High-density lithium batteries hold vast amounts of energy – and when they drop their guts, they can do so in absolutely spectacular destructive fashion. So researchers have built fire extinguishing capabilities right into the cells themselves.
The lithium battery has been an enormous leap forward for mankind. Smartphones, multirotor drones, long-distance electric cars, ebikes, all-day laptops, electric monowheels and skateboards – we owe them all to lithium.
They don't go into thermal runaway and let go often, particularly if they're well-built to tight standards and properly cared for. But there are so many now in our homes and businesses, garages, backpacks and vehicles – and so many cheap, non-standards-compliant cells out there – that lithium battery fires are now a fact of life, with more than 200 incidents recorded in New York City alone in 2022. And you sure don't want to be around when it happens.
"Fires" might not even be strong enough language; even a small one can explode with enough force to blow the windows out of a room. They can turn into molten-metal-spitting flamethrowers, setting fire to nearby buildings and vehicles. They can be very difficult to suppress once they get going. This video from the NYC Fire Department makes the case fairly powerfully, complete with some sound advice – like for Pete's sake don't charge an ebike in a hallway if it's the only way out of your home.
Handle high-density batteries with care; enough said. But researchers from Clemson University and Hunan University say they've made a breakthrough on a solution.
The team has created a new type of rechargeable lithium battery by replacing the typical, highly-combustible electrolyte fluid with ... well, more or less the stuff you'd normally find in a fire extinguisher. Instead of using the normal, flammable organic solvents for the battery electrolyte, the researchers used a modified version of 3M's Novec 7300 non-flammable heat transfer fluid.
"An electrolyte," writes one of the researchers in a piece for The Conversation, "allows lithium ions that carry an electric charge to move across a separator between the positive and negative terminals of a lithium-ion battery. By modifying affordable commercial coolants to function as battery electrolytes, we were able to produce a battery that puts out its own fire."
The self-extinguishing electrolyte performed well in both lithium and potassium-ion batteries, refusing to catch fire even when nails were driven through them. The team didn't supply video of these tests, but here's what it looks like when a battery fails a nail penetration test. So just imagine the below video, except that nothing happens.
The fire extinguisher solution performed well as an electrolyte, too, working well between -100 to 175 °F (-75 to 80 °C), handling extreme hot and cold significantly better than conventional electrolytes, and in some cases retaining battery capacity over a considerably higher number of charge cycles.
And the best news? It seems it should be remarkably easy to roll out at commercial scale.
"Since our alternative electrolyte has similar physical properties to currently used electrolytes," write the researchers, "it can be readily integrated with current battery production lines. If the industry embraces it, we expect that companies will be able to manufacture nonflammable batteries using their existing lithium-ion battery facilities."
Very neat work!
The research has been published in the journal Nature Sustainability.
Source: The Conversation
But more importantly the much more useful long range aircraft also need safe short term power for the VTOL power demands as their backup power. These safe batteries will add to their much safer lower power cruise with hydrogen fuel cell liquid fuel tanks. Those cold H2 tanks are safely at neutral pressure but need high insulation for lowest heat gain requirements. Aerogels and vacuums offer great insulation with very light weight and low volume for aircraft low weight and low frontal area benefits.
eVTOL will have a great future once efficient thrust arrives.