** Contributed from Nature Communications Open Source Article
The ever-increasing demands for advanced lithium-ion batteries have greatly stimulated the quest for robust electrodes with a high areal capacity. Producing thick electrodes from a high-performance active material would maximize this parameter. However, above a critical thickness, solution-processed films typically encounter electrical/mechanical problems, limiting the achievable areal capacity and rate performance as a result.
Herein, we show that two-dimensional titanium carbide or carbonitride nano sheets, known as MXenes, can be used as a conductive binder for silicon electrodes produced by a simple and scalable slurry-casting technique without the need of any other additives.
“The nano sheets form a continuous metallic network, enable fast charge transport and provide good mechanical reinforcement for the thick electrode (up to 450μm). Consequently, very high areal capacity anodes (up to 23.3 mAh cm-2) have been demonstrated.” Utilization of Li-ion chemistry to store the energy electro-chemically can address the ever-increasing demands from both portable electronics and hybrid electrical vehicles.
Such stringent challenges on the battery safety and lifetime issues require high-performance battery components, with most of the focus being on electrodes or electrolytes with novel nano-structures and chemistries.
However, equally important is the development of electrode additives, which are required to main-tain the electrode’s conductive network and mechanical integrity. Traditionally, electrode additives are made of dual components based on a conductive agent (i.e. carbon black, CB) and a poly-meric binder.
While the former ensures the charge transport throughout the electrode, the latter mechanically holds the active materials and CB together during cycling. Although these traditional electrode additives have been widely applied in Li-ion battery technologies, they fail to perform well in high-capacity electrodes, especially those displaying large volume changes.
This is because the polymeric binder is not mechanically robust enough to withstand the stress induced during lithiation/deli-thiation, leading to severe disruption of the conducting networks. This results in rapid capacity fade and poor lifetime.
In summary, the efficient utilization of 2D MXene nanosheets as a new class of conductive binder for high volume-change Si electrodes is of fundamental importance to the electrochemical energy storage field.
The continuous network of MXene nanosheets not only provides sufficient electrical conductivity and free space for accommodating the volume change issue but also well resolves the mechanical instability of Si. Therefore, the combination of viscous MXene ink and high-capacity Si demonstrated here offers a powerful technique to construct advanced nanostructures with exceptional performance.
Of equal importance is that the formation of these high-mass-loading Si/MXene electrodes can be achieved by means of a commercially compatible, slurry-casting technique, which is highly scalable and low cost, allowing for large-area production of high-performance, Si-based electrodes for advanced batteries.
Considering that more than 30 MXenes are already reported, with more predicted to exist, there is certainly much room for further improving the electrochemical performance of such electrodes by tuning the electrical, mechanical and physicochemical properties of this exciting 2D MXene family.
Professor Valeria Nicolosi
Professor of Nanomaterials and Advanced Microscopy at Trinity College Dublin
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.
(Article continues below)
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.
Specific energy and specific power of rechargeable batteries. Specific energy is the capacity a battery can hold in watt-hours per kilogram (Wh/kg); specific power is the battery’s ability to deliver power in watts per kilogram (W/kg). (Source: Battery University)
” … a research team from Sichuan University in China and Clarkson University in the U.S. have discovered a key design rule for Li metal batteries: If you want to suppress dendrites, you have to use a defect-free host. More generally, carbon defects catalyze dendrite growth in metal anodes … “
Rechargeable lithium-ion (Li-ion) batteries are the dominant technology not only for portable electronics but it also is becoming the battery of choice for electric-vehicle and electric-grid energy-storage applications.
In a Li-ion battery, the cathode (positive electrode) is a lithium metal oxide while the anode (negative electrode) is graphite. But researchers are looking for ways to replace graphite with lithium metal as the anode to boost the battery’s energy density.
Lithium metal-based batteries such as Li–sulfur and Li–air batteries have received considerable attention because the packing density of lithium atoms is the highest in its metallic form and Li metal can store 10 times more energy than graphite.
However, there are safety and performance concerns for these types of batteries that arise from the formation of dendrites on the metal electrodes; an issue that has been known and investigated since the 1960s.
These dendrites form when metal ions accumulate on the surface of the battery’s electrodes as the electrode degrades during the charging process. Dendrites are often responsible for the highly publicized violent battery failures reported in the news.
When these branch-like filament deposits elongate until they penetrate the barrier between the two halves of the battery, they can cause electrical shorts, overheating and fires. They also cause significant cycling efficiency losses.
To avoid dendrites, researchers are experimenting with new battery electrolyte chemistries, new separator technologies, and new physical hosts for the lithium metal.
Carbon hosts, in particular, are very promising, since they may be added to the anode with little additional cost and minimal modification of the manufacturing process and they are becoming an important way to stabilize Li metal anodes.
