Electrodes Push Charging Rate Limits in Energy Storage: Using MXene in Electrode Design: Drexel University


Drexel Energy Storage Electrodes Key rd1707_MXene-electrode-crop

Drexel researchers developed electrode designs using MXene that allow for much faster charging because they open up paths for ions to quickly travel within the material. Source: Drexel University

 

Can you imagine fully charging your cell phone in just a few seconds? Researchers in Drexel University’s College of Engineering can, and they took a big step toward making it a reality with their recent work unveiling of a new battery electrode design in the journal Nature Energy.

The team, led by Yury Gogotsi, PhD,Distinguished University and Bach professor in Drexel’s College of Engineering, in the Department of Materials Science and Engineering, created the new electrode designs from a highly conductive, two-dimensional material called MXene. Their design could make energy storage devices like batteries, viewed as the plodding tanker truck of energy storage technology, just as fast as the speedy supercapacitors that are used to provide energy in a pinch — often as a battery back-up or to provide quick bursts of energy for things like camera flashes.

“This paper refutes the widely accepted dogma that chemical charge storage, used in batteries and pseudocapacitors, is always much slower than physical storage used in electrical double-layer capacitors, also known as supercapacitors,” Gogotsi said. “We demonstrate charging of thin MXene electrodes in tens of milliseconds. This is enabled by very high electronic conductivity of MXene. This paves the way to development of ultrafast energy storage devices than can be charged and discharged within seconds, but store much more energy than conventional supercapacitors.”

The key to faster charging energy storage devices is in the electrode design. Electrodes are essential components of batteries, through which energy is stored during charging and from which it is disbursed to power electronic devices. So the ideal design for these components would be one that allows them to be quickly charged and store more energy.

To store more energy, the materials should have places to put it. Electrode materials in batteries offer ports for charge to be stored. In electrochemistry, these ports, called “redox active sites” are the places that hold an electrical charge when each ion is delivered. So if the electrode material has more ports, it can store more energy — which equates to a battery with more “juice.”

Collaborators Patrice Simon, PhD, and Zifeng Lin, from Université Paul Sabatier in France, produced a hydrogel electrode design with more redox active sites, which allows it to store as much charge for its volume as a battery. This measure of capacity, termed “volumetric performance,” is an important metric for judging the utility of any energy storage device.

To make those plentiful hydrogel electrode ports even more attractive to ion traffic, the Drexel-led team, including researchers Maria Lukatskaya, PhD, Sankalp Kota, a graduate student in Drexel’s MAX/MXene Research Group led by Michel Barsoum, PhD,distinguished professor in the College of Engineering; and Mengquiang Zhao, PhD, designed electrode architectures with open macroporosity — many small openings — to make each redox active sites in the MXene material readily accessible to ions.

Mxene 2 containingou“In traditional batteries and supercapacitors, ions have a tortuous path toward charge storage ports, which not only slows down everything, but it also creates a situation where very few ions actually reach their destination at fast charging rates,” said Lukatskayathe first author on the paper, who conducted the research as part of the A.J. Drexel Nanomaterials Institute. “The ideal electrode architecture would be something like ions moving to the ports via multi-lane, high-speed ‘highways,’ instead of taking single-lane roads. Our macroporous electrode design achieves this goal, which allows for rapid charging — on the order of a few seconds or less.”

The overarching benefit of using MXene as the material for the electrode design is its conductivity. Materials that allow for rapid flow of an electrical current, like aluminum and copper, are often used in electric cables. MXenes are  conductive, just like metals, so not only do ions have a wide-open path to a number of storage ports, but they can also move very quickly to meet electrons there. Mikhael Levi, PhD, and Netanel Shpigel, research collaborators from Bar-Ilan University in Israel, helped the Drexel group maximize the number of the ports accessible to ions in MXene electrodes.mxene-polymer-nanocomposite-material

Use in battery electrodes is just the latest in a series of developments with the MXene material that was discovered by researchers in Drexel’s Department of Materials Science and Engineering in 2011. Since then, researchers have been testing them in a variety of applications from energy storage to electromagnetic radiation shielding, and water filtering. This latest development is significant in particular because it addresses one of the primary problems hindering the expansion of the electric vehicle market and that has been lurking on the horizon for mobile devices.

