More Powerful Computing Possible from Ultra-thin memory storage device: University of Texas, Austin


ultrathinmemIllustration of a voltage-induced memory effect in monolayer nanomaterials, which layer to create “atomristors,” the thinnest memory storage device that could lead to faster, smaller and smarter computer chips. Credit: Cockrell School of Engineering, The University of Texas at Austin

Engineers worldwide have been developing alternative ways to provide greater memory storage capacity on even smaller computer chips. Previous research into two-dimensional atomic sheets for memory storage has failed to uncover their potential—until now.

A team of electrical engineers at The University of Texas at Austin, in collaboration with Peking University scientists, has developed the thinnest  device with dense  capacity, paving the way for faster, smaller and smarter computer chips for everything from consumer electronics to big data to brain-inspired computing.

“For a long time, the consensus was that it wasn’t possible to make memory devices from materials that were only one atomic layer thick,” said Deji Akinwande, associate professor in the Cockrell School of Engineering’s Department of Electrical and Computer Engineering. “With our new ‘atomristors,’ we have shown it is indeed possible.”

Made from 2-D nanomaterials, the “atomristors”—a term Akinwande coined—improve upon memristors, an emerging memory storage technology with lower memory scalability. He and his team published their findings in the January issue of Nano Letters.

“Atomristors will allow for the advancement of Moore’s Law at the system level by enabling the 3-D integration of nanoscale memory with nanoscale transistors on the same chip for advanced computing systems,” Akinwande said.

Memory storage and transistors have, to date, always been separate components on a microchip, but atomristors combine both functions on a single, more efficient computer system. By using metallic  (graphene) as electrodes and semiconducting atomic sheets (molybdenum sulfide) as the active layer, the entire memory cell is a sandwich about 1.5 nanometers thick, which makes it possible to densely pack atomristors layer by layer in a plane. This is a substantial advantage over conventional flash memory, which occupies far larger space. In addition, the thinness allows for faster and more efficient electric current flow.

Given their size, capacity and integration flexibility, atomristors can be packed together to make advanced 3-D chips that are crucial to the successful development of brain-inspired computing. One of the greatest challenges in this burgeoning field of engineering is how to make a memory architecture with 3-D connections akin to those found in the human brain.

“The sheer density of memory  that can be made possible by layering these synthetic atomic sheets onto each other, coupled with integrated transistor design, means we can potentially make computers that learn and remember the same way our brains do,” Akinwande said.

The research team also discovered another unique application for the technology. In existing ubiquitous devices such as smartphones and tablets, radio frequency switches are used to connect incoming signals from the antenna to one of the many wireless communication bands in order for different parts of a device to communicate and cooperate with one another. This activity can significantly affect a smartphone’s battery life.

The atomristors are the smallest radio frequency memory switches to be demonstrated with no DC battery consumption, which can ultimately lead to longer battery life.

“Overall, we feel that this discovery has real commercialization value as it won’t disrupt existing technologies,” Akinwande said. “Rather, it has been designed to complement and integrate with the silicon chips already in use in modern tech devices.”

 Explore further: A more efficient way to write data into non-volatile memory devices improves their performance

More information: Ruijing Ge et al, Atomristor: Nonvolatile Resistance Switching in Atomic Sheets of Transition Metal Dichalcogenides, Nano Letters (2017). DOI: 10.1021/acs.nanolett.7b04342

 

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Promising New Research for High Performance Lithium Batteries – Engineering 2D Nanofluidic Channels


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Abstract: In article number 1703909, Gang Chen, Guihua Yu, and co-workers present a novel concept of 2D nanofluidic lithium-ion transport channels based on stacked Co3O4nanosheets for high-performance lithium batteries. This unique nanoarchitecture exhibits exceptional capacity and outstanding long-term cycling stability for lithium-ion storage at high-rates in both half- and full-cells.

 

Despite being a promising electrode material, bulk cobalt oxide (Co3O4) exhibits poor lithium ion storage properties. Nanostructuring, e.g. making Co3O4 into ultrathin nanosheets, shows improved performance, however, Co3O4-based nanomaterials still lack long-term stability and high rate capability due to sluggish ion transport and structure degradation.

