Lithium-ion batteries, those marvels of lightweight power that have made possible today’s age of handheld electronics and electric vehicles, have plunged in cost since their introduction three decades ago at a rate similar to the drop in solar panel prices, as documented by a study published last March.
But what brought about such an astonishing cost decline, of about 97 percent?
Some of the researchers behind that earlier study have now analyzed what accounted for the extraordinary savings. They found that by far the biggest factor was work on research and development, particularly in chemistry and materials science. This outweighed the gains achieved through economies of scale, though that turned out to be the second-largest category of reductions.
The new findings are being published in the journal Energy and Environmental Science, in a paper by MIT postdoc Micah Ziegler, recent graduate student Juhyun Song Ph.D. ’19, and Jessika Trancik, a professor in MIT’s Institute for Data, Systems and Society.
The findings could be useful for policymakers and planners to help guide spending priorities in order to continue the pathway toward ever-lower costs for this and other crucial energy storage technologies, according to Trancik. Their work suggests that there is still considerable room for further improvement in electrochemical battery technologies, she says.
The analysis required digging through a variety of sources, since much of the relevant information consists of closely held proprietary business data. “The data collection effort was extensive,” Ziegler says. “We looked at academic articles, industry and government reports, press releases, and specification sheets. We even looked at some legal filings that came out. We had to piece together data from many different sources to get a sense of what was happening.” He says they collected “about 15,000 qualitative and quantitative data points, across 1,000 individual records from approximately 280 references.”
Data from the earliest times are hardest to access and can have the greatest uncertainties, Trancik says, but by comparing different data sources from the same period they have attempted to account for these uncertainties.
Overall, she says, “we estimate that the majority of the cost decline, more than 50 percent, came from research-and-development-related activities.” That included both private sector and government-funded research and development, and “the vast majority” of that cost decline within that R&D category came from chemistry and materials research.
That was an interesting finding, she says, because “there were so many variables that people were working on through very different kinds of efforts,” including the design of the battery cells themselves, their manufacturing systems, supply chains, and so on. “The cost improvement emerged from a diverse set of efforts and many people, and not from the work of only a few individuals.”
The findings about the importance of investment in R&D were especially significant, Ziegler says, because much of this investment happened after lithium-ion battery technology was commercialized, a stage at which some analysts thought the research contribution would become less significant. Over roughly a 20-year period starting five years after the batteries’ introduction in the early 1990s, he says, “most of the cost reduction still came from R&D. The R&D contribution didn’t end when commercialization began. In fact, it was still the biggest contributor to cost reduction.”
The study took advantage of an analytical approach that Trancik and her team initially developed to analyze the similarly precipitous drop in costs of silicon solar panels over the last few decades. They also applied the approach to understand the rising costs of nuclear energy. “This is really getting at the fundamental mechanisms of technological change,” she says. “And we can also develop these models looking forward in time, which allows us to uncover the levers that people could use to improve the technology in the future.”
One advantage of the methodology Trancik and her colleagues have developed, she says, is that it helps to sort out the relative importance of different factors when many variables are changing all at once, which typically happens as a technology improves. “It’s not simply adding up the cost effects of these variables,” she says, “because many of these variables affect many different cost components. There’s this kind of intricate web of dependencies.” But the team’s methodology makes it possible to “look at how that overall cost change can be attributed to those variables, by essentially mapping out that network of dependencies,” she says.
This can help provide guidance on public spending, private investments, and other incentives. “What are all the things that different decision makers could do?” she asks. “What decisions do they have agency over so that they could improve the technology, which is important in the case of low-carbon technologies, where we’re looking for solutions to climate change and we have limited time and limited resources? The new approach allows us to potentially be a bit more intentional about where we make those investments of time and money.”
David Chandler MIT Technology
More information: Determinants of lithium-ion battery technology cost decline, Energy and Environmental Science (2021). DOI: 10.1039/d1ee01313k
Journal information: Energy and Environmental Science
Iron-flow technology from ESS is being deployed at scale in the U.S.
The world’s electric grids are creaking under the pressure of volatile fossil-fuel prices and the imperative of weaning the world off polluting energy sources. A solution may be at hand, thanks to an innovative battery that’s a cheaper alternative to lithium-ion technology.
SB Energy Corp., a U.S. renewable-energy firm that’s an arm of Japan’s SoftBank Group Corp., is making a record purchase of the batteries manufactured by ESS Inc. The Oregon company says it has new technology that can store renewable energy for longer and help overcome some of the reliability problems that have caused blackouts in California and record-high energy prices in Europe.
The units, which rely on something called “iron-flow chemistry,” will be used in utility-scale solar projects dotted across the U.S., allowing those power plants to provide electricity for hours after the sun sets. SB Energy will buy enough batteries over the next five years to power 50,000 American homes for a day.
“Long-duration energy storage, like this iron-flow battery, are key to adding more renewables to the grid,” said Venkat Viswanathan, a battery expert and associate professor of mechanical engineering at Carnegie Mellon University.
ESS was founded in 2011 by Craig Evans, now president, and Julia Song, the chief technology officer. They recognized that while lithium-ion batteries will play a key role in electrification of transport, longer duration grid-scale energy storage needed a different battery. That’s because while the price of lithium-ion batteries has declined 90% over the last decade, their ingredients, which sometimes include expensive metals such as cobalt and nickel, limit how low the price can fall.
The deal for 2 gigawatt-hours of batteries is worth at least $300 million, according to ESS. Rich Hossfeld, chief executive officer of SB Energy, said the genius of the units lies in their simplicity.
“The battery is made of iron salt and water,” said Hossfeld. “Unlike lithium-ion batteries, iron flow batteries are really cheap to manufacture.”
Every battery has four components: two electrodes between which charged particles shuffle as the battery is charged and discharged, electrolyte that allows the particles to flow smoothly and a separator that prevents the two electrodes from forming a short circuit.
