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Yu F.,Shihezi University | Yu F.,Key Laboratory of Materials Oriented Chemical Engineering of Xinjiang Uygur Autonomous Region | Zhang L.,Institute of Chemical and Engineering Sciences, Singapore | Li Y.,Shihezi University | And 3 more authors.
RSC Advances | Year: 2014

Olivine-structured lithium ion phosphate (LiFePO4) is one of the most competitive candidates for fabricating energy-driven cathode material for sustainable lithium ion battery (LIB) systems. However, the high electrochemical performance is significantly limited by the slow diffusivity of Li-ion in LiFePO4 (ca. 10-14 cm2 s-1) together with the low electronic conductivity (ca. 10-9 S cm-1), which is the big challenge currently faced by us. To resolve the challenge, many efforts have been directed to the dynamics of the lithiation/delithiation process in LixFePO4 (0 ≤ x ≤ 1), mechanism of electrochemical modification, and synthetic reaction process, which are crucial for the development of high electrochemical performance for LiFePO4 material. In this review, in order to reflect the recent progress ranging from the very fundamental to practical applications, we specifically focus on the mechanism studies of LiFePO4 including the lithiation/delithiation process, electrochemical modification and synthetic reaction. Firstly, we highlight the Li-ion diffusion pathway in LixFePO4 and phase translation of LixFePO4. Then, we summarize the modification mechanism of LiFePO4 with high-rated capability, excellent low-temperature performance and high energy density. Finally, we discuss the synthetic reaction mechanism of high-temperature carbothermal reaction route and low-temperature hydrothermal/solvothermal reaction route. © the Partner Organisations 2014.

Nan H.,Nanjing Southeast University | Wang Z.,Nanjing Southeast University | Wang W.,Nanjing Southeast University | Liang Z.,Graphene Energy | And 8 more authors.
ACS Nano | Year: 2014

We report on a strong photoluminescence (PL) enhancement of monolayer MoS2 through defect engineering and oxygen bonding. Micro-PL and Raman images clearly reveal that the PL enhancement occurs at cracks/defects formed during high-temperature annealing. The PL enhancement at crack/defect sites could be as high as thousands of times after considering the laser spot size. The main reasons of such huge PL enhancement include the following: (1) the oxygen chemical adsorption induced heavy p doping and the conversion from trion to exciton; (2) the suppression of nonradiative recombination of excitons at defect sites, which was verified by low-temperature PL measurements. First-principle calculations reveal a strong binding energy of ∼2.395 eV for an oxygen molecule adsorbed on a S vacancy of MoS2. The chemically adsorbed oxygen also provides a much more effective charge transfer (0.997 electrons per O2) compared to physically adsorbed oxygen on an ideal MoS2 surface. We also demonstrate that the defect engineering and oxygen bonding could be easily realized by mild oxygen plasma irradiation. X-ray photoelectron spectroscopy further confirms the formation of Mo-O bonding. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defects sites of MoS2 may have promising applications in optoelectronic devices. © 2014 American Chemical Society.

Lu W.,Zhejiang University | Nan H.,Nanjing Southeast University | Hong J.,Zhejiang University | Chen Y.,Nanjing Southeast University | And 6 more authors.
Nano Research | Year: 2014

There have been continuous efforts to seek novel functional two-dimensional semiconductors with high performance for future applications in nanoelectronics and optoelectronics. In this work, we introduce a successful experimental approach to fabricate monolayer phosphorene by mechanical cleavage and a subsequent Ar+ plasma thinning process. The thickness of phosphorene is unambiguously determined by optical contrast spectra combined with atomic force microscopy (AFM). Raman spectroscopy is used to characterize the pristine and plasma-treated samples. The Raman frequency of the A2g mode stiffens, and the intensity ratio of A2g to A1g modes shows a monotonic discrete increase with the decrease of phosphorene thickness down to a monolayer. All those phenomena can be used to identify the thickness of this novel two-dimensional semiconductor. This work on monolayer phosphorene fabrication and thickness determination will facilitate future research on phosphorene. [Figure not available: see fulltext.] © 2014 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

Ahn J.,Graphene Energy | Seo J.-W.,Graphene Energy | Lee T.-I.,Korea Advanced Institute of Science and Technology | Kwon D.,Korea Advanced Institute of Science and Technology | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2016

We propose a fabrication process for extremely robust and easily patternable silver nanowire (AgNW) electrodes on paper. Using an auxiliary donor layer and a simple laminating process, AgNWs can be easily transferred to copy paper as well as various other substrates using a dry process. Intercalating a polymeric binder between the AgNWs and the substrate through a simple printing technique enhances adhesion, not only guaranteeing high foldability of the electrodes, but also facilitating selective patterning of the AgNWs. Using the proposed process, extremely crease-tolerant electronics based on copy paper can be fabricated, such as a printed circuit board for a 7-segment display, portable heater, and capacitive touch sensor, demonstrating the applicability of the AgNWs-based electrodes to paper electronics. © 2016 American Chemical Society.