“If we start using low-dimensional and electronically conducting materials as battery electrodes, we can make batteries working much, much faster than today,” Gogotsi said. “Eventually, appreciation of this fact will lead us to car, laptop and cell-phone batteries capable of charging at much higher rates — seconds or minutes rather than hours.”

This research was supported by Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy’s Office of Science and Office of Basic Energy Sciences; as well as the National Science Foundation and Binational Science Foundation, which supported collaborations with France and Israel, respectively.

What are MXenes ?

MXenes are a new family of two-dimensional (2D) transition metal carbides, carbonitrides and nitrides that were discovered and developed in collaboration with Prof. Barsoum’s group, that can be used in many applications. These applications include lithium-ion and sodium-ion energy storage systems, electromagnetic interference (EMI) shielding, and water purification. MXenes are highly desirable in EMI shielding due to their good flexibility, easy processing, and high conductivity with minimal thickness, having the highest EMI shielding effectiveness of all synthetic materials of similar thickness. MXenes are also promising antibacterial agents, with higher efficiency than graphene oxide in diminishing bacterial cell viability.

 

 

AE_Nanomaterials_Figure 1Read More: 2D Carbides and Nitrides (MXenes)

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Creating the Future of Batteries


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We need better ways to store and use energy, that’s no secret. Cell phones need charging every day, electric cars only have a range of about a hundred miles and our ability to use solar and wind energy to feed the power grid is still very limited. These are things we’ve taken for granted, but if you look, historically, at the rate in which our technology improves — just think about cell phones and computers in the last 20 years — it’s easy to see that this area of technological development has severely lagged.

energy storage device.jpgWhile there are a number of political, philosophical and theoretical explanations for why energy storage development has fallen behind, experts agree that if the problem is going to be fixed in our lifetime, it needs to start now.

Energy storage is a limiting factor that researchers have been aware of for quite a while, but their work to improve our storage devices has taken many, disparate directions. In a recent edition of Nature Communications, Drexel materials science and engineering researchers Yury Gogotsi, PhD, and Maria Lukatskaya, PhD, who have been surveying the landscape of energy storage research for years, offer a unified route for bringing our energy storage and distribution capabilities level with our energy production and consumption.

rice-nanoporus-battery-102315-untitled-1You May Also Want To Read: Nanoporous Material Combines the Best of Batteries and Supercapacitors for ESS (Energy Storage Systems)

 

Read about the work of Dr. Jim Tour at Rice University – “Changing the Equation” for how we think about Batteries, Super Capacitors and Energy Storage.        Rice logo_rice3

 

 

Lukatskaya and Gogotsi unpacked the problem for the News Blog and offered up three ways in which energy storage research and development need to change right now to get things moving in the right direction:

 So, the directions where we want our energy storage devices — such as batteries — to go are pretty intuitive: we want them to store more energy per unit of volume (or mass) so that it would provide longer autonomy times for portable electronics without making them bulkier. We also want to enable fast charging of the devices, so that five minutes of charging would provide full-day power for device operation. And last, but not least, we want to increase the lifespan of batteries — meaning the number of charge/discharge cycles they can undergo without performance degradation.  

To achieve that, we need to rethink conventional electrode architectures and materials that are currently used in energy storage devices, such as batteries and supercapacitors.

  1. Clean up all the wasted space

For example, in state of the art batteries, too much volume is occupied by the cell components that do not store charge. It is estimated that in smaller devices more than 80 percent of the volume is occupied by the inert cell components: current collectors, separators and casings. So new design concepts that minimize use of current collectors would lead to substantial improvement in energy that can be stored per unit of mass or volume of the device.

