Adding a ‘Golden Shield’ to New Energy Vehicle Batteries

Chongqing - On December 26, at Chinese NEV brand Deepal's third-party battery testing site, a battery thermal runaway test had just been completed, and the entire area was filled with a strong, pungent odor.

Zhang Youqun, dressed in a black protective suit, removed his sweat-soaked gas mask and took a deep breath.

"This is the 126th new energy vehicle battery safety test we've completed in 2024, and the results are very encouraging!" Zhang said.

This experiment demonstrated that the new generation Golden Shield battery sample developed by Deepal and Changan Automobile achieved the milestone of "no fire, no explosion" and broke through to the industry-leading level of "no smoke."

Researching with a gas mask

Zhang Youqun and his team took six years to reach an industry-leading level. The first challenge they had to overcome was the pungent odor produced when batteries burned.

"That smell is truly unforgettable," said Zhang, pointing to the protective equipment in the lab. After the batteries burned and emitted smoke, a lingering foul odor remained, "It’s dozens of times worse than the smell of rotten eggs."

This posed a serious challenge to the olfactory nerves. During the first few trials, newcomers to the experiments would often vomit uncontrollably from the stench, and the smell would cling to their clothes for days after the experiment. However, over time, the team became accustomed to it.

"In fact, during long holidays, we sometimes even miss that smell," Zhang joked. 

In addition to the stench, Zhang and his team had to endure high temperatures and intense physical exertion.

During the scorching summer in Chongqing, after completing battery thermal runaway experiments, they had to immediately put on heavy protective suits, like firefighter gear, to disassemble the battery packs.

Since the structure of the battery packs was destroyed, finishing the task would take at least five to six hours, leaving them drenched in sweat. They have conducted countless such experiments.

Despite these hardships, Zhang and his colleagues persisted.

"This work is meaningful," Zhang said. When he received the task after the National Day holiday in 2018 to form the first specialized battery safety R&D team for Changan Automobile, he knew the responsibility was significant.

"At that time, the new energy vehicle industry was just starting, and there were occasional news reports of battery fires," Zhang explained. He realized that if the safety issues with batteries couldn't be solved, consumers would have concerns about new energy vehicles.

Over the six years, Zhang and his team conducted more than a hundred battery experiments annually. The company invested tens of millions of yuan in the effort, ultimately deciphering the mechanism behind thermal runaway and conducting a series of targeted applications research. They successfully developed the Golden Shield battery, which is fire-resistant and explosion-proof.

By the end of 2023, the Golden Shield battery was released.

A steel needle with a diameter of 5mm pierced the battery cell, yet the entire pack did not catch fire or explode. Even after being submerged in water for 60 minutes, no fire or explosion occurred, and when the battery was directly exposed to flames for 140 seconds, it did not explode even after two hours. These experimental standards and results far exceed national standards.

"We're not fighting alone," Zhang emphasized. He added that Chinese new energy vehicle companies are increasingly focusing on battery safety, investing more in relevant research and development, and continuously improving the safety of new energy vehicles. 

Data shows that in the first quarter of 2023, the self-ignition rate of new energy vehicles in China dropped to 0.44 incidents per 10,000 vehicles, lower than the 0.58 per 10,000 for fuel vehicles.

Solving new problems with new thinking

Every year, Zhang and his team conduct over a hundred experiments and encounter new problems almost every time. So, how do they solve these new challenges?

The answer is with new thinking.

When a battery module overheats, it generates a large amount of high-temperature gas, leading to thermal runaway in surrounding batteries. If high-temperature materials are released through the exhaust valve, they could ignite the vehicle and harm passengers.

"If we could find a way to cool down these high-temperature materials, we could prevent these situations," Zhang said.

During one battery pack overheating experiment, Zhang saw the exhaust valve emit a roaring "fire dragon," which immediately sparked an idea.

High-temperature materials are everywhere, but designing channels within the battery pack to direct them to cooler areas could help cool them down. “It’s like fireworks: when they are shot out, they are very hot, but as they fall, they cool down,” Zhang explained.

With this insight, Zhang and his team quickly designed a flow path structure. Ultimately, they successfully reduced the temperature of gases above 700°C to below 80°C while also controlling the gas emission direction.

There are many other examples of solving new problems with new thinking.

For instance, the industry traditionally uses expensive specialized pressure or smoke sensors to detect thermal runaway in a battery pack. Zhang's team, however, used a distributed temperature sensor solution, which costs only one percent of the traditional approach and responds much faster.

Additionally, Zhang's team designed a special device for the battery pack's explosion-proof valve. When the valve opens, this device, in combination with hardware circuits, can immediately detect battery abnormalities.

Driven by this spirit of innovation, Zhang and his team worked on battery safety R&D for over six years, solving hundreds of key technical issues related to battery safety and obtaining more than 40 patents.

Safety first

Zhang explained that as consumers demand higher driving ranges for new energy vehicles, the energy density of batteries must also continue to improve, and the mainstream battery models used in these vehicles are constantly evolving. Previously, some automakers favored a new battery model with relatively higher energy density.

However, when it came time to decide whether Deepal should choose this type of battery, Zhang's team voted against it.

"This type of battery is prone to thermal runaway under high temperatures or external impact and could even catch fire," Zhang said. After repeated testing, they found that the safety risks associated with this battery were too great.

"The battery project team wanted to showcase Changan's technical strength and insisted that we pursue higher energy density," Zhang admitted, recalling the immense pressure at the time. He and his team argued persistently and ultimately persuaded the company's decision-makers to adopt a lower-risk battery model.

Some in the industry saw this decision as a step backward. However, the market performance that followed showed that some brands that adopted this battery model faced numerous battery safety issues, while Changan's products maintained an extremely low accident rate.

Zhang and his team are developing the next-generation battery safety solution. "After 'fire-resistant and explosion-proof,' our 'smoke-free' technology battery will go into mass production this year," Zhang said, pointing to the latest prototype in the lab. This global first will elevate battery safety to a new level.

(Zhuang Chunmeng, as an intern, also contributed to this report.)

(Bai Lin and He Qingyu, reporters from Chongqing Daily, contributed the Chinese version of this report.)