However, there are seemingly contradictory findings reported in hundreds of prior publications on the subject: The hosts, which are predominantly made from various nanostructured carbons such as graphene, are in some cases very effective in eliminating dendrites. In other cases, they don’t work at all, or actually make the dendrite problem worse.
Up to now, design of such host systems has been largely Edisonian: researchers use a trial-and-error approach to find an architecture/structure that works better than the rest.
These findings address the major scientific problem of explaining how the structure and chemistry of the carbon per se affects dendrite growth.
Left half: Defect-free graphene protecting lithium metal anode from the electrolyte. Right half: Defective graphene catalyzing dendrite growth. (Source: Mitlin Research Group, Clarkson University)
“We discovered a critical and unexpected relationship between the host (graphene) chemical/structural defectiveness and its ability to suppress dendrites,” Prof. David Mitlin, who led the work, explains to Nanowerk. “To do this, we created what may be the world’s most pure and ordered graphene and compared it to a standard graphene based on reduced graphene oxide. Using such opposite materials, provided unique and fundamental insight into the way lithium dendrites form and grow.”
“The key finding, which will rationally guide future lithium battery design efforts, is that the carbon defects are themselves catalytic for dendrite growth,” Prof Wei Liu from Sichuan University’s Institute of New Energy and Low Carbon Technology, and the paper’s first author, points out. “Much of the ‘damage’ to the anode ultimately responsible for the dendrites occurs even before the battery is fully charged for the first time. Defects in the carbon host corrode the electrolyte at low voltages, leading to early dendrite formation.”
The team hypothesized that it was the host structure/chemistry that mattered, but needed to create ideal model systems to test the hypothesis.
Prof. Wei Liu’s unique Flow Assisted Sonication (FAS) approach allowed them to create nearly defect-free graphene. Literally, such oxygen-free and structural defect-free graphene has never been synthesized prior by a wet chemistry method.
This graphene is 1-3 atomic layers thick and with only about one and a half percent oxygen. This is much purer than the typical eight percent or more oxygen found in most graphene materials.
“It served as a perfect test bed to explore our hypothesis,” says Liu. “Without such a pristine structure, it would not have been possible to obtain the conclusive answers to the dendrite growth problem.”
He emphasizes that this in itself is a transformative accomplishment for the carbon and energy communities, since prior only vapor deposition could obtain such ideal defect-free structures.
The team then compared their defect-free graphene to a standard highly defective Hummers graphene baseline found in literature.
“A direct one-to-one comparison allowed us to obtain unique insight into the role of carbon defects on Li dendrite growth,” says Mitlin. “A critical new finding is that solid electrolyte interphase (SEI) formation occurring BEFORE metal plating actually dictates dendrites. The fate of the Li metal anode is in effect sealed once the carbon host forms SEI at the initial charge!”
Going forward, the researchers plan to commercialize defect-free graphene host materials for next- generation lithium batteries. They also plan to further understand the complex relationship between carbon defects and metal dendrites by examining carbons with tuned structure/chemistry for lithium, sodium and potassium batteries.
Finding and improving renewable energy sources is becoming increasingly important. One strategy to generate energy is breaking water molecules (H2O) apart in an electrochemical reaction known as electrolysis.
This process allows us to convert energy from the sun or other renewable sources into chemical energy. However, electrochemically splitting water molecules requires an overpotential—an excess voltage that has to be applied in addition to the theoretical voltage (1.23V vs. reversible hydrogen electrode or RHE) so that the necessary reactions can occur.
Electrocatalysts are materials that, because of their electrical and morphological features, facilitate electrochemical processes. Researchers have been searching for electrocatalysts that can aid in the electrolysis of water, and some of the best catalysts are noble-metal oxides, which are rare and costly. Nickel-based hydroxide (Ni(OH)2) compounds are, fortunately, a better alternative.
A team of scientists, including Profs. Hyunsik Im and Hyungsang Kim from Dongguk University, intercalated polyoxovanadate (POV) nanoclusters into Ni(OH)2 arranged in ordered layers and found that doing this improves its conducting and morphological properties, which in turn enhances its catalytic activity.
File Photo: Dongguk University
They employed a promising method called chemical solution growth (CSG), wherein a highly saturated solution is prepared, and the desired material structure naturally forms as the solutes precipitate in a predictable and controlled fashion, creating a layer-by-layer structure with POV nanoclusters intercalated between the Ni(OH)2 layers.
The team demonstrated that the resulting house-of-cards-like structure greatly reduced the overpotential needed for the electrolysis of water. They attributed this to the morphological features of this material; the POV nanoclusters increase the spacing between the Ni(OH)2 layers and induce the formation of micropores, which increases the surface area of the final material and the number of catalytic sites where water molecules can be split. “Our results demonstrate the advantages of the CSG method for optimizing the pore structure of the resulting material,” explains Prof. Im.
