Engineering news
While many projects have explored the use of specialised materials or new chemistries to boost cell performance, engineers at the University of Cambridge have found that keeping lithium-ion 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 five to 10%,” a Cambridge announcement said yesterday (30 June).
As conventional lithium-ion batteries charge and discharge they physically expand and contract, the result of ions moving from the anode to the cathode and back again. “Batteries don’t tend to like this cycle of stress and release,” said Professor Michaël 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.”
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,” said De Volder. “We didn’t have to change anything about their electrolyte or electrode composition.”
The team found that the pressure needs to be in the ‘Goldilocks’ zone: about 12.5 bar, or roughly four times the standard in conventional coin cell batteries. Outside that 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,” said De Volder. “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,” said De Volder. “And we are very bad at recycling batteries at the moment.”
Longer-lasting EV batteries could also 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,” said De Volder. “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 would need to be scaled up for commercial battery applications. A patent has been filed by Cambridge Enterprise, the university’s innovation arm.
The research was supported in part by the European Research Council, the Faraday Institution and the Engineering and Physical Sciences Research Council, part of UK Research and Innovation. It was reported in Nature Energy.
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.