  1. Come up with a better recipe

Secondly, new electrolyte and electrode chemistries should be explored. Currently, oxide materials dominate the “insides” of batteries. Oxides have many advantages, being among the most studied material, and they provided a reliable energy storage solution for quite a while, but in order to address growing needs for high-energy batteries, other electrode materials should be explored that have high electrical conductivity and can enable multielectron redox reactions (storing more charges per atom than lithium).

  1. Get electrons and ions on the expressway

In order to make energy storage devices fast, it is again necessary to reconsider electrode architectures to ensure rapid accessibility of ions and electrons toward active sites. Basically, we need to create such architectures where, instead of a “maze,” ions can move on “highways” providing fast charging.

 

Gogotsi is Distinguished University and Trustee Chair professor in the College of Engineering and director of the A.J. Drexel Nanomaterials Institute. Lukatskaya, was a doctoral candidate in the Department of Materials Science and Engineeringwhen she worked with Gogotsi on this research. She is now a post-doctoral research fellow at Stanford University.

You can read their Nature Communications paper “Multidimensional materials and device architectures for future hybrid energy storage” here:http://www.nature.com/articles/ncomms12647

 

“Just Add Salt” Drexel U Researchers Discover Method for Improvong Energy Storage Materials: May also offer attractive properties for Desalination Membranes and Photocatalysis


energy_storage_2013 042216 _11-13-1The secret to making the best energy storage materials is growing them with as much surface area as possible. Like baking, it requires just the right mixture of ingredients prepared in a specific amount and order at just the right temperature to produce a thin sheet of material with the perfect chemical consistency to be useful for storing energy.

A team of researchers from Drexel University, Huazhong University of Science and Technology (HUST) and Tsinghua University recently discovered a way to improve the recipe and make the resulting materials bigger and better and soaking up energy—the secret? Just add salt.

The team’s findings, which were recently published in the journal Nature Communications, show that using salt crystals as a template to grow thin sheets of conductive metal oxides make the materials turn out larger and more chemically pure—which makes them better suited for gathering ions and storing energy.

“The challenge of producing a metal oxide that reaches theoretical performance values is that the methods for making it inherently limit its size and often foul its chemical purity, which makes it fall short of predicted performance,” said Jun Zhou, a professor at HUST’s Wuhan National Laboratory for Optoelectronics and an author of the research. Our research reveals a way to grow stable with less fouling that are on the order of several hundreds of times larger than the ones that are currently being fabricated.”

In an energy storage device—a battery or a capacitor, for example—energy is contained in the chemical transfer of ions from an electrolyte solution to thin layers of conductive materials. As these devices evolve they’re becoming smaller and capable of holding an electric charge for longer periods of time without needing a recharge. The reason for their improvement is that researchers are fabricating materials that are better equipped, structurally and chemically, for collecting and disbursing ions.

In theory, the best materials for the job should be thin sheets of metal oxides, because their chemical structure and high makes it easy for ions to attach—which is how energy storage occurs. But the metal oxide sheets that have been fabricated in labs thus far have fallen well short of their theoretical capabilities.

According to Zhou, Tang and the team from HUST, the problem lies in the process of making the nanosheets—which involves either a deposition from gas or a chemical etching—often leaves trace chemical residues that contaminate the material and prevent ions from bonding to it. In addition, the materials made in this way are often just a few square micrometers in size.

Using salt crystals as a substrate for growing the crystals lets them spread out and form a larger sheet of oxide material. Think of it like making a waffle by dripping batter into a pan versus pouring it into a big waffle iron; the key to getting a big, sturdy product is getting the solution—be it batter, or chemical compound—to spread evenly over the template and stabilize in a uniform way.

“This method of synthesis, called ‘templating’—where we use a sacrificial material as a substrate for growing a crystal—is used to create a certain shape or structure,” said Yury Gogotsi, PhD, University and Trustee Chair professor in Drexel’s College of Engineering and head of the A.J. Drexel Nanomaterials Institute, who was an author of the paper. “The trick in this work is that the crystal structure of salt must match the crystal structure of the oxide, otherwise it will form an amorphous film of oxide rather than a thing, strong and stable nanocrystal. This is the key finding of our research—it means that different salts must be used to produce different oxides.”

