The panel, moderated by CARS Executive Director Stephen Zoepf, features companies that seek to catalyze electrification of transport, each focused on a different sector of the market.
From an all-electric chassis to electric mobility services at scale to fast & portable electric chargers to electric, highly-utilized AVs, this Energy Seminar will highlight the cutting edge in electric mobility.
How to build a better Battery through Nanotechnology
PALO ALTO, CALIFORNIA (Note to Readers: This original article was published in 2016 May. Recent updates, News Releases and a YouTube Video have been provided)
On a drizzly, gray morning in April, Yi Cui weaves his scarlet red Tesla in and out of Silicon Valley traffic. Cui, a materials scientist at Stanford University here, is headed to visit Amprius, a battery company he founded 8 years ago. Amprius Latest News Release(December 2018)
It’s no coincidence that he is driving a battery-powered car, and that he has leased rather than bought it. In a few years, he says, he plans to upgrade to a new model, with a crucial improvement: “Hopefully our batteries will be in it.”
Cui and Amprius are trying to take lithium–ion batteries—today’s best commercial technology—to the next level. They have plenty of company. Massive corporations such as Panasonic, Samsung, LG Chem, Apple, and Tesla are vying to make batteries smaller, lighter, and more powerful. But among these power players, Cui remains a pioneering force.
Unlike others who focus on tweaking the chemical composition of a battery’s electrodes or its charge-conducting electrolyte, Cui is marrying battery chemistry with nanotechnology. He is building intricately structured battery electrodes that can soak up and release charge-carrying ions in greater quantities, and faster, than standard electrodes can, without producing troublesome side reactions. “He’s taking the innovation of nanotechnology and using it to control chemistry,” says Wei Luo, a materials scientist and battery expert at the University of Maryland, College Park.
“I wanted to change the world, and also get rich, but mainly change the world.”
In a series of lab demonstrations, Cui has shown how his architectural approach to electrodes can domesticate a host of battery chemistries that have long tantalized researchers but remained problematic. Among them: lithium-ion batteries with electrodes of silicon instead of the standard graphite, batteries with an electrode made of bare lithium metal, and batteries relying on lithium-sulfur chemistry, which are potentially more powerful than any lithium-ion battery. The nanoscale architectures he is exploring include silicon nanowires that expand and contract as they absorb and shed lithium ions, and tiny egg like structures with carbon shells protecting lithium-rich silicon yolks.
(Article continues below Video)
Watch a YouTube Video on the latest Update from Professor Cui (November 2018). A very concise and informative Summary of the State of NextGen Batteries.
** Amprius already supplies phone batteries with silicon electrodes that store 10% more energy than the best conventional lithium-ion batteries on the market.
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Another prototype beats standard batteries by 40%, and even better ones are in the works. So far, the company does not make batteries for electric vehicles (EVs), but if the technologies Cui is exploring live up to their promise, the company could one day supply car batteries able to store up to 10 times more energy than today’s top performers. That could give modest-priced EVs the same range as gas-powered models—a revolutionary advance that could help nations power their vehicle fleets with electricity provided by solar and wind power, dramatically reducing carbon emissions.
Cui says that when he started in research, “I wanted to change the world, and also get rich, but mainly change the world.” His quest goes beyond batteries. His lab is exploring nanotech innovations that are spawning startup companies aiming to provide cheaper, more effective air and water purification systems. But so far Cui has made his clearest mark on batteries. Luo calls his approach “untraditional and surprising.” Jun Liu, a materials scientist at the Pacific Northwest National Laboratory in Richland, Washington, put it more directly: Cui’s nanotech contributions to battery technology are “tremendous.”
Making leaps in battery technology is surprisingly hard to do. Even as Silicon Valley’s primary innovation, the computer chip, has made exponential performance gains for decades, batteries have lagged. Today’s best lithium-ion cells hold about 700 watt-hours per liter. That’s about five times the energy density of nickel-cadmium batteries from the mid-1980s—not bad, but not breathtaking. In the past decade, the energy density of the best commercial batteries has doubled.
Battery users want more. The market for lithium-ion batteries alone is expected to top $30 billion a year by 2020, according to a pair of recent reports by market research firms Transparency Market Research and Taiyou Research. The rise in production of EVs by car companies that include Tesla, General Motors, and Nissan accounts for some of that surge.
