In the 4th quarter of 2020, Hyundai recalled 82,000 electric vehicles globally due to battery fire risks at a cost of nearly a billion dollars. General Motors also recalled 69,000 Bolt EVs for battery fire risks. BMW, too, recalled nearly 27,000 plug-in hybrid EVs for potential fire hazards in the battery. And then there are countless anecdotal stories of Tesla vehicles catching fire either on the road or in someone’s garage. This is not a pretty picture.
As EVs increasingly become popular on the road, the safety of lithium-ion batteries becomes a top concern for drivers, car manufacturers, battery makers, insurance companies, firefighters and government regulators. Yet there is no consensus on improving battery safety; the clock is ticking for a possible future disaster.
Drivers are waiting on the automakers to deliver safe vehicles. Car manufacturers largely relied on the battery manufacturers for safety. Battery manufacturers thought their batteries were safe — until they weren’t. Firefighters would rather not see battery fires — they are more difficult to contain than conventional fires. Insurance companies are struggling with the economics of underwriting policies for electric vehicles. Government agencies are globally looking into imposing safety regulations. For example, China’s new 2021 battery safety standards aim to contain a vehicle fire long enough to give the driver 5 minutes to evacuate the EV. But what if the EV is parked in your own garage? How will this new standard protect your home from burning down?
The United Nations Economic Commission for Europe (UNECE) is seeking to harmonize global vehicle battery safety regulations under its Global Technical Regulation No. 20 (GTR 20) initiative. Much work remains ahead — yet it is clear that safety regulations will come some time during this decade.
To be clear, battery fires are rare, occurring at a rate well below 0.1%! But that should be no reason for comfort for these rare events can have catastrophic and traumatic consequences. Safety comes with maturity of the product/technology, concentrated effort across the entire supply chain, investment to reduce the incidence of accidents, along with requisite regulations. As the EV industry grows, it invests primarily in scaling its manufacturing capabilities and pace of product launches…but it is time now to make safety a top global priority.
Lithium-ion batteries can catch fire for a variety of reasons. One common cause of failure is the presence of minute defects in the battery cell itself or within the pack containing 100s or 1,000s of individual cells. These defects are often difficult or uneconomical to screen out during manufacturing. They remain latent leading to a potential disaster months or possibly years downstream.
At a more fundamental level, these minute defects (for example, a manufacturing defect in the anode layer, or a mechanical deformation in the separator) can, under certain operating conditions (for example, cold temperatures), become sites where the lithium ions accumulate to form metallic lithium dendrites. Over time, these dendrites grow within the cell until they create an electric short between the two electrodes leading to a fire. The moment of fire can happen any time: during charging, or while driving, or with the vehicle just parked.
A battery’s failure makes it difficult to assign blame to any one entity in the supply chain. The defect itself is likely to be the responsibility of the battery manufacturer or pack assembly. But the defect alone is not sufficient to cause a fire. The vehicle manufacturer, the choice of battery management system, and the driver’s behavior all play a role that can lead to a catastrophic failure.
The task is to identify and exclude these rare potential problems, not only during the vehicle manufacturing phase but more essentially throughout the life of the vehicle. In other words, the vehicle itself needs to be intelligent to conduct self-diagnostics, continuously, over all the cells in its pack, and predict the probability that the battery may contain a defective cell…at which point, the vehicle can be taken in for closer inspection and preventive maintenance.
That intelligence is squarely in the realm of the battery management system (BMS). These new BMS must be capable to monitoring the integrity of each and every cell in the battery pack, alerting the driver to a potential future hazard, and intervening in advance to mitigate a potential fire. If you are wondering whether such intelligence exists, the answer is an emphatic yes!