Facilitating the electrolysis of water using novel catalysts is a step toward achieving a greener future. What’s more, the CSG method could be useful in many other fields. “The facile CSG deposition of nanohybrid materials may be useful for applications such as the production of Li-ion batteries and biosensors,” states Prof. Kim. Only time will tell what new uses CSG will find.
More information: Jayavant L. Gunjakar et al, Two-Dimensional Layered Hydroxide Nanoporous Nanohybrids Pillared with Zero-Dimensional Polyoxovanadate Nanoclusters for Enhanced Water Oxidation Catalysis, Small (2018). DOI: 10.1002/smll.201703481
Your knees and your smartphone battery have some surprisingly similar needs, a University of Michigan professor has discovered, and that new insight has led to a ‘structural battery’ prototype that incorporates a cartilage-like material to make the batteries highly durable and easy to shape. Credit: Evan Doughtry
Your knees and your smartphone battery have some surprisingly similar needs, a University of Michigan professor has discovered, and that new insight has led to a “structural battery” prototype that incorporates a cartilage-like material to make the batteries highly durable and easy to shape.
The idea behind structural batteries is to store energy in structural components — the wing of a drone or the bumper of an electric vehicle, for example. They’ve been a long-term goal for researchers and industry because they could reduce weight and extend range. But structural batteries have so far been heavy, short-lived or unsafe.
In a study published in ACS Nano, the researchers describe how they made a damage-resistant rechargeable zinc battery with a cartilage-like solid electrolyte. They showed that the batteries can replace the top casings of several commercial drones. The prototype cells can run for more than 100 cycles at 90 percent capacity, and withstand hard impacts and even stabbing without losing voltage or starting a fire.
“A battery that is also a structural component has to be light, strong, safe and have high capacity. Unfortunately, these requirements are often mutually exclusive,” said Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering, who led the research.
Harnessing the properties of cartilage
To sidestep these trade-offs, the researchers used zinc — a legitimate structural material — and branched nanofibersthat resemble the collagen fibers of cartilage.
“Nature does not have zinc batteries, but it had to solve a similar problem,” Kotov said. “Cartilage turned out to be a perfect prototype for an ion-transporting material in batteries. It has amazing mechanics, and it serves us for a very long time compared to how thin it is. The same qualities are needed from solid electrolytes separating cathodes and anodes in batteries.”
In our bodies, cartilage combines mechanical strength and durability with the ability to let water, nutrients and other materials move through it. These qualities are nearly identical to those of a good solid electrolyte, which has to resist damage from dendrites while also letting ions flow from one electrode to the other.
Dendrites are tendrils of metal that pierce the separator between the electrodes and create a fast lane for electrons, shorting the circuit and potentially causing a fire. Zinc has previously been overlooked for rechargeable batteries because it tends to short out after just a few charge/discharge cycles.
Not only can the membranes made by Kotov’s team ferry zinc ions between the electrodes, they can also stop zinc’s piercing dendrites. Like cartilage, the membranes are composed of ultrastrong nanofibers interwoven with a softer ion-friendly material.
In the batteries, aramid nanofibers — the stuff in bulletproof vests — stand in for collagen, with polyethylene oxide (a chain-like, carbon-based molecule) and a zinc salt replacing soft components of cartilage.
Demonstrating safety and utility
To make working cells, the team paired the zinc electrodes with manganese oxide — the combination found in standard alkaline batteries. But in the rechargeable batteries, the cartilage-like membrane replaces the standard separator and alkaline electrolyte. As secondary batteries on drones, the zinc cells can extend the flight time by 5 to 25 percent — depending on the battery size, mass of the drone and flight conditions.
Safety is critical to structural batteries, so the team deliberately damaged their cells by stabbing them with a knife. In spite of multiple “wounds,” the battery continued to discharge close to its design voltage. This is possible because there is no liquid to leak out.
For now, the zinc batteries are best as secondary power sources because they can’t charge and discharge as quickly as their lithium ion brethren. But Kotov’s team intends to explore whether there is a better partner electrode that could improve the speed and longevity of zinc rechargeable batteries.
The research was supported by the Air Force Office of Scientific Research and National Science Foundation. Kotov teaches in the Department of Chemical Engineering. He is also a professor of materials science and engineering, and macromolecular science and engineering.
Drive for innovation: Electric vehicles are a major target for R&D on novel battery materials. (Image courtesy: imec)
31 Oct 2018
Note to Readers: This article first appeared in the 2018 Physics World Focus on Energy Technologies Engineering a sustainable, electrified future means developing battery materials with properties that surpass those found in current technologies.