But today’s EVs leave much to be desired. For a Tesla Model S, depending on the exact model, the 70- to 90-kilowatt-hour batteries alone weigh 600 kilograms and account for about $30,000 of the car’s price, which can exceed $100,000. Yet they can take the car only about 400 kilometers on a single charge, substantially less than the range of many conventional cars. Nissan’s Leaf is far cheaper, with a sticker price of about $29,000. But with a smaller battery pack, its range is only about one-third that of the Tesla.
Improving batteries could make a major impact. Doubling a battery’s energy density would enable car companies to keep the driving range the same while halving the size and cost of the battery—or keep the battery size constant and double the car’s range. “The age of electric vehicles is coming,” Cui says. But in order for EVs to take over, “we have to do better.”
He recognized the need early in his career. After finishing his undergraduate degree in his native China in 1998, Cui moved first to Harvard University and then to the University of California (UC), Berkeley, to complete a Ph.D. and postdoc in labs that were pioneering the synthesis of nanosized materials. Those were the early days of nanotechnology, when researchers were struggling to get a firm handle on how to create just the materials they wanted, and the world of applications was only beginning to take shape.
While at UC Berkeley, Cui spent time with colleagues next door at the Lawrence Berkeley National Laboratory (LBNL). At the time, LBNL’s director was Steven Chu, who pushed the lab to invent renewable energy technologies that had the potential to combat climate change, among them better batteries for storing clean energy. (Chu later went on to serve as President Barack Obama’s secretary of energy from 2009 to 2013.)
“At the beginning, I wasn’t thinking about energy. I had never worked on batteries,” Cui says. But Chu and others impressed on him that nanotechnology could give batteries an edge.
As Chu says now, it offers “a new knob to turn, and an important one,” enabling researchers to control not only the chemical composition of materials on the smallest scales, but also the arrangement of atoms within them—and thus how chemical reactions involving them proceed.
After moving to Stanford, Cui quickly gravitated to the nexus between nanotechnology and the electrochemistry that makes batteries work—and accounts for their limitations. Take lithium-ion rechargeable batteries. In principle, these batteries are simple: They consist of two electrodes divided by a membrane “separator” and a liquid electrolyte that allows ions to glide back and forth between the electrodes.
When a battery is charging, lithium ions are released from the positive electrode, or cathode, which consists of a lithium alloy, commonly lithium cobalt oxide or lithium iron phosphate. They are drawn toward the negatively charged electrode, called the anode, which is usually made of graphite. There they snuggle in between the graphite’s sheets of carbon atoms. Voltage from an external power source drives the whole ionic mass migration, storing power.
When a device—say, a power tool or a car—is turned on and demands energy, the battery discharges: Lithium atoms in the graphite give up electrons, which travel through the external circuit to the cathode. Meanwhile, the lithium ions slip out of the graphite and zip through the electrolyte and the separator to the cathode, where they meet up with electrons that have made the journey through the circuit (see diagram below).
Nano to the rescue
Cui and colleagues have applied several nanotechnology-inspired solutions to keep silicon anodes from breaking down and to prevent battery-killing side reactions.
Graphite is today’s go-to anode material because it is highly conductive and thus readily passes collected electrons to the metal wires in a circuit. But graphite is only so-so at gathering lithium ions during charging. It takes six carbon atoms in graphite to hold on to a single lithium ion. That weak grip limits how much lithium the electrode can hold and thus how much power the battery can store.
Silicon has the potential to do far better. Each silicon atom can bind to four lithium ions. In principle, that means a silicon-based anode can store 10 times as much energy as one made from graphite. Electrochemists have struggled in vain for decades to tap that enormous capacity.
It’s easy enough to make anodes from chunks of silicon; the problem is that the anodes don’t last. As the battery is charged and lithium ions rush in to bind to silicon atoms, the anode material swells as much as 300%. Then, when the lithium ions rush out during the battery’s discharge cycle, the anode rapidly shrinks again. After only a few cycles of such torture, silicon electrodes fracture and eventually split into tiny, isolated grains. The anode—and the battery—crumbles and dies.
Cui thought he could solve the problem. His experience at Harvard and UC Berkeley had taught him that nanomaterials often behave differently from materials in bulk. For starters, they have a much higher percentage of their atoms at their surface relative to the number in their interior. And because surface atoms have fewer atomic neighbors locking them in place, they can move more easily in response to stresses and strains. Other types of atomic movement explain why thin sheets of aluminum foil or paper can bend without breaking more easily than chunks of aluminum metal or wood can.