Flow batteries, however, look nothing like the battery inside smartphones or electric cars. That’s because the electrolyte needs to be physically moved using pumps as the battery charges or discharges. That makes these batteries large, with ESS’s main product sold inside a shipping container.
What they take up in space, they can make up in cost. Lithium-ion batteries for grid-scale storage can cost as much as $350 per kilowatt-hour. But ESS says its battery could cost $200 per kWh or less by 2025.
Crucially, adding storage capacity to cover longer interruptions at a solar or wind plant may not require purchasing an entirely new battery. Flow batteries require only extra electrolyte, which in ESS’s case can cost as little as $20 per kilowatt hour.
“This is a big, big deal,” said Eric Toone, science lead at Breakthrough Energy Ventures, which has invested in ESS. “We’ve been talking about flow batteries forever and ever and now it’s actually happening.”
The U.S. National Aeronautics and Space Administration built a flow battery as early as 1980. Because these batteries used water, they presented a much safer option for space applications than lithium-ion batteries developed around that time, which were infamous for catching on fire. Hossfeld says he’s been able to get permits for ESS batteries, even in wildfire-prone California, that wouldn’t have been given to lithium-ion versions.
Still, there was a problem with iron flow batteries. During charging, the battery can produce a small amount of hydrogen, which is a symptom of reactions that, left unchecked, shorten the battery’s life. ESS’s main innovation, said Song, was a way of keeping any hydrogen produced within the system and thus hugely extending its life.
“As soon as you close the loop on hydrogen, you suddenly turn a lab prototype into a commercially viable battery option,” said Viswanathan. ESS’s iron-flow battery can endure more than 20 years of daily use without losing much performance, said Hossfeld.
At the company’s factory near Portland, yellow robots cover plastic sheets with chemicals and glue them together to form the battery cores. Inside the shipping containers, vats full of electrolyte feed into each electrode through pumps — allowing the battery to do its job of absorbing renewable power when the sun shines and releasing it when it gets dark.
It’s a promising first step. ESS’s battery is a cheap solution that can currently provide about 12 hours of storage, but utilities will eventually need batteries that can last much longer as more renewables are added to the grid. Earlier this month, for example, the lack of storage contributed to a record spike in power prices across the U.K. when wind speeds remained low for weeks. Startups such as Form Energy Inc. are also using iron, an abundant and cheap material, to build newer forms of batteries that could beat ESS on price.
So far, ESS has commercially deployed 8 megawatt-hours of iron flow batteries. Last week, after a six-month evaluation, Spanish utility Enel Green Power SpA signed a single deal for ESS to build an equivalent amount. SB Energy’s Hossfeld, who also sits on ESS’s board, said the company would likely buy still more battery capacity from ESS in the next five years.
Even as its order books fill up, ESS faces a challenging road ahead. Bringing new batteries to market is notoriously difficult and the sector is littered with failed startups. Crucially, lithium-ion technology got a head start and customers are more familiar with its pros and cons. ESS will have to prove that its batteries can meet the rigorous demands of power plant operators.
The new order should help ESS as it looks to go public within weeks through a special-purpose acquisition company at a valuation of $1.07 billion. The listing will net the company $465 million, which it plans to use to scale up its operations.
Lithium-metal batteries (LMBs), an emerging type of rechargeable lithium-based batteries made of solid-state metal instead of lithium-ions, are among the most promising high-energy-density rechargeable battery technologies. Although they have some advantageous characteristics, these batteries have several limitations, including a poor energy density and safety-related issues.
In recent years, researchers have tried to overcome these limitations by introducing an alternative, anode-free lithium battery cell design. This anode-free design could help to increase the energy density and safety of lithium-metal batteries.
Researchers at the National Institute of Advanced Industrial Science and Technology recently carried out a study aimed at increasing the energy density of anode-free lithium batteries. Their paper, published in Nature Energy, introduces a new high-energy-density and long-life anode-free lithium battery based on the use of a Li2O sacrificial agent.
Anode-free full-cell battery architectures are typically based on a fully lithiated cathode with a bare anode copper current collector. Remarkably, both the gravimetric and volumetric energy densities of anode-free lithium batteries can be extended to their maximum limit. Anode-free cell architectures have several other advantages over more conventional LMB designs, including a lower cost, greater safety and simpler cell assembly procedures.
To unlock the full potential of anode-free LMBs, researchers should first figure out how to achieve the reversibility/stability of Li-metal plating. While many have tried to solve this problem by engineering and selecting more favorable electrolytes, most of these efforts have so far been unsuccessful.
Others have also explored the potential of using salts or additives that could improve the Li-metal plating/stripping reversibility. After reviewing these previous attempts, the researchers at the National Institute of Advanced Industrial Science and Technology proposed the use of Li2O as a sacrificial agent, which is pre-loaded onto a LiNi0.8Co0.1Mn0.1O2 surface.
“It is challenging to realize high Li reversibility, especially considering the limited Li reservoir (typically zero lithium excess) in the cell configuration,” the researchers wrote in their paper. “In this study we have introduced Li2O as a preloaded sacrificial agent on a LiNi0.8Co0.1Mn0.1O2 cathode, providing an additional Li source to offset the irreversible loss of Li during long-term cycling in an initial-anode-free cell.”
In addition to employing Li2O as a sacrificial agent, the researchers proposed the use of a fluoropropyl ether additive to neutralize nucleophilic O2-, which is released during the oxidation of Li2O, and prevent the additional evolution of gaseous O2 resulting from the fabrication of a LiF-based electrolyte coated on the surface of the battery’s cathode.
“We show that O2– species, released through Li2O oxidation, are synergistically neutralized by a fluorinated ether additive,” the researchers explained in their paper. “This leads to the construction of a LiF-based layer at the cathode/electrolyte interface, which passivates the cathode surface and restrains the detrimental oxidative decomposition of ether solvents.”
