Electric vehicle batteries could last more than twice as long if they are assembled in away to control the pressure inside them more accurately, according to new research published today (Monday 29 June).
The team discovered that keeping batteries under the right amount of pressure as they charge and discharge significantly slows the damage that causes them to lose capacity over time.
The findings could one day mean fewer phones are thrown away only because their batteries no longer hold enough charge, while also helping electric cars and renewable energy storage systems last longer.
Heng Wang, first author of the study published in Nature Energy, and a postgraduate student at St John's College and the University of Cambridge's Department of Engineering, said: " Much of today’s battery research focuses on improving materials and chemistry.
“We've shown that simply controlling how the battery is compressed can have a huge impact on how long it lasts. That could help manufacturers build batteries that last much longer without fundamentally changing what's inside them."
Michael DeVolder, lead author of the study, Professor of Advanced Materials Engineering at the University of Cambridge, and a Fellow, College Lecturer and Director of Studies in Engineering at St John's, said: "Batteries don't tend to like stress build-up and release as they are charged and discharged. Much of the fascinating work on improving lithium-ion batteries is done from a chemistry and material science perspective, but as a mechanical engineer, I also wanted to understand the role that mechanics play."
Lithium-ion batteries naturally expand and contract every time they are charged and discharged, almost like breathing. While most research has focused on developing new battery materials and electrolytes, the Cambridge team investigated whether the way batteries are physically compressed also plays an important role.
To test the idea, rather than designing a new battery, they bought commercial batteries and built a high-precision device that keeps constant pressure on a battery even as it swells and shrinks during charging. This enabled them to identify an optimum level of compression.
Under the experimental conditions, batteries maintained at the optimum pressure retained their capacity for more than twice as many charge cycles as those tested under more conventional pressure conditions.
The findings would not increase the distance an electric car can travel on a single charge because they do not change how much energy a battery can store. Instead, they could allow batteries to retain their original driving range for much longer, delaying battery ageing and reducing the need for expensive replacements. Longer-lasting batteries could also help strengthen the second-hand electric vehicle market, giving buyers greater confidence that older cars will still have many years of useful battery life ahead of them.
The same approach could also help people keep smartphones and other rechargeable devices for longer before their batteries begin to fail.
Professor DeVolder, who supervised Wang’s PhD at St John’s, said the team found there was a"Goldilocks zone" for battery pressure – not too little, not too much, but just right. The researchers also found that both too little pressure and too much pressure reduced battery life - but for different reasons.
"When there isn't enough pressure, the cathode particles crack more easily," Wang said. "But if there's too much pressure, lithium can't move through the battery as efficiently and you begin to see damaging lithium plating. The trick is finding the sweet spot in the middle."
The researchers believe many batteries are currently being tested - and possibly manufactured -under less-than-optimal pressure conditions.
Professor DeVolder added: "We didn't have to change the chemistry or the materials inside the batteries. That makes this a relatively simple engineering solution that manufacturers could adopt without redesigning the battery itself."
The study examined NMC811-graphite pouch batteries, one of the leading lithium-ion battery technologies used in electric vehicles. The researchers believe the same principle could now be explored in other battery designs, potentially offering manufacturers a relatively straightforward way to improve battery durability without changing the underlying chemistry.
Professor DeVolder added: "If we can extend battery lifetime without changing the materials inside the cell, we can help improve sustainability and make electric vehicles an even more attractive long-term option."
Lithium-ion batteries power almost all electric vehicles as well as billions of smartphones, laptops, tablets, power tools and other rechargeable devices worldwide. If the findings can be replicated across other battery formats and chemistries, they could influence the design of a vast range of products, helping batteries last longer, reducing the number that need replacing and easing demand for the critical minerals needed to make new ones.