In 2008, Cui thought that fashioning a silicon anode from nanosized silicon wires might alleviate the stress and strain that pulverize bulk silicon anodes. The strategy worked. In a paper in Nature Nanotechnology, Cui and colleagues showed that when lithium ions moved into and out of the silicon nanowires, the nanowires suffered little damage. Even after 10 repeated cycles of charging and discharging, the anode retained 75% of its theoretical energy storage capacity.
Unfortunately, silicon nanowires are much more difficult and expensive to fashion than bulk silicon. Cui and colleagues started devising ways to make cheaper silicon anodes. First, they found a way to craft lithium-ion battery anodes from spherical silicon nanoparticles. Though potentially cheaper, these faced a second problem: The shrinking and swelling of the nanoparticles as the lithium atoms moved in and out opened cracks in the glue that bound the nanoparticles together. The liquid electrolyte seeped between the particles, driving a chemical reaction that coated them in a non-conductive layer, known as a solid-electrolyte interphase (SEI), which eventually grew thick enough to disrupt the anode’s charge-collecting abilities. “It’s like scar tissue,” says Yuzhang Li, a graduate student in Cui’s lab.
A few years later, Cui and his colleagues hit on another nanotech solution. They created egg like nanoparticles, surrounding each of their tiny silicon nanoparticles—the yolk—with a highly conductive carbon shell through which lithium ions could readily pass. The shell gave silicon atoms in the yolk ample room to swell and shrink, while protecting them from the electrolyte—and the reactions that form an SEI layer. In a 2012 paper in Nano Letters, Cui’s team reported that after 1000 cycles of charging and discharging, their yolk-shell anode retained 74% of its capacity.
They did even better 2 years later. They assembled bunches of their yolk-shell nanoparticles into micrometer-scale collections resembling miniature pomegranates. Bunching the silicon spheres boosted the anode’s lithium storage capacity and reduced unwanted side reactions with the electrolyte. In a February 2014 issue of Nature Nanotechnology, the group reported that batteries based on the new material retained 97% of their original capacity after 1000 charge and discharge cycles.
Earlier this year, Cui and colleagues reported a solution that outdoes even their complex pomegranate assemblies. They simply hammered large silicon particles down to the micrometer scale and then wrapped them in thin carbon sheets made from graphene. The hammered particles wound up larger than the silicon spheres in the pomegranates—so big that they fractured after a few charging cycles. But the graphene wrapping prevented the electrolyte compounds from reaching the silicon. It was also flexible enough to maintain contact with the fractured particles and thus carry their charges to the metal wires. What’s more, the team reported in Nature Energy, the larger silicon particles packed more mass—and thus more power—into a given volume, and they were far cheaper and easier to make than the pomegranates. “He has really taken this work in the right direction,” Jun Liu says.
Powered by such ideas, Amprius has raised more than $100 million to commercialize lithium-ion batteries with silicon anodes. The company is already manufacturing cellphone batteries in China and has sold more than 1 million of them, says Song Han, the company’s chief technology officer. The batteries, based on simple silicon nanoparticles that are cheap to make, are only 10% better than today’s lithium-ion cells. But at Amprius’s headquarters, Han showed off nanowire-silicon prototypes that are 40% better. And those, he says, still represent only the beginning of how good silicon anodes will eventually become.
Now, Cui is looking beyond silicon. One focus is to make anodes out of pure lithium metal, which has long been viewed as the ultimate anode material, as it has the potential to store even more energy than silicon and is much lighter.
But there have been major problems here, too. For starters, an SEI layer normally forms around the lithium metal electrode. That’s actually good news in this case: Lithium ions can penetrate the layer, so the SEI acts as a protective film around the lithium anode. But as the battery cycles, the metal swells and shrinks just as silicon particles do, and the pulsing can break the SEI layer. Lithium ions can then pile up in the crack, causing a metal spike, known as a dendrite, to sprout from the electrode. “Those dendrites can pierce the battery separator and short-circuit the battery and cause it to catch fire,” says Yayuan Liu, another graduate student in Cui’s group.
Conventional approaches haven’t solved the problem. But nanotechnology might. In one approach to preventing dendrite formation, Cui’s team stabilizes the SEI layer by coating the anode with a layer of interconnected nanocarbon spheres. In another, they’ve created a new type of yolk-shell particle, made of gold nanoparticles inside much larger carbon shells. When the nanocapsules are fashioned into an anode, the gold attracts lithium ions; the shells give the lithium room to shrink and swell without cracking the SEI layer, so dendrites don’t form.
