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Silicon and Graphene Combo Finally Achieve Lithium-Ion Battery Greatness
By Dexter Johnson Posted 31 Mar 2016 | 20:00 GMT
Illustration: Kansas State University/Nature Communications Silicon, graphene, and sometimes the two of them combined together have all been suggested as potential replacements for graphite in the electrodes of lithium-ion batteries.
While all three of these options bring attractive properties to the table—most importantly, a very high theoretical capacity—those properties are lost in the real world. Silicon electrodes crack and break after just a short number of charge/discharge cycles. Meanwhile, the use of graphene on electrodes is limited because graphene’s attractive surface area is only possible in single stand-alone sheets, which don’t provide enough volumetric capacitance. Layer the graphene sheets on top of each other to gain that volumetric capacity, and you begin to lose that attractive surface area.
Now researchers at Kansas State University (KSU) claim to have developed a technique that uses silicon oxycarbide that makes the combination of silicon and graphene achieve its expected greatness as an electrode material.
“Silicon combined with graphene is better than a bulk silicon electrode,” explained Gurpreet Singh, an associate professor at KSU and one of the researchers, in an e-mail interview with IEEE Spectrum. “However, nano-silicon/graphene electrodes fail to satisfy key requirements for any practical applications.” Among other things, they have poor volumetric capacity, high cost, and low cycling efficiency—too much lithium is lost irreversibly with each charge-discharge cycle. What’s more, their mechanical and chemical instability that can lead to rapid capacity decay.
To overcome this, the KSU researchers turned to the high temperature glass ceramic, silicon oxycarbide. In research described in the journal Nature Communications, the KSU team created a self-standing anode material consisting of silicon oxycarbide glass particles embedded into a chemically modified graphene oxide matrix.
A heated silicon resin decomposes so that “the constituent silicon, carbon, and oxygen atoms are arranged in a random 3-D structure, and any excess carbon precipitates out into string-like or cellular regions. Such an open 3-D structure renders large sites for reversible lithium storage and smooth channels for solvated lithium-ion transportation from the electrolyte.”
This stands in stark contrast to crystalline silicon, which undergoes an alloying reaction with lithium that results in enormous volume changes and also an irreversible reaction with the electrolyte that leads to chemical instability and fading capacity as the charge-discharge cycles add up.
The KSU researchers claim that the electrode has a capacity of approximately 600 miliampere-hour per gram or 400 miliampere-hour per cubic centimeter of the electrode after 1020 cycles. The researchers expect that the power density (the maximum amount of power that can be supplied per unit mass) will be more than three times that of today’s Li-ion batteries.
In future research, the KSU team aims to produce electrode materials with larger dimensions. As a benchmark, the researchers are looking at today’s pencil cell battery that uses a graphite-coated copper foil electrode, which is more than 30 cm in length.
Singh added: “We are also looking at batteries as structural materials, such as load bearing batteries that can be charged and discharged while under dynamic loads.”
(From left) T. Phanindra Sai, Amogh Kinikar, Arindam Ghosh resorted to mechanical exfoliation to make graphene conduct current along the edge.
The new way of making graphene with a perfect edge structure was the key to success Researchers from the Indian Institute of Science (IISc), Bengaluru have been able to experimentally produce a new type of electrical conductor that was theoretically predicted nearly 20 years ago.
A team led by Arindam Ghosh from the Department of Physics, IISc successful produced graphene that is single- or a few-layers thick to conduct current along one particular edge — the zigzag edge. The zigzag edge of graphene layer has a unique property: It allows flow of charge without any resistance at room temperature and above.
“This is the first we found the perfect edge structure in graphene and demonstrated electrical conductance along the edge,” says Prof. Ghosh. The results of the study were published in the journal Nature Nanotechnology.
A few-layers-thick graphene that conducts current along one edge does not experience any resistance and so can lead to realising power-efficient electronics and quantum information transfer, even at room temperature.
Getting an edge
Many groups over the world have been trying to access these edges since the emergence of graphene in 2004, but have been largely unsuccessful because when current flows through graphene, it flows through both the edge as well as the bulk. “We succeeded in this endeavour by creating the bulk part of graphene extremely narrow (less than 10 nanometre thick), and hence highly resistive, thus forcing the current to flow through the edge alone,” he says.
