24M Unveils the Reinvented Lithium-Ion Battery
Five years ago, 24M Technologies spun out from parent company A123 with plans to turn a mysterious, semi-solid electrode material into a revolution in how lithium-ion batteries are designed and built.
Back then, co-founder and Massachusetts Institute of Technology professor Yet-Ming Chiang described a “clean sheet of paper” approach, combining concepts from flow batteries and fuel cells, and stripping the modern lithium-ion battery architecture of all its inactive materials and complex manufacturing steps.
On Monday, the Cambridge, Mass.-based startup unveiled the results: a lithium-ion battery that the firm says can be built at $100 per kilowatt-hour at scale, or half the cost of today’s competition. And by using a fluid-like set of electrodes that can be formed into a working cell in one step, 24M says its manufacturing facilities could be one-tenth the cost of today’s battery plants, and come in much smaller, modular packages.
“Nobody has ever made a battery this way,” Chiang said in a phone interview last week. 24M has made about 10,000 test cells so far using a “single wet process from beginning to end,” he said. Compared to the multi-stage process used in today’s lithium-ion batteries, it’s “simplified, streamlined, with a lot of metrology, to make it as reliable and bulletproof as we can.”
24M’s approach can also incorporate a multitude of today’s various lithium-ion chemistries into its semi-solid materials process, he said. By early 2017, the startup intends to start producing utility-scale grid storage batteries, using lithium iron phosphate as the cathode and graphite as the anode.
To scale up to this goal, 24M has raised $50 million in private investment, adding to the $10 million raised in 2010 from Charles River Ventures and North Bridge Venture Partners with new investment from these VCs and some new strategic investors, CEO Throop Wilder said.
These include Japan’s IHI, a major manufacturer of jet engines, power turbines and other heavy industrial equipment; PTT, Thailand’s state-owned oil and gas company; and a third, as-yet-unnamed investor that’s working on joint development of manufacturing systems for 24M’s technology, he said.
The startup expects to have sample cells available early next year and is in the midst of raising a Series C round to set up its first production facility with its anonymous manufacturing partner by the end of 2016, he said. “Our defining goal is to chop 50 percent out of the current cost of lithium-ion,” he said. “We will enter at a very competitive price, but the volumes will be lower. Once we get to high volumes, that’s where we get to this $100 per kilowatt-hour cost.”.....
..... A “liquid wire” for thicker electrodes and reduced inactive materials
During 24M’s early days, Chiang and startup co-founder and fellow MIT professor W. Craig Carter saw its semi-solid electrode material -- dubbed “Cambridge crude” for its MIT roots -- as a material to be used in flow batteries, or perhaps as a “fuel” for electric vehicles. These facts, and published papers from the two scientists, have fed much of the media coverage and speculation on the startup’s plans until now.
In simple terms, “It’s a fluid that can conduct electricity. A friend of mine referred to it as a 'liquid wire,'” Chiang said last week. “Furthermore, it stores a ton of energy.” The startup received early funding from the Department of Energy’s ARPA-E program to explore the potential uses for this material.
“We originally conceived of using this type of electrode in a flow battery,” he said. “But what we realized upon forming the company was that this semi-solid electrode capability had a much better [application]: reinventing how lithium-ion batteries are made.”
Chiang identified two main problems in today’s lithium-ion battery design. “One is that the current lithium-ion battery itself contains a great deal of material that doesn’t store any energy,” he said. He’s referring to the inactive material that’s layered between the super-thin electrodes that allow today’s lithium-ion batteries to charge and discharge quickly.
“Having a thin electrode means that the distance the lithium ion has to travel is short -- and in the beginning, this was really necessary,” he said. “But our semi-solid electrode design allows you to get around this problem, and to create a battery that has much thicker electrodes, and thus much less inactive materials.”
“Up until now, it has not been possible to create electrodes that are this thick and which still allow the lithium to be transported fast enough” to provide fast charge-discharge characteristics, he said. 24M seeks to solve that problem through “a combination of the physical arrangement of the charge material within these electrodes, and the material we actually use,” he said.
“The key technical concept is reducing something called tortuosity,” he said -- a term that describes the state of diffusion in porous materials, like the semi-solid materials that 24M forms into anodes and cathodes. “What we do is provide more line-of-sight paths for the lithium ions to get out of the electrode, rather than provide a tortuous path through a maze of inactive material.”
That’s accomplished in the single-step process by which 24M layers its anode and cathode materials together, with an electrolyte material in between. “The electrolyte lies between the two layers, but it also permeates both of the electrodes. It’s infused into both the cathode and the anode. That’s necessary for the lithium ions to get out of the back of the battery,” he said.
