California is committed to 33 percent energy from renewable resources by 2020. With that deadline fast approaching, researchers across the state are busy exploring options.
Solar energy is attractive but for widespread adoption, it requires transformation into a storable form. This week in ACS Central Science, researchers report that nanowires made from multiple metal oxides could put solar ahead in this race.
One way to harness solar power for broader use is through photoelectrochemical (PEC) water splitting that provides hydrogen for fuel cells. Many materials that can perform the reaction exist, but most of these candidates suffer from issues, ranging from efficiency to stability and cost.
Peidong Yang and colleagues designed a system where nanowires from one of the most commonly used materials (TiO2) acts as a “host” for “guest” nanoparticles from another oxide called BiVO4. BiVO4 is a newly introduced material that is among the best ones for absorbing light and performing the water splitting reaction, but does not carry charge well while TiO2 is stable, cheap and an efficient charge carrier but does not absorb light well.
Together with a unique studded nanowire architecture, the new system works better than either material alone.
The authors state their approach can be used to improve the efficiencies of other photoconversion materials.
We report the use of Ta:TiO2|BiVO4 as a photoanode for use in solar water splitting cells. This host−guest system makes use of the favorable band alignment between the two semiconductors. The nanowire architecture allows for simultaneously high light absorption and carrier collection for efficient solar water oxidation.
Metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells. However, their performance is often limited by poor charge carrier transport. We show that this problem can be addressed by using separate materials for light absorption and carrier transport. Here, we report a Ta:TiO2|BiVO4 nanowire photoanode, in which BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. Electrochemical and spectroscopic measurements provide experimental evidence for the type II band alignment necessary for favorable electron transfer from BiVO4 to TiO2. The host–guest nanowire architecture presented here allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent density of 2.1 mA/cm2 at 1.23 V vs RHE.
Article adapted from a American Chemical Society news release. To Read the FULL release, please click on the link provided below.
Publication: TiO2/BiVO4 Nanowire Heterostructure Photoanodes Based on Type II Band Alignment. Resasco, J et al. ACS Central Science (3 February, 2016): Click here to view.
Genesis Nanotechnology – “Great Things from Small Things”
21 Oct 2015
The opportunity is electricity storage, which until now has been limited by technology to a relatively modest scale. That’s about to change. And it means that Canada – and specifically Ontario – can become an ideal seedbed for storage technology, because there are ready markets for both large- and small-scale storage systems.
First, the large scale. Ontario has a fleet of nuclear generators that operate around the clock, and come close to filling the demand for power at off-peak hours. In addition, Ontario has developed a large renewable energy sector of wind and solar generation (in addition to its traditional hydro stations.) Problems sometimes arise when the natural weather cycles that drive wind and solar production are out of synch with the market cycle. On a sunny, breezy Saturday afternoon in May, with the nuclear plants running flat out, the hydro stations churning out power with the spring runoff and solar and wind systems near peak production, Ontario may have more electricity than it needs.
Our electricity system operators have a solution, of course: Sell the excess electricity to our neighbours. But since our neighbours are often in the same boat, Ontario must cut the price close to zero – or in extreme situations, even pay neighbouring states or provinces to absorb our overproduction.
Wouldn’t it make far more sense to store that excess energy, knowing that it will be needed in a matter of days, or even hours? What’s been lacking is the technology to do the job.
That’s changing however, as Ontario’s current program to procure 50 megawatts of storage capacity demonstrates. Companies with a variety of approaches are working hard to bring their solutions to market – many of them clustered at the MaRS centre in Toronto. Some, such as Hydrogenics Corp., convert electricity into hydrogen, which can be used to supplement natural gas.
My own company, NRStor, has partnered with Temporal Power and is operating a flywheel storage system in Minto, Ont., that helps the market operator to maintain consistent voltage on the grid.
Of course, businesses around the globe are looking at the same opportunities as we are, and here lies the opportunity for Canada to rebrand its energy economy.
A recent report by Deutsche Bank calls battery storage the “holy grail of solar penetration,” and believes that with the current rate of progress in improving efficiency, mass adoption of lithium ion batteries at a commercial/utility scale could occur before 2020.