Nanofluidic channels possess desired properties to address above issues. However, while these unique structures have been studied in hollow nanotubes and recently in restacked layered materials such as graphene, it remains challenging to construct nanofluidic channels in intrinsically non-layered materials.
Motived by the large number of non-layered materials, e.g. transition metal oxides, which hold great promise in battery applications, scientists aim to extend the concept of nanofluidic channels into these materials and improve their electrochemical properties.
Nanofluidic channels feature a unique unipolar ionic transport when properly designed and constructed. By controlling surface charge and channel spacing, enhanced and selective ion transport can be achieved in these channels by constructing them with dimensions comparable to the double Debye length and opposite surface charge with respect to the transporting ion.
In a new study published in Advanced Materials (“Engineering 2D Nanofluidic Li-Ion Transport Channels for Superior Electrochemical Energy Storage”), researchers have developed a Co3O4-based two-dimensional (2D) nano-architecture possessing nanofluidic channels with specially designed interlayer characteristics for fast lithium ion transport, leading to exceptional performance in lithium ion batteries ever reported for this material.
“Such constructed 2D nanofluidic channels in non-layered materials manifest a general structural engineering strategy for improving electrochemical properties in a vast number of different electrode materials,” Guihua Yu, a professor in Materials Science and Engineering, Mechanical Engineering, at the Texas Materials Institute, University of Texas at Austin. “The enhanced and selective ion transport demonstrated in our study is of broad interest to many applications where fast kinetics of ion transport is essential.”
Illustration of lithium ion transport in the 2D nanofluidic channels
Illustration of lithium ion transport in 2D nanofluidic channels. (Reprinted with permission by Wiley-VCH)
On the one hand, an intercalated molecule acts as interlayer pillar in the stacked oxide, constituting transport channels with proper spacing. On the other hand, negatively charged functional groups anchored on the nanosheets surface facilitate transport of positively charged lithium ions inside the channels.
“Satisfying aforementioned conditions for unipolar ionic transport, combined with other advantageous features – extra storage capacity contributed by the surface functional groups, buffered structural stress from the interlayer spacing, and shortened lithium ion diffusion distance due to the ultrathin nanosheet morphology – the resulting nanoarchitecture exhibit exceptional electrochemical performance as tested in lithium-ion batteries,” notes Yu.
In a next step, the researchers are going to extend the concept of 2D nanofluidic channels to other electrode materials with or without layering structures. With ability to further tune interlayer spacing, they expect some promising energy storage applications in beyond-lithium-ion batteries.
It might also be interesting to examine this structural engineering strategy in other applications, for example, catalysis.
Design and LIBs application of Co3O4 nanosheets with 2D nanofluidic channels
Design and LIBs application of Co3O4 nanosheets with 2D nanofluidic channels. (a) The synthetic route from Co-based layered hydroxide precursor to Co3O4 nanosheets with 2D nanofluidic channels. (b) Cycling performance of a full cell (anode: Co3O4 nanosheets /cathode: commercial LiCoO2). (Reprinted with permission by Wiley-VCH)
Constructing 2D nanofluidic channels for energy storage application is still in its infancy and the success of using non-layered materials demonstrated in this study promises a bright future in this direction with a broader material coverage.
“We are also taking this research direction even further by looking into the transport and storage properties for energy storage systems based on larger charge-carrying ions, such as Na+ and Mg2+, ” concludes Yu. “In order to realize that, an important challenge is to tune the channel spacing in a controlled manner. It is also imperative to investigate structural stability and scalability of this specially designed nanoarchitecture for its utilization in practical applications.”
@Michael Berger © Nanowerk

BEYOND LITHIUM PROJECTS: TESLA’S PARTNER PANASONIC HINTS AT ELECTRIC VEHICLE BATTERY IMPROVEMENTS


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Lithium-ion batteries represent a landmark technology that has made the current generation of electric vehicles possible. However, the day of their demise, while it still lies years in the future, is within view. Lithium-ion chemistries have a certain maximum energy density, dictated by those pesky laws of physics, and today’s batteries are not so far from that theoretical maximum. If drivers keep demanding longer ranges and faster charging times, then a better technology will have to be found.

Above: Panasonic’s 18650 lithium-ion battery cell used in the Tesla Model S and X (Image: Daily Sabah)

Safety is also an issue. The spectacular explosions and fireballs that some documentary-makers revel in are not the norm (when was the last time your phone or computer caught fire?), but Li-ion batteries do have to be handled carefully, and necessary safety features add complexity and cost to battery packs. A new chemistry that is safer could also prove to be cheaper.

Researchers around the world are working on “beyond lithium” projects, and the past year has seen several significant breakthroughs. Of course, advances in the lab take years to make their way to the marketplace, but if and when one of these promising technologies can be commercialized, we could see game-changing improvements in the performance and cost of EVs.

One technology that’s been getting a tremendous amount of attention from researchers is the solid-state battery, which uses a solid electrolyte instead of the liquid electrolyte used today. Solid-state batteries could theoretically have double the energy density of current batteries, and last several times longer. They also use a non-flammable electrolyte – usually glass, polymer, or a combination – so they would eliminate the safety issues that plague Li-ion cells.