Based on the design they devised, Yu Qiao and the rest of the team at the National Institute of Advanced Industrial Science and Technology were able to realize a long-life 2.46 Ah initial-anode-free pouch cell. This cell exhibited a gravimetric energy density of 320 Wh kg-1, maintaining an 80% capacity after 300 operation cycles.
In the future, the anode-free lithium battery introduced by this research group could help to overcome some of the commonly reported limitations of LMBs. In addition, its design could inspire the creation of safer lithium-based rechargeable batteries with higher energy densities and longer lifetimes.
Last week, the US International Trade Commission (ITC) proposed a 10-year import ban on South Korean battery producer, SK Innovation, after the conclusion of an IP lawsuit filed by fellow South Korean battery maker, LG Chem. This decision to ban imports essentially cuts material supply from two factories with a combined capacity of almost 22GWh (9.8GWh and 11.7GWh respectively), expected to commence production in 2022 and 2023. However, there is still an option of local material sourcing, though there are limited opportunities to source the required materials, such as active cathode materials domestically within the USA at the scale required.
Roskill’s analysis shows that in 2020, the USA accounted for 1% of the global cathode materials market, which is forecast to increase to around 5% by 2030. The legislation passed by the US ITC, however, maintains SK innovation’s ability to supply battery cells to Volkswagen’s MEB line in North America for two years and Ford’s F-150 for four years, in addition to supplying spare parts for Kia models. Considering sales/production levels of Ford and Volkswagen in USA, Roskill estimates SK Innovation’s potential market size to be 9GWh through to February 2023, falling to 3GWh until February 2025, as potential to supply VW’s requirements expires. As a result, it seems unlikely for SK Innovation to invest further capital and time developing and commissioning its two USA based factories, only to achieve production of battery cells for 2-3 years at 14% planned utilization rate.
The removal of 22GWh of pipeline production capacity would represent a 10% decrease in total giga-factories capacity in North America in 2023, while EV demand in North America is expected to triple in the next five years and requires nearly 75GWh in installed battery capacity. As a result, the ITC’s decision, if not reversed or altered, would negatively impact the supply of Li-ion batteries for EV applications in the USA. The absence of SK Innovation would also place greater reliance on other battery makers in the USA, including Tesla/Panasonic, LG Chem and Envision AESC.
Roskill publishes annual Market Outlook reports for lithium-ion batteries and for a range of commodities across the lithium-ion battery supply chain, including lithium, cobalt, nickel sulphate and graphite. To see our full range of analysis, click here.
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Electric planes could be the future of aviation. In theory, they will be much quieter, cheaper, and cleaner than the planes we have today. Electric planes with a 1,000 km (620 mile) range on a single charge could be used for half of all commercial aircraft flights today, cutting global aviation’s carbon emissions by about 15%.
It’s the same story with electric cars. An electric car isn’t simply a cleaner version of its pollution-spewing cousin. It is, fundamentally, a better car: Its electric motor makes little noise and provides lightning-fast response to the driver’s decisions. Charging an electric car costs much less than paying for an equivalent amount of gasoline. Electric cars can be built with a fraction of moving parts, which makes them cheaper to maintain.
So why aren’t electric cars everywhere already? It’s because batteries are expensive, making the upfront cost of an electric car much higher than a similar gas-powered model. And unless you drive a lot, the savings on gasoline don’t always offset the higher upfront cost. In short, electric cars still aren’t economical.
Similarly, current batteries don’t pack in enough energy by weight or volume to power passenger aircrafts. We still need fundamental breakthroughs in battery technology before that becomes a reality.
Battery-powered portable devices have transformed our lives. But there’s a lot more that can batteries can disrupt, if only safer, more powerful, and energy-dense batteries could be made cheaply. No law of physics precludes their existence.
And yet, despite over two centuries of close study since the first battery was invented in 1799, scientists still don’t fully understand many of the fundamentals of what exactly happens inside these devices. What we do know is that there are, essentially, three problems to solve in order for batteries to truly transform our lives yet again: power, energy, and safety.
THERE ISN’T A ONE-SIZE-FITS-ALL LITHIUM-ION BATTERY
Every battery has two electrodes: a cathode and an anode. Most anodes of lithium-ion batteries are made of graphite, but cathodes are made of various materials, depending on what the battery will be used for. Below, you can see how different cathode materials change the way battery types perform on six measures.
The power challenge
In common parlance, people use “energy” and “power” interchangeably, but it’s important to differentiate between them when talking about batteries. Power is the rate at which energy can be released.
A battery strong enough to launch and keep aloft a commercial jet for 1,000 km requires a lot of energy to be released in very little time, especially during takeoff. So it’s not just about having lots of energy stored but also having the ability to extract that energy very quickly.
Tackling the power challenge requires us to look inside the black box of commercial batteries. It’s going to get a little nerdy, but bear with me. New battery technologies are often overhyped because most people don’t look closely enough at the details.
The most cutting-edge battery chemistry we currently have is lithium-ion. Most experts agree that no other chemistry is going disrupt lithium-ion for at least another decade or more. A lithium-ion battery has two electrodes (cathode and anode) with a separator (a material that conducts ions but not electrons, designed to prevent shorting) in the middle and an electrolyte (usually liquid) to enable the flow of lithium ions back and forth between the electrodes. When a battery is charging, the ions travel from the cathode to the anode; when the battery is powering something, the ions move in the opposite direction.
Imagine two loaves of sliced bread. Each loaf is an electrode: the left one is the cathode and the right is one the anode. Let’s assume the cathode is made up of slices of nickel, manganese, and cobalt (NMC)—one of the best in the class—and that the anode is made up of graphite, which is essentially layered sheets, or slices, of carbon atoms.
