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Li-Ion battery is safe, high powered and lasts for 1 million miles

09 March 2020

Electric vehicle batteries typically require a trade-off between safety and energy density. Researchers have found that high energy Li-Ion battery is safer for electric vehicles.

Illustration of a new lithium-ion battery that is both safe and high-performing, developed by researchers at Penn State. (Image: JENNIFER MCCANN/PENN STATE)

If the battery has high energy and power density, which is required for uphill driving or merging on the freeway, then there is a chance the battery can catch fire or explode in the wrong conditions. 

However, materials that have low energy/power density, and therefore high safety, tend to have poor performance. There is no material that satisfies both. For that reason, battery engineers opt for performance over safety.

“In this work, we decided we were going to take a totally different approach,” said Chao-Yang Wang, Professor of Mechanical, Chemical and Materials Science and Engineering, and William E. Diefenderfer Chair in Mechanical Engineering at Penn State. 

“We divided our strategy into 2 steps. First, we wanted to build a highly stable battery with highly stable materials.”

Their second step was to introduce instant heating. About 4 years ago, Wang developed a self-heating battery to overcome the problem of poor performance in cold climates. The battery uses an electric current to heat up in seconds, compared to the hours an external heater required.

By heating the battery from room temperature to around 60°C, the battery gets an instant boost in reactivity because the law of kinetics is that reactivity increases exponentially with temperature.

“With these 2 steps, I can get high safety when the battery is not being used and high power when it is,” he said.

The self-heating battery, called the All Climate battery, has been adopted by several car companies, including BMW, and was chosen to power a fleet of 10,000 vehicles that will be used to ferry people between venues at the next Winter Olympics in Beijing.

Researchers at The Battery and Energy Storage Technology (BEST) Centre test the safety of the battery using nail penetration equipment. They drive the nail into the cell causing short-circuiting. They then monitor the cell for temperature and voltage. 

The difference in temperature for the passivated cell was 100°C, compared to a standard battery cell which was 1000°C – an enormous improvement.

Because the batteries are built using stable materials, they have a long cycle life. Even at 60°C, their cycle number is over 4000, which translates to over a million miles.

The team’s next project will be to develop a solid-state battery, which will likely require heating as well.

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