In the evolving landscape of electric vehicles (EVs), battery safety remains a top priority, especially when it comes to preventing thermal runaway—a dangerous phenomenon that can lead to catastrophic outcomes. As battery technology advances in 2024, companies are doubling down on strategies to mitigate these risks, from regulatory compliance to cutting-edge innovations. In this blog, we’ll dive into what thermal runaway is, how it differs from thermal propagation, and the advanced methods being used today to prevent these hazardous events. We'll also look closer at Maxwell's proprietary algorithm designed to detect and mitigate thermal runaway in real time.
What is Thermal Runaway?
Thermal runaway occurs when a Cell’s temperature exceeds a safe threshold, often due to internal failure or external stress, triggering a chain reaction that leads to further heat generation. This feedback loop can cause battery packs to overheat, catch fire, or even explode. The primary causes of thermal runaway include:
- Mechanical stress (e.g., punctures or compression of cells)
- Electrochemical imbalances (e.g., overcharging, high discharge rates)
- Extended exposure to high ambient temperatures
Given the increased focus on electric mobility and renewable energy storage, industries are employing advanced technologies to minimize these risks.
Thermal Runaway vs. Thermal Propagation?
Before diving into prevention methods, it's essential to differentiate between thermal runaway and thermal propagation.
- Thermal Runaway: This occurs at the cell level within a battery. It happens when a cell's temperature rises uncontrollably, often due to internal failures like short circuits or overcharging, leading to further heat generation.
- Thermal Propagation: This refers to the spread of heat or fire from one cell to neighboring cells within a battery pack, eventually resulting in the failure of the entire pack (i.e., the catastrophic "boom").
Preventing thermal runaway is crucial because if it escalates into thermal propagation, it can cause large-scale damage to the battery pack and potentially endanger passengers or surrounding infrastructure.
Mandated Safety Standards: AIS 156 Amendment
In response to the growing safety risks, regulatory bodies such as the Automotive Industry Standard (AIS) have implemented mandates since March’23 for thermal runaway detection, particularly in EVs. The AIS 156 Amendment specifically requires all EV manufacturers to integrate systems capable of detecting early signs of thermal runaway, ensuring that countermeasures can be taken to protect users.
The amendment is significant because it not only improves safety but also standardizes the technology used across the industry, making advanced battery management systems (BMS) with thermal runaway detection a necessity rather than an optional feature.
How Battery Manufacturers & OEMs are Preventing Thermal Runaway in 2024
1. Enhanced Monitoring: Beyond Traditional Sensors
Modern Battery Management Systems (BMS) incorporate advanced sensors to detect abnormal battery behavior. These sensors include not just traditional voltage and temperature monitors but also gas sensors and pressure sensors.
- Voltage and Temperature Sensing: Detect early signs of thermal runaway by monitoring irregularities in a cell’s voltage and temperature.
- Gas Sensors: Monitor the buildup of gases (such as oxygen and hydrogen), which can signal cell failure or venting due to overheating.
- Pressure Sensors: Measure pressure fluctuations inside battery cells or packs, often caused by swelling/venting of cells or other mechanical failures.
These multi-layered sensing technologies offer a more comprehensive safety net compared to earlier BMS systems.
2. Cooling Mechanisms to Avoid Overheating
One of the most significant advancements in thermal management is the shift from traditional air cooling to liquid cooling systems. Both strategies aim to maintain battery temperatures within safe limits, but they work in fundamentally different ways.
- Air Cooling Systems: These systems rely on airflow to dissipate heat away from the battery pack. While cost-effective and lightweight, air cooling has limitations in environments with high temperatures or heavy battery loads, where it struggles to effectively prevent overheating.
- Liquid Cooling Systems: In contrast, liquid cooling systems circulate a coolant (usually a water-glycol mixture) around the battery cells, absorbing and transferring heat away from the pack more efficiently. Liquid cooling is particularly effective in high-performance EVs and large-scale energy storage applications where temperature control is critical. Companies like Tesla, BMW, and Rivian have adopted liquid cooling for their high-energy-density battery packs due to its ability to manage heat better under high loads.