In the discharged state—i.e., after it has been drained of energy—the NMC loaf has lithium ions sandwiched between each slice. When the battery is charging, each lithium ion is extracted from between the slices and forced to travel through the liquid electrolyte. The separator acts as a checkpoint ensuring only lithium ions pass through to the graphite loaf. When fully charged, the battery’s cathode loaf will have no lithium ions left; they will all be neatly sandwiched between the slices of the graphite loaf. As the battery’s energy is consumed, the lithium ions travel back to the cathode, until there are none left in the anode. That’s when the battery needs to be charged again.
The battery’s power capacity is determined by, essentially, how fast this process happens. But it’s not so simple to turn up the speed. Drawing lithium-ions out of the cathode loaf too quickly can cause the slices to develop flaws and eventually break down. It’s one reason why the longer we use our smartphone, laptop, or electric car, the worse their battery life gets. Every charge and discharge causes the loaf to weaken that little bit.
Various companies are working on solutions to the problem. One idea is to replace layered electrodes with something structurally stronger. For example, the 100-year-old Swiss battery company Leclanché is working on a technology that uses lithium iron phosphate (LFP), which has an “olivine” structure, as the cathode, and lithium titanate oxide (LTO), which has a “spinel” structure, as the anode. These structures are better at handling the flow of lithium ions in and out of the material.
Leclanché currently uses its battery cells in autonomous warehouse forklifts, which can be charged to 100% in nine minutes. For comparison, the best Tesla supercharger can charge a Tesla car battery to about 50% in 10 minutes. Leclanché is also deploying its batteries in the UK for fast-charging electric cars. These batteries sit at the charging station slowly drawing small amounts of power over a long period from the grid until they are fully charged. Then, when a car docks, the docking-station batteries quick-charge the car’s battery. When the car leaves, the station battery starts recharging again.
Efforts like Leclanché’s show it’s possible to tinker with battery chemistries to increase their power. Still, nobody has yet built a battery powerful enough to rapidly deliver the energy needed for a commercial plane to defeat gravity. Startups are looking to build smaller planes (seating up to 12 people), which could fly on relatively lower power-dense batteries, or electric hybrid planes, where jet fuel does the hard lifting and batteries do the coasting.
But there’s really no company working in this space anywhere near commercialization. Further, the kind of technological leap required for an all-electric commercial plane will likely take decades, says Venkat Viswanathan, a battery expert at Carnegie Mellon University.
REUTERS/ALISTER DOYLE A two-seat electric plane made by Slovenian firm Pipistrel stands outside a hangar at Oslo Airport, Norway.
The energy challenge
The Tesla Model 3, the company’s most affordable model, starts at $35,000. It runs on a 50 kWh battery, which costs approximately $8,750, or 25% of the total car price.
That’s still amazingly affordable compared to not that long ago. According to Bloomberg New Energy Finance, the average global cost for lithium-ion batteries in 2018 was about $175 per kWh—down from nearly $1,200 per kWh in 2010.
The US Department of Energy calculates that once battery costs fall below $125 per kWh, owning and operating an electric car will be cheaper than a gas-powered car in most parts of the world. It doesn’t mean electric vehicles will win over gas-powered vehicles in all niches and domains—for example, long-haul trucks don’t yet have an electric solution. But it’s a tipping point where people will start to prefer electric cars simply because they will make more economical sense in most cases.
One way to get there is to increase the energy density of batteries—to cram more kWh into a battery pack without lowering its price. Battery chemist can do that, in theory, by increasing the energy density of either the cathode or the anode, or both.
The most energy-dense cathode on the way to commercial availability is NMC 811 (each digit in the number represents the ratio of nickel, manganese, and cobalt, respectively, in the mix). It’s not yet perfect. The biggest problem is that it can only withstand a relatively small number of charge-discharge life cycles before it stops working. But experts predict that industry R&D should solve the problems of the NMC 811 within the next five years. When that happens, batteries using NMC 811 will have higher energy density by 10% or more.
However, a 10% increase is not that much in the big picture.
And, while a series of innovations over the past few decades have pushed the energy density of cathodes ever higher, anodes are where the biggest energy-density opportunities lie.
Graphite has been and remains far and away the dominant anode material. It’s cheap, reliable, and relatively energy dense, especially compared to current cathode materials. But it’s fairly weak when stacked up against other potential anode materials, like silicon and lithium.
Silicon, for example, is theoretically much better at absorbing lithium ions as graphite. That’s why a number of battery companies are trying to pepper some silicon in with the graphite in their anode designs; Tesla CEO Elon Musk has said his company is already doing this in its lithium-ion batteries.
A bigger step would be to develop a commercially viable anode made completely from silicon. But the element has traits that make this difficult. When graphite absorbs lithium ions, its volume does not change much. A silicon anode, however, swells to four times its original volume in the same scenario.
Unfortunately, you can’t just make the casing bigger to accommodate that swelling, because the expansion breaks apart what’s called the “solid electrolyte interphase,” or SEI, of the silicon anode.
You can think of the SEI as a sort of protective layer that the anode creates for itself, similar to the way that iron forms rust, also known as iron oxide, to protect itself from the elements: When you leave a piece of newly forged iron outside, it slowly reacts with the oxygen in the air to rust. Underneath the layer of rust, the rest of the iron doesn’t suffer from the same fate and thus retains the structural integrity.
At the end of a battery’s first charge, the electrode forms it’s own “rust” layer—the SEI—separating the uneroded part of the electrode from the electrolyte. The SEI stops additional chemical reactions from consuming the electrode, ensuring that lithium ions can flow as smoothly as possible.
But with a silicon anode, the SEI breaks apart every time the battery is used to power something up, and reforms every time the battery is charged. And during each charge cycle, a little bit of silicon is consumed. Eventually, the silicon dissipates to the point where the battery no longer works.
