Keeping lithium ion EV batteries under constant physical pressure could double their lifespan, according to initial findings of a study led by the University of Cambridge.
However, the researchers said in a paper released on June 30, that too much or too little pressure can cause the batteries to fail.
The pressure needs to be just right and in the ‘Goldilocks zone’ — referencing the British fairy-tale character who enters the home of three bears and declares the smallest bowl of porridge she tries to be “just right”.
Such gains are unheard of in battery development, where tweaks to battery composition usually result in gains of 5%-10%, according to Michael De Volder of the university’s Department of Engineering.
De Volder co-led the research team that built a custom device to keep the pressure on the battery in the ‘Goldilocks zone’, without the need for any specialised chemistry.
The device squeezes pouch cell batteries 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.
They found that the pressure from the bellows needed to be in the ‘Goldilocks zone’, defined as about 12.5 bar, or roughly four times what is standard in conventional coin cell batteries. Outside this zone, the batteries failed faster. If the pressure was too high, it could cause lithium plating to form on the anode, and too little could cause the cathode to crack.
Lithium ion batteries, at their most basic level, are composed of an anode, a cathode and an electrolyte, De Volder said. 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. 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 said researchers found that keeping the pressure on batteries relatively constant throughout each charge and discharge cycle is much better for the overall lifetime of the battery.
“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.”
De Volder said his team used commercial batteries and tested them for their lifetime under different pressures, without changing anything about their electrolyte or electrode composition.
Extending the lifetime of 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.
De Volder said the results, while early stage, could have important implications for the fast-growing EV market, especially in second-hand sales.
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.
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.
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.