Read About: Lithium-ion battery inventor (Dr. John Goodenough – UT Ausitn – introduces new technology for fast-charging, noncombustible batteries – Is it “Goodenough?”

Above: Lithium-ion battery vs. solid state battery (Image: Toyota)

Lithium-air batteries likewise could offer far greater energy density – maybe as much as 10 times more – but they suffer from poor cycle life. In 2015, Cambridge scientists wowed the battery world with an announcement that they had demonstrated a highly efficient and long-lasting lithium-oxygen battery. Alas, researchers from several universities and national labs have since been unable to duplicate the original results.

Other promising battery chemistries use other elements in place of lithium. Sodium batteries powered Jules Verne’s futuristic submarine in “20,000 Leagues Under the Sea.” More recently, in 2015, researchers created a prototype sodium-ion battery in the industry-standard 18650 cylindrical format.

According to a recent article in the Nikkei Asian Review, battery research has seen a big shift in recent years. At one time, nearly half of the presentations at the Battery Symposium in Japan were about fuel cells and Li-ion battery cathode materials. But since 2012, these topics have been supplanted by presentations about solid-state, lithium-air and non-lithium batteries.

Above: How a lithium-air battery works (Image: Money Inc)

Toyota has been focusing on solid-state and Li-air batteries. At the latest Battery Symposium, battery researcher Shinji Nakanishi discussed a scenario for transitioning from Li-ion batteries to solid-state and then Li-air batteries. “We want our electric cars to go 500 km” on a single charge, he said. “And for this, we want rechargeable batteries that can generate 800 to 1,000 watt-hours per liter.” That would be two to three times the energy density of today’s best Li-ion batteries.

Panasonic, Tesla’s battery supplier, is also taking a hard look at solid-state technology. “We think the existing technology can still extend the energy density of Li-ion batteries by 20% to 30%,” President Kazuhiro Tsuga told Nikkei. “But there is a trade-off between energy density and safety. So if you look for even more density, you have to think about additional safety technology as well. Solid-state batteries are one answer.”

Engineers have been pushing the limits of Li-ion technology for decades. Today’s best Li-ion cells can reach an energy density of about 300 watts per kilogram, *** which is getting close to the theoretical maximum. “Existing Li-ion batteries still have room to improve their energy density because you can raise the density by introducing a nickel-based cathode material, so you can expect the batteries will still be used in the next few years,” said battery expert Naoaki Yabuuchi of Tokyo Denki University. He expects lithium-ion technology to reach its limits around 2020.

Above: Tesla Model X on display at Panasonic’s booth at CES (Image: Business Wire)

Is Tesla working on any of these post-lithium chemistries? It would be strange if they were not. We know that the company is constantly evaluating new battery technologies. “Tesla has one of the largest cell characterization laboratories in the world – we have just about every cell you can imagine on test,” Tesla Product Planner Ted Merendino told me back in 2013. However, both Elon Musk and JB Straubel have said that so far, they’ve seen no viable replacement for lithium-ion, and believe me, they’ve been asked the question many times.

Tesla Model 3hqdefault“We have yet to see even a single example… of a cell working at the laboratory level that is better than the one that we have, or the ones that we expect to come out with,” said Elon Musk in 2014. Now, the way I parse this statement, he isn’t saying that there’s no improved battery technology in the offing – on the contrary, he’s saying that Tesla will be the one to develop it.

When Model 3 was announced, some EV-watchers opined that, in order to deliver the new vehicle at the desired price point, Tesla would need to make a major battery breakthrough. In the event, Tesla has developed a new battery for Model 3, but it looks more like an incremental improvement than a paradigm shift. The new 2170 cell, which is now being produced at the Gigafactory, is slightly larger than the trusty 18650, and can store more energy. According to Elon Musk, it’s “the highest energy density cell in the world, and also the cheapest.” Advances in the way the cells are assembled into modules and packs are also expected to yield a significant reduction in battery costs.

Above: Tesla’s battery pack in the floorpan of the Model S (Image: First Reporter)

So, it appears that lithium will continue its reign for a few more years at least. However, the post-lithium Holy Grail is still out there, and as likely as not, the knights of Tesla’s round table will be the ones to bring it home. Battery superstar Jeff Dahn and his colleagues aren’t working for Tesla just to make speeches at conferences. It’s entirely possible that, at some super-secret facility in California or Nevada, test mules are being powered by solid-state or lithium-air batteries even as we speak.