Over the last decade, a few Silicon Valley startups have been working to solve this problem. For example, Sila Nano’s approach is to encase silicon atoms inside a nano-sized shell with lots of empty room inside. That way, the SEI is formed on the outside of the shell and the expansion of silicon atoms happens inside it without shattering the SEI after each charge-discharge cycle. The company, valued at $350 million, says its technology will power devices as soon as 2020.
Enovix, on the other hand, applies a special manufacturing technique to put a 100% silicon anode under enormous physical pressure, forcing it to absorb fewer lithium ion and thus restricting the expansion of the anode and preventing the SEI from breaking. The company has investments from Intel and Qualcomm, and it also expects to have its batteries in devices by 2020.
These compromises mean the silicon anode can’t reach its theoretical high energy density. However, both companies say their anodes perform better than a graphite anode. Third parties are currently testing both firms’ batteries.
TESLA In 2020, the new Tesla Roadster is set to become the first electric car that offers 1,000 km (620 miles) on a single charge.
The safety challenge
All the molecular tinkering done to pack more energy in batteries can come at the cost of safety. Ever since its invention, the lithium-ion battery has caused headaches because of how often it catches fire. In the 1990s, for example, Canada’s Moli Energy commercialized a lithium-metal battery for use in phones. But out in the real world, its batteries started catching fire, and Moli was forced to make a recall, and, eventually, file for bankruptcy. (Some of its assets were bought by a Taiwanese company and it still sells lithium-ion batteries the brand name E-One Moli Energy.) More recently, Samsung’s Galaxy Note 7 smartphones, which were made with modern lithium-ion batteries, started exploding in people’s pockets. The resulting 2016 product recall cost the South Korean giant $5.3 billion.
Today’s lithium-ion batteries still have inherent risks, because they almost always use flammable liquids as the electrolyte. It’s one of nature’s unfortunate (for us humans) quirks that liquids able to easily transport ions also tend to have a lower threshold to catching fire. One solution is to use solid electrolytes. But that means other compromises. A battery design can easily include a liquid electrolyte that’s in contact with every bit of the electrodes—making it able to efficiently transfer ions. It’s much harder with solids. Imagine dropping a pair of dice into a cup of water. Now imagine dropping those same dice into a cup of sand. Obviously, the water will touch far more surface area of the dice than the sand will.
So far, the commercial use of lithium-ion batteries with solid electrolytes has been limited to low-power applications, such as for internet-connected sensors. The efforts to scale up solid-state batteries—that is, containing no liquid electrolyte—can be broadly classified into two categories: solid polymers at high temperatures and ceramics at room temperature.
SOLID POLYMERS AT HIGH TEMPERATURES
Polymers are long chains of molecules linked up together. They’re extremely common in everyday applications—single-use plastic bags are made of polymers, for example. When some types of polymers are heated, they behave like liquids, but without the flammability of the liquid electrolytes used in most batteries. In other words, they have the high ion conductivity as a liquid electrolyte without the risks.
But they have limitations. They can only operate at temperatures above 105°C (220°F), which means they aren’t practical options for, say, smartphones. But they can be used for storing energy from the grid in home batteries, for example. At least two companies—US-based SEEO and France-based Bolloré—are developing solid-state batteries that use high-temperature polymers as the electrolyte.
CERAMICS AT ROOM TEMPERATURE
Over the last decade, two classes of ceramics—LLZO (lithium, lanthanum, and zirconium oxide) and LGPS (lithium, germanium, phosphorus sulfide)—have proven almost as good at conducting ions at room temperature as liquids.
Toyota, as well as the Silicon Valley startup QuantumScape (which raised $100 million in funding from Volkswagen last year), are both working on deploying ceramics in lithium-ion batteries. The inclusion of big players in the space is indicative that a breakthrough might be nearer than many think.
“We are quite close to seeing something real [using ceramics] in two or three years,” says Carnegie Mellon‘s Viswanathan.
A balancing act
Batteries are already big business, and the market for them keeps growing. All that money attracts a lot of entrepreneurs with even more ideas. But battery startups are difficult bets—they fizzle even more often than software companies, which are known for their high failure rate. That’s because innovation in material sciences is hard.
So far battery chemists have found that, when they try to improve one trait (say energy density), they have to compromise on some other trait (say safety). That kind of balancing act has meant the progress on each front has been slow and fraught with problems.
But with more eyes on the problem—MIT’s Yet-Ming Chiang reckons there are three times as many battery scientists in the US today than just 10 years ago—the chances of success go up. The potential of batteries remains huge, but given the challenges ahead, it’s better to look at every claim about new batteries with a good dose of skepticism.
A scanning electron microscope image of lithium titanate (lithium, titanium, oxygen) “nanoflowers.”
Lithium-ion batteries work by shuffling lithium ions between a positive electrode (cathode) and a negative electrode (anode) during charging and in the opposite direction during discharging.
Our smartphones, laptops, and electric vehicles conventionally employ lithium-ion batteries with anodes made of graphite, a form of carbon.
Lithium is inserted into graphite as you charge the battery and removed as you use the battery.
While graphite can be reversibly charged and discharged over hundreds or even thousands of cycles, the amount of lithium it can store (capacity) is not enough for energy-intensive applications.
For example, electric cars can only travel so far before they need to be recharged. In addition, graphite cannot be charged or discharged at very high rates (power). Because of these limitations, scientists have been on the hunt for alternative anode materials.
One such promising anode material is lithium titanate (LTO), which contains lithium, titanium, and oxygen. In addition to its high-rate capability, LTO has good cycling stability and maintains empty sites within its structure to accommodate lithium ions. However, LTO conducts electricity poorly, and lithium ions are slow to diffuse into the material.
