For most of the history of the lithium-ion battery, safety monitoring has meant two things: voltage and temperature. The battery management system watches every cell, balances the pack and flags an overheating module. It is a proven approach, but it has a blind spot. By the time a thermocouple or thermistor reports a sharp temperature rise, the chemistry inside a failing cell is often already well advanced. That is why gas measurement instruments, compact enough to sit inside the pack itself, are moving from the laboratory to the production line.<\/p>\n
A lithium-ion cell rarely fails without warning. Internal short circuits, separator damage, manufacturing defects or mechanical abuse all trigger a chain of reactions. As the electrolyte begins to decompose, the cell generates gas. Pressure rises inside the cell casing until the safety vent opens, and a plume of volatile organic compounds, carbon monoxide, carbon dioxide and hydrogen escapes into the pack enclosure. This is cell venting, and it is the clearest early signature of a cell heading towards thermal runaway.<\/p>\n
The critical point is timing. Venting can occur well before the surface temperature of neighbouring cells rises enough to register on the BMS. Voltage can also be misleading, because healthy cells connected in parallel can prop up the voltage of a failing one and mask the problem. Gas, by contrast, has nowhere to hide. Once it leaves the cell, it disperses through the enclosure and can be detected by a sensor positioned anywhere in the airflow path.<\/p>\n
Traditional gas measurement instruments were designed for fixed industrial sites or handheld use: portable detectors for confined spaces, fixed gas monitors on factory walls, analysers in laboratories. None of these translate easily to an electric vehicle, an off-highway machine or a containerised energy storage system, where space is tight, power budgets are limited and the sensor has to survive vibration, shock, condensation and a temperature range from sub-zero to well above ambient.<\/p>\n
Embedding gas measurement directly inside the battery enclosure solves this. A small, multi-parameter sensor reads the atmosphere in the pack continuously and reports over the same vehicle network as the BMS. Rather than waiting for heat to reach a temperature sensor, the control system receives a chemical warning at the moment of venting and can act on it: warn the driver, open contactors, isolate the pack or trigger a fire suppression response.<\/p>\n
The benefit has been measured independently. Sandia National Laboratories in the United States published independent testing in the Journal of the Electrochemical Society comparing Metis Engineering’s Cell Guard with two other commercially available detection approaches. Cell Guard detected the thermal event in under 60 seconds. One of the alternatives, a hydrogen-only sensor, took a full seven minutes longer to register the event, by which point thermal runaway was well advanced.<\/p>\n
Seven minutes is the difference between an orderly evacuation and a vehicle fire. It is also the difference between a pack that can be isolated and investigated and one that is lost entirely, with all the cost, downtime and reputational damage that follows.<\/p>\n
One lesson from that research is that measuring a single gas is not enough. Different chemistries, states of charge and failure modes produce different gas signatures, and some gases appear earlier than others. A robust battery safety sensor therefore combines several measurements and lets the control system cross-reference them.<\/p>\n
Cell Guard measures volatile organic compounds from 0 to 6,553.5 ppm alongside absolute pressure, air temperature, relative humidity, absolute humidity and dew point, with an optional triple-axis accelerometer to record shock loads up to \u00b124g. A VOC spike on its own might prompt closer monitoring. A VOC spike combined with a sudden pressure step and a rising air temperature is a much stronger indicator that a cell has vented. That cross-check reduces false alarms and gives engineers confidence to act automatically.<\/p>\n
For applications where hydrogen is the principal concern, including fuel cell systems and energy storage installations with high background VOC levels from adhesives, the related H Guard sensor adds hydrogen measurement from 0 to 20% by volume, a range that spans the 4% lower flammability limit of hydrogen in air.<\/p>\n
Detection has no value if the data cannot reach the controller that acts on it. Gas measurement instruments for mobile and embedded applications need to speak the same language as the rest of the system. Every Metis sensor communicates over CAN bus with a configurable address and baud rate, and each one ships with a DBC file so that engineers can decode the data in their existing tools within minutes rather than weeks.<\/p>\n
Cell Guard has been developed in line with ISO 26262 processes and tested to automotive standards including ISO 7637-2:2011, ISO 16750-2:2012 and ISO 16750-4:2010. It is used by OEMs and Tier 1 suppliers in ASIL B applications and has been deployed in more than 500 systems across electric vehicles, energy storage and industrial applications. It works consistently across NMC, LFP and LMFP chemistries, and over 100 units can be daisy chained for large stationary installations.<\/p>\n
The industry direction of travel is clear. China’s GB 38031-2025 traction battery standard, in force for new type approvals from 1 July 2026, requires that a battery system produces no fire or explosion for at least two hours after thermal runaway and that an alarm is raised within five minutes. Meeting requirements like these calls for early, reliable detection data, not simply stronger containment.<\/p>\n
Inside the battery pack, they become part of the control loop, turning a chemical event into a digital signal the vehicle or energy storage system can act on in seconds. Combined with pressure, humidity and shock data, they also build a lifetime record of pack health that supports warranty decisions, insurance assessments and second-life use.<\/p>\n
For engineers designing the next generation of battery systems, gas sensing belongs in the specification from the first prototype. To discuss Cell Guard or H Guard for your application, contact the Metis Engineering team at info@metisengineering.com.<\/p>","protected":false},"excerpt":{"rendered":"
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