Electric vehicle batteries are a problematic business: About half of the carbon generated by building the whole car is dedicated to the lithium-ion cell system, they weigh a lot—the Tesla Model S’ clocks in at 1,200 pounds, even at the smaller 85kWh size—and then there’s charging time, which for your current average electric car is measured in hours and not minutes.
So what about the emerging technology of flow batteries—a type of cell that uses refillable liquids to generate electricity—for the next generation of clean vehicles? Well, it’s promising, but not quite there yet either.
A Jalopnik reader asked why other technologies aren’t being trialled and I, your battery-slapping electrochemical correspondent, was summoned. He asks:
As a regular Jalopnik reader, I’d be interested in learning more about the emerging technology of flow battery electric vehicles. From what I’ve read so far, they seem to hold the promise of a more practical answer to electric vehicle deployment than the current generation of EV’s, and avoid many of the downsides of hydrogen fuel cells that have prevented the widespread adoption of that technology.
As a quick-refueling technology, they could lead to much lighter electric cars (since you wouldn’t need a 200 mile battery capacity if you can refuel in five minutes), which is of interest to driving enthusiasts, not just environmentalists. I haven’t found a good survey of the various academic and commercial research and development projects for vehicular flow batteries.
It’s a fair question because although large-scale battery development stalled for almost the whole 20th century we do have other options, some of which are mind-blowingly good.
The most obvious alternative to the heavy, chemical consumption lithium-ion batteries that power nearly everything from watches to Teslas is called a “flow battery.” Unlike some alternatives, they currently exist and are used in large scale energy storage, made of essentially infinite tanks of electrolyte. They have massive advantages, including the fact that unlike lithium-ion cells they work best when you make them really big, at a 20kWh minimum.
They also have a huge advantage in that instead of being recharged by sending electricity directly into the cells, which then electrochemically absorb energy to store the charge, a flow battery is “charged” by cycling all the liquid out of it and putting new in.
In a sense it’s incredibly simple, and amazing. You could put electrical charge in a solution that’s basically water (unlike the chemicals needed for lithium-ion batteries) externally in tanks and then push it into the vehicle’s cell when it’s needed. Charging times could be brought down to 5-10 minutes from currently a minimum of half an hour.
All the charging is done outside the vehicle, which means tanks can pick up off-peak energy supply and hold it until rush hour. For energy grids like the US, which is still heavily reliant on fossil fuels, it could be the best green option we have for reducing emissions on vehicles. Pretty amazing, no? We should be looking into it, surely?
Well, people are. Or at least, they say they are.
In 2014, Jalopnik reported that European company nano_Flowcell were making some insane-sounding “saltwater-powered” hypercars. Of course, we did have to report that they also sounded like bullshit owing to the way they sounded, sadly, like complete bullshit.
In theory the physics of the concept is sound—two massive tanks of electrolyte fluid in a car, one negatively charged, one positively charged, would meet and create that sweet, sweet go-go-juice. That’s how flow cells would work in a vehicle. What was baffling was how they’d managed to get their electrolyte so concentrated that it claimed to be holding more than five times the energy density of Tesla battery fluid, which would mean it was such an earth-shaking energy science breakthrough they were surely about to be showered in Nobel prizes.
Well, it’s 2018 and they haven’t made a car. I thought I’d check what our pals were up to, and maybe it’s good news: in April they said they were looking to secure a site for a factory in the second half of this year. If they do have magic salty concentrate, something that at this point in the 21st Century doesn’t seem at all implausible, then all well and good. It’s just that until they actually prove they do, the car is in the same limbo as your girlfriend who totally exists and just goes to another school, and no, your friend wouldn’t know her. (It’s a school in Canada.)
Feasibility studies have been done to examine what it would take to run flow batteries in EVs, but there are a few colossal stumbling blocks that are why lithium-ion continues to be pursued. And that’s despite Tesla partner Panasonic having acknowledged we are already pushing the limits of its capabilities.
Most of the alternatives to LI batteries, like lithium-air cells, have major issues with lifespan. That’s not the case for flow batteries, which do not degrade for over 20 years in industrial usage. However, they are prey to some of the other issues that the ubiquity of LI cells has somewhat overcome.
Flow batteries don’t have the energy density of chemical batteries—that’s partly why they’re so robust, but also makes them a bit limiting for vehicles as you’d need, in essence, two enormous fuel tanks to get good range out of them. Most feasibility studies about converting them to vehicles are looking at buses or other relatively short-range, large vehicles because they’re reliant on topping up at flow tanks so regularly—that particular study suggested every 18 miles.
Flow batteries are incredibly useful for grid management. Japan has some that hold a whacking 60MWh of energy. But unless you have some kind of massive power generation facility, they don’t quite work. While you could feed them off the grid—and they have some home storage potential—the idea that a regular gas station could be generating the power to fill multi-mWh tanks of energy storage would be pretty impractical without a small nuclear reactor.
One of the other problems with flow batteries is that they’re heavily reliant on a metal called vanadium, which sounds a bit like something Marvel made up and is, you may have guessed, not just lying around everywhere.
There is mining for it and a large deposit of battery-grade has recently been found in Nevada. But that’s the only recent one discovered and the mining project isn’t actually active there yet. While scientists are furiously searching for a cheap and available alternative, vanadium is currently a huge barrier to creating flow batteries on a mass scale.
There’s also the problem with a flow battery of what to do with recoverable energy. EVs can massively extend their range by recovering energy under braking, then feeding it back into the battery. But that would be non-trivial with a flow battery, which “charges” by reversing the flow of electrolyte, not by receiving direct current.
So if you use a flow battery you have to accept that this chunky thing only goes one way. That’s maybe less of a problem if you can refuel in seconds but still a loss of efficiency that limits your range. Flow batteries are still heavy, especially with their lower energy density so any power lost remains a significant problem.
As with the idea of putting graphene solid-state batteries into cars, which Fisker absolutely swears it’s doing, the problem comes down to the fact we haven’t developed the technologies. Ultimately it’s possible that we might be able to do it—and that in particular flow batteries might, as a few studies have suggested, be amazing as an EV solution that ultimately replace lithium within a decade.
This idea offers a major opportunity to move away from national power grids and to localized, battery-reinforced supply not just for EVs, but all electricity demands. The problem is not only that no one has built one, but also that we don’t have the grid for it. Converting existing gas station fuel tanks for storing and charging extremely stable electrolyte would be possible. But then hooking up power generation to them would be much harder.
Countries without established grids are pioneering the usage of some new technologies. Unfortunately, unless a viable and widely available alternative to vanadium can be discovered then it’s unlikely flow batteries will be able to become part of that, limiting their current development potential.
So it’s not impossible we will end up with cars magically charged with electrolyte, like me guzzling a Powerade before churning out some electrochemically complicated copy on my lunch break. But it’s unfortunately not as trivial as just being able to plug a flow battery in and driving off.
So for the moment, long live lithium ion.
Hazel Southwell is a freelance journalist who covers motorsports, electric vehicles and more. She officially lives in London and unofficially on the departures side of Heathrow Terminal 2. She has one cat.