“Pure LTO has moderate usable capacity but can deliver power quickly,” said Amy Marschilok, an associate professor in the Department of Chemistry and an adjunct faculty member in the Department of Materials Science and Chemical Engineering at Stony Brook University—where she also serves as deputy director of the Center for Mesoscale Transport Properties (m2M)—and Energy Storage Division manager and scientist in the Interdisciplinary Science Department at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory.
“High-rate battery materials are appealing for applications where you want to use stored energy quickly, over minutes—such as electric vehicles, portable power tools, and emergency power supply systems.”
Marschilok is part of an interdisciplinary Brookhaven Lab–Stony Brook team that began collaborating on LTO research in 2014. In their latest effort, they increased the capacity of LTO by 12 percent by adding chlorine through a process known as doping.
“Controlled doping can change the electronic and structural properties of a material,” explained Stanislaus Wong, distinguished professor in the Department of Chemistry at Stony Brook University, where he is also the principal investigator in charge of the student-based team comprising the Wong Group.
“In my group, we are interested in developing and using chemistry to direct favorable structure-property correlations.
For LTO, the incorporation of dopant atoms can increase electrical conductivity and expand the crystal lattice, such that the channel for lithium ions to migrate becomes wider. Scientists have been testing out many different types of dopants, but chlorine has not been explored as much.”
To make “chlorine-doped” LTO, the team used a solution-based method called hydrothermal synthesis. In hydrothermal synthesis, scientists add a solution containing relevant precursors (materials that react to form the desired product) in water, place the mixture in a sealed vessel, and expose it to relatively modest temperatures and pressures for a certain duration. In this case, to enable a scaling up of their procedure, the scientists selected a liquid-based titanium precursor instead of the solid titanium foil that had been previously used in these types of reactions.
Following the hydrothermal synthesis of both pure LTO and chlorine-doped LTO for 36 hours, they performed additional chemical processing steps to isolate the desired materials.
The team’s imaging studies using scanning electron microscopy (SEM) at the Electron Microscopy Facility of Brookhaven’s Center for Functional Nanomaterials (CFN) revealed that both sample types were characterized by “flower-shaped” nanostructures.
This result suggested that the chemical treatment did not destroy the original structure.
“Our novel synthesis approach facilitates a more rapid, uniform, and efficient reaction for the large-scale production of these 3-D nanoflowers,” said Wong. “This relatively unique kind of architecture has a high surface area, with flower-like “petals” radially disseminating from a central core. This structure provides multiple pathways for lithium ions to access the material.
By varying the concentration of chlorine, lithium, and precursor; the purity of the precursor; and the reaction time, the scientists found the optimal conditions for making highly crystalline nanoflowers.
At the CFN, the team performed several characterization experiments based on how the samples interact with x-rays and electrons: x-ray diffraction to obtain crystallinity information and chemical composition, SEM to visualize morphology (shape), energy-dispersive x-ray spectroscopy to map the distribution of elements, and x-ray photoelectron spectroscopy (XPS) to confirm chemical composition and derive chemical oxidation states.
“The XPS data are key in this study because they prove that titanium—which ordinarily exists in LTO as 4+, meaning four electrons have been removed—is reduced to 3+,” said Xiao Tong, a staff scientist in the CFN Interface Science and Catalysis Group.
“This change in chemical state is significant because the material transforms from an insulator to a semiconductor, increasing electrical conductivity and lithium-ion mobility.”
With the optimized samples, the scientists performed several electrochemical tests. They found that chlorine-doped LTO has more usable capacity under a high-rate condition in which the battery discharges in 30 minutes. This improvement was maintained over more than 100 charge/discharge cycles.
“Chlorine-doped LTO is not only better initially but also remains stable over time,” said Marschilok.
To understand why this improvement occurred, the team turned to computational theory, modeling the structural and electronic changes that arise from chlorine doping.
“When we do basic science experiments, we need to understand what we observe to see how the material is functioning and gain insights on how to improve the material’s performance,” explained Ping Liu, a chemist in Brookhaven’s Chemistry Division who was led the theoretical studies.
“Theory is a very effective way to achieve such mechanistic understanding, especially for complex materials like LTO.”
In calculating the most energetically stable geometry of LTO with chlorine doping, the team found that chlorine prefers to substitute sites where oxygen sits in the LTO structure.
“This substitution throws one electron to the system, causing electronic redistribution,” said Liu. “It causes titanium, which interacts directly with chlorine, to be reduced from 4+ to 3+, consistent with the experimental XPS results.
We also did calculations that showed once chlorine is substituted for oxygen, more lithium can be inserted into LTO during discharge. Chlorine is bigger than oxygen, so it provides an enlarged tunnel for lithium transport.”
Next, the team is studying how the microscopic structure of the 3-D nanoflowers affects transport. They also are exploring other atomic-level substitutions in both anode and cathode materials that may lead to improved transport.
“Improving both the electronic and ionic conductivity through one process is often challenging,” said Marschilok. “But beyond improving the performance of any one material, at m2M, we’re always thinking about designing model studies that can show the scientific community ways to develop new battery materials in a comprehensive way.
The combination of material synthesis, advanced material characterization, and computational theory, as well as the collaboration between Stony Brook and Brookhaven, are strengths of m2M’s work.”
This research—published in a special issue on “Low Temperature Solution Route Approaches to Oxide Functional Nanoscale Materials” in Chemistry–A European Journal—was funded as part of m2M, an Energy Frontier Research Center supported by the DOE Office of Science, Basic Energy Sciences. The scientists performed the theoretical calculations using computational resources at the CFN and the Scientific Data and Computing Center, part of Brookhaven’s Computational Science Initiative.
The CFN is a DOE Office of Science User Facility. Some co-authors were also supported by the National Science Foundation Graduate Research Fellowship and the William and Jane Knapp Chair for Energy and the Environment atStony Brook University.
Save for a few rare announcements, the promising technology class has gone quiet.