*** New Li-Io Technology Reports 400-500 Wh/kg with a $200/ kWh Cost

UT Austin & Stony Brook U Team Up to Construct Polymer Gels at the Nanoscale to Improve Cycling & Performance of Li-Io Batteries


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The electrode in lithium-ion (Li-ion) batteries is an integrated system in which both active materials and binder systems play critical roles in determining its final properties. In order to improve battery performance, a lot of research is focussing on the development of high-capacity active materials. However, without an efficient binder system, these novel materials can’t fulfill their potentials.A group of researchers now has contributed to this field from a slight different aspect, developing a high-performance and general binder system for batteries.

This entirely new binder system with a nano-architecture promotes both electron and ion transport, which enhances the energy per unit mass and volume of the electrode.This work by Guihua Yu group at University of Texas at Austin and Esther Takeuchi group at Stony Brook University, demonstrates a new generation of nanostructured conductive polymer gel based novel binder materials for fabrication of high-energy lithium-ion battery electrodes.

This gel framework could become a next-generation binder system for commercial Li-ion batteries.”Compared to conventional binder system which typically consists of conductive additive and polymer binder, our novel binder plays dual functionalities simultaneously combining conductive and adhesive features, thus greatly improving the better utility of active electrode materials,”Professor Yu tells Nanowerk. “More importantly, owing to its unique 3D network structure, this gel binder promotes both electron and ion transport in electrode and improves the distribution of active particles, thus enhancing the rate performance and cycle life of battery electrodes.”

He points out that this invention is important because it presents a new generation of powerful yet scalable binder materials for lithium ion batteries that show great potential in industrial manufacturing.This novel gel binder can overcome the drawbacks of conventional binder systems, leading to next-generation lithium ion battery with high performance.The researchers have reported their findings in two papers in Nano Letters (“Nanostructured Conductive Polymer Gels as a General Framework Material To Improve Electrochemical Performance of Cathode Materials in Li-Ion Batteries”) and Advanced Materials (“A Tunable 3D Nanostructured Conductive Gel Framework Electrode for High-Performance Lithium Ion Batteries”).

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Schematic of synthetic and structural features of commercial lithium iron phosphate (C-LFP)/cross-linked polypyrrole (C-PPy) hybrid gel framework. The conductive polymer chains can be polymerized in situ with electrode materials and cross-linked by molecules with multiple functional groups, resulting in a polymeric network connecting all active particles. (Reprinted with permission by American Chemical Society) (click on image to enlarge)”

Li Io Polymer id46234xA traditional binder system in Li-ion battery electrodes is a binary hybrid with components acting separate functionalities,” explains Yu. “In such system, polymer binders such as polyvinylidene fluoride (PVDF) adhere the active materials and other additives together to hold the mechanical integrity while a conductive additive (usually carbon particles) ensures the conductivity of the entire electrode.”In these electrodes, electrons transport through chains of particles while ions move through the liquid or solid electrolyte that fills the pores of the electrode.

However, the conductive phases are randomly distributed, which may lead to bottlenecks and poor contacts that impede effective access to parts of the battery.And both organic and inorganic components tend to aggregate, which also negatively impact electron and ion transport.The team’s novel conductive gel binder can overcome these drawbacks and thus improve the rate and cyclic performance of Li-ion batteries.

The conductive polymer gels potentially could also be used for responsive/smart electronics such as biosensors, artificial skins and soft robotics.The scientific core of this work is that three-dimensional nanostructured conductive polymer gels can be built up by tunable molecule crosslinking and this unique conductive framework material can promote the electron/ion transport within battery electrodes.”Firstly, our work provides a new method for synthesis of conductive polymer gel,” elaborates Yu. “Traditionally, conductive polymer gels are synthesized by template-based method, which usually results in low conductivity and poor mechanical properties.

The method we developed is to crosslink conductive polymer chains with functional molecules with multiple functional groups, enabling a network, interconnected structure promoting high electronic conductivity and electrochemical activity.””Secondly, we demonstrated that this newly developed conductive polymer gel can be used as binder system and significantly improve conventional lithium-ion battery performance owing to their advantageous structural features,” he continues. “The ease of processability and excellent chemical and physical properties of these nanostructured conductive gels enable a new class of binder materials for fabricating next-generation high-energy lithium-ion batteries.”Although the researchers’ binder gel is mechanically strong, it lacks flexibility and stretchability.

The plan is to further modify the mechanical properties by tailoring the molecular backbones of conductive polymers through the addition of side chains or other building block polymers.The scientists further intend to demonstrate the versatility of their gel binders for other important electrode materials, such as some commercial electrode materials, as well as some next-generation ultrahigh-capacity materials, such as silicon, and sulfur.

Micheal Berger/ Nanowerk   UT Austin Stony Brook University