Improving anodes is only half the battle in making better batteries. Cui’s team has taken a similar nano inspired approach to improving cathode materials as well, in particular sulfur. Like silicon on the anode side, sulfur has long been seen as a tantalizing option for the cathode. Each sulfur atom can hold a pair of lithiums, making it possible in principle to boost energy storage several fold over conventional cathodes. Perhaps equally important, sulfur is dirt cheap. But it, too, has problems. Sulfur is a relatively modest electrical conductor, and it reacts with common electrolytes to form chemicals that can kill the batteries after a few cycles of charging and discharging. Sulfur cathodes also tend to hoard charges instead of giving them up during discharge.
Seeking a nanosolution, Cui’s team encased sulfur particles inside highly conductive titanium dioxide shells, boosting battery capacity fivefold over conventional designs and preventing sulfur byproducts from poisoning the cell. The researchers have also made sulfur-based versions of their pomegranates, and they have trapped sulfur inside long, thin nanofibers. These and other innovations have not only boosted battery capacity, but also raised a measure known as the coulombic efficiency—how well the battery releases its charges—from 86% to 99%. “Now, we have high capacity on both sides of the electrode,” Cui says.
Down the road, Cui says, he intends to put both of his key innovations together. By coupling silicon anodes with sulfur cathodes, he hopes to make cheap, high-capacity batteries that could change the way the world powers its devices. “We think if we can make it work, it will make a big impact,” Cui says.
It just might help him change the world, and get rich on the side.
Bio – Professor Yi Cui
Professor of Materials Science and Engineering, of Photon Science, Senior Fellow at the Precourt Institute for Energy and Prof, by courtesy, of Chemistry PhD, Harvard University (2002)
Cui studies nanoscale phenomena and their applications broadly defined. Research Interests: Nanocrystal and nanowire synthesis and self-assembly, electron transfer and transport in nanomaterials and at the nano interface, nanoscale electronic and photonic devices, batteries, solar cells, microbial fuel cells, water filters and chemical and biological sensors.
Electric vehicles are set to overcome historic and significant hurdles: sticker price, range anxiety and limited model options. Annual sales are forecasted to jump from 1% today to 25% in 2030 and cross 50% by 2040.
Nearly every major car maker has announced new models for EVs. By 2020, there will be 44 models of EVs available in North America.
Watch the Video Discussionwith Panelists from Daimler Benz, Chargepoint and Lucid
Please join us for a lively panel discussion with diverse electric vehicle experts as they provide their take on the future of the industry and tackle tough questions like:
What are the remaining technical, economic and political hurdles that will impact the mass adoption of EVs?
Charging infrastructure vs EVs – the chicken and the egg problem.
What’s the right amount and mix of charging infrastructure?
Connected, Autonomous, Shared and Electric – How important is “electric” to this futuristic concept?
When will EVs be cheaper to own than conventional internal combustion engine vehicles?
Battery costs have fallen 74% since 2010 – what other technology opportunities exist i.e. new battery chemistry, economies of scale?
China’s EV targets outpace Europe and the US. What are the implications for traditional automakers and Silicon Valley startups?
California’s latest Executive Order targets 5 million EVs on the road by 2030. How do we get there?
Sven Beiker – Moderator & Keynote Speaker, Stanford GSB
Pat Romano – CEO Chargepoint
Fred Kim – R&D Group Manager – Daimler Benz
Albert Liu – Director of Battery Technology, Lucid Motor
“Tenka Energy, Inc. Building Ultra-Thin Energy Dense SuperCaps and NexGen Nano-Enabled Pouch & Cylindrical Batteries – Energy Storage Made Small and POWERFUL!”
Super Capacitor Assisted Silicon Nanowire and Graphene Batteries for EV and Small Form Factor Markets. A New Class of Battery /Energy Storage Materials is being developed to support the High Energy – High Capacity – High Performance and Cycle Battery Markets.
“Ultrathin Asymmetric Porous-Nickel Graphene-Based Supercapacitor with High Energy Density and Silicon Nanowire,” A New Generation Battery that is:
Read More:Quantum Computing and the New Space Racehttp://nationalinterest.org/feature/q… “In January 2017, Chinese scientists officially began experiments using the world’s first quantum-enabled satellite, which will carry out a series of tests aimed at investigating space-based quantum communications over the course of the next two years.”
Quantum Leap in Computer Simulationhttps://pursuit.unimelb.edu.au/articl… “Ultimately it will help us understand and test the sorts of problems an eventually scaled-up quantum computer will be used for, as the quantum hardware is developed over the next decade or so.”
Nevertheless, we are still waiting for a true market impact. Quantum computing and graphene have been around for decades and still haven’t hit on their “killer app.” Perovskite solar cells and CRISPR are newer, but haven’t really impacted their industries yet. And those are just the most prominent examples.