October’s SoftBank-ledinvestment in iron flow battery startup ESSrepresented an unusual event in 2019: a piece of good news for the flow battery sector. The $30 million cash injection was a rare sign that there may still be life in an energy storage technology class that had almost faded from view in recent months.
Leading players such as Sumitomo Electric and Dalian Rongke Power, the latter of which once boasted the world’s largest vanadium flow battery project, have gone silent. EnSync Energy Systems pivotedaway from flowbatteries last year andfolded in March.
CellCube Energy Storage Systems has also run into problems this year. In Octoberit advised shareholdersthat “each division is suffering from a lack of working capital” and added that management was “reviewing strategic alternatives focused on maximizing shareholder value.”
Go Big:This factory produces vanadium redox-flow batteries destined for the world’s largest battery site: a 200-megawatt, 800-megawatt-hour storage station in China’s Liaoning province.
Even those companies still touting contract wins in 2019 have hardly set the world on fire. RedT Energy installed Australia’s largest commercial energy storage system,a 1-megawatt-hour systemat Monash University, but more recently announced a merger with Avalon following reported losses.
Meanwhile, UniEnergy Technology’s soledeal-related press releasethis year was to celebrate the commissioning of a 7.5-kilowatt, 30-kilowatt-hour flow battery in Brussels.
Despite this, a smattering of players, including Avalon, Lockheed Martin and U.S. Vanadium, remain bullish. And Dan Finn-Foley, head of energy storage at Wood Mackenzie Power & Renewables, cautions against writing the sector off just yet.
“We haven’t seen much activity from the flow battery space in terms of deployments or major announcements,” he acknowledged, “but there are key steps happening behind the scenes.”
Researchers advancing flow battery technology are either partnering with companies with large balance sheets or securing insurance to back up their claims of long system lifetimes and low degradation, he said.
“The next steps will be continued pilot programs and strategic targeting of favorable market niches, all critical stepping stones toward true commercialization,” Finn-Foley said.
Image: Vanadium Redox Flow Batteries
Flow battery vendors could benefit from state-level 100 percent clean or renewable energy policies in the U.S., Finn-Foley noted, since it is remains unclear whether lithium-ion batteries alone can meet storage needs beyond durations of approximately eight hours.
Flow batteries are seen as ideal for large-scale, long-duration storage because they can store large amounts of energy using scalable tanks of relatively cheap electrolyte. The problem is that nobody seems to need this long-duration capacity just yet.
Finn-Foley said the biggest unknowns for the flow battery sector “are the timing of when these long-duration needs will emerge and how low vendors will be able to drive costs by then with few other opportunities to scale.”
This is emerging as a significant issue in 2019. While flow battery technology is waiting for prime time, its main competitor, lithium-ion, is already racing ahead on scale and cost-competitiveness thanks to the growth of the electric vehicle industry.
In March, QY Research Group predicted the global redox flow battery market would be worth$370 millionby 2025, based on a roughly 14 percent compound annual growth rate (CAGR) from 2018.
For comparison, a May study by Prescient & Strategic Intelligence estimated the lithium-ion market would be worth close to$107 billionby 2024, with a CAGR of almost 22 percent.
Even ignoring the fact that the lithium-ion industry is on a quest to uselower-cost materials, it is hard to see how flow batteries will be able to compete on price against such a thoroughly commoditized rival.
The state of play was perhaps best summed up by Rebecca Kujawa, chief financial officer and executive vice president of finance at NextEra Energy, duringan earnings callin October.
Asked by Pavel Molchanov, an analyst at Raymond James & Associates, whether NextEra had found any storage technologies other than lithium-ion that are worth commercializing, she said: “We always remain technology-agnostic.”
But she added: “What we continue to see, and what we are currently signing contracts for with our customers, is predominantly lithium-ion. Those producing lithium-ion batteries are investing in manufacturing scale, which is producing significant cost improvements.”
Kujawa concluded: “In the middle part of the next decade, you’re talking about a $5 to $7 per megawatt-hour added to get to a nearly firm wind or solar resource, and that’s a pretty attractive price.
Image: 100% Renewable Energy
To beat that, you’d have to see a pretty big step change in where some of these other technologies are.”
High-energy-density polymeric cathode for fast-charge sodium- and multivalent-ion batteries.
Next-generation batteries will probably see the replacement of lithium ions by more abundant and environmentally benign alkali metal or multivalent ions. A major challenge, however, is the development of stable electrodes that combine high energy densities with fast charge and discharge rates. In the journalAngewandte Chemie,US and Chinese scientists reporta high-performance cathode made of an organic polymer to be used in low-cost, environmentally benign, and durable sodium-ion batteries.
Lithium-ion batteries are the state-of-the-art technology for portable devices, energy storage systems, and electric vehicles, the development of which has been awarded with this year’s Nobel prize.
Nevertheless, next-generation batteries are expected to provide higher energy densities, better capacities, and the usage of cheaper, safer, and more environmentally benign materials. New battery types that are most explored employ essentially the same rocking-chair charging-discharging technology as the lithium battery, but the lithium-ion is substituted with cheap metal ions such as sodium, magnesium, and aluminum ions.
Unfortunately, this substitution brings along major adjustments to the electrode materials.
Organic compounds are favorable as electrode materials because, for one, they do not contain harmful and expensive heavy metals, and they can be adapted to different purposes. Their disadvantage is that they dissolve in liquid electrolytes, which makes electrodes inherently unstable.
Chunsheng Wang and his team from the University of Maryland, USA, and an international team of scientists have introduced an organic polymer as a high-capacity, fast-charging, and insoluble material for battery cathodes.
For the sodium ion, the polymer outperformed current polymeric and inorganic cathodes in capacity delivery and retention, and for multivalent magnesium and aluminum ions, the data did not lag far behind, according to the study.
