Watt's next for batteries? It'll be more of the same, not longer life, because physics and chemistry are hard
Lithium-ion had a lucky break early on. Successors will need billions of dollars to catch up – if they don't flame out first
Feature "There are liars, damned liars, and battery guys" – or some variation thereof – is an aphorism commonly attributed to US electro-whizz Thomas Edison.
Edison's anecdotal frustrations remain valid today because scarcely a month goes by without a promised battery revolution, and scarcely a month goes by without that revolution arriving.
In October, for example, The Register encountered Jagdeep Singh, CEO of QuantumScape, a battery startup that boasted a new type of battery that could double the range of electric vehicles, charge in 15 minutes, and is safer than the lithium-ion that dominates the rechargeable market.
"Ten years ago, we embarked on an ambitious goal that most thought was impossible," Singh said in a canned statement. "Through tireless work, we have developed a new battery technology that is unlike anything else in the world."
Singh might disprove Edison's aphorism and deliver the better batteries the world will so clearly appreciate. But to do so he'll have to buck a 30-year trend that has seen lithium-ion reign supreme.
Why has the industry stalled? The short answer is that chemistry hasn't found a way to build a better battery.
If you want a breakthrough, it must come from a fundamental change in the chemistry.
"The basic concept of what a battery is hasn't shifted since the 18th century," says Professor Thomas Maschmeyer, a chemist at the University of Sydney and founding chairman of Gelion Technology, a battery developer. All batteries, Maschmeyer explains, consist of three main building blocks: a positive electrode; a negative electrode; and an electrolyte that acts as a catalyst between the two sides. "These three elements cannot change. So, if you want a breakthrough, it must come from a fundamental change in the chemistry," Maschmeyer says.
Better living through chemistry
Battery boffins have proposed a periodic table's worth of alternative compounds that could surpass lithium-ion batteries.
These largely fall into two categories. First, batteries that are trying to surpass the energy densities that lithium offers, such as solid-state batteries, lithium-sulphur, and lithium-air. The other is batteries comprised of more abundant materials such as sodium-ion batteries, aluminium-ion, and magnesium-ion batteries.
But changing the chemistry of batteries is easier said than done, says Professor Jacek Jasieniak, a professor of material sciences and engineering at Monash University. He compares changing one element in a battery to changing a chemical in a pharmaceutical. "Often solving one problem exacerbates another," he says.
To understand why changing the chemistry of batteries is so difficult, consider that batteries generate energy through a series of chemical reactions. Lithium-ion batteries, for example, use a graphite anode, a metal-oxide cathode (usually cobalt, nickel, manganese, iron, or aluminium), and a lithium salt in an organic solvent as an electrolyte.
When a lithium-ion battery powers up, the graphite anode reacts with the lithium in the electrolyte, producing electrons that accumulate around the anode. Another chemical reaction at the cathode, allows it to attract these electrons, creating a flow of electrons – in other words, electricity. Scientists call this process a reduction-oxidation process or, more commonly, a "redox" reaction.
For an expendable battery, such as your manganese-alkaline AAs, this flow of electrons only needs to work in one direction. Once all the electrons have shifted from one side of the battery to the other, the battery dies, many of us just buy more and try not to think about where the little cylinder of metal and electrolytes ends up.
Wanted: Reverse gear
But for rechargeable batteries, the process must be reversible. This means that the electrons shuttling from the anode to the cathode must be able to do the same process in reverse without consuming or damaging the active chemicals.
In lithium-ion batteries, the redox reaction is exceptionally well behaved. The electrons can move in both directions for thousands of cycles before the material of the battery begins to degrade. But the reaction is not perfect; charge-discharge cycles produce tiny metal whiskers called "dendrites" that can pass through the electrolyte and shorten the life of the battery. In rare cases – think Samsung's Galaxy Note 7 – lithium-ion batteries can catch fire. But Samsung admitted that it asked a lot of its battery experts for the ill-fated phablet, and that they messed up. Many experts rate lithium-ion batteries as generally safer than gasoline engines.
But not all compounds are so well behaved when they cycle, says Monash University's Jasieniak. As an example, he cites magnesium-ion batteries, which can reach a similar energy density to lithium-ion using magnesium. Magnesium is easier to find and mine than Lithium. But it makes lousy batteries.
"The same chemical reaction that works for lithium doesn't work for magnesium – nor for sodium, aluminium, or basically any other system," Jasieniak says. "In lithium-ion batteries, the lithium diffuses through and is stabilised within the graphite anode through a process called intercalation. But magnesium cannot diffuse in the same way."
An understanding of how to stabilise magnesium in the anode remains elusive. "Magnesium also reacts at the interface of the anode to form a solid-electrolyte interface that dramatically impedes magnesium ion diffusion between the electrode and electrolyte," Jasieniak says. "Its formation results in rapid degradation of the device performance."
The troubles that hamper magnesium are not unusual. Many alternative battery chemistries can hold a charge or be recharged. But they do both imperfectly.
Magnesium-ion batteries' diffusion dramas mean they can't store a lot of energy. Lithium-air batteries offer a high energy density but have issues with stability. Sodium-ion batteries are made using one of the most abundant elements on Earth but have such low energy density that they are practically useless for consumer electronics or electric vehicles.
Lithium-sulphur offers hope
One new battery chemistry that has made it to market is lithium-sulphur. This technology excites many because it promises up to five times the energy density of conventional lithium-ion.
But when lithium-sulphur batteries cycle, the lithium and sulphur react, creating a lithium polysulphide, which is so soluble that it diffuses into the electrolyte and can cross the membrane that separates the anode and cathode. Instead of the redox reaction that one wants from a battery, the lithium polysulphide forms a coat on the anode, passivating it and rapidly reducing its capacity until it ultimately stops working.