The batteries we depend on for our mobile phones and computers are based on a technology that is more than a quarter-century old. Rechargeable lithium-ion (Li-ion) batteries were first introduced in 1991, and their appearance heralded a revolution in consumer electronics. From then on, we could pack enough energy in a small volume to start engineering a whole panoply of portable electronic devices – devices that have given us much more flexibility and comfort in our lives and jobs.
In recent years, Li-ion batteries have also become a staple solution in efforts to solve the interlinked conundrums of climate change and renewable energy. Increasingly, they are being used to power electric vehicles and as the principal components of home-based devices that store energy generated from renewable sources, helping to balance an increasingly diverse and smart electrical grid. The technology has improved too: over the past two and a half decades, battery experts have succeeded in making Li-ion batteries 5–10% more efficient each year, just by further optimizing the existing architecture.
Ultimately, though, getting from where we are now to a truly carbon-free economy will require better-performing batteries than today’s (or even tomorrow’s) Li-ion technology can deliver. In electric vehicles, for example, a key consideration is for batteries to be as small and lightweight as possible.
Achieving that goal calls for energy densities that are much higher than the 300 Wh/kg and 800 Wh/L which are seen as the practical limits for today’s Li-ion technology.
Another issue holding back the adoption of electric vehicles is cost, which is currently still around 300–200 $/kWh, although that is widely projected to go below 100 $/kWh by 2025 or even earlier. The time required to recharge a battery pack – still in the range of a few hours – will also have to come down, and as batteries move into economically critical applications such as grid storage and grid balancing, very long lifetimes (a decade or more) will become a key consideration too.
There is still some room left to improve existing Li-ion technology, but not enough to meet future requirements. Instead, the process of battery innovation needs a step change: materials-science breakthroughs, new electrode chemistries and architectures that have much higher energy densities, new electrolytes that can deliver the necessary high conductivity – all in a battery that remains safe and is long-lasting as well as economical and sustainable to produce.
To appreciate why this is such a challenge, it helps to understand the basic architecture of existing batteries. Rechargeable Li-ion batteries are made up of one or more cells, each of which is a small chemical factory essentially consisting of two electrodes with an electrolyte in between. When the electrodes are connected (for example with a wire via a lamp), an electrochemical process begins. In the anode, electrons and lithium ions are separated, and the electrons buzz through the wire and light up the lamp. Meanwhile, the positively-charged lithium ions move through the electrolyte to the cathode. There, electrons and Li-ions combine again, but in a lower energy state than before.
The beauty of rechargeable batteries is that these processes can be reversed, returning lithium ions to the anode and restoring the energy states and the original difference in electrical potential between the electrodes. Lithium ions are well suited for this task. Lithium is not only the lightest metal in the periodic table, but also the most reactive and will most easily part with its electrons. It has been chosen as the basis for rechargeable batteries precisely because it can do the most work with the least mass and the fewest chemical complications. More specifically, in batteries using lithium, it is possible to make the electric potential difference between anodes and cathodes higher than is possible with other materials.
To date, therefore, the main challenge for battery scientists has been to find chemical compositions of electrodes and electrolyte that will let the lithium ions do their magic in the best possible way: electrodes that can pack in as many lithium ions as possible while setting up as high an electrical potential difference as possible; and an electrolyte that lets lithium ions flow as quickly as possible back and forth between the anode and cathode.
Seeking a solid electrolyte
The electrolyte in most batteries is a liquid. This allows the electrolyte not only to fill the space between the electrodes but also to soak them, completely filling all voids and spaces and providing as much contact as possible between the electrodes and the electrolyte. To complete the picture, a porous membrane is added between the electrodes. This inhibits electrical contact between the electrodes and prevents finger like outgrowths of lithium from touching and short-circuiting the battery.
For all the advantages of liquid electrolytes, though, scientists have long sought to develop solid alternatives. A solid electrolyte material would eliminate several issues at the same time. Most importantly, it would replace the membrane, allowing the electrodes to be placed much closer together without touching, thereby, making the battery more compact and boosting its energy density. A solid electrolyte would also make batteries stronger, potentially meaning that the amount of protective and structural casing could be cut without compromising on safety.
Unfortunately, the solid electrolytes proposed so far have generally fallen short in one way or another. In particular, they lack the necessary conductivity (expressed in milli-Siemens per centimetre, or mS/cm). Unsurprisingly, ions tend not to move as freely through a solid as they do through a liquid. That reduces both the speed at which a battery can charge and, conversely, the quantity of power it can release in a given time.