Researchers have used a variety of chemicals, compounds, polymers and objects as growth templates for nanomaterials. But this discovery shows the importance of matching a template to the structure of the material being grown. Salt crystals turn out to be the perfect substrate for growing oxide sheets of magnesium, molybdenum and tungsten.

The precursor solution coats the sides of the salt crystals as the oxides begin to form. After they’ve solidified, the salt is dissolved in a wash, leaving nanometer-thin two-dimensional sheets that formed on the sides of the salt crystal—and little trace of any contaminants that might hinder their energy storage performance. By making oxide nanosheets in this way, the only factors that limit their growth is the size of the salt crystal and the amount of precursor solution used.

“Lateral growth of the 2D oxides was guided by salt crystal geometry and promoted by lattice matching and the thickness was restrained by the raw material supply. The dimensions of the are tens of micrometers and guide the growth of the 2D oxide to a similar size,” the researchers write in the paper. “On the basis of the naturally non-layered crystal structures of these oxides, the suitability of salt-assisted templating as a general method for synthesis of 2D oxides has been convincingly demonstrated.”

As predicted, the larger size of the oxide sheets also equated to a greater ability to collect and disburse ions from an electrolyte solution—the ultimate test for its potential to be used in energy storage devices. Results reported in the paper suggest that use of these materials may help in creating an aluminum-ion battery that could store more charge than the best lithium-ion batteries found in laptops and mobile devices today.

Gogotsi, along with his students in the Department of Materials Science and Engineering, has been collaborating with Huazhong University of Science and Technology since 2012 to explore a wide variety of materials for energy storage application. The lead author of the Nature Communications article, Xu Xiao, and co-author Tiangi Li, both Zhou’s doctoral students, came to Drexel as exchange students to learn about the University’s supercapacitor research. Those visits started a collaboration, which was supported by Gogotsi’s annual trips to HUST. While the partnership has already yielded five joint publications, Gogotsi speculates that this work is only beginning.

“The most significant result of this work thus far is that we’ve demonstrated the ability to generate high-quality 2D oxides with various compositions,” Gogotsi said. “I can certainly see expanding this approach to other oxides that may offer attractive properties for , water desalination membranes, photocatalysis and other applications.”

Explore further: New nanosheet growth technique has potential to revolutionize nanotechnology industry

More information: Nature Communications, DOI: 10.1038/NCOMMS11296

 

Nanotechnology – ‘Nano-Behavior’ Changes as the ‘Scale’ Gets Smaller


???????????????????????????????????????????????????????????????????????????????????????????To fully understand how nanomaterials behave, one must also understand the atomic-scale deformation mechanisms that determine their structure and, therefore, their strength and function.
Researchers at the University of Pittsburgh, Drexel University, and Georgia Tech have engineered a new way to observe and study these mechanisms and, in doing so, have revealed an interesting phenomenon in a well-known material, tungsten. The group is the first to observe atomic-level deformation twinning in body-centered cubic (BCC) tungsten nanocrystals.
The team used a high-resolution transmission electron microscope (TEM) and sophisticated computer modeling to make the observation. This work, published in Nature Materials (“In situ atomic-scale observation of twinning-dominated deformation in nanoscale body-centred cubic tungsten”), represents a milestone in the in situ study of mechanical behaviors of nanomaterials.
atomic-level deformation twinning in a tungsten nanowire under axial compression
The computer model (left) and experimental image reveal the atomic-level deformation twinning in a tungsten nanowire under axial compression. The lattice of the deformation-induced twin band (between yellow lines) is a mirror image of that of the parent crystal.

Deformation twinning is a type of deformation that, in conjunction with dislocation slip, allows materials to permanently deform without breaking. In the process of twinning, the crystal reorients, which creates a region in the crystal that is a mirror image of the original crystal. Twinning has been observed in large-scale BCC metals and alloys during deformation. However, whether twinning occurs in BCC nanomaterials or not remained unknown.