This process, called polysulphide shuffling, is nothing new. It has left boffins scratching their heads for more than two decades. But despite the mass of work in the area, a commercially viable workaround remains difficult to find. British battery startup Oxis Energy has produced lithium-sulphur batteries and made good on the promise of five times the energy density of conventional lithium-ion.
But if you are wondering why you haven't seen them in shops, it's because their working lives are only about a fifth of their lithium-ion rivals.
Even if boffins do one day find a compound that makes it possible to create energy-dense and long-lived rechargeable batteries, bringing these technologies to market will take years.
Solid state is vapourware
To understand why, consider solid-state batteries, a technology many in the industry consider the "holy grail" of battery technologies. The basic idea behind these batteries is to replace the liquid lithium electrolyte with a metallic lithium. Doing so, boffins argue, would make the battery more energy dense – it is smaller and therefore packs more punch for its weight – and safer, given that metal lithium does not catch fire as easily as liquid lithium.
Solid-state batteries come with their own problems. While getting electrons to shuttle through a liquid electrolyte is relatively simple, it is much more difficult to do so using a solid electrolyte. "It's like putting some salt on the side of a rock and then hoping that it will somehow turn out on the other end. That's very hard stuff at room temperature," says Maschmeyer.
Some companies, such as QuantumScape and Toyota, claim to have perfected this process. But often the manufacturing process is so complex that it is not commercially viable. Toyota's solid-state battery, for instance, requires extremely high temperatures and atmospheric pressures that make mass manufacturing prohibitively expensive.
Sony's lucky break
There's also the added complication of getting such technology to scale. Lithium-ion technology got lucky – it came about around the time Sony began producing CDs to replace magnetic tape. That shift left many of the company's thin-film factories idle. When Sony realised that it could make lithium-ion batteries using those thin-film factories, the company was able to repurpose its existing infrastructure without having to put up a massive initial investment. Lithium-ion was practically born with scaled-up manufacturing at the ready.
What people want to hear is, 'Here is a new type of battery that is completely different from what we otherwise have and solves all our problems.' And that just doesn't happen in this industry.
"The penalty for that is that you can no longer use any of the battery factories or factory technologies developed over the last 30 years," says Gene Berdichevsky, a former Tesla battery engineer and chief exec of battery startup Sila Nanotechnologies. "You need to start from scratch because you're fundamentally incompatible."
He explains: "If you're making a new anode, you only need to fund the equipment to make that anode – for the rest you can use the existing battery factories around the world. But if you're trying to make an entirely new battery architecture, you must make all the new pieces of equipment yourself. The cost of the initial plant, even a baby-sized one, would be billions of dollars."
By comparison, lithium-ion prices have dropped off a cliff in the last three decades as battery makers have expanded their manufacturing capabilities. In 1994, the cost of manufacturing an 18650 lithium-ion cell, the most-used cell, was over $10 for 1,100mAh. By 2001, the price had dropped to $3 and capacity jumped to 1,900. Today, these cells can deliver over 3,000mAh and costs continue to drop.
The lithium age holds its charge
Battery boffins therefore think that lithium-ion has at least a decade of dominance ahead of it.
"The battery industry is all about cost," says Sam Jaffe of Cairn ERA, a battery research outfit. "And cost is a function of scale: you need big factories and mature supply chains. That's not something you can build overnight. It took lithium-ion 15 years before it went from a highly specialised product to more of a mass-market product. That will be true of any upcoming battery technology: it takes decades."
Jaffe remains sceptical of any new battery technology that promises to revolutionise the industry in the next decade. "The battery industry doesn't progress by leaps and bounds," he says. "It progresses by inches. But over time inches become feet, and then miles. That's just the nature of electrochemistry: it's hard and it takes a long, long time. What people want to hear is, 'Here is a new type of battery that is completely different from what we otherwise have and solves all our problems.' And that just doesn't happen in this industry."
He may be right. But for battery makers, the problem is that such inch-by-inch progression takes time and money. Much of the hype that companies make about new battery technologies often comes off as a desperate attempt to keep investors interested. Yet few investors have an appetite to wait a decade for chemists to solve tough problems when a software startup can reach a billion users in half that time.
This makes better batteries just the kind of thing that governments like to fund. Japan, China, South Korea, and the US have all thrown money at researchers working on next-gen batteries, but only modest amounts. For instance, Japan's Consortium for Lithium-Ion Battery Technology and Evaluation Center, or Libtec, shares a cumulative $90m across a group of 25 companies. In the US, the Joint Center for Energy Research has put down only $120m. By comparison, when China wanted to bolster its local chipmaking facilities in the early 2010s, it invested a $150bn into local firms.
Some startups are taking a more cautious approach. Don't reinvent the wheel, just improve it, they argue. Berdichevsky's company, Sila Nanotechnology, is developing a new type of silicon-based anode for lithium-ion batteries, which would increase their energy densities significantly without upending existing manufacturing processes. Others are looking to replace the anode with graphene, which is said to help the tech hold more energy and charge ten times faster.
But despite lithium-ion's continued dominance, the industry is waking up to the fact that lithium-ion is not a one-size-fits-all solution. "Lithium-ion is great as [a] high-energy-density battery solution, but if you don't need high energy density then it may not be the right technology for your application," says Jasieniak.
He concedes that many of these alternative technologies are "not there yet". But neither was lithium-ion 10 years ago. "We improved lithium-ion piece by piece, through advances in electrochemistry, of the interfaces, of the composition changes, of the electrolyte. We have a totally different understanding of the charge-discharge process and how to control it than when we first started. So there's a real opportunity here to do the same for other technologies."
And what should one make of the next lab to claim it has invented a world-changing battery? Well, perhaps Thomas Edison has the last word there. ®