In 2024, many EV manufacturers are optimizing liquid cooling to increase both battery lifespan and safety, especially as energy densities rise. However, some companies are exploring hybrid approaches, combining liquid and air cooling systems for specific use cases where balance between cost and efficiency is needed.
3. Thermally Stable Battery Materials
Companies like QuantumScape and Solid Power are working on the next generation of battery technology: solid-state batteries. These batteries replace the liquid electrolyte found in traditional lithium-ion cells with a solid electrolyte, significantly reducing the risk of thermal runaway.
- Why Solid-State? Solid-state batteries eliminate the flammable liquid electrolyte that is often the source of thermal runaway in lithium-ion batteries. With solid-state, there’s a greater emphasis on thermal stability, higher energy densities, and longer lifespans.
4. AI-Powered Predictive Analytics
Artificial Intelligence (AI) and machine learning are playing an increasingly important role in battery management. AI systems can analyze vast amounts of sensor data to predict failure points and alert users before a runaway occurs. Companies are leveraging machine learning algorithms that detect subtle patterns in the performance of individual cells, providing predictive diagnostics that can spot early signs of instability.
5. Passive Venting Systems
Many companies are incorporating venting systems that allow gases to escape from the battery pack in the event of overheating. By releasing pressure and gas buildup, these systems prevent conditions from escalating into thermal runaway. This is commonly used in conjunction with flame retardant materials, which help contain and suppress fires in case of ignition.
6. Gas Detection Sensors
Some battery manufacturers are adding gas detection sensors to monitor the buildup of combustible gases (e.g., oxygen, hydrogen) within battery packs. This additional layer of protection ensures that potential thermal runaway triggers can be identified even before heat buildup begins.
Maxwell’s Proprietary Algorithm: Leading Battery Safety
At Maxwell, safety is at the core of our BMS design, and we’ve developed a proprietary algorithm to tackle thermal runaway prevention head-on. Built into our CT-Lite BMS, this algorithm offers advanced early detection capabilities by monitoring critical battery parameters and flagging warning signs before runaway conditions materialize.
Key Features of Maxwell's Thermal Runaway Detection:
- Internal Short Circuit Detection Our system monitors for voltage drops within cells, which could indicate an internal short circuit—a common precursor to thermal runaway. If a cell’s voltage drops below a configurable threshold and the drop persists over five seconds, the system triggers a runaway warning.
- Overcharging Detection Overcharged cells are a major cause of thermal runaway. The Maxwell BMS algorithm continually monitors for overvoltage conditions and sets off an alert if any cell exceeds the configured threshold.
- Abnormal Temperature Rise Detection By tracking the rate of temperature increase in each cell, our system flags abnormal temperature rises that could lead to runaway. If the rate exceeds a predefined limit, the BMS triggers protective measures.
- High-Temperature Detection Once any cell in the pack crosses a temperature threshold, the BMS sets off an error, stopping the situation from escalating into a runaway.
Built-in Safety Communications
Maxwell’s BMS also features advanced communication systems like CAN messages and GPIO outputs, which send real-time alerts to other vehicle systems. This ensures that any signs of thermal runaway can be addressed immediately, either by shutting down systems or triggering visual and audio alarms.
The Future of Thermal Runaway Prevention
As battery technology continues to evolve, the industry’s approach to thermal runaway is becoming more sophisticated. From enhanced cooling systems to AI-powered analytics and thermally stable materials, the industry is moving rapidly toward safer, more reliable battery systems.
At Maxwell, we’re staying ahead of the curve with our proprietary thermal runaway detection algorithm, ensuring that our BMS provides the highest level of safety and performance. As innovations continue, companies and consumers alike can look forward to a future where thermal runaway becomes a manageable, preventable risk.
By focusing on cutting-edge detection and prevention technologies, we’re not just preparing for the future of battery safety—we’re leading the way.
