A new sensor that can ‘sniff out’ the early signs of battery failure presents a comprehensive solution to avoiding potential fire hazards.
With the battery at the heart of any electric vehicle (EV), ensuring its safety and health is paramount. Yet, even with today’s most sophisticated Battery Management Systems (BMS), which monitor cells to detect potential issues of thermal events, they have their limitations.
“A single faulty cell within a battery pack can escalate into a major safety hazard if left undetected,” explains Joe Holdsworth, founder and CEO of Metis Engineering. “Typical lithium-ion battery management systems in electric cars or energy storage systems primarily rely on a BMS monitoring subtle voltage fluctuations and cell temperature to detect potential issues. However, the issue with using both these methods is that if you have many cells in a parallel arrangement, voltage fluctuations may be masked by other cells, thereby hiding a faulty cell.”
Metis Engineering was established by Holdsworth in 2016, an aerospace engineering expert who has worked on projects ranging from unmanned nuclear submarines to the Bloodhound Land Speed Record 1,000mph jet and rocket powered car. The company specialises in battery sensor technology and developed an innovative solution called Cell Guard, aimed at enhancing battery safety and maintenance.
Holdsworth reveals that it may surprise many that not all cells in EV battery packs have temperature sensors, leaving a portion of the battery pack vulnerable to thermal events.
“Most Battery Management Systems won’t look at all the temperatures of the cells. At best, 50% of them will have a temperature sensor, so in most cases over half the cells in a pack are not having their temperature measured, which leaves batteries open to undetected thermal events.”
“Even though cells may appear identical, there are subtle variations in manufacturing quality, tolerances, and operating conditions that can lead to different rates of aging. Without temperature monitoring, a cell experiencing degradation and overheating could go unnoticed,” he adds. “If venting is not addressed and the pack remains under load, the cell will continue to heat up. This can lead to the breakdown of the membrane between the cathode and anode, resulting in an internal short circuit and potentially a fire, depending on the battery chemistry involved.”
Cell Guard, a matchbox-sized CAN-based sensor that can be easily integrated into almost any battery system via its 5-pin automotive-rated Molex Nano-Fit Power connector, addresses these challenges by introducing a new approach to battery safety. Working as a complementary monitor alongside the BMS, the non-contact sensor is fitted inside the battery pack where it has the ability to measure ambient conditions and analyses the gases emitted and pressure changes from hot cells. By complementing existing battery management systems, Cell Guard provides comprehensive cell coverage and early detection of potential hazards.
“Cell Guard’s early detection capabilities, focused on the venting stage, offer the best chance to prevent thermal runaway, a phenomenon in which overheating cells trigger a cascade reaction,” Holdsworth continues. “As temperature and pressure increase, there is a risk of cell venting, releasing gaseous electrolyte. This is where Cell Guard plays a crucial role by detecting the signs of cell venting. Early detection allows for actions such as unloading the pack to prevent further heating. By promptly identifying cell venting, Cell Guard allows for timely intervention, to prevent further escalation of potential hazards.”
With the increasing prevalence of EVs, the need for an integrated solution became evident, he adds, emphasising that, “Cell Guard’s unique combination of features sets it apart from other products in the market, making it the go-to solution for comprehensive battery safety.”
Ensuring operation in optimum conditions
Cell Guard goes beyond the detection of cell venting, offering a range of parameters that provide a comprehensive assessment of battery health. Its ability to measure moisture, dew point, water ingress, and pressure changes contributes to maintaining an optimal battery environment. In addition, a variant of Cell Guard incorporates an automotive accelerometer, enabling the assessment of crash loads on battery packs, providing vital information for post-accident analysis.
The first-to-market innovative solution features an accelerometer to measure Shock load and duration up to +/-24G, relaying any shock data over a configurable CAN interface to a control unit, such as the vehicle’s ECU.
By capturing and analysing this data, Holdsworth highlights that vehicle owners and insurance companies can make informed decisions to ensure the longevity and safety of the battery, avoiding the unsustainable practice of needless scrappage if an EV is involved in a minor collision, in turn helping to drive insurance premiums down. The data will also inform if the battery pack can be used in a Second Life Application.
“Having the ability to monitor impact forces on the battery pack is valuable, especially in situations like car accidents where it is crucial to determine if the pack has surpassed its designated G ratings,” he says. “Currently, the collection and accessibility of this data are lacking, resulting in many battery packs being unnecessarily discarded, even if they are still in good condition.”
Holdsworth acknowledges that the transition from an R&D version of the sensor to mass production posed significant challenges. However, Metis Engineering successfully mastered the production process, ensuring the availability of Cell Guard to the market. Looking ahead, the company plans to enhance its offerings by introducing an easy-to-connect system that allows multiple, daisy-chained, sensors to be integrated into energy storage systems seamlessly.
“While battery safety is a legitimate concern, the data-driven approach offered by Cell Guard ensures that batteries are kept within their intended parameters,” Holdsworth concludes. “Through continuous monitoring and early detection of potential hazards, Cell Guard provides peace of mind to manufacturers, owners, and the general public alike.”