Pressure shown to extend EV battery lifespan

Researchers led by the University of Cambridge studied the role of physical pressure on the lifetime of lithium-ion batteries and found that keeping batteries under constant pressure could double their lifespan.

Such gains are unheard of in battery development, where tweaks to battery composition usually result in gains of 5–10%. Extending the lifetime of electric vehicle (EV) batteries would not only reduce the rate at which they end up in landfill or recycling, but would also reduce the environmental pressures associated with nickel or cobalt mining.

However, the pressure needs to be just right — too much or too little will cause the batteries to fail. The researchers built a custom device to keep the pressure on the battery in this ‘Goldilocks’ zone, without the need for any specialised chemistry. Their results are reported in the journal Nature Energy.

At their most basic level, lithium-ion batteries are composed of an anode, a cathode and an electrolyte. As the battery goes through each charge and discharge cycle, lithium ions shuttle from the anode to cathode and back again. This causes the battery to physically expand and contract, almost like breathing.

“Batteries don’t tend to like this cycle of stress and release,” said Professor Michael De Volder from Cambridge’s Department of Engineering, who co-led the research. “Much of the work on improving lithium-ion batteries is done by chemists and physicists, but as a mechanical engineer, I also wanted to look into the role that mechanics play.”

To study this, De Volder and his colleagues built a device that squeezes a type of battery known as a pouch cell using pneumatic ‘bellows’: small air-filled cushions that act like a self-adjusting clamp. The bellows maintain a continuous pressure, while a sensor monitors tiny volume changes as the battery charges and discharges.

“We just bought commercial batteries and tested them for lifetime under different pressures,” De Volder said. “We didn't have to change anything about their electrolyte or electrode composition.”

They found that the pressure from the bellows needs to be in the ‘Goldilocks’ zone: about 12.5 bar, or roughly four times what’s standard in conventional coin cell batteries. Outside this zone, the batteries fail faster. If the pressure is too high, it can cause lithium plating to form on the anode, and too little can cause the cathode to crack.

“We found that when you keep the pressure on them relatively constant throughout each charge and discharge cycle, it’s much better for the overall lifetime of the battery,” De Volder said. “If you press too hard, the anode is unhappy. If you don’t press hard enough, the cathode starts degrading. Our experiments identified where the ‘happy place’ is for batteries when it comes to pressure.”

The results, while early stage, could have important implications for the fast-growing EV market, especially in the second-hand market. “The longer your product will last, the fewer the number of times you’ll have to recycle the materials,” De Volder said. “And we are very bad at recycling batteries at the moment.”

In addition, longer-lasting EV batteries could reduce the volume of raw materials that need to be mined, often in extremely poor conditions, to produce new batteries. “We’ve produced a solution for cleaner electric cars, but we have to make sure that on the back of it, we are not creating new ecologic disasters in other parts of the world,” De Volder said. “If we can reduce the pressure on these mining operations a bit, that would be another important benefit.”

The technology has been tested at a laboratory scale, but will need to be scaled up for commercial battery applications. A patent has been filed by Cambridge Enterprise, the University’s innovation arm.

This is a modified version of a news item published by the University of Cambridge under CC BY-NC-SA 4.0. This version is similarly licensed under CC BY-NC-SA 4.0. The original version of the news item can be accessed here.

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