Solutions for the electric vehicle industry through temperature monitoring of lithium batteries
INTRODUCTION
The electric vehicle or EV industry has grown exponentially in recent years. It has gained popularity due to the alarming climate change crisis and the urgent need to find an alternative to current fuel-powered vehicles.
As the demand for electric vehicles has increased significantly, so has battery production and manufacturing and the associated challenges. This increase in electric vehicle production has also led to numerous headlines about battery fires. These incidents are not limited to small companies, but also include companies such as Tata, TESLA and OLA. This issue is moving very fast and there may be multiple reasons behind all the battery fires.
One of the high-tech solutions that can help reduce some battery fires is thermography. This article discusses predictive maintenance and materials research for electric vehicles.
To understand the application, we first need to understand some basic concepts. Therefore, I will cover them before discussing the main applications.
BASICS OF LITHIUM-ION BATTERIES
Among the many attractive factors of lithium-ion batteries, one of the most notable attractions is the combination of lithium's electronegativity and its low density. This combination is responsible for producing the highest amount of electrical energy per unit weight among solid elements.
A standard lithium-ion battery contains an anode and a cathode. Typically, lithium oxide is used for the cathode and a carbon compound for the anode. The constant internal movement of electrons between the cathode and anode creates the famous rechargeable battery.
When a lithium-accepting compound is placed as the cathode of the chemical battery, lithium ions begin to flow in the opposite direction during the charge and discharge cycle. The oxidation and reduction reactions in the battery cause the battery to charge and discharge (fig. 1,2).
Fig. 1. Source: UL Research Institutes
MANUFACTURING
1. Classification
Cells are typically imported by manufacturers from India and, to ensure that no defective cells enter the manufacturing line, they are manually sorted, checking each cell for visible deformities, damage, leakage and internal resistance range. These factors determine the condition of the cell and ensure the quality of the final product.
Manufacturing of a package
All cells are welded together in a package in a series or parallel combination, depending on the required production specifications. This forms the basic structure of the battery pack. During this process, the pack is checked by hand for weld deformities. The internal strength and resistance determine whether the pack can move forward on the production line.
3. Combination of battery packs
The battery packs are connected by circuits and a control system. This completes the manufacturing process of a lithium-ion battery pack and is distributed to companies that manufacture electric vehicles.
4. Tests
The finished product is subjected to charge and discharge cycles. During this process the performance of the battery is monitored.
(fig. 3)
Fig. 2. Thermography of a lithium-ion battery
Fig. 3. Nissan, Sunderland Plant, United Kingdom
Source : www.greencarreports.com
FUNDAMENTALS OF THERMAL IMAGING
The principle of thermal imaging is the infrared radiation emitted by an object. This radiation is invisible to the human eye, but can be seen using cameras optimized for its specific wavelength (fig. 4).
Although an estimate of the temperature of a point can be obtained using thermocouples, they can only provide data from a single point at a time and they need to be in close contact with the object to be measured. With thermal cameras it is possible to view a wide range of such points and monitor the temperature of the object without contact, from a safe distance and under operating conditions. These thermal cameras can measure temperature to an accuracy of 0.1 degrees Celsius.
Thermography is widely used in other industrial sectors for fire and safety, as it is a non-contact, non-destructive testing and monitoring method.
Fig. 4. Electromagnetic and infrared spectra
VISIBLE VS IR
It is only possible to see the thermal signature of an object when it reaches a temperature of 1,000 degrees Celsius. However, an infrared camera can capture thermal signatures of objects as low as -60 degrees.
Infrared technology is accessible in the absence of light, but is very different from a night vision camera. The wavelengths of the two cameras are different.
A night vision camera amplifies small amounts of light, but a thermal imaging camera detects the temperature emitted by objects. Thermal imaging cameras can be used in absolute darkness.
Fig. 5. A lion in Infrared vs. Night Vision
SOME CHARACTERISTICS
This technology has some limitations, an infrared camera cannot see through glass, as it only reads surface temperatures. However, this technology has the ability to see through fog, thin plastic and an infrared inspection window that can be installed in factors to see through surfaces. The resolution, lens size and number of detectors determine the distance at which it can be seen from the infrared camera.
