Lessons From China: Battery Safety in EVs

Article By : Junko Yoshida

China’s EV startup WM Motor issued a recall for more than 1,000 vehicles after four of its vehicles caught fire in just a month...

Chinese EV startup WM Motor (Shanghai) in late October issued a recall for more than 1,000 vehicles after four of its automobiles caught fire in just a month, according to several news reports.

The recall centers on WM Motor’s EX5 model, produced this year between June and September. An EV startup founded in 2015, WM blamed the fires on possible contaminants in the battery cells.

The news of “four fires in a month” in the same model set several experts wondering:

  • Is this an outlier?
  • Was its cause associated with the battery cell supply chain?
  • Does China have an EV battery safety standard?
  • If so, did WM’s vehicles comply to the standard and why didn’t it work?
  • What about the role of battery management systems? If put in place, couldn’t they have flagged overheating battery cells as an early warning system for users and EV suppliers?

Given the proliferation of Chinese EV startups, it’s tempting to dismiss this as an isolated incident perhaps unique to inexperienced Chinese OEMs.

But digging deeper, it becomes clear that ensuring the safety of EV batteries is never a “case-closed, solved problem” for EV makers, Chinese or otherwise.

It is, rather, a growing challenge as EV vendors everywhere race to extend range and promote higher-speed charging. Such technology improvements are necessary, but the demand for steady improvement can put EV batteries under tremendous pressure, turning innovations into potential hazards.

WM Motor reported that nobody got hurt in the fires. But even when accidents are infrequent and non-lethal, catching fire is every EV supplier’s worst nightmare.

Phil Magney, founder and president of VSI Labs, said, “This is a hot issue (no pun intended).  Lithium Ion batteries are highly combustible, burn at a very high temp and hard to extinguish.” Because EV fires are so serious, he added, EMTs and fire departments undergo special training to deal with them. Given the severity of battery fires, he noted, all battery management components should be rated to meet ASIL-D, the highest level of functional safety.

Supply chain issues
In its early days, Tesla made Panasonic the company’s main battery supplier. Veteran automotive industry expert Egil Juliussen believes that reliance on a single Japanese company known for its quality eased Tesla’s battery supply chain management issues in the beginning, while maintaining the quality of EV batteries.

Battery supplies have become increasingly constrained in recent years.

In 2018, when Tesla started to ramp up production of Model 3, Elon Musk famously blamed a shortage of cells at Panasonic for Tesla’s “production hell.” Tesla, subsequently, came to depend on batteries supplied by China’s CATL and South Korea’s LG Chem, in addition to those from Panasonic. In September, Tesla announced plans to go vertical by developing and manufacturing its own battery that will presumably improve EV range and power.

Most EV startups, however, don’t have the luxury of self-supply.

In sourcing EV batteries, Juliussen pointed out, “It becomes increasingly important for OEMs to manage and track supply chains at every level.” This includes everything from acquisition of battery-cell raw materials to placing quality control in production.

China’s foray into the EV
Compared to the market for internal combustion vehicles, where China remains weak, barriers to the EV market are much lower for Chinese EV startups. Juliussen wrote previously in his “Egil’s Eye” column on EE Times:

China is counting on becoming a leader in intellectual property (IP) for Battery Electric Vehicles (BEVs), Autonomous Vehicles (AVs) and their underlying technologies…China is betting that AV technology, along with BEVs, will be a major factor in gaining better control of its automotive industry.

The reality is that EVs still represent a new and growing market that requires vendors to keep up with constantly evolving technologies, Juliussen said. The low entry cost for materials acquisition and variable quality control at multiple points in the supply chain, coupled with Chinese OEMs’ rush to get batteries and EVs to market add more issues, he said. “All of these complexities leave a lot of room for small errors, which can literally cause ‘flash-points.’”

China’s EV safety standards
It is a mistake to underestimate China’s aspirations to be the global EV leader.

In an interview with EE Times, Ken Boyce, UL corporate fellow and engineering director, highlighted China’s heavy push for vehicle electrification and concerted efforts to become a global leader in the transportation sector. China is making “big progress in a condensed time frame” in folding the Global Technical Regulations (GTR) for EV standards into China’s own national regulations.

Currently there are EV standards for 1) EV safety covering battery safety; 2) EV (passenger vehicle) safety in use, and 3) electric bus safety. Compared to a North American automotive industry that prefers self-certification over mandated regulations, China operates under a state-centered regulatory scheme. Today, the three EV safety standards are voluntary standards (GB/T) in China, but as of January 2021, they will be upgraded to mandatory standards (GB), explained Boyce.