The problem isn’t necessarily with the discoveries themselves, many of which are truly path-breaking, but that there’s a fundamental difference between discovering an important new phenomenon in the lab and creating value in the marketplace.
“We need to get a lot better at bridging that gap. To do so, we need to create a new innovation ecosystem for commercializing science.”
The Valley Of Death And The Human Problem
The gap between discovery and commercialization is so notorious and fraught with danger that it’s been unaffectionately called the “Valley of Death.” Part of the problem is that you can’t really commercialize a discovery, you can only commercialize a product and those are two very different things.
The truth is that innovation is never a single event, but a process of discovery, engineering and transformation. After something like graphene is discovered in the lab, it needs to be engineered into a useful product and then it has to gain adoption by winning customers in the marketplace. Those three things almost never happen in the same place.
So to bring an important discovery to market, you first need to identify a real world problem it can solve and connect to engineers who can transform it into a viable product or service. Then you need to find customers who are willing to drop whatever else they’ve been doing and adopt it on a large scale. That takes time, usually about 30 years.
The reason it takes so long is that there is a long list of problems to solve. To create a successful business based on a scientific discovery, you need to get scientists to collaborate effectively with engineers and a host of specialists in other areas, such as manufacturing, distribution and marketing. Those aren’t just technology problems, those are human problems. Being able to collaborate effectively is often the most important competitive advantage.
Wrong Industry, Wrong Application
One of the most effective programs for helping to bring discoveries out of the lab is I-Corps. First established by the National Science Foundation (NSF) to help recipients of SBIR grants identify business models for scientific discoveries, it has been such an extraordinary success that the US Congress has mandated its expansion across the federal government.
Based on Steve Blank’s lean startup methodology, the program aims to transform scientists into entrepreneurs. It begins with a presentation session, in which each team explains the nature of their discovery and its commercial potential. It’s exciting stuff, pathbreaking science with real potential to truly change the world.
The thing is, they invariably get it wrong. Despite their years of work to discover something of significance and their further efforts to apply and receive commercialization grants from the federal government, they fail to come up with a viable application in an industry that wants what they have to offer.
Ironically, much of the success of the I-Corps program is due to these early sessions. Once they realize that they are on the wrong track, they embark on a crash course of customer discovery, interviewing dozens — and sometimes hundreds — of customers in search of a business model that actually has a chance of succeeding.
What’s startling about the program is that, without it, scientists with important discoveries often wasted years trying to make a business work that never really had a chance in the first place.
The Silicon Valley Myth
Much of the success of Silicon Valley has been based on venture-funded entrepreneurship. Startups with an idea to change the world create an early stage version of the product they want to launch, show it to investors and get funding to bring it to market. Just about every significant tech company was started this way.
Yet most of the success of Silicon Valley has been based on companies that sell either software or consumer gadgets, which are relatively cheap and easy to rapidly prototype. Many scientific startups, however, do not fit into this category. Often, they need millions of dollars to build a prototype and then have to sell to industrial companies with long lead times.
The myth of Silicon Valley is that venture-funded entrepreneurship is a generalizable model that can be applied to every type of business. It is not. In fact, it is a specific model that was conceived in a specific place at a specific time to fund mature technologies for specific markets. It’s not a solution that fits every problem.
The truth is that venture funds are very adept with assessing market risk, but not so good at taking on technology risk, especially in hard sciences. That simply isn’t what they were set up to do.
We Need A New Innovation Ecosystem For Science Entrepreneurship
In 1945, Vannevar Bush delivered a report, Science, The Endless Frontier, to President Truman, in which he made the persuasive argument that expanding the nation’s scientific capacity will expand its economic capacity and well being. His call led, ultimately, to building America’s scientific infrastructure, including programs like the NSF and the National Institutes of Health (NIH).
It was Bush’s vision that made America a technological superpower. Grants from federal agencies to scientists enabled them to discover new knowledge. Then established businesses and, later, venture backed entrepreneurs would then take those discoveries to bring new products and services to market.
That’s exciting, but also poses new challenges, because these technologies are ill-suited to the Silicon Valley model of venture-funded entrepreneurship and need help to them get past the Valley of Death. So we need to build a new innovation ecosystem on top of the scientific architecture Bush created for the post-war world.
Still much more needs to be done, especially at the state and local level to help build regional hubs for specific industries, if we are going to be nearly as successful in the 21st century as were were in the 20th.