“To gain a deep understanding of deformation in BCC nanomaterials,” Scott X. Mao, the paper’s senior author, said, “we combined atomic-scale imaging and simulations to show that twinning activities dominated for most loading conditions due to the lack of other shear deformation mechanisms in nanoscale BCC lattices.”
The team chose tungsten as a typical BCC crystal. The most familiar application of tungsten is its use as filaments for light bulbs.
The observation of atomic-scale twinning was made inside a TEM. This kind of study had not been possible in the past due to difficulties in making BCC samples less than 100 nanometers in size as required by TEM imaging. Jiangwei Wang, a Pitt graduate student and lead author of the paper, developed a clever way of making the BCC tungsten nanowires. Under a TEM, Wang welded together two small pieces of individual nanoscale tungsten crystals to create a wire about 20 nanometers in diameter. This wire was durable enough to stretch and compress while Wang observed the twinning phenomenon in real time.
To better understand the phenomenon observed by Mao and Wang’s team at Pitt, Christopher R. Weinberger, an assistant professor in Drexel’s College of Engineering, developed computer models that show the mechanical behavior of the tungsten nanostructure—at the atomic level. His modeling allowed the team to see the physical factors at play during twinning. This information will help researchers theorize why it occurs in nanoscale tungsten and plot a course for examining this behavior in other BCC materials.
“We’re trying to see if our atomistic-based model behaves in the same way as the tungsten sample used in the experiments, which can then help to explain the mechanisms that allow it to behave that way,” Weinberger said. “Specifically, we’d like to explain why it exhibits this twinning ability as a nanostructure but not as a bulk metal.”
In concert with Weinberger’s modeling, Ting Zhu, an associate professor of mechanical engineering at Georgia Tech, worked with a graduate student, Zhi Zeng, to conduct advanced computer simulations using molecular dynamics to study deformation processes in 3-D.
Zhu’s simulation revealed that tungsten’s “smaller is stronger” behavior is not without drawbacks when it comes to applications.
“If you reduce the size to the nanometer scale, you can increase strength by several orders or magnitude,” Zhu said. “But the price you pay is a dramatic decrease in the ductility.
We want to increase the strength without compromising the ductility in developing these nanostructured metals and alloys. To reach this objective, we need to understand the controlling deformation mechanisms.”
The twinning mechanism, Mao added, contrasts with the conventional wisdom of dislocation nucleation-controlled plasticity in nanomaterials. The results should motivate further experimental and modeling investigation of deformation mechanisms in nanoscale metals and alloys, ultimately enabling the design of nanostructured materials to fully realize their latent mechanical strength.
“Our discovery of the twinning dominated deformation also opens up possibilities of enhancing ductility by engineering twin structures in nanoscale BCC crystals,” Zhu said.
Source: University of Pittsburgh

Read more: Understanding nanotechnology – why a material’s behavior changes as it gets smaller

Bending but not breaking: In search of new materials


1-Drexal 141110161040-largeMaking a paper airplane in school used to mean trouble. Today it signals a promising discovery in materials science research that could help next-generation technology -like wearable energy storage devices- get off the ground. Researchers at Drexel University and Dalian University of Technology in China have chemically engineered a new, electrically conductive nanomaterial that is flexible enough to fold, but strong enough to support many times its own weight. They believe it can be used to improve electrical energy storage, water filtration and radiofrequency shielding in technology from portable electronics to coaxial cables.

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MXene-polymer nanocomposite material, created by researchers at Drexel University, is both strong and conductive and flexible enough to fold.
Credit: Drexel University

Finding or making a thin material that is useful for holding and disbursing an electric charge and can be contorted into a variety of shapes, is a rarity in the field of materials science. Tensile strength -the strength of the material when it is stretched- and compressive strength -its ability to support weight- are valuable characteristics for these materials because, at just a few atoms thick, their utility figures almost entirely on their physical versatility.