News Article | April 24, 2009

Graphene Energy, an Austin, Tex. startup based on technology from the University of Texas and Virginia’s College of William and Mary, has taken a $500,000 seed round from Quercus Trust and 21Ventures. Ultracapacitors (insulating layers between conductors that house electric fields) are being explored by a variety of startups for their energy storage, usually as a component accompanying batteries in electric cars. Graphene is seeking to improve the technology by improving capacitance, or the amount of energy stored, and increasing the energy density of its capacitors. Other companies in the field include Apowercap Technologies, Eestor and Maxwell Technologies, all three of which hope to install their products in electric vehicles.

News Article | January 13, 2009

Graphene Energy, an Austin-based developer of ultracapacitor technology, has raised $500,000 in seed investment from Quercus Trust and 21Ventures. The investment represents yet another move by David Gelbaum’s Quercus Trust, which was the third-most active venture fund investing in cleantech in all of 2008, according to the Cleantech Group. Graphene Energy works with the strongest material ever tested — a one-atom thick sheet of graphite — to build ultracapacitors. The material, known as graphene, was hailed as the new silicon last year when researchers discovered that electrons could travel up to 100 times faster in graphene than silicon. Around the same time, a new generation of ultracapacitors emerged that aimed to seize the future of the auto industry. With ultra-fast charge times, they can absorb voltage drops and surges to extend battery life — or store electricity on their own. But capacity has lagged somewhere around 5 percent of battery’s storage capacity. Graphene Energy plans to solve this problem by stacking several sheets of graphene (pictured below), which it says could as much as double the capacity offered by today’s commercial ultracapacitors (usually made with activated carbon). The company, which emerged from research at the University of Texas, foresees applications in electric and hybrid vehicles, mobile devices, and wind- and solar-powered electric grids.

News Article | July 10, 2009

Less than a year has passed since Quercus Trust and 21Ventures threw down $500,000 in seed money for a small Austin, Texas, startup, Graphene Energy, with a big idea for disrupting the energy storage market. The idea: Develop a technology using graphene, a one-atom-thick sheet of carbon, with at least twice the storage capacity of commercially available ultracapacitors — devices that have ultra-fast charge and discharge times, but lag far behind batteries in terms of the amount of energy they can store. Fast-forward six months, and Graphene Energy has used that seed money to make big strides toward its target of achieving twice the storage capacity — at least in the lab. CEO Dileep Agnihotri told us in an interview today that the startup is on track to reach its goal by year’s end. At that point, Agnihotri tells us it expects to raise a new round of investment or secure stimulus funds (the company has applied for grants under ARPA-E and smart grid programs, among others) to help it go into the next phase: taking the technology out of the lab and packaging it into ultracapacitors. If the company reaches its goal in this time frame, it would be fast work. Back when Graphene Energy first raised funding, it had only demonstrated energy storage capacities that were about on par with commercially available options. But the team has leveraged the resources of founder Rodney Ruoff, a leading researcher in the field of novel carbon materials, and a novel plan to use graphene, which was hailed as the new silicon last year when researchers discovered that electrons could travel up to 100 times faster in graphene than silicon. While Agnihotri acknowledged that the economic climate is “not very good” for fund-raising, he said Graphene Energy is finding no shortage of interest among venture capitalists. As Agnihotri put it, “Graphene itself is a very exciting material.” It’s stronger than any other material ever tested (about 200 times the strength of steel), and particularly appealing for energy storage devices — potentially an $877 million market by 2014 — because electricity can flow through sheets of graphene very quickly without scattering. Graphene Energy is eying government grants, Agnihotri said, because “like any startup, I would prefer non-dilutive funds.” This week, scientists from Arizona State University published research on what they say are some of the first direct measurements of graphene’s ability to store energy, and the study confirms part of what Graphene Energy is banking on — that composites of graphene may “be capable of storing much larger amounts of renewable energy from solar, wind or wave energy than current technologies permit.” For Graphene, the idea is to deliver ultracapacitors with super-fast charge times for applications in electric and hybrid vehicles, mobile devices and power grids within the next couple of years. At this point, Agnihotri said Graphene is also experimenting with new electrolytes, a key part of each ultracapacitor cell (illustrated in a schematic from the National Renewable Energy Laboratory, below) that could eventually help increase storage capacity. “Electrolytes used today operate at a certain voltage,” he explained. Increase that voltage, and “you can pack more energy into the same volume.” But more than a few hurdles remain. In addition to financing and setting up manufacturing (not small feats), Graphene Energy will need a steady supply of graphene — in tons, rather than the ounces that the company is working with now in the lab. Agnihotri said the company is in talks with “a few” startups working on large-scale graphene production, as well as several big chemical companies that are trying to develop graphene production processes. While Graphene produces graphene for its R&D work, Agnihotri said that the company plans to focus on the ultracapacitors, leaving graphene production to outside suppliers. Graphene Energy certainly wouldn’t be the only customer. The material has huge potential for applications beyond energy storage, notably in solar cells and semiconductors. But those applications remain several years (in the case of solar) to possibly a decade away from commercial viability, said Agnihotri. “It’s the right timing for storage technology. It’s needed yesterday.”

