Extreme heat can heal Li-Ion batteries, say Chinese boffins
Researchers at China’s Ningbo Institute of Materials Technology and Engineering have found a way to restore the energy density of old Lithium-Ion batteries by heating them to over 150°C.
Rechargeable Lithium-Ion (Li-Ion) batteries are already ubiquitous and are increasingly in demand for applications like powering electric cars. However even the best of them lose capacity over time, because each charge and discharge cycles changes their internal chemistry in ways that mean they can store less energy. The change in battery capacity can even be visible to the naked eye as a phenomenon called “thermal expansion” means batteries can expand after use.
Recycling Li-Ion batteries is possible, but not easy or cheap.
One more thing worth knowing about Li-Ion batteries is that when heated they can experience “thermal runaway” – a state in which they burst into flames that are extremely hard to douse. The combination of low-quality Li-Ion batteries and shoddy chargers have become a problem for fire departments around the world as devices like electric bikes and so-called “hoverboards” catch fire and threaten their owners’ homes.
Exposing Li-Ion batteries to high temperatures therefore sounds bonkers … until one considers the Ningbo Institute team’s paper in Nature, titled “Negative thermal expansion and oxygen-redox electrochemistry” which explains how heating the batteries to between 150-250°C can cause them to shrink rather and see their internal structure return to a state that reverses the capacity-reducing effects of past use.
The Ninbgo team were surprised that heating batteries produced that outcome, describing their findings as “unusual behavior, contrary to conventional thermodynamic expectations”.
They theorize that the structural disorder that develops inside batteries could become a “tunable parameter” that, if tweaked using chargers that use precise voltages to alter battery composition, could rejuvenate batteries.
The Institute’s promo for the discovery doesn’t offer any info on how close this is to commercialization, but raises the prospect of “making old electric vehicles like new”, creating self-healing devices, and if all else fails opening “new frontiers in zero thermal expansion material engineering.” ®