“Take the electrode of the small lithium-ion battery that powers your watch, for example, ideally the conductive material in that electrode would be very small -so you don’t have a bulky watch strapped to your wrist- and hold enough energy to run your watch for a long period of time,” said Michel Barsoum, PhD, Distinguished Professor in the College of Engineering. “But what if we wanted to make the watch’s wristband into the battery? Then we’d still want to use a conductive material that is very thin and can store energy, but it would also need to be flexible enough to bend around your wrist. As you can see, just by changing one physical property of the material -flexibility or tensile strength- we open a new world of possibilities.”

This flexible new material, which the group has identified as a conductive polymer nanocomposite, is the latest expression of the ongoing research in Drexel’s Department of Materials Science and Engineering on a family of composite two-dimensional materials called MXenes.

This development was facilitated by collaboration between research groups of Yury Gogotsi, PhD, Distinguished University and Trustee Chair professor in the College of Engineering at Drexel, and Jieshan Qiu, vice dean for research of the School of Chemical Engineering at Dalian University of Technology in China. Zheng Ling, a doctoral student from Dalian, spent a year at Drexel, spearheading the research that led to the first MXene-polymer composites. The researchat Drexel was funded by grants from the National Science Foundation and the U.S. Department of Energy.

The Drexel team has been diligently examining MXenes like a paleontologist carefully brushing away sediment to unearth a scientific treasure. Since inventing the layered carbide material in 2011 the engineers are finding ways to take advantage of its chemical and physical makeup to create conductive materials with a variety of other useful properties.

One of the most successful ways they’ve developed to help MXenes express their array of abilities is a process, called intercalation, which involves adding various chemical compounds in a liquid form. This allows the molecules to settle between the layers of the MXene and, in doing so, alter its physical and chemical properties. Some of the first, and most impressive of their findings, showed that MXenes have a great potential for energy storage.

To produce the flexible conductive polymer nanocomposite, the researchers intercalated the titanium carbide MXene, with polyvinyl alcohol (PVA) -a polymer widely used as the paper adhesive known as school or Elmer’s glue, and often found in the recipes for colloids such as hair gel and silly putty. They also intercalated with a polymer called PDDA (polydiallyldimethylammonium chloride) commonly used as a coagulant in water purification systems.

“The uniqueness of MXenes comes from the fact that their surface is full of functional groups, such as hydroxyl, leading to a tight bonding between the MXene flakes and polymer molecules, while preserving the metallic conductivity of nanometer-thin carbide layers. This leads to a nanocomposite with a unique combination of properties,” Gogotsi said.

The results of both sets of MXene testing were recently published in the Proceedings of the National Academy of Sciences. In the paper, the researchers report that the material exhibits increased ability to store charge over the original MXene; and 300-400 percent improvement in strength.

“We have shown that the volumetric capacitance of an MXene-polymer nanocomposite can be much higher compared to conventional carbon-based electrodes or even graphene,” said Chang Ren, Gogotsi’s doctoral student at Drexel. “When mixing MXene with PVA containing some electrolyte salt, the polymer plays the role of electrolyte, but it also improves the capacitance because it slightly enlarges the interlayer space between MXene flakes, allowing ions to penetrate deep into the electrode; ions also stay trapped near the MXene flakes by the polymer. With these conductive electrodes and no liquid electrolyte, we can eventually eliminate metal current collectors and make lighter and thinner supercapacitors.”

The testing also revealed hydrophilic properties of the nanocomposite, which means that it could have uses in water treatment systems, such as membrane for water purification or desalinization, because it remains stable in water without breaking up or dissolving.

In addition, because the material is extremely flexible, it can be rolled into a tube, which early tests have indicated only serves to increase its mechanical strength. These characteristics mark the trail heads of a variety of paths for research on this nanocomposite material for applications from flexible armor to aerospace components. The next step for the group will be to examine how varying ratios of MXene and polymer will affect the properties of the resulting nanocomposite and also exploring other MXenes and stronger and tougher polymers for structural applications.


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The above story is based on materials provided by Drexel University. Note: Materials may be edited for content and length.