The world is moving toward cleaner and more sustainable technology, especially in transportation. The electric vehicle (EV) market is growing at a rapid pace. In the first quarter of 2025, global EV sales have reached 4.1 million units, which is 29% more compared to the same period last year. This growth of the EV market is led by China, Europe and North America, with 36%, 22% and 16%  rise in sales, respectively.¹

Lithium-ion (Li-ion) batteries are central to EV technology. Their ability to store large amounts of energy in compact volumes enables the performance and range of modern EVs. However, with the increasing energy density of batteries, safety becomes a bigger concern, especially the risk of thermal runaway, which can cause fires or even explosions. 

Traditional battery monitoring systems typically rely on temperature or voltage sensors to detect abnormalities. These systems are somewhat effective but often fall short of identifying the early warning signs of battery failure. This article discusses how gas sensing technology tackles thermal runaway and how ScioSense, a leader in advanced environmental and gas sensing technologies, offers a proactive alternative with its Battery Condition Monitoring (BCM1) module.

Understanding Thermal Runaway and Its Triggers

Thermal runaway is a dangerous and self-perpetuating failure process in lithium-ion batteries, where a small issue like localized heating can quickly escalate into a full-scale thermal event. Thermal runaway begins when internal temperatures rise beyond a critical threshold and start decomposing battery materials to release heat and gas. The heat generated accelerates further breakdown, creating a chain reaction that rapidly spirals out of control. Thermal runaway is particularly dangerous since it does not necessarily require a catastrophic event to initiate; even minor faults can serve as the spark.

Thermal runaway can have various causes. For instance, overcharging or over-discharging can destabilize battery chemistry, which leads to overheating. Manufacturing defects like impurities or misaligned layers can result in internal short circuits that go undetected. Similarly, external mechanical damage, like vibrations or impacts, or prolonged exposure to high ambient temperatures can weaken battery integrity over time.  

Early-stage signs are often too subtle to detect using conventional voltage or temperature sensors, and by the time these indicators register a change, the runaway process may already be well underway. Moreover, heat or fire can pass on from one battery cell to the adjacent cell, causing thermal propagation, which can exponentially increase the effect of thermal runaway. Therefore, more sophisticated condition monitoring approaches that can identify the earliest chemical changes inside the cell well before traditional metrics start to shift are necessary.

Why Gas-Based Detection Matters

Usually, traditional battery monitoring systems focus primarily on electrical and thermal parameters. These indicators often change only after a fault has progressed significantly. In contrast, gas-based detection offers a more sensitive and proactive approach to identifying early-stage failures in lithium-ion batteries. 

A physical sign of internal battery issues, well before temperature spikes or voltage anomalies, is the release of volatile organic compounds (VOCs) and gases such as hydrogen (H₂), carbon monoxide (CO), and low-molecular-weight hydrocarbons. These gases are byproducts of electrolyte decomposition, internal short circuits, or cell degradation, and their presence indicates a critical early warning sign of impending failure. Therefore, a gas-based monitoring system capable of detecting these gases can improve the safety of battery systems.

In this regard, the ScioSense BCM1 module is designed to recognize and classify these emissions in real time using metal oxide (MOX) sensor technology. MOX sensors provide high sensitivity and fast response times to detect even trace amounts of gas before conditions escalate. The BCM1’s sensing algorithm is tailored to distinguish battery-related outgassing events from benign environmental fluctuations, which reduces false alarms. 

Key Features of BCM1 for Reliable Detection

The BCM1 module from ScioSense is designed with high-performance, safety-critical applications like EV battery packs in mind. It is engineered for smooth integration and long-term reliability in demanding automotive environments. BCM1 can detect a broad spectrum of gases including VOCs, CO, H₂, and electrolyte vapors. 

Along with MOX-based gas sensing, BCM1 also offers optional pressure and humidity sensors, enabling a more nuanced interpretation of detected anomalies. For instance, humidity data can help differentiate between benign environmental changes and serious internal events. Similarly, pressure variations can indicate swelling or leakage within the battery enclosure. This environmental context strengthens diagnostic accuracy and reduces false positives, supporting better-informed responses from the battery management system.

Integration of BCM1 into existing vehicle platforms is simplified through support for LIN (Local Interconnect Network) and PWM (Pulse Width Modulation) communication interfaces. These standardized protocols ensure compatibility with modern automotive control networks and allow real-time data exchange with minimal overhead. This flexibility allows OEMs and system integrators to incorporate BCM1 into diverse battery architectures without major redesigns or protocol conversions.

The BCM1 module’s design adheres to stringent automotive quality and reliability benchmarks. It meets AEC-Q100 qualification standards for electronic components in automotive environments and complies with ISO/IATF 16949 and VDA 6.3, which are critical for supplier quality management in the automotive sector. These certifications validate the robustness of BCM1 and simplify approval processes for OEMs.