“While the bulk is totally insulating, the edge alone has the ability to conduct because of the unique quantum mechanics of the edge. Because of the zigzag orientation of carbon atoms [resulting from the hexagonal lattice], the electron wave on each carbon atom overlaps and forms a continuous train of wave along the edge. This makes the edge conducting,” explains Prof. Ghosh. The edge will remain conductive even if it is very long but has to be chemically and structurally pristine.
In the past, others researchers had tried making narrow graphene through chemical methods. But the use of chemicals destroys the edges. So the IISc team resorted to mechanical exfoliation to make graphene that are single- and few-layers thick. They used a small metal robot to peel the graphene from pyrolytic graphite. “If you take a metal tip and crash it on graphite and take it back, a part of the graphite will stick to the tip. The peeling was done slowly and gradually (in steps of 0.1 Å),” says Amogh Kinikar from the Department of Physics at IISc and the first author of the paper.
Effect of chemicals
The exfoliation was carried out at room temperature but under vacuum and the electrical conductance was measured at the time of exfoliation before the pristine nature of the edge was affected. The unsatisfied bonds of the carbon atoms make them highly reactive and they tend to react with hydrogen present in the air. “The edges conduct without any resistance as long as the edges don’t come in contact with any chemicals,” says Prof. Ghosh. “It is very easy to passivate [make the surface unreactive by coating the surface with a thin inert layer] the edges to prevent contamination [when narrow graphene is used for commercial purposes].”
As the carbon atoms have a hexagonal structure, exfoliation is by default at 30 degree angle and one of the edges has a zigzag property. “The steplike changes observed for small values of conductance when other variables were changed were surprising. Through theoretical work we were able to link this to edge modes in graphene,” says Prof. H.R.Krishnamurthy from the Department of Physics, IISc and one of the authors of the paper.
There are currently several chemical methods to produce very narrow graphene nanoribbons. But these chemicals tend to destroy the edges. “So the challenge is to produce graphene nanoribbons using chemicals that do not destroy the edges,” Prof. Ghosh says. “We believe that this successful demonstration of the dissipation-less edge conduction will act as great incentive to develop new chemical methods to make high-quality graphene nano-ribbons or nano-strips with clean edges.”
I was looking for any concrete laced with graphene news, and I found this story. I'm posting it because it has a graphite company, Zenyata (ZEN on the Israeli exchange) that is developing graphene for concrete, and is investable if you have access to the Israeli market (I don't).
I am not sure how these graphite to graphene plays will work out against the other mass production forms that don't use graphite and have showed promise recently, but there are a bunch of them out there.
Zenyatta Ventures Graphene – Wonder material makes concrete stronger
By now most investors have heard of the new wonder material called graphene. This single carbon atom super material can be derived from natural graphite. Graphene can truly be called the material of the future as it is 200 times stronger than steel but very flexible, and it conducts electricity better than any other material. Graphene is so thin that it may be thought of as two-dimensional and can be mixed with all manner of materials to increase strength. Due to these and other properties, it has the potential to literally revolutionize several industries. Thousands of researchers all over the world are working to develop many disruptive and game changing graphene applications. One such revolutionary application is the addition of graphene to cement creating a strong and environmentally “green” concrete.
Zenyatta Ventures Ltd. (TSXV-ZEN) partnership with Ben-Gurion University (‘BGU’) and Larisplast Ltd. is putting the junior mining company on the leading edge of a graphene concrete application because of its purity and crystallinity derived from a rare igneous (or volcanic) style of graphite. The deposit, called Albany, is especially well suited to form graphene from graphite as noted by scientists from BGU and Lakehead University in Thunder Bay.