Analysis by Prof. Andrew Ford of Washington State University calculates that a 1,000-megawatt air storage system from U.S.-based General Compression Inc. could deliver $6- to $8-billion of value to Ontario – in the form of lower energy costs to local utilities – over a 20-year period. All this is of interest to large-scale electricity system operators, big utilities and their customers.
But there is another reason for us to pay attention to energy storage – a reason grounded on a much more human scale. There are still large rural areas around the globe where there is no reliable electrical grid – including Northern Canada.
There is great potential for these communities, including remote First Nations communities, to improve their standard of living by installing microscale renewable generation in combination with storage, and relying less on carbon-spewing diesel generators, powered by fuel that must be transported long distances at great expense.
Storage is the key to making renewable energy a fully competitive component of any electrical grid. It can make our grid cleaner and more efficient, for the benefit of all consumers – large and small, urban and rural. We have the chance, in Canada, to become world leaders in developing this technology. Let’s seize it.
Annette Verschuren is the chairwoman and CEO of NRStor and on the board of MaRS Discovery District.
Annette Verschuren is speaking at the Cleantech Canadian Innovation Exchange (CIX Cleantech) conference in Toronto on Oct. 15.
By Michael Berger – Nanowerk. During 2002 and 2003, Nobel laureate Richard E. Smalley developed a list of the Top Ten Problems Facing Humanity over the next 50 years. The Richard E. Smalley Institute for Nanoscale Science and Technology at Rice University (which in May 2015 has been merged with the Rice Quantum Institute into a new entity: the Smalley-Curl Institute) has identified 5 of these problems as society’s Grand Challenges – and energy tops the list.
Since then, researchers around the world have demonstrated the potential for nanotechnology to be a key technology on the path to a sustainable energy future. Against the double-whammy backdrop of an energy challenge – the world’s appetite for energy keeps growing1 – plus a climate challenge – climate goals (2°C target) require substantial reduction in greenhouse gases (see: Climate change: Action, trends and implications for business. pdf) – it is the role of innovative energy technologies to provide socially acceptable solutions through energy savings; efficiency gains; and decarbonization.
Why is nanotechnology relevant here? Many effects important for energy happen at the nanoscale: In solar cells, for instance, photons can free electrons from a material, which can then flow as an electric current; the chemical reactions inside a battery or fuel cell release electrons which then move through an external circuit; or the role of catalysts in a plethora of chemical reactions. These are just a few examples where nanoscale engineering can significantly improve the efficiency of the underlying processes.
The working principle of a solar cell. (Image: University of Massachusetts Amherst)
Nanotechnologies are not tied exclusively to renewable energy technologies. While researchers are exploring ways in which nanotechnology could help us to develop energy sources, they also develop techniques to access and use fossil fuels much more efficiently. Corrosion resistant nanocoatings, nanostructured catalysts, and nanomembranes have been used in the extraction and processing of fossil fuels and in nuclear power. There is no silver bullet – nanotechnology applications for energy are extremely varied, reflecting the complexity of the energy sector, with a number of different markets along its value chain, including energy generation, transformation, distribution, storage, and usage. Nanotechnology has the potential to have a positive impact on all of these – albeit with varying effects.
Nanomaterials could lead to energy savings through weight reduction or through optimized function:
- In the future, novel, nano-technologically optimized materials, for example plastics or metals with carbon nanotubes (CNTs), will make airplanes and vehicles lighter and therefore help reduce fuel consumption;
- Novel lighting materials (OLED: organic light-emitting diodes) with nanoscale layers of plastic and organic pigments are being developed; their conversion rate from energy to light can apparently reach 50 % (compared with traditional light bulbs = 5%);
- Nanoscale carbon black has been added to modern automobile tires for some time now to reinforce the material and reduce rolling resistance, which leads to fuel savings of up to 10%;
- Self-cleaning or “easy-to-clean”-coatings, for example on glass, can help save energy and water in facility cleaning because such surfaces are easier to clean or need not be cleaned so often;
- Nanotribological wear protection products as fuel or motor oil additives could reduce fuel consumption of vehicles and extend engine life;
- Nanoparticles as flow agents allow plastics to be melted and cast at lower temperatures;
- Nanoporous insulating materials in the construction business can help reduce the energy needed to heat and cool buildings.