Fig. 6. Infrared Inspection Window
SOME APPLICATIONS
Thermal imaging cameras are actively used for various applications in different industries. Some of the examples of their applications are:
- Electrical services for predictive maintenance
- Oil and gas industry, VOC visualization, furnace inspection and flare monitoring
- Manufacturing companies
- Predictive maintenance
- Quality insurance
- I+D
APPLICATIONS OF THERMOGRAPHIC IMAGING IN THE ELECTRIC VEHICLE INDUSTRY
Welding
Lithium cells must be welded together to form a battery. However, if the soldering is not done correctly, failures can occur in the final product. Resistance and output can be affected and the longevity of the battery is directly affected. Normally, the soldering is checked manually by factory workers, which is a destructive testing method, whereby the cell may break. A non-destructive and non-contact method to check the solder joint is the use of thermal imaging. We can easily detect a poorly soldered joint due to the slightly different temperature shown by its seam. An uneven seam or a slightly elevated temperature indicates a defective weld. This method of testing is already prevalent in all U.S. industries.
Cell leakage
Almost invisible to the naked eye, cell leakage can occur at any time during the manufacturing process and can damage the battery. A leaking cell can be extremely dangerous if it comes into contact with the skin. We can use methods such as mass spectrometry to detect leaks, but there is a better method to detect these small leaks: thermal imaging. When the cell seal is broken, liquid is deposited on the outer layer of the cell and a temperature difference is detected. A high-resolution thermal camera can effectively identify these tiny leaks in a matter of seconds without contact, as shown in the figure.
Fig. 7. Identification of cell leakage using a T-series camera.
Unexpected heating
Although thorough testing is performed at all stages, sometimes a defective cell may enter the production line. During the testing phase, defective cells may show a slight temperature difference. This is invisible to the human eye, but thermographic cameras pick it up perfectly. As seen in Figure 8, the camera picks up the slightly elevated temperature with an accurate temperature reading to the decimal place. Another example of uneven heating during testing of battery packs after assembly. During the charge and discharge cycles, the batteries
Fig. 8. Uneven heating displayed by the lithium battery unit
tend to heat up. However, during this test phase, there is a high risk of the battery catching fire if the temperature is not monitored. This can be done using a thermocouple, a non-destructive contact method, but it is only possible to monitor the temperature of one point at a time. If the back of a lithium battery catches fire in the installation, it will be really difficult to put out, as lithium reacts very fast and the fire is difficult to extinguish because lithium reacts with water on contact.
Loading and unloading
The last phase of testing involves charging and discharging the lithium-ion battery. During this phase, the temperature of the battery can rise up to 5 to 6 degrees Celsius above ambient temperature. With a thermal imaging camera, we can record the surface temperature of the lithium-ion battery and estimate the internal temperature without touching it. We can clearly see the hot spots of the battery pack through the surface while it is charging. This helps us isolate a potential problem and its location. (fig. 9) Batteries under test can be monitored 24 hours a day to prevent possible battery fires if any unit becomes hot.
Fig. 9. A battery in charging cycle
Electric vehicles
The electric vehicle consists of three main components: the battery, the motor and the inverter. Once the vehicle is assembled, thermal technology can be used to monitor its thermal behavior while in use. (fig. 10) This application is very valuable considering the recent increase in electric vehicle battery fires in India, as it not only offers solutions for battery manufacturing, but is also capable of monitoring other components of the machine.
Fig. 11. Image of the interior of an electric vehicle.
Batteries in charge and discharge cycle
Fig.10. Image of the interior of an electric vehicle.
CONCLUSION
While there are multiple preventive methods that can be used on the electric vehicle production line, this solution provides predictive, battery fire and safety maintenance for this particular industry. Thermography can be applied at various steps during the manufacturing process to monitor the target object and check for defects.
This technology is not only useful for identifying defects and malfunctions, but is crucial for the safety of the workforce involved in manufacturing, as well as the customer using the finished product, such as electric vehicles, which are prone to battery fires if not used or maintained correctly. The use of this technology promotes safety by quickly picking up slight temperature differences and identifying uneven heating, symptoms that a battery is on fire.
Although faulty systems may go undetected in a manual inspection, it is highly unlikely that they will go undetected with a thermal camera, since it operates in the infrared range and converts heat signals into images.
As demand and supply in this sector increases, so will the need for more reliable testing and data for prevention and safety, where thermography proves to be a more than viable option to reduce the likelihood of an electric vehicle failure or battery fire.
The ideal solution to detect such problems and prevent a battery fire from occurring during battery production, is IRTIMthe hot spot detection system that, by means of thermography, is able to detect abnormal overheating of lithium-ion batteries in the production line. All the information on the website. Do not hesitate to inform yourself and keep your company protected.
A free webinar on IRTIMfire and thermographic systems for fire detection in waste plants is available for you to access now!
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