Scientists at imec – one of Europe’s premier nanotechnology R&D centres, and a partner in the EnergyVille consortium for sustainable energy and intelligent energy systems research – recently came up with a potential solution. The new material is a nanoporous oxide mix filled with ionic compounds and other additives, with the pores giving it a surface area of about 500 m2/mL – “comparable to an Olympic swimming pool folded into a shot glass,” says Philippe Vereecken, imec’s head of battery research. Because ions move faster along the pores’ surface than in the middle of a lithium salt electrolyte, he explains, this large surface area amplifies the ionic conductivity of the nanoengineered solid. The result is a material with a conductivity of 10 mS/cm at room temperature – equivalent to today’s liquid electrolytes.
Using this new electrolyte material, imec’s engineers have built a cell prototype using standard available electrodes: LFP (LiFePO4) for the cathode and LTO (Li4Ti5O12) for the anode. While charging, the new cell reached 80% of its capacity in one hour, which is already comparable to a similar cell made with a liquid electrolyte. Vereecken adds that the team hopes for even better results with future devices. “Computations show that the new material might even be engineered to sustain conductivities of up to 100 mS/cm,” he says.
Meanwhile, back at the electrode
Electrodes are conventionally made from sintered and compressed powders. Combining these with a solid electrolyte would normally entail mixing the electrode as a powder with the electrolyte also in powder form, and then compressing the result for a maximum contact. But even then, there will always remain pores and voids that are not filled and the contact surface will be much smaller than is possible with a liquid electrolyte that fully soaks the electrode.
Lithium-sulphur is a promising material that could store more energy than today’s technology allows
Imec’s new nano-composite material avoids this problem because it is actually applied as a liquid, via wet chemical coating, and only afterwards converted into a solid. That way it can impregnate dense powder electrodes, filling all cavities and making maximum contact just as a liquid electrolyte would. Another benefit is that even as a solid, the material remains somewhat elastic, which is essential as some electrodes expand and contract during battery charging and discharging. A final advantage is that because the solid material can be applied via a wet precursor, it is compatible with current Li-ion battery fabrication processes – something that Vereecken says is “quite important for the battery manufacturers” because otherwise more “disruptive” fabrication processes would have to be put in place.
To arrive at the energy densities required to give electric vehicles a long driving range, though, still more changes are needed. One possibility is to make the particles in the electrode powders smaller, so that they can be packed more densely. This would produce a larger contact surface with the electrolyte per volume, improving the energy density and charging rate of the cell. There is a catch, though: while a larger contact surface results in more ions being created and changing sides within the battery, it also gives more way for unwanted reactions that will degrade the battery’s materials and shorten its lifetime. “To improve the stability,” says Vereecken, “imec’s experts work on a solution where they coat all particles with an ultrathin buffer layer.” The challenge, he says, is to make these layers both chemically inert and highly conductive.
Introducing new materials
By combining solid electrolytes with thicker electrodes made from smaller particles, it may be possible to produce batteries with energy densities that exceed the current maximum of around 800 Wh/L. These batteries could also charge in 30 minutes or less. But to extend the energy density even further, to 1000 Wh/L and beyond, a worldwide effort is on to look for new and better electrode materials. Anodes, for example, are currently made from carbon in the form of graphite. That carbon could be replaced by silicon, which can hold up to ten times as many lithium ions per gram of electrode. The drawback is that when the battery is charged, a silicon anode will expand to more than three times its normal size as it fills with lithium ions. This may break up the electrode, and possibly even the battery casing.
A better alternative may be to replace carbon with pure lithium metal. A lithium anode will also store up to ten times as much lithium ions per gram of electrode as graphite, but without the swelling seen in silicon anodes. Lithium anodes were, in fact, used in the early days of Li-ion batteries, but as the metal is very reactive, especially in combination with liquid electrolytes, the idea was dropped in favour of more stable alternatives. Vereecken, however, believes that progress in solid electrolytes means it is “high time to revisit lithium metal as a material for the anode”, especially since it is possible to add protective functional coatings to nanoparticles.
Disruptive innovations are on the horizon for cathodes as well. Lithium-sulphur, for example, is a promising material that could store more energy than today’s technology allows. Indeed, the “ideal” lithium battery might well feature a lithium-air (lithium peroxide) cathode in combination with a pure lithium anode. But whereas the material composition of these batteries sounds simple, the path to realizing them will not be so easy, and there is still some way to go before any of these developments will be integrated into commercial batteries. Once that happens, though, huge payoffs are possible. The most obvious would be electrical cars that drive farther and charge faster, but better lithium batteries could also be the breakthrough needed to make renewable power ubiquitous – and thus finally let us off the fossil-fuel hook.
Genesis Nanotechnology, Inc. is pleased to present Tenka Energy, Inc. Building Ultra-Thin Energy Dense SuperCaps and NexGen Nano-Enabled Pouch & Cylindrical Batteries – Energy Storage Made Small and POWERFUL! YouTube Video
A team of material researchers has succeeded in producing a composite material that is particularly suited for electrodes in lithium batteries. The nanocomposite material might help to significantly increase the storage capacity and lifetime of batteries as well as their charging speed.