Once layered together, these intertwined materials are fixed in permanent position -- something that’s possible because 24M’s material isn’t a true liquid, which would just “ooze all over the place,” he said. Instead, “it has a consistency that, under its own weight, doesn’t deform. It’s foldable, but it’s actually quite dense. […] Think of it as being like caulk.”
The end result is a battery cell that combines high energy capacity and high current density in the same set of materials, he said. The following graph, which shows a 24M test cell’s range of performance across different states of charge and discharge via the tan, as compared to typical lithium-ion batteries for power tools, tablets and electric vehicles.
We believe these to be the safest lithium-ion batteries ever created,” he added, largely due to the lack of brittle, breakable separator materials within the battery cells. To prove that, 24M shared a series of photographs of a test pouch cell being folded up like an accordion, while still maintaining a constant state of power output.
“Throughout the whole series of folds, it never creates an internal short circuit; it still works at the end of it, and after we were done, we left the battery on the shelf for a month and it still worked,” he said. That’s not just a safety bonus -- it also shows that you can shape the battery, which offers potential advantages in terms of how cells are designed to work in different form factors, he said.
A single-step manufacturing process for faster, cheaper replication
“The second aspect of lithium-ion technology that we felt needed to be reconsidered is the whole manufacturing process,” Chiang said. “Why does a conventional lithium-ion battery plant have to be so expensive and so large? To get in the game, you need at least half a billion dollars,” or at the grand scale of Tesla’s Gigafactory, up to 10 times that amount, he said.
At the root of this high cost and complexity is a multi-stage manufacturing process that hasn’t fundamentally changed since the late 1980s, he said. First of all, a conventional lithium-ion battery plant starts with metal foil, and then layers liquid “ink or paint” on it to form its electrodes, he said. That coated metal foil then has to be dried in a series of ovens, before it’s sent off for further processing, including the use of solvents that have to be recovered for reuse on the next round of products.
“We bypass all that by starting with a wet electrode that has everything you need in it,” he said, “and process that as a semi-solid. All of those steps you would normally use to make a battery electrode that would take a full day, we can do it in an hour.”
At the same time, “these electrodes do not have any exotic, costly components in them,” he said. “Everything they use is already in the lithium-ion supply chain.” And because all the materials that 24M puts into the process end up in the final product, there’s no need to remove any chemicals along the way, he said.
Others have tried to adapt similar manufacturing processes to the battery business before, he noted. “For example, people have tried to make extruded batteries,” he said, but “they had to have so much plastic to make that process possible, by the time they’re done, they have a ton of inactive material and a really poorly performing battery.” That’s in contrast to 24M’s process, in which “what goes into the electrodes is just what we need to [allow them to] perform their function,” he said.
There’s plenty about how 24M gets its layers of anode, cathode and electrolyte to form this perfect blend of battery performance characteristics that Chiang didn’t reveal in this interview. But he did say that the startup has put together a set of methods that can be replicated in a production environment that’s much, much simpler than the processes used to make lithium-ion batteries today.
“The formulation process for making these electrodes is exacting. We’ve spent a lot of time on that, and we have a lot of trade secrets around that,” he said. “There are key parts to it, which are very specific to our manufacturing process -- custom-designed -- that we’ve developed with our mass-production partner.”
Even so, “the equipment to make this stuff is fairly simple,” he said, using commercial off-the-shelf gear in common use in today’s battery manufacturing plants, as well as from industries with less of a reputation for cutting-edge technology, like the food industry.
The end result, he said, is “a different way of thinking about how to scale production to high volumes. In this field, success means there will be many, many gigawatt-hours of batteries produced every year. We believe the most cost-efficient way to get there is to create manufacturing modules that you can just replicate,” he said. In bottom-line terms, “We can get almost all the economies of scale with a $12 million factory” that would require a $500 million factory today.
24M and its unnamed manufacturing partner are “designing and developing a mini-plant, which can be replicated by using a copy-exact model” along these lines, he said. Fewer individual process steps along the way mean fewer opportunities for something to go wrong as 24M scales from prototype-scale to commercial-scale production, he added.
The startup plans to build its utility-scale batteries in partnership with its strategic investors, rather than licensing the technology itself, Wilder said. It’s already working with unnamed potential customers, one of which has about 75 megawatt-hours per year of demand-charge management business to fulfill, and another that’s looking at hundreds of megawatt-hours per year of utility-facing energy storage project business, he said.
