-based VOC sensors for early detection.
- Secondary Sensors: Complement with electrochemical H2, CO, and smoke sensors for confirmation.
- Temperature and Pressure Monitoring: Monitor temperature and pressure for additional confirmation, especially during ignition conditions.
- Sensor Placement: Place sensors strategically around the batteries to ensure uniform coverage.
- Alarm Thresholds: Set appropriate alarm thresholds based on the sensor evaluation results to minimize false alarms while ensuring timely detection.
6. Conclusion
This paper evaluated the effectiveness of various sensors for early detection of thermal runaway in LFP battery storage compartments. The results indicate that catalytic combustion-based H2 sensors and PID-based VOC sensors are most effective for early warning. A detection strategy incorporating these sensors, along with complementary electrochemical sensors, temperature and pressure monitoring, is proposed. The findings provide valuable insights for enhancing the safety of LFP battery storage systems.