Lithium-ion batteries power most of our modern technology, from smartphones to electric vehicles, but the game-changing energy source can cause dangerous fires. By Peter Calder
Melanie Sandford was sitting in bed early on a rainy Sunday in February 2019 listening to a podcast when there was a loud explosion in her kitchen.
What she remembers as "a nanosecond later", an orange flash "ripped down the hall" of her terrace house in the inner Sydney suburb of Leichhardt, straight past the bedroom door.
She jumped out of bed and looked down the short hallway to the kitchen, where her electronic bicycle battery had been charging on the floor overnight. The battery was on fire. Two nearby wooden bench stools were on fire. The curtain was on fire.
"It was a hot fire," she told the Sydney Morning Herald. "Some fires you might run towards with a blanket, but this was not that kind of fire."
A similar scene occurred in Wānaka this year, this time blamed on a power tool left charging overnight. There has also been at least one recent report of a phone bursting into flames in Auckland after being smashed. And just last week, an e-bike battery erupted in flames at a home in Ostend, on Waiheke Island. The battery was not charging at the time, though it was fully charged. No damage, other than to the bike, was reported.
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These kinds of fires are known to chemical engineers – and people who work with lithium-ion (Li-ion) batteries – as thermal runaway. In simple terms, the battery gets too hot, which causes a chemical change in the battery that makes it get hotter. It's an uncontrolled positive feedback loop and it always ends badly.
Thermal runaway is a known risk with Li-ion batteries, which are the energy heartbeat of almost all consumer electronics, from smartwatches through cellphones to laptops; e-bikes and e-scooters; electric vehicles, from scooters through cars to buses; and massive battery energy storage systems (Bess) that store energy for later use – think electricity generators managing demand or householders with solar panels on the roof.
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Advertise with NZME.If something you own is not antique and is powered by a rechargeable battery, it's using one or more Li-ion cells. And, says a fire-research engineer, each of them is a ticking time bomb.
Power-packed battery
Lithium-ion batteries are not new. When John Goodenough, M. Stanley Whittingham and Akira Yoshino were awarded the Nobel Prize for Chemistry in 2019 for their work in developing Li-ion cells, the citation praised them for having "created the right conditions for a wireless and fossil fuel-free society, and so [bringing] the greatest benefit to humankind".
But their research that gave birth to the battery began in the 1970s, and the first commercial production of it (a partnership between Sony and chemical giant Asahi Kasei) began 30 years ago.
From the start, the new battery was a game-changer. Its high energy density (the amount of power it packs relative to weight) opened up the possibility of many new or vastly improved consumer applications. It also overcame the dreaded "memory effect" that had plagued its rechargeable predecessors, nickel-metal hydride (NiMH) and nickel-cadmium (NiCad), whereby the battery, unless it was regularly drained to near-dead, would "remember" the previous discharge level and not recharge properly.
Best of all, the cadmium in NiCad batteries is very toxic, so lithium was seen as a more environmentally friendly alternative.
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But the advance came with strings attached. Li-ion chemistry is inherently dangerous, although the risk can be mitigated by careful management. But as the demand has increased for portable electronics and, latterly, e-mobility –in particular electric vehicles (EVs) and e-bikes – the pressure on manufacturers has mounted for ever-higher energy densities to make smaller, lighter and longer-lasting batteries.
According to George Hare, a fire-research engineer for the Building Research Association of New Zealand (Branz), "This has resulted in the use of more compact designs and more unstable chemistries, resulting in increased numbers of thermal-runaway events, leading to fires, explosions and injuries around the world."
To say the risk of these fires is high would be an exaggeration; to say that it is increasing is to state the obvious. Hare was commissioned by Fire and Emergency New Zealand (Fenz) to explore the ramifications of the proliferation of Li-ion batteries.
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Advertise with NZME.His report, published in January 2020, includes Energy Safety NZ (ESNZ) figures showing that incidents rose from virtually zero in 2009 to more than 20 in 2019. The projection is for 80 by 2025. Moreover, Hare points out, several incidents reported in the press did not appear in the ESNZ data, and not all incidents are being reported to, or by, Fenz. In short, the chances are that the problem is far bigger than anyone realises.
Those are not heart-stopping numbers, but it is self-evident that the incidence will be growing, because the number of batteries is growing. There were 5363 electric cars on our roads in October 2017. By the end of last year, there were 24,000.
The Government's projections of 64,000 by the end of this year and a further 60,000 by the end of 2023 may seem wildly optimistic but the recently announced incentive scheme seems certain to accelerate uptake.
E-bike and e-scooter numbers are on a similar trajectory. Statistics New Zealand figures (which lump both modes together) show imports, a mere 1300 in 2008, rose from 23,000 in 2017 to 47,000 in 2018 and reached 65,000 in 2019.
Shock damage
So how high is the risk? Statistically, it's quite low for hybrid and electric vehicles (EVs). Elon Musk, the chief executive of prestige brand Tesla, drew on United States fire-agency data to show that one petrol-fuelled car burst into flame for every 20 million miles (32 million km) driven compared with one fire per 100 million miles for Tesla.
But those numbers are misleading. First, the average age of the US vehicle fleet is 12 years, so old bangers with perished or leaking fuel lines are in the risk pool. Second, Tesla is at the high-spec end of the market; including early-generation small EVs might make for a very different picture.