Lithium-ion batteries are the ultimate benchmark when it comes to mobile phones, tablet devices, and electric cars. Their storage capacity and power density are far superior to other rechargeable battery systems. Despite all the progress that has been made, however, smartphone batteries only last a day and electric cars need hours to be recharged. Scientists are therefore working on ways to improve the power densities and charging rates of all-round batteries. “An important factor is the anode material,” explains Dina Fattakhova-Rohlfing from the Institute of Energy and Climate Research (IEK-1).
“In principle, anodes based on tin dioxide can achieve much higher specific capacities, and therefore store more energy, than the carbon anodes currently being used. They have the ability to absorb more lithium ions,” says Fattakhova-Rohlfing. “Pure tin oxide, however, exhibits very weak cycle stability — the storage capability of the batteries steadily decreases and they can only be recharged a few times. The volume of the anode changes with each charging and discharging cycle, which leads to it crumbling.”
One way of addressing this problem is hybrid materials or nanocomposites — composite materials that contain nanoparticles. The scientists developed a material comprising tin oxide nanoparticles enriched with antimony, on a base layer of graphene. The graphene basis aids the structural stability and conductivity of the material. The tin oxide particles are less than three nanometres in size — in other words less than three millionths of a millimetre — and are directly “grown” on the graphene. The small size of the particle and its good contact with the graphene layer also improves its tolerance to volume changes — the lithium cell becomes more stable and lasts longer.
Three times more energy in one hour
“Enriching the nanoparticles with antimony ensures the material is extremely conductive,” explains Fattakhova-Rohlfing. “This makes the anode much quicker, meaning that it can store one-and-a-half times more energy in just one minute than would be possible with conventional graphite anodes. It can even store three times more energy for the usual charging time of one hour.”
“Such high energy densities were only previously achieved with low charging rates,” says Fattakhova-Rohlfing. “Faster charging cycles always led to a quick reduction in capacity.” The antimony-doped anodes developed by the scientists, however, retain 77 % of their original capacity even after 1,000 cycles.
“The nanocomposite anodes can be produced in an easy and cost-effective way. And the applied concepts can also be used for the design of other anode materials for lithium-ion batteries,” explains Fattakhova-Rohlfing. “We hope that our development will pave the way for lithium-ion batteries with a significantly increased energy density and very short charging time.”
Florian Zoller, Kristina Peters, Peter M. Zehetmaier, Patrick Zeller, Markus Döblinger, Thomas Bein, Zdeneˇk Sofer, Dina Fattakhova-Rohlfing. Making Ultrafast High-Capacity Anodes for Lithium-Ion Batteries via Antimony Doping of Nanosized Tin Oxide/Graphene Composites. Advanced Functional Materials, 2018; 28 (23): 1706529 DOI: 10.1002/adfm.201706529
Maintaining a global supply chain is one of the most secretive and understated keys to the success of a military campaign. As described by the U.S. Army, the quick and efficient transport of goods like water, food, fuel, and ammunition has been essential in winning wars for thousands of years. Supply chain and logistics management has evolved to include, “storage of goods, services, and related information between the point of origin and the point of consumption”. In essence, that means the movement of vehicles bringing precious cargo from the home base to the soldiers fighting on the front lines.
Security and strategic operations are critical elements in the fulfillment of this potentially hazardous supply chain. Enemy forces hiding in the bushes can open fire to try to slow down the troops’ movement. With mines littered all over the war zone, all it would take is one wrong step, and the truck and the people in them, would be blown to smithereens.
One ingenious solution is the deployment of an automated military convoy run by a military commander, which can reduce risks and their accompanying vulnerabilities. In line with this, advanced defense contractor Lockheed Martin Canada (NYSE:LMT) has successfully tested “driverless trucks” on two active U.S. military bases.
Call it the soldier’s equivalent of a smart fleet of cars that would take the currently popular concept of self-driving vehicles to a whole new, safer level. Human operators would still be needed to guide the vehicles towards their destinations. However, because this could be accomplished remotely, very little time would be lost to the exchange of hostilities, as these smart military vehicles would be impervious to the enemy’s usual attempts at distraction. And in case firepower does break out, the loss of life, as well as injury to the troops, would be minimal.
The memorandum of agreement signed between Elcora and Lockheed Martin, is not the usual corporate alliance but bears important long-term repercussions for sectors such as transport, security, and the military-industrial complex. Lockheed Martin is a leviathan in the aerospace, defense, weaponry, and other technologies that have been instrumental in keeping many of the nations of the world safe.
The Lithium-ion (or Li-ion) batteries that it uses to store energy in many of its technologies and processes are critical to upholding the operations being conducted in many of its devices, plants, and facilities. The more energy that these batteries can store, the longer the systems and machines can function, without interruption, and in compliance with the highest standards of safety.