Tony Seba, Silicon Valley entrepreneur, Author and Thought Leader, Lecturer at Stanford University, Keynote
The reinvention and connection between infrastructure and mobility will fundamentally disrupt the clean transport model. It will change the way governments and consumers think about mobility, how power is delivered and consumed and the payment models for usage. Will we be ALL Electric Vehicles by 2030? Is the ICE Dead? Impossible?
Graphene handles the issues that come with an electrode’s lithium moving elsewhere.
Lithium ion batteries, as the name implies, work by shuffling lithium atoms between a battery’s two electrodes. So, increasing a battery’s capacity is largely about finding ways to put more lithium into those electrodes. These efforts, however, have run into significant problems.
If lithium is a large fraction of your electrode material, then moving it out can cause the electrode to shrink. Moving it back in can lead to lithium deposits in the wrong places, shorting out the battery.
Now, a research team from Stanford has figured out how to wrap lots of lithium in graphene. The resulting structure holds a place open for lithium when it leaves, allowing it to flow back to where it started.
Tests of the resulting material, which they call a lithium-graphene foil, show it could enable batteries with close to twice the energy density of existing lithium batteries.
Lithium behaving badly
One obvious solution to increasing the amount of lithium in an electrode is simply to use lithium metal itself. But that’s not the easiest thing to do. Lithium metal is less reactive than the other members of its column of the periodic table (I’m looking at you, sodium and potassium), but it still reacts with air, water, and many electrolyte materials.
In addition, when lithium leaves the electrode and returns, there’s no way to control where it re-forms metal. After a few charge/discharge cycles, the lithium electrode starts to form sharp spikes that can ultimately grow large enough to short out the battery.
To have better control over how lithium behaves at the electrode, the Stanford group has looked into the use of some lithium-rich alloys. Lithium, for example, forms a complex with silicon where there are typically over four lithium atoms for each atom of silicon. When the lithium leaves the electrode, the silicon stays behind, providing a structure to incorporate the lithium when it returns on the other half of the charge/discharge cycle.
While this solves the problems with lithium metal, it creates a new one: volume changes. The silicon left behind when the lithium runs to the other electrode simply doesn’t take up as much volume as it does when the same electrode is filled with the lithium-silicon mix.
As a result, the electrode expands and contracts dramatically during a charge-discharge cycle, putting the battery under physical stress. (Mind you, a lithium metal electrode disappears entirely, possibly causing an even larger mechanical stress.)
And that would seem to leave us stuck. Limiting the expansion/contraction of the electrode material would seem to require limiting the amount of lithium that moves into and out of it. Which would, of course, mean limiting the energy density of the battery.
Between the sheets
In the new work, the researchers take their earlier lithium-silicon work and combine it with graphene. Graphene is a single-atom-thick sheet of carbon atoms linked together, and it has a number of properties that make it good for batteries. It conducts electricity well, making it easy to shift charges to and from the lithium when the battery charges and discharges. It’s also extremely thin, which means that packing a lot of graphene molecules into the electrode doesn’t take up much space. And critically for this work, graphene is mechanically tough.
To make their electrode material, the team made nanoparticles of the lithium-silicon material. These were then mixed in with graphene sheets in an eight-to-one ratio. A small amount of a plastic precursor was added, and the whole mixture was spread across a plastic block. Once spread, the polymer precursor created a thin film of polymer on top of the graphene-nanoparticle mix. This could be peeled off, and then the graphene-nanoparticle mix could be peeled off the block as a sheet.
The resulting material, which they call a foil, contains large clusters of the nanoparticles typically surrounded by three to five layers of graphene. Depending on how thick you make the foil, there can be several layers of nanoparticle clusters, each separated by graphene.
The graphene sheets make the material pretty robust, as you can fold and unfold it and then still use it as a battery electrode. They also help keep the air from reacting with the lithium inside. Even after two weeks of being exposed to the air, the foil retained about 95 percent of its capacity as an electrode. Lower the fraction of graphene used in the starting mix and air becomes a problem, with the electrode losing nearly half of its capacity in the same two weeks.
And it worked pretty well as an electrode. When the lithium left, the nanoparticles did shrink, but the graphene sheets held the structure together and kept it from shrinking. And it retained 98 percent of its original capacity even after 400 charge-discharge cycles. Perhaps most importantly, when paired with a vanadium oxide cathode, the energy density was just over 500 Watt-hours per kilogram. Current lithium-ion batteries top out at about half that.