In any event, as levies and rebates combine to push more electric vehicles on to the road, and as improvements in cycling infrastructure persuade more city commuters to abandon the crowded motorways and expensive car parking in favour of riding an e-bike to work, the numbers – of bikes, cars and fires – are certain to rise. And, as Sandford will tell you, these are serious fires, uncontrollable without specialist expertise and equipment.
Maurice Wells, the proprietor of Auckland e-bike dealership Electric Bike Team, is understandably more concerned about e-bikes (and e-scooters, which are lumped in with bikes in statistical surveys) since their batteries are more vulnerable to the shock damage that can increase their fire risk.
Removing the battery for regular charging increases the chance of dropping it, and scooters, which some riders use as if they were motorised skateboards with handlebars, get bumped and banged on kerbs and potholes.
Under normal conditions, EV batteries are well insulated from being bumped – that's why the vast majority of EV battery fires are in vehicles that have been in a prang – but, says Wells, "E-scooters and e-bikes have the same sort of risk because they are close to the ground and vulnerable to damage from kerbs and so on."
By contrast, it is the older EVs that have Hare worried.
"When they get towards the end of their battery life, which some of the early-generation ones already are doing, there will be a push to see those batteries given a second life in stationary energy-storage systems," Hare told the Listener. "As they become degraded, the chances of their developing a fault increase."
He says the dangers of lithium batteries are inherent in their design: "The energy density, the flammable electrolytes, all add up to what is essentially a ticking time bomb. New technologies coming along are looking at non-flammable or solid electrolytes so they don't produce flammable gases.
"Refinements will mitigate some, though not all, risks in newer batteries. But by that time, you have to consider how many of the current generation of batteries are out there and how long it will take to get them out of the system."
Hare found, among other things, that there was widespread public ignorance about the dangers. In particular, he was concerned users didn't know enough about the safe use and disposal of the batteries; the danger of using cheap counterfeits – a constant temptation, since a replacement battery will typically set you back at least a quarter of what you paid for the unit it powers – and the risks of charging the batteries in homes and garages, near combustible furnishings or chemicals (including the petrol in the family car's tank).
"The previous batteries' technology was relatively immune to these kinds of problems," says Hare. "And when the new technology arrived, people treated it as they treated the old battery. They would leave their cellphones and laptops on charge permanently, they charge their e-bike battery under the curtains.
"In general, the public does not appreciate the risk. We got away with it with NiMH and NiCads, but we may not get away with it with lithium-ion."
Public awareness
Wells appreciates the risk all too well, and for good reason: He used to own the Sydney store that sold Melanie Sandford the battery that caught fire in Leichhardt in 2019. (In March this year, seven people escaped another battery fire that gutted a terrace house in the inner-Sydney suburb of Darlinghurst.)
Sandford's battery was one of a faulty batch, fitted to eZee bicycles and since recalled. The insurers are still wrangling, although Sandford has had her house replaced.
Having since established the Auckland business, Wells remains so concerned about the low level of public awareness of the dangers of Li-ion batteries that he has written a comprehensive battery-care guide for all users, not just his customers. The guide emphasises the importance of good recharging practice.
Lithium batteries are at their highest level of stress when at full charge, he explains, which is why he recommends charging your e-bike battery when it is less than half full rather than topping it up after every use. (I was given the exact opposite advice by the chap who sold me my first e-bike six years ago.)
"The standard commuter behaviour is to get home, plug in the battery, make dinner and forget about it until morning. Most of the fires I have seen have been related to that kind of behaviour, because that's what we all do."
He recommends spending a few dollars on a plug timer to control charging time and, if possible, to charge the battery on the bike, rather than removing it each time.
"A battery fire in the garage is still a pretty big deal, but there's a good chance the fire brigade will get to the fire before the house is alight. But if you take it off your bike, there's a risk of damaging it if you drop it and when you take it inside to charge it, you're taking the potential fire into a smaller, more confined space.
"There are things you shouldn't do: Leave your battery in the sun, short it out, take gambles by using a cheaper charger – just because it's got the same plug doesn't mean it's going to work correctly.
"But the fact is that a lithium battery can catch fire for no discernible reason. You have to ask yourself, if a fire does break out, what does it look like and what would you need to do. Take smoke alarms seriously and set your charger on a timer to turn on at 6am so there's enough charge to get to work and back. If a fire happens then, I'm awake and I can open the garage door, wheel the bike out and start taking videos. I am certainly not going to stop using my e-bike."
Wells says e-bike battery fires remain a rarity. But they are an ever-present and growing danger. At the end of June, the Government issued a recall notice on Specialized Kenevo battery packs sold between November 2017 and March 2019, because of an identified short-circuit danger. But Wells reckons the official numbers are a serious underestimate of the scale of the problem.
"I've had two of mine [catch fire] since I started in New Zealand in 2015 – both were related to the recalled batch – and in Australia I had five – four from the recall batch. But you won't get many retailers admitting to them. Privately, I've heard from others about fires that were never officially recorded."
He wants people to be informed and careful, but not to be dissuaded from pursuing e-mobility options - and he doesn't expect demand to be dampened by better public awareness.
"People will still want e-bikes," he says. "If your house burns down because of an electrical fire, you will generally put electricity in your next house."