One element that can ensure the consistent and reliable powering up for the Li-ion batteries is graphene, an element derived from graphite minerals. Elcora is one of the few companies that produce and distribute graphene in one dynamic end-to-end operation, from the time that the first rocks are mined in Sri Lanka, to the time that they are refined, developed, and purified in the company’s facilities in Canada. The quality of the graphene that comes out of Elcora’s pipeline is higher than those usually found in the market. This pristine quality can help the Li-ion batteries increase their storage of power without adding further cost.
Li-ion batteries are already being sought after for prolonging the lifespan of power charged in a wide range of devices, from the ubiquitous smartphones, to the electric cars that innovators like Elon Musk are pushing to become more mainstream in our roads and highways. Lockheed Martin will also be using them in the military vehicles that will be guided by their Autonomous Mobility Applique Systems (AMAS), or the ‘driverless military convoy’, as described above. The tests have shown that these near-smart vehicles have already clocked in 55,000 miles. Lockheed is looking forward to completing the tests and fast-forwarding to deploying them for actual use in military campaigns.
The importance of long-lasting Li-ion batteries in the kind of combat arena that Lockheed Martin is expert in cannot be overestimated. With electric storage given a lengthier lifespan by the graphene anode in the batteries, the military commanders guiding the smart convoys do not have to fear any anticipated technical breakdown. They can also count on the batteries to sustain the vehicles’ power and carry them through to the completion of their mission if something unexpected happens. The juice in those Li-ion batteries will last longer, which is critical in crises such as the sudden appearance of combatants.
Sometimes, the winner in war turns out to be the force that is the more resilient and sustaining power. As the ancient Chinese master of war Sun Tzu had warned eons ago, sometimes “the line between order and disorder”—or victory or defeat—“lies in logistics.” Through its graphene-constituted Li-ion batteries, The Lockheed Martin-Elcora alliance can certainly enhance any military force’s capacity in that area.
* Article from Technology.org
Also Read About:
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 Energy Dense – High Capacity – High Performance High Cycle Battery and Super Capacitor Markets.
Genesis Nanotechnology: “Great Things from Small Things”
Research at Sandia National Laboratories has identified a major obstacle to advancing solid-state lithium-ion battery performance in small electronics: the flow of lithium ions across battery interfaces.
Sandia’s three-year Laboratory Directed Research and Development project investigated the nanoscale chemistry of solid-state batteries, focusing on the region where electrodes and electrolytes make contact. Most commercial lithium-ion batteries contain a liquid electrolyte and two solid electrodes, but solid-state batteries instead have a solid electrolyte layer, allowing them to last longer and operate more safely.
“The underlying goal of the work is to make solid-state batteries more efficient and to improve the interfaces between different materials,” Sandia physicist Farid El Gabaly said. “In this project, all of the materials are solid; we don’t have a liquid-solid interface like in traditional lithium-ion batteries.”
The research was published in a Nano Letters paper titled, “Non-Faradaic Li+ Migration and Chemical Coordination across Solid-State Battery Interfaces.” Authors include Sandia postdoctoral scientist Forrest Gittleson and El Gabaly. The work was funded by the Laboratory Directed Research and Development program, with supplemental funding by the Department of Energy’s Office of Science.
El Gabaly explained that in any lithium battery, the lithium must travel back and forth from one electrode to the other when it is charged and discharged. However, the mobility of lithium ions is not the same in all materials and interfaces between materials are a major obstacle.
Speeding up the intersection
El Gabaly compares the work to figuring out how to make traffic move quickly through a busy intersection.
“For us, we are trying to reduce the traffic jam at the junction between two materials,” he said.
El Gabaly likened the electrode-electrolyte interface to a tollbooth or merge on a freeway.
“We are essentially taking away the cash tolls and saying everybody needs to go through the fast track, so you’re smoothing out or eliminating the slowdowns,” he said. “When you improve the process at the interface you have the right infrastructure for vehicles to pass easily. You still have to pay, but it is faster and more controlled than people searching for coins in the glove box.”
There are two important interfaces in solid state batteries, he explained, at the cathode-electrolyte junction and electrolyte-anode junction. Either could be dictating the performance limits of a full battery.
Gittleson adds, “When we identify one of these bottlenecks, we ask, ‘Can we modify it?’ And then we try to change the interface and make the chemical processes more stable over time.”
Sandia’s interest in solid-state batteries
El Gabaly said Sandia is interested in the research mainly because solid-state batteries are low maintenance, reliable and safe. Liquid electrolytes are typically reactive, volatile and highly flammable and are a leading cause of commercial battery failure. Eliminating the liquid component can make these devices perform better.