News Article | July 21, 2009

David Gelbaum’s Quercus Trust is at it again. The quiet venture capital firm, along with frequent co-investor 21Ventures, has just led a second round of investment in startup Advanced Telemetry, which has built a wireless dashboard for monitoring and managing energy consumption. True to form, the firms aren’t disclosing the size of the investment, but the play ups Gelbaum’s stake in the smart grid market, where he has already led a $15 million round of funding for smart grid software developer GridPoint. While many of the Quercus Trust plays that have come to light so far (Variable Wind Solutions, Graphene Energy) involve clean power and energy storage, 2-year-old Advanced Telemetry is working on a energy and resource management system with an eye toward getting in on “the burgeoning $15 billion smart grid industry,” according to the company’s statement this morning. San Diego, Calif.-based Advanced Telemetry plans to use today’s Series B investment to ramp up production and “expand sales channels” for both the commercial and residential versions of its EcoView product — a wireless dashboard for monitoring and managing energy use, water and other resources, which the company claims can reduce utility bills by up to 25 percent. Advanced Telemetry has plenty of competition. An influx of funding from the stimulus package and renewed attention to energy savings means 2009 is shaping up to be the year that companies are vying to launch monitoring devices like EcoView using low-cost hardware and open standards. So if Quercus Trust’s latest investment will help Advanced Telemetry accelerate its efforts to nab market share early on, it can’t come too soon.