BCM1 is housed in a watertight enclosure rated for IP5K4K, IPx7, and IP9K protection. These ratings ensure resistance to dust, water jets, temporary submersion, and high-pressure cleaning, as such conditions are often encountered in electric vehicles during operation and servicing. The rugged design ensures long-term stability and reliability in harsh environments or thermally dynamic battery compartments.

Along with its advanced capabilities and ruggedness, BCM1 is highly power-efficient. It draws less than 30 mA at 12 V and operates with minimal energy overhead, preserving EV range and reducing thermal output. This makes it suitable for continuous monitoring without compromising overall system efficiency. BCM1 also features flexible mounting options, including Delphi-clip and bayonet configurations that support diverse battery pack designs and manufacturing workflows. 

Real-World Testing: Proving the Advantage of Gas-Based Detection

ScioSense has performed multiple tests to validate the effectiveness of early gas detection, some in collaboration with TÜV Süd and the Fraunhofer Society, on both pouch-type and cylindrical Li-ion cells. These tests involved deliberate overcharging, short circuits, and other stress conditions known to induce thermal runaway.²

For instance, in one test, a 5Ah LiCoO₂ pouch cell was subjected to a 12C overcharge condition. The BCM1 module detected gas outgassing nearly 40 seconds before the onset of thermal runaway. This early warning window offers ample time for mitigation strategies, such as isolating the failing cell or initiating cooling protocols.²

Similarly, another test involved a 700mAh IMR14500 cylindrical LiMn cell overcharged at 4C. Again, BCM1 successfully detected outgassing events in a hermetically sealed chamber. The distinction between pouch cells (which vent earlier due to low-pressure housings) and hard cylindrical cells (which vent later under higher pressure) was clearly demonstrated. This shows the importance of detecting gases rather than waiting for temperature or pressure thresholds to be breached.²

Integrating BCM1 in EV Battery Systems

The modular nature of BCM1 allows it to be smoothly integrated at multiple levels of the battery system, including module, stack, and duct levels. Its compact size and tool-free installation simplify retrofitting into existing architectures and enable precise placement near potential venting points.

Once BCM1 is installed, it continuously monitors the battery environment. If early-stage gas emissions are detected, the system can initiate various safety responses through the BMS, like lowering the charging or discharging current, activating localized or global cooling, isolating individual cells or modules, and initiating a controlled system shutdown. BCM1 prevents the physical propagation of thermal runaway by catching the earliest signs of battery distress and extends the life and resilience of the entire battery system.

BCM1 Battery Condition Monitor for Li-lon batteries.

Beyond EVs: Smart Energy Systems

Although BCM1 primarily focuses on EV applications, its benefits extend naturally to stationary battery energy storage systems (BESS). These systems are often deployed in grid-balancing, backup power, or renewable energy installations and operate under fluctuating load and temperature conditions for years.

In this regard, gas-based condition monitoring offers long-term diagnostic insight, enabling predictive maintenance and preventing battery failures that could jeopardize uptime or lead to expensive replacements. As energy storage systems become more critical to grid stability, safety monitoring solutions like BCM1 are becoming necessary for reliable operation.

Conclusion

Thermal runaway is one of the most serious and complex challenges in designing and operating EVs and stationary battery systems. Its consequences are severe, and traditional monitoring tools are not sufficient enough to guarantee safety in the increasingly energy-dense batteries of modern EVs.

ScioSense’s BCM1 module provides a vital layer of protection by detecting the earliest signs of gas release. BCM1 enables engineers to intervene long before failure occurs, protecting users, preserving assets, and building the trust of EV consumers.

OEMs and battery system designers seeking a robust, integration-friendly, and highly responsive safety solution can visit the ScioSense Website to find out more about the BCM1 module and their other products.

References

1. Global EV Sales Up 29% In 2025 From Previous Year. (2025) Rho Motion. [Online] Available at: https://rhomotion.com/news/global-ev-sales-up-29-in-2025-from-previous-year/ (Accessed on April 28, 2025)

2. Rolf Pauly (2025) Detecting Thermal Runaway In EV Batteries: Advancing Early Warning Systems. ScioSense. Available at: https://drive.google.com/file/d/1dgGNCjR4VQzc8mHzBnVl1E8Bsf5FcGt5/view 

3. BCM1 Battery Condition Monitor for Li-lon batteries. [Online] ScioSense. Available at: https://www.sciosense.com/bcm1-battery-condition-monitor-2/ (Accessed on April 28, 2025)

4. Factsheet BCM1. [Online] ScioSense. Available at: https://www.sciosense.com/wp-content/uploads/2023/12/BCM1-Factsheet-1.pdf (Accessed on April 28, 2025)