“Our focus wasn’t on large batteries, like in electric vehicles,” El Gabaly said. “It was more for small or integrated electronics.”
Since Sandia’s California laboratory did not conduct solid-state battery research, the project first built the foundation to prototype batteries and examine interfaces.
“This sort of characterization is not trivial because the interfaces that we are interested in are only a few atomic layers thick,” Gittleson said. “We use X-rays to probe the chemistry of those buried interfaces, seeing through only a few nanometers of material. Though challenging to design experiments, we have been successful in probing those regions and relating the chemistry to full battery performance.”
Processing the research
The research was conducted using materials that have been used in previous proof-of-concept solid-state batteries.
“Since these materials are not produced on a massive commercial scale, we needed to be able to fabricate full devices on-site,” El Gabaly said. “We sought methods to improve the batteries by either inserting or changing the interfaces in various ways or exchanging materials.”
The work used pulsed laser deposition and X-ray photoelectron spectroscopy combined with electrochemical techniques. This allowed very small-scale deposition since the batteries are thin and integrated on a silicon wafer.
“Using this method, we can engineer the interface down to the nanometer or even subnanometer level,” Gittleson said, adding that hundreds of samples were created.
Building batteries in this way allowed the researchers to get a precise view of what that interface looks like because the materials can be assembled so controllably.
The next phase of the research is to improve the performance of the batteries and to assemble them alongside other Sandia technologies.
“We can now start combining our batteries with LEDs, sensors, small antennas or any number of integrated devices,” El Gabaly said. “Even though we are happy with our battery performance, we can always try to improve it more.”
Researchers have demonstrated a novel approach toward smart orthodontics based on near-infrared red light from a mechanically flexible LED powered by flexible bio-safe batteries all integrated in a single 3D-printed dental brace.
“Integration of electronic devices in 3D printed dental aligners, as we have demonstrated here, is a pragmatic approach towards implementing a flexible electronic technology in personalized advanced healthcare, particularly in orthodontics,” Muhammad Mustafa Hussain, an Associate Professor of Electrical Engineering at KAUST, tells Nanowerk. ” The next stage of our work will be to demonstrate diagnostics in the smart dental brace in which sensors are able to detect the pressure exerted by aligners on teeth. This might help orthodontists estimate the force required by aligners; thus providing both diagnostic and treatment capabilities in dental braces. “
The scientific core of the team’s findings is to approach flexible energy storage solutions in a way that is pragmatic, fast and well integrated with other components. A major challenge to integrate any traditional lithium-based energy storage is their toxicity. The scientists circumvented this issue by introducing non-toxic micro-scale flexible batteries to be used as on-demand power supply.
Furthermore, they integrated near-infrared (NIR) capability as well as an optoelectronic system of light emitting diodes (LED) arrays in a personalized, 3D-printed semi-transparent dental brace. Of course, such a device would not have been possible without an appropriate energy storage solution.
Key to this smart brace is the use of a high-performance flexible solid-state microbattery. A standalone all thin-film lithium-ion battery already can be readily thinned down to about 30 microns thickness to achieve flexibility. The team’s flexing process for thin-film-based micro-batteries achieves two major objectives: 1) utilization of mature and reliable CMOS process with 90% yield and repeated electrochemical measurements on multiple devices, and 2) the ability to withstand high annealing temperatures of cathode material or soldering that are unachievable using direct film deposition on plastic substrates.
“Our flexile biocompatible lithium-ion battery can be transferred on polyethylene terephthalate (PET) and interconnected via aluminum engraved interconnections to create a battery module,” explains Hussain. “During testing we found that the battery module exhibits minimal strain while most of the stress is experienced by the PET film.”
Continuous intra-oral NIR light therapy for patients is becoming a growing necessity for accelerating the rate of the bone remodeling process. Near-infrared light can be absorbed by bone cells to stimulate the bone regeneration for faster orthodontic treatment.
That’s why the team integrated near-infrared LEDs with the flexible batteries and interconnected them on a soft PET substrate. The whole device is embedded in semi-transparent 3D-printed brace.
To summarize, this smart dental brace relies on two main functionalities: Firstly, a customizable, personalized, and semitransparent brace, which provides required external loading to stimulate healthy rebuilding of bone structures. Secondly, a miniaturized, soft, biocompatible optoelectronic system for an intraoral (conformable on the mouth) near-infrared light therapy, which allows rapid, temporally specific control of osteogenic cell activity via targeted exposure and light sensitive proteins present in bone cells.
“The combination of both strategies in one single platform provides affordable, multifunctionality dental braces,” concludes Hussain. “Such capability enhances the bone regeneration significantly and reduces the overall cost and discomfort. Our future work will include integration of compliant soft-substrate-based LEDs and miniaturized ICs with enhanced wireless capability for smart gadget-based remote control for cleaning and therapy.”