News Article | March 2, 2010

When most people think about changing the way America uses energy, they imagine new ways of generating electricity like solar farms or new nuclear reactors. But at an innovation summit organized by the Department of Energy’s high-risk, high-reward research branch, ARPA-E (modeled after Darpa), it’s not just power generation that’s getting a makeover. The companies hawking their ideas there, which all received grant money from ARPA-E or were finalists, are trying to reinvent the entire energy system. Everything is getting a technological re-evaluation from the actual wires that power is transmitted on to the waste heat produced in industrial processes. And of course there are also new ways of making electricity beyond just burning some rocks or oil to create steam to drive a turbine. Here are 10 companies that caught our attention. Any one technology is unlikely to solve the looming climate change and peak oil problems, but working together within the larger system, they could tilt the globe away from catastrophe and towards a sustainable future. Now, ethanol is made with corn cobs, which are just a small amount of the corn plant’s total biomass. For years, people have been trying to come up with ways to use all the rest of the plant to make fuel. They call that stuff “cellulosic ethanol,” because it doesn’t just use the sugars in the cobs, but the cellulose in the rest of the plant. It turns out, though, that it’s not so easy to do the chemistry that transforms a corn stalk into a liquid fuel that works. Agrivida is working on plants that release enzymes to degrade the cellulose in their own cell walls — on command. They throw a molecular switch, and the plants start turning themselves into sugar, saving fuel processors a key and energy-intensive step. Most industrial processes generate heat as a byproduct. Not only does that heat do no useful work, it also damages machinery. But there are materials that can directly convert heat into electricity without running some working fluid through a traditional generator. Phononic Devices is out to make these thermoelectric materials, which have been around for a good while, much more efficient and cheaper through nanotechnology. If scavenging heat to make electricity gets a lot cheaper, it could increase the overall efficiency of many processes. But to do that, you need much better materials. “Thermoelectrics is a pure materials field,” said Gerbrand Ceder, an MIT materials scientist who is not associated with Phononic Devices. “Thermoelectrics is going to leapfrog forward if you have better materials.” Wind power is already cost-competitive with fossil fuels (.pdf) in many places — and cheaper in really windy places. But it’s not perfect. The wind close to the ground is streakier than the stuff higher up, and it doesn’t blow as hard. Because the power available in the wind varies with the cube of its speed, a bit more speed gets you a lot more power. The best ground-based sites have a wind-power density of about a kilowatt per square meter of area swept. The wind-power density near the jet stream above New York is more than 15 times better than that. Makani Power wants to use large kites tethered at high altitudes to take advantage of the better wind resource that exists up there. It sounds crazy, but Google has already invested $15 million in the company. Diamonds might be a girl’s best friend, but graphene, the one-atom thick configuration of carbon atoms, is every nerd’s favorite form of C. Researchers can already imagine all kinds of wonderful applications for the stuff — like bendy electronics — but it might come in handy for energy storage, too. Graphene Energy is developing ultracapacitors based on the material. Ultracaps are considered a very attractive technology because — unlike your laptop battery — they can be cycled many times over and they can also provide big bursts of power. The problem is that they don’t have anywhere near the energy density. Graphene Energy’s technology is based on the work of the University of Texas’ Rod Ruoff. Ruoff has claimed that graphene could double the capacity of existing ultracapacitors by increasing the amount of carbon surface area that’s actively storing energy. The existing power grid has received a lot of attention because it loses some of the electricity that’s pumped into it. New, long transmission lines would also be required to get power from windy and sunny places to where people live if those renewable technologies are going to provide large amounts of power in the future. While many people are focusing on new meters or other “smart grid” ideas, Superconductor Technologies is trying to reinvent the actual power line. Not the idea of it, but the wire itself. They claim that by replacing the copper and aluminum wires in the grid with a ceramic, high-temperature superconductor, the lines could have five times the capacity and waste less electricity. An energy system that can accommodate the intermittency of renewable power will probably need large-scale storage. Companies are trying to commercialize all kinds of storage technologies, from pumping compressed air into caverns to using new kinds of ultracapacitors. Flywheels are another promising technology. They store the energy mechanically by rotating mass around an axis. Energy placed into the system by a motor gets the flywheels spinning, and the same motor can be run the opposite way to pull energy out of the system. They are commonly used in industry, but are considered too expensive and immature for deployment. Velkess has a promising flywheel system that the company claims could reduce storage costs by a factor of 10. Biofuels have come under attack as a solution to climate change, but if world oil production has peaked, coming up with a cheap way to make liquid fuels out of something else would still be very important technology. The Fischer-Tropsch process is a well-known way of making synthetic fuels from other types of carbon. In the past, that’s largely been coal, such as when the Germans used the process (see the plant above) to manufacture fuel during World War II. But it could also be used with biomass to make biofuel. The downside to Fischer-Tropsch is that it’s an energy-intensive and therefore expensive chemical process. Velocys says it has a better way of mixing the ingredients in the process to bring down the cost of making hydrocarbons out of regular old carbon. New materials have driven the power industry for decades, as better heat- and pressure-resistant materials allowed electrical plants to grow larger and larger. Now, there are all kinds of new materials that would be nice to have. Better batteries, carbon capture and photovoltaics all depend on the material science, yet it’s still a very trial-and-error science. Wildcat Discovery Technologies is trying to bring high-throughput automation to the discovery and synthesis of new materials. Their technology is one way to bring the accelerating advances in robotics and computing to bear on the energy problem. Photo: Plug-in module for the Nissan Leaf, an electric vehicle. Jim Merithew/ Photovoltaic panels have to do two jobs, which often come into conflict. First, because sunlight is a diffuse energy source, they need to spread out over a large area as cheaply as possible. Second, they need to convert those photons into electrons as efficiently as possible. Those two tasks call for different kinds of materials. Collecting photons isn’t difficult and can be done with cheap materials, but converting them into electrons is really tough. But what if you could separate those tasks? That’s the idea behind concentrating photovoltaics technologies like Xtreme Energetics. You use a cheap material to focus the sun’s rays on a very efficient, very expensive small piece of photovoltatic material. Xtreme Energetics says its technology could make electricity at a cost of $1.50 per watt with 43 percent efficiency and a smaller footprint than traditional solar panels. Tapping the heat of the Earth has proven a cost-effective way of making electricity in most of the places around the globe where earthquakes are likely. Geothermal reservoirs are like capped geysers: When humans drill a hole, hot stuff comes up, which can be used to run a turbine. But the big play in geothermal energy has always been to simply use the hot rocks down there and create your own reservoir. To do that, you have to drill into rocks much harder than those you normally encounter in oil fields. Potter Drilling is trying to commercialize a new drilling technique that replaces drill bits with … hot water. The company thinks it can halve the costs associated with drilling enhanced geothermal fields. Of course, right now, geothermal may have bigger problems than drilling. The bad press over small earthquakes caused by an enhanced geothermal project in Switzerland has taken some of the shine off a technology that had been anointed by a big MIT study as a big piece of out energy future. It’s worth noting, though, that the vast majority of human-caused quakes are caused by traditional mining and by hydroelectric-dam reservoirs.

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