UL’s team under Boyce is known for its ultra-fast, successful development of safety requirement standards for hoverboards. UL’s agile footwork, backed by its deep safety expertise, led to its publication of UL 2272 in January 2016 governing fires in hoverboards — which were a must-have gift item for the holiday season in 2015.

The process of safety analysis and technology research required for hoverboards is no different from that required for EV safety standards. But Boyce explained that the differences lie in “varying regulatory schemes” applied to different industries and different countries. Further, more complexities are involved in establishing EV safety. They include the examination of the “design process” for battery cells, setting up “validation” for battery standards (i.e. “Are we testing out battery performance based on evidence?”), considerations of the “physical abuse” applied to batteries and “quality control of production.”

Given that most batteries are made in China and the safety of EVs must be managed in a holistic manner, testing of both batteries and EVs is becoming crucial. Boyce noted that UL last year broke the ground in Changzhou for a large-scale battery laboratory to support the growing EV market. The facility became operational on October 28 — the day when the recall of WM Motor’s EX5 model was announced.

With continued growth in the EV sector, demand for EV battery and charging testing will accelerate, said UL, “as manufacturers seek a knowledgeable and trusted third-party lab to improve battery and charging performance and safety.”

China is squarely aimed at raising standards and promoting safety science for EVs and batteries.

Thermal runaway
On the company’s website, WM Motor, which styles itself a leading provider of new energy mobility solutions in China, wrote that it “designs, manufactures and markets affordable battery electric vehicles.” Further, it noted, “WM Motor’s vehicles are equipped with best-in-class proprietary battery management systems; robust driving ranges; and industry leading autonomous driving and smart connectivity feature.”

Indeed, it is customary to find active safeguards in multi-cell batteries used in EVs. Their purpose is to mitigate or prevent some failures. However, as EV suppliers try to balance safety and performance (i.e. extending the range and enabling faster charging), major challenges emerge, affecting the thermal stability of active materials within the battery at high temperatures, and threatening the occurrence of short circuits that may lead to “thermal runaway” (otherwise known as “fire”).

Art of battery management systems
NXP recently announced a new battery management system scalable across all EV platforms. Contacted by EE Times, Antonio Leone, NXP’s battery management chief, noted that testing for contaminated cells during production, to root out the likely cause of some fires, is difficult even with specialized equipment. It’s not the BMS’s place to discover battery-cell impurities. Leone, however, added that a BMS “can monitor cell voltage, impedance and temperature to detect suspicious cells and provide early warning well before any thermal runaway takes place.”

Click the image to enlarge. (Source: NXP)


The first order of business for the BMS is to “make sure that battery cells should never be put in an uncomfortable zone,” noted Leone. But as vendors compete by extending range and enabling faster charging, they end up putting much more energy and power into a battery, overstressing its cells.

The job of the BMS is to constantly monitor the battery. An effective BMS accurately measures the power left in each cell and monitors temperature. It balances power by deciding to either leave a cell alone or charge it. The objective is to leverage the full energy available in the battery without damaging it.

Beyond real-time monitoring, it’s vital that the BMS measures the long-time health of the battery cell, said Leone. “You need to make sure it is not drifting over time. You want to guarantee its long-time capacity and quality of battery.”

In other words, the BMS is critical to “measure cell trends while catching any suspicious cells.”

The BMS can alert consumers and OEMs about emerging signs of potential malfunctions in batteries. Car OEMs already installing cloud-based services for over-the-air software updates, for example, can leverage such an infrastructure to communicate early warning signals.

Magney shared a recent anecdote on what happened to his Tesla Model S.

Just last week I got an error in my Tesla Model S that my thermal battery management system was going bad. I booked an appointment (via my app) for service with a normal lead time of two weeks. Later that day Tesla called me and said they want my car ASAP due to the potential severity of the problem! They fixed the problem in a couple of days.

Magney suspects that the battery management system in the Tesla is very sophisticated and is one of their most important technologies.

Meanwhile, NXP’s Leone pointed out that the BMS could give OEMs “the power to judge batteries.” Projecting an inevitable shortage of battery supplies, he noted that EV vendors must source batteries from a variety of battery suppliers. The BMS in theory would allow EV vendors to see which batteries are performing better. It helps them select the best technology, Leone said.

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