Normally, work like this can take a while to get out of an academic lab and have a company start looking into it. In this case, however, the head of the research group Yi Cui already has a startup company with batteries on the market. So, this could take somewhat less time for a thorough commercial evaluation. The biggest sticking point may be the cost of the graphene. A quick search suggests that graphene is still thousands of dollars per kilogram, although it has come down, and lots of people are looking for ways to make it even less expensive.
If they succeed, then the rest of the components of this electrode are pretty cheap. And the process for making it seems pretty simple.
In a newly discovered twist, Argonne scientists and collaborators found that palladium nanoparticles can repair atomic dislocations in their crystal structure. This self-healing behavior could be worth exploring in other materials. (Image by Argonne National Laboratory.)
Our bodies have a remarkable ability to heal from broken ankles or dislocated wrists. Now, a new study has shown that some nanoparticles can also “self-heal” after experiencing intense strain, once that strain is removed.
New research from the U.S. Department of Energy’s (DOE) Argonne National Laboratory and Stanford University has found that palladium nanoparticles can repair atomic dislocations in their crystal structure. This newly discovered twist could ultimately advance the quest to introduce self-healing behaviors in other materials.
“It turns out that these nanoparticles function much more like the human body healing from an injury than like a broken machine that can’t fix itself.” – Andrew Ulvestad, Argonne materials scientist
The research follows a study from last year, in which Argonne researchers looked at the sponge-like way that palladium nanoparticles absorb hydrogen.
When palladium particles absorb hydrogen, their spongy surfaces swell. However, the interiors of the palladium particles remain less flexible. As the process continues, something eventually cracks in a particle’s crystal structure, dislocating one or more atoms.
“One would never expect the dislocation to come out under normal conditions,” said Argonne materials scientist Andrew Ulvestad, the lead author of the study. “But it turns out that these nanoparticles function much more like the human body healing from an injury than like a broken machine that can’t fix itself.”
Ulvestad explained that the dislocations form as a way for the material to relieve the stress placed on its atoms by the infusion of additional hydrogen. When scientists remove the hydrogen from the nanoparticle, the dislocations have room to mend.
Using the X-rays provided by Argonne’s Advanced Photon Source, a DOE Office of Science User Facility, Ulvestad was able to track the motion of the dislocations before and after the healing process. To do so, he used a technique called Bragg coherent diffraction imaging, which identifies a dislocation by the ripple effects it produces in the rest of the particle’s crystal lattice.
In some particles, the stress of the hydrogen absorption introduced multiple dislocations. But even particles that dislocated in multiple places could heal to the point where they were almost pristine.
“In some cases, we saw five to eight original dislocations, and some of those were deep in the particle,” Ulvestad said. “After the particle healed, there would be maybe one or two close to the surface.”
Although Ulvestad said that researchers are still unsure exactly how the material heals, it likely involves the relationship between the material’s surface and its interior, he explained.
By better understanding how the material heals, Ulvestad and his colleagues hope to tailor the dislocations to improve material properties. “Dislocations aren’t necessarily bad, but we want to control how they form and how they can be removed,” he said.
The study, entitled “The self-healing of defects induced by the hydriding phase transformation in palladium nanoparticles,” appeared November 9 in Nature Communications.
The work was supported by DOE’s Office of Science and the National Science Foundation.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.
The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website.
For someone who’s all in for fossil fuels, President* Trump sure has a thing for electric vehicles.
Last October the US Energy Department announced $15 million in funding to jumpstart the next generation of “extremely” fast charging systems, and last week the agency’s SLAC National Accelerator Laboratory announced a breakthrough discovery for doubling the range of EV batteries.
Put the two together, and you have EVs that can go farther than any old car, and fuel up just about as quickly.
Add the convenience factor of charging up at home or at work, and there’s your recipe for killing oil. #ThanksTrump!
A Breakthrough Energy Storage Discovery For Electric Vehicles
No, really! The current crop of lithium-ion batteries use just half of their theoretical capacity, so there is much room for improvement.
To get closer to 100%, all you have to do is “overstuff” the positive electrode — the cathode — with more lithium. Theoretically, that would enable the battery to absorb more ions in the same space. Theoretically.
Unfortunately, previous researchers have demonstrated that supercharged cathodes lose voltage too quickly to be useful in EVs, because their atomic structure changes.
During the charge cycle, lithium ions leave the supercharged cathode and transition metal atoms move in. When the battery discharges, not all of the transition metal atoms go back to where they came from, leaving less space for the lithium ions to return.
It’s kind of like letting two friends crash on your couch, and one of them never leaves.