As a suitable cathodic material, the scientists identified the organic compound hexaazatrinaphthalene (HATN), which has already been tested in lithium batteries and supercapacitors, where it functions as a high-energy-density cathode that rapidly intercalates lithium ions.
However, like most organic materials, HATN dissolved in the electrolyte and made the cathode unstable during cycling.
The trick was now to stabilize the material’s structure by introducing linkages between the individual molecules, the scientists explained. They obtained an organic polymer called polymeric HATN, or PHATN, which offered fast reaction kinetics and high capacities for sodium, aluminum, and magnesium ions.
After assembling the battery, the scientists tested the PHATN cathode using a high-concentrated electrolyte. They found excellent electrochemical performances for the non-lithium ions.
The sodium battery could be operated at high voltages up to 3.5 volts and maintained a capacity of more than 100 milliampere hours per gram even after 50,000 cycles, and the corresponding magnesium and aluminum batteries were close behind these competitive values, reported the authors.
The researchers envision these polymeric pyrazine-based cathodes (pyrazine is the organic substance upon which HATN is based; it is an aromatic benzol-like, nitrogen-rich organic substance with a fruity flavor) to be employed in environmentally benign, high-energy-density, fast and ultrastable next generation rechargeable batteries.
Reference: “A Pyrazine‐Based Polymer for Fast‐Charge Batteries” by Dr. Minglei Mao, Prof. Chao Luo, Travis P. Pollard, Singyuk Hou, Dr. Tao Gao, Dr. Xiulin Fan, Chunyu Cui, Jinming Yue, Yuxin Tong, Gaojing Yang, Tao Deng, Prof. Ming Zhang, Prof. Jianmin Ma, Prof. Liumin Suo, Dr. Oleg Borodin and Prof. Chunsheng Wang, 30 September 2019,Angewandte Chemie.
Dr. Chunsheng Wang holds the Robert Franklin and Frances Riggs Wright Distinguished Chair in the Department of Chemical and Biomolecular Engineering at the University of Maryland, College Park, Maryland, USA. His groupâ€™s research interests span the development and improvement of nonflammable water-in-salt, all-fluorinated or solid electrolytes, and organic active materials for alkali-ion and multivalent batteries.
Nearly all your devices run on lithium batteries. They have revolutionised the way we use, manufacture and charge our devices. Here’s a Nobel Prizewinner on his part in their invention – and their future.
British-born scientist M. Stanley Whittingham, of Binghamton University, was one of three scientists who won the 2019 Nobel Prize in Chemistry for their work developing lithium-ion batteries.
Maybe you know exactly what a lithium-ion battery is but even if you don’t, chances are you’re carrying one right now. They’re the batteries used to power mobile phones, laptops and even electric cars.
When it comes to energy storage, they’re vastly more powerful than conventional batteries and you can recharge them many more times.
Their widespread use has driven global demand for the metal lithium – demand that Opposition Leader Anthony Albanese this weeksaidAustralia should do more to meet.
Lithium ion batteries revolutionised the way we use, manufacture and charge our devices. They’re used to power mobile phones, laptops and even electric cars.
The University of Queensland’s Mark Blaskovich, who trained in chemistry and pennedthis article about Whittingham’s selection for the chemistry Nobel Prize, sat down with the award-winner this week.
They discussed what the future of battery science may hold and how we might address some of the environmental and fire risks around lithium-ion batteries.
He began by asking M. Stanley Whittingham how lithium batteries differ from conventional, lead-acid batteries, like the kind you might find in your car.
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A toothpaste-like composite with hexagonal boron nitride developed by researchers at Rice University is an effective electrolyte and separator in lithium-ion batteries intended for high-temperature applications in a number of industries, including aerospace and oil and gas. (Source: Jeff Fitlow/Rice University)
One major and dangerous problem with lithium-ion batteries is that they can catch fire when heated to high temperatures, an issue that has caused damage and even death when devices ignited without warning.
Now researchers at Rice University have come up with a solution to this very serious safety problem in the form of a combined electrolyte and separator for rechargeable lithium-ion batteries that supplies energy at usable voltages and in high temperatures. The material is a toothpaste-like composite that is capable of performing well at and withstanding high temperatures without combusting.
The problem with most current lithium-battery chemistries is that they present safety concerns when heated beyond 50C (122F) due to the electrolyte/separator combination used in them, explained Marco-Tulio Rodrigues, a Rice graduate student and one of the authors of a paper on the research published in Advanced Materials Science.
“The separator is usually a thin polymer film and may deform at high temperatures, causing a short circuit,” Rodrigues told Design News. “The electrolytes are based on organic solvents, which tend to boil at high temperatures, increasing the internal pressure of the cell. Although commercial batteries implement some protection mechanisms to avoid these problems, any damages to the cell case may potentially lead to ignition, since the electrolyte is also highly flammable.”
The work of the Rice team addresses both the issue of developing a separator that will not cause a short circuit and an electrolyte that doesn’t have the tendency to catch fire, he said.
The batteries made with the components they developed functioned as intended in temperatures of 50C (122F) for more than a month without losing efficiency, according to researchers. Moreover, test batteries consistently operated from room temperature to 150C (302F), setting one of the widest temperature ranges ever reported for such devices, they said.
To solve the electrolyte problem, researchers used solutions based on ionic liquids in the electrolytes, which have largely been proposed as substitutes for organic solvents in the electrolyte of lithium-ion batteries because they present a much higher thermal stability, Rodrigues explained.
“These chemicals are basically special salts with a very low melting point, in such a way that they are liquid at room temperatures,” he said. “They are completely nonflammable and they do not evaporate at all until they decompose, which occurs beyond 350C (662F).”
With the electrolyte situation solved, researchers turned their attention to finding a new separator, which they addressed with a material called hexagonal boron nitride, also known as white graphene.