The stories are getting too numerous to track. An electric bike battery fire injured four, one critically, in Brooklyn in June. Scooter batteries set off a house blaze in Sydney in May, and an apartment fire in San Francisco in July, injuring several people. An e-bike battery fire in upper Manhattan in February injured 17, four of them seriously, and killed one man.
Safety experts put the blame not so much on the technology behind the batteries—in this case, lithium ion batteries—but on human error: specifically, cheap manufacturing by sellers and rough handling by users. “The bottom line is that when a lithium ion battery is abused by crushing, overcharge, penetration, heating, et cetera, you generate huge quantities of explosive and toxic gas inside the cells,” says Paul Christensen, chair of pure and applied electrochemistry at Newcastle University in the U.K.
Battery Basics
There is an inherent danger in how lithium-ion batteries work. In a charged battery cell, one end, called the anode and typically made of graphite, holds lithium in a chemically high-energy state. The other end, called the cathode, typically contains oxides of metals—such as cobalt, manganese, or nickel.
The cathode can achieve a more chemically stable state if it incorporates the lithium from the anode. Electrons from the lithium leave the anode and pass through a phone, bike, or whatever device the battery is powering, before reentering the battery at the cathode. The remaining positively charged lithium ions move from anode to cathode by passing through a liquid called an electrolyte inside the battery. (To charge a battery, the opposite sequence occurs, wherein the ions and electrons flow back from the cathode to the anode and create potential energy for the battery to store.)
The whole process depends on a thin plastic separator that allows only the positive lithium ions to pass through the inside of the battery. If that separator breaks down, the anode and cathode can touch, in a short circuit that heats up the electrolyte, turning it into a toxic, flammable gas.
“Eventually it’s going to find a seam or some weak spot and shoot out,” says Brian O’Connor, senior engineer at the National Fire Protection Association (NFPA). “And that’s flammable, it’s toxic. It can create an explosive atmosphere.” Once one cell in a battery pack ignites, or even gets very hot, it can set off the next cell in a battery pack, and the next and the next in what’s called “thermal runaway” or “thermal propagation.”
Human Error
“Lithium ion batteries don’t commit suicide. They are murdered by people,” says Newcastle University’s Christensen, whose research focuses on thermal runaway and propagation in large lithium ion battery systems. “The human factor is always in there somewhere.”
Some battery cells are doomed from birth. In 2016, Samsung canceled and recalled its entire Galaxy Note7 smartphone line after short circuits caused dozens of battery fires around the world, including burning cars and a garage. A typical e-bike or scooter battery can hold from about 30 to 120 times as much energy as a typical phone battery, making it far more explosive. And they don’t always come from the best manufacturers.
That includes DIYers who buy generic battery cells, spot welders, and soldering irons online to build their own packs. Other hackers try to do their own repairs, such as replacing a cell that’s gone bad, says the NFPA’s O’Connor.
The Hazards of Charging
The key safety measure in power packs is a battery management system (BMS), which monitors voltage to prevent overcharging. Higher-end versions might also have temperature sensors and the ability to monitor and even turn off individual cells that are acting strangely due to damage or defects. A cheaper BMS will have a harder time heading off trouble. Even with a BMS, a battery needs to be paired with the charger designed for it, say Christensen and O’Connor, since different cell designs may have different charging requirements.
As mentioned above, charging a dead battery pushes the lithium ions and electrons away from the cathode and back into the anode. If that push happens too fast, the lithium metal may pile on top of the anode, rather than going into it. This causes reactions that produce heat and can also form filaments, called dendrites, that may puncture the separator, causing a short circuit.
Fully charging also causes the anode to swell up with lithium. “So then the separator gets a little compressed, and the anode and cathode get a little closer together,” says Celina Mikolajczak, the chief battery technical officer at materials science company Lyten, and a former battery engineering executive at Tesla and Uber. “If you’re going to have a dendritic short, the distance that short has to grow is the smallest when you’re at top of charge.”
All these dangers seem to be far bigger for electric bikes and scooters than for cars and trucks, although data is not definitive. The best accounting for automobiles, experts say, comes from EV FireSafe, a research company funded by the Australian Department of Defence. Its latest report, from June 30, tallies 511 thermal runaway events in electric and plug-in hybrid autos since 2010. It doesn’t report any deaths. (EV FireSafe warns that its research can’t capture every incident because many are never reported.)
In New York City alone, just since 2019, there have been 733 lithium-ion battery fires in bikes or scooters, which killed 29 people (per a July 22 city report).
Carmakers can afford to spend more on battery quality, says O’Connor. “Once we get down to electric bikes, typically the margin for profit’s a lot smaller,” he says. Also, “bicycles are just more likely to crash, you’re more likely to drop them over, and they’re cheaper. So you don’t treat them as nicely as you treat a $100,000 car.”