That’s the problem tackled by a research team based at the SLAC National Accelerator Laboratory (SLAC is located at Stanford University and the name is a long story involving some trademark issues, but apparently it’s all good now).
Here’s Stanford grad student and study leader William E. Gent enthusing over the new breakthrough:
It gives us a promising new pathway for optimizing the voltage performance of lithium-rich cathodes by controlling the way their atomic structure evolves as a battery charges and discharges.
In other words, the SLAC team discovered a way to manipulate the atomic structure of supercharged cathodes, so the battery doesn’t lose voltage during the charge/discharge cycle.
And, here’s where oil dies:
The more ions an electrode can absorb and release in relation to its size and weight — a factor known as capacity — the more energy it can store and the smaller and lighter a battery can be, allowing batteries to shrink and electric cars to travel more miles between charges.
No, Really — How Does It Work?
To get to the root of the problem, the research team deployed some fancy equipment at SLAC’s SSRL (Stanford Synchotron Radiation Lightsource) to track the atomic-level changes that a lithium-rich battery undergoes during charging cycles.
First, they defined the problem:
…clarifying the nature of anion redox and its effect on electrochemical stability requires an approach that simultaneously probes the spatial distribution of anion redox chemistry and the evolution of local structure.
The research team “unambiguously confirmed” the interplay between oxygen and the transition metal, along with the mechanism for controlling that reaction:
Our results further suggest that anion redox chemistry can be tuned through control of the crystal structure and resulting TM migration pathways, providing an alternative route to improve Li-rich materials without altering TM–O bond covalency through substitution with heavier 4d and 5d TMs.
The equipment angle is essential, btw. Apparently, until the new SLAC study nailed it down there was widespread disagreement on the root cause of the problem.
The new research was made possible in part by a new soft X-ray RIXS system, which was just installed at the lab last year (RIX stands for resonant inelastic X-ray scattering).
Last November, Samsung unveiled a new version of its SM3 ZE sedan, in which the size of the battery was doubled without increasing the weight of the vehicle. That’s a significant achievement and the company has been tight-lipped on that score, too.
Although the green chemistry movement is gathering steam, the US petrochemical industry has been taking off like a rocket in recent years. That means both oil and natural gas production could continue apace for the foreseeable future, with or without gasmobiles.
Graphene’s unique combination of electrical and physical properties marks it out as a potential candidate for transparent, stretchable electronics, which could enable a new generation of sophisticated displays, wearable health monitors, or soft robotic devices. But, although graphene is atomically thin, highly transparent, conductive, and more stretchable than conventional indium tin oxide electrodes, it still tends to crack at small strains.
“To enable excellent strain-dependent performance of transparent graphene conductors, we created graphene nanoscrolls in between stacked graphene layers,” explains first author of the study, Nan Liu
Illustration of the stacked graphene MGG structure.
The team led by Zhenan Bao dub their combination of rolled up sheets of graphene sandwiched in between stacked graphene layers ‘multi-layer G/G scrolls’ or MGG. The scrolls, which are 1–20 microns long, 0.1–1 microns wide, and 10–100 nm high, form naturally during the wet transfer process as graphene is moved from one substrate to another.
“By using MGG graphene stretchable electrodes (source/drain and gate) and semiconducting carbon nanotubes, we were able to demonstrate highly transparent and highly stretchable all-carbon transistors,” says Liu.
The all-carbon devices fabricated by the team retain 60% of their original current output when stretched to 120% strain (parallel to the direction of charge transport). This is the most stretchable carbon-based transistor reported to date, believe the researchers.
The graphene scrolls are key to the stretchable electrode’s remarkable properties because they seem to provide a conductive path even when graphene sheets start to crack at high strain levels.
“Taking into account the electronic and optical properties as well as the cost, our MGG exhibits substantial strengths over other conductors, such as carbon nanotubes and metal nanowires,” says Liu.
Transparent, stretchable graphene electrodes could be useful as contacts in flexible electronic circuits such as backplane control units for displays, as well as functional sensors and digital circuits for electronic skin.
“This is a very important area of research with a variety of possible applications,” comments Andrea C. Ferrari of the University of Cambridge. “The approach taken by Bao et al. is an interesting one that could be quite general.”
The concept of using a mixture of graphene scrolls and platelets to enable an electrode to stretch without significant losses in transmittance or conductivity is a good and should, in principle, not be too complicated to scale up for real devices, he adds.
“We are now seeking to extend this method to other two-dimensional materials, such as MoS2, to enable stretchable two-dimensional semiconductors,” says Liu.