Zenyatta is traded on the US OTC under ticker ZENYF. Company is actually Canadian-based (their Albany graphite deposit is located in Northern Ontario). Its main listing is on the Toronto Stock Exchange. The NR you made reference to is regarding a partnership with an Israeli University named Ben-Gurion. Here's the 5-year chart on ZENYF (been quite a ride!)...there's a number of active SI Zenyatta boards that you can also easily find if interested:
also just ran into this interview uploaded a few days ago with CEO Aubrey J. Eveleigh of Zenyatta Ventures Ltd. (OTCQX: ZENYF)....basically they have an extremely rare form of graphite called "volcanic graphite" (vs. the flake type graphite that is very abundant). Mr. Eveleigh really gets into the graphene interest for their graphite at 1:30....says that every single corporation is working on graphene applications right now (at 2:07)....at 3:16 gets into the concrete application for graphene and their graphite:
Zenyatta's graphene oxide tested by U.S. materials firm
2017-05-16 09:28 ET - News Release
Mr. Aubrey Eveleigh reports
ZENYATTA NANO-MATERIAL SUCCESSFULLY TESTED IN ADVANCED SILICON-GRAPHENE ANODE FOR NEW LITHIUM ION BATTERIES BY A U.S. BASED ADVANCED MATERIALS COMPANY
Zenyatta Ventures Ltd.'s graphene oxide material has been successfully tested by a leading U.S.-based advanced materials company (U.S. Co.) developing silicon-graphene anodes for the next generation of lithium-ion batteries. Preliminary results show ease of processing with Zenyatta's graphene oxide and similar electrochemical performance compared with the control material that is currently being used by U.S. Co. The superior dispersion qualities and good electrochemical performance of the company's graphene oxide are desirable properties for this silicon-graphene battery application. Zenyatta's high-purity graphite was recently converted to graphene oxide by Dr. Aicheng Chen, professor at Lakehead University, and then sent to the U.S. Co. for testing as an advanced nanomaterial in a new lithium-ion battery.
Lithium-ion batteries are widely used globally for portable electronic devices and electric vehicles. Unfortunately, lithium-ion batteries still lack the required level of energy storage to completely meet the demands of such applications as electric vehicles. A new silicon-graphene composite anode enables higher-capacity and faster-charging batteries that could meet consumer demand for increasing power and range.
Aubrey Eveleigh, president and chief executive officer of Zenyatta, commented: "Given the present limitations on the existing lithium-ion battery, the world needs to develop a superbattery. Silicon-graphene is the next-generation anode being developed for batteries by many advanced material companies. Zenyatta's graphene oxide has properties that make it a suitable material to be used with silicon in these next-generation lithium-ion batteries. While silicon has many times the capacity of graphite, it cannot be used alone due to rapid degradation. A significant amount of research has been carried out to encapsulate silicon in a graphene material to enhance the cycle life while also increasing charge capacity and durability for advanced lithium-ion batteries."
Mr. Eveleigh added: "We are very excited with the potential of our graphene to play a key role as a component of the next-generation batteries. The adaption of silicon-graphene-based anode batteries could further accelerate the fast-growing market for energy storage, especially for the automotive sector. Having a consistent and high-quality raw material source in North America for an end-user's supply chain is critical in order to maintain long-term quality control for product specifications."
U.S. Co. will continue to carry out advanced testing on Zenyatta's graphene oxide for use in lithium-ion anode composite material. Additional testing will include the determination of the following:
Aqueous dispersion quality;
Compatibility with processing method and yield;
Electrochemical performance;
Characterization of the composite material.
Zenyatta Ventures is developing the Albany graphite deposit situated in Northeastern Ontario, Canada. The deposit is a unique type of igneous-hosted, fluid-derived graphite mineralization containing highly crystalline carbon in two large breccia pipes. The company is collaborating with several partners in Asia, Europe and North America using its high-purity graphite for lithium-ion batteries, fuel cells and graphene. The outlook for the global graphite and graphene market is very promising, with demand growing rapidly from new applications. It is now considered one of the more strategic elements by many leading industrial nations, particularly for its growing importance in high-technology manufacturing and in the emerging green industries such as electric vehicle components.
The Albany graphite deposit is situated 30 kilometres north of the Trans-Canada Highway, power line and natural gas pipeline near the communities of Constance Lake First Nation and Hearst. A rail line is located 70 kilometres away with an all-weather road approximately 10 kilometres from the graphite deposit. The world trend is to develop nanomaterial products for technological applications that need extraordinary performance using ultrahigh-purity graphite powder at an affordable cost. Albany graphite can be upgraded to approximately 99.9 per cent carbon with very good crystallinity without the use of aggressive acids (hydrofluoric) or high-temperature thermal treatment, therefore having an environmental advantage over other types of upgraded high-purity graphite material.
Aubrey Eveleigh, PGeo, Zenyatta's president and CEO, is the qualified person for the purposes of National Instrument 43-101, and has reviewed, prepared and supervised the preparation of the technical information contained in this news release.
Illustration: Kansas State University/Nature Communications