People also tend to spend more time close to their fire-prone bikes and scooters, especially in crowded cities. “You bring it home to your apartment, you leave it right next to your door,” says O’Connor. “I wouldn’t store a tank of propane next to my only exit from the building. And if my tank of propane was dented or damaged, I probably wouldn’t use it anymore.”
Safety Tech
Short of changing people’s habits, there are steps to take to change batteries themselves to make them safer. One method is called propagation resistance. “There’s a lot of ways to accomplish this. Some of it is, you space the cells out, so they don’t touch each other,” says Mikolajczak. “The other thing is, you try to understand which way gasses will vent. And you try to make sure that you’re not venting hot gas from one cell onto another cell.” Designers can also put insulating material between cells to block heat or electric arcs from passing between them, she says.
(Mikolajczak also offers a great anecdote about her Tesla days: “When I first met the guys at Tesla, which was like 2006 … they had all these cells close packed together, and welded together, and all the cells were touching,” she says, “and I looked at this, and I said, ‘You’re gonna burn your cars to the ground.’” Six years later, she joined Tesla as technical leader on cell development and worked on improving propagation resistance.)
“Is it just the insulation that’s doing it? Or is it the fact that it’s a very expensive battery now that has all this technology?” says O’Connor. “We try to do testing and make sure we know exactly the cause of something being safer [or] more dangerous. I can’t comment on whether or not that’s making them safer.”
“We have in our own packs materials for isolating [cells], but we . . . don’t rely on those to be the last line of defense,” says Joe Kraus, president of e-bike and e-scooter startup Lime. The company designs its own packs, including a sophisticated battery management system, which he says is the first line of defense. Another line is charging: Lime swaps out batteries on its bikes and scooters and charges the dead ones at warehouses, where each pack resides in an insulated slot to prevent a possible fire from spreading.
Safety in Newer Tech
Some newer battery technologies seem less likely to catch fire. Lithium ferrous phosphate (LFP) which uses iron phosphate in the cathode, can withstand higher temperatures before collapsing and triggering a fire.
The biggest drawback to LFP batteries is their lower energy density—as little as half that of the metal oxide ones. That hasn’t stopped EV carmakers—including BYD, Ford, Renault, Rivian, and Tesla—from using LFP for their lower-priced models. Cars, after all, have a lot of room for batteries. “I think LFPs are certainly interesting, but at the moment, don’t carry the energy densities that you’d like to see in a small form factor,” says Kraus.
LFP still uses a flammable liquid electrolyte. But solid-state batteries that employ nonflammable ceramics as both electrolyte and separator are on the horizon. “The crystal structure is made up of larger ions, and so there’s space within it that those lithium ions can move [through],” says Eric Wachsman, director of the Maryland Energy Innovation Institute at the University of Maryland. Wachsman is also founder of battery startup Ion Storage Systems, which promises higher energy density along with lower fire risk.
“In theory, [solid state batteries] could be much safer,” says Mikolajczak. “No one has built a large solid state pack and tested it in all the ways that you test a battery pack for failure to really determine that.”
But it will take quite some time before solid state batteries are hitting the mainstream. “You’re building an entire new [manufacturing] plant, or you’re changing a significant fraction of that manufacturing line,” says Wachsman. He does expect to have cells for customers such as the Department of Defense next year. “When it gets to EVs, that’s more of the capital costs of scaling up a fabrication line to do that,” he says.
Common Sense Today
While future technologies can make batteries safer, common sense goes a long way to reduce risk with today’s tech. There are basic safety tips throughout the life of the battery: Buy products from well-known makers, and use the charger that came with the battery; don’t leave a battery charging overnight or when you are away from home, since a fully charged battery is at its most fire-prone state; don’t keep a potentially explosive bike or scooter in your home (and if you must, don’t block the exit with it); and be sure to get the battery pack checked out by a professional following a crash.
There are some signs of progress on the safety front. In July, the New York Fire Department launched a public education campaign on battery safety. It also reported that, while the number of battery fires had gone up a bit vs. the previous year, the number of injuries had nearly halved, from 92 to 55, and deaths had plummeted from 13 to 1. The reason: People are charging their bikes inside less. And the city plans to build outdoor chargers to make this easier.
“Every one of these fires, which destroys people’s lives, every one of these fatalities and the hundreds of injuries we’ve had . . . could be prevented by some simple guidelines,” says Christensen.
Autentifică-te pentru a adăuga comentarii
Alte posturi din acest grup
OpenAI on Tuesday announced a new ChatGPT system for U.S. government workers that it calls more secure than its Enterprise
With its powerful camera, the French Navy surveillance plane scouring the Baltic Sea zoomed
The release of Chinese AI company DeepSeek’s R1 model on January 20 trigge
Andy Hunter decided something needed to be done about the endless rise of Amazon in 2018—the year that the e-commerce giant surpassed 50% of book sales in the U.S. market. “I was concerned at that
“Isn’t AI supposed to make things simpler?” asks a student in ">a new Saturday Night Live sketch.
Technically, the answer
The Chinese AI company DeepSeek has put the AI industry in an uproar. Deni