Nanomaterials could improve energy generation and energy efficiencies:
- Various nanomaterials can improve the efficiency of photovoltaic facilities;
- Dye solar cells (‘Grätzel cells’) with nanoscale semiconductor materials mimic natural photosynthesis in green plants;
- Plastics with carbon nanotubes as coatings on the rotor blades of wind turbines make these lighter and increase the energy yield;
- Nano optimized lithium-ion batteries have an improved storage capacity as well as an increased lifespan and find use in electric vehicles for example;
- Fuel cells with nanoscale ceramic materials for energy production require less energy and resources during manufacturing;
- The effectiveness of catalytic converters in vehicles can be increased by applying catalytically active precious metals in the nanoscale size range.
We have compiled an overview of Nanotechnology in Energy that shows how nanotechnology innovations could impact each part of the value-added chain in the energy sector – energy sources; energy conversion; energy distribution; energy storage; and energy usage.
The European GENNESYS project identified a range of nanomaterial application and requirements for future energy applications3. (click on image to enlarge) In the short term, energy nanotechnology is likely to have the greatest impact in the areas of efficiency of photovoltaics (among renewables, solar has by far the biggest global energy potential) and energy storage where it can help overcome current performance barriers and substantially improve the collection and conversion of solar energy. Nanotechnology for Solar Energy Collection and Conversion is one of the five Signature Initiatives funded by the U.S. National Nanotechnology Initiative. The goals are to enhance understanding of conversion and storage phenomena at the nanoscale, improve nanoscale characterization of electronic properties, and help enable economical nanomanufacturing of robust devices. The initiative has three major thrust areas:
- – improve photovoltaic solar electricity generation;
- – improve solar thermal energy generation and conversion; and
- – improve solar-to-fuel conversions.
The thermodynamic limit of 80% efficiency is well beyond the capabilities of current photovoltaic technologies, whose laboratory performance currently approaches only 43% 2. Nanomaterials even make it possible to raise light yield of traditional crystalline silicon solar cells. By using cheaper, nanoscale materials than the current dominant technology (single-crystal silicon, which uses a large amount of fossil fuels for production), the cost of solar cells could be brought down. Numerous research labs are working on nanotechnology-enabled batteries to increase their efficiencies for electric vehicles, home, or grid storage systems. Improving the efficiency/storage capacity of batteries and supercapacitors with nanomaterials will have a substantial economical impact.
Graphene has already been demonstrated to have many promising applications in energy-related areas. (read more: “Graphene materials for energy storage applications“). Nanotechnology also has the potential to deliver the next generation lithium-ion batteries with improved performance, durability and safety at an acceptable cost (“The promise of nanotechnology for the next generation of lithium-ion batteries“).
A major push on basic research for energy technologies is coming from the U.S. Department of Energy, which since 2009 has invested nearly $800m as part of the Energy Frontier Research Center (EFRC) program. For example, the Joint Center for Artificial Photosynthesis (JCAP) has developed a nanowire-based design that incorporates two semiconductors to enhance absorption of light; or the Nanostructures for Electrical Energy Storage (NEES) EFRC Center has demonstrated that precise nanostructures can be constructed to test the limits of 3-D nanobatteries by designing billions of tiny batteries inside nanopores.
Against the double-whammy backdrop of an energy challenge and a climate challenge it is the role of innovative energy technologies to provide socially acceptable solutions through energy savings; efficiency gains; and decarbonization.
So where does that leave ‘nanotechnology’? It may not be the silver bullet, but nanomaterials and nanoscale applications will have an important role to play.
Notes 1) Energy demand grows by 37% to 2040 on planned policies, an average rate of growth of 1.1%. World electricity demand increases by almost 80% over the period 2012-2040. 1.6bn people still without access to electricity, thereof 950 million in sub-Saharan Africa. (Source: IEA World Energy Outlook 2014) 2) Source: NSI Solar White Paper (pdf) 3) Source: GENNESYS White paper
22 Jul 2015
Tesla Motors CTO JB Straubel was the headliner at Intersolar North America last week. He talked about the transition to lithium-ion batteries and how that opened the floodgates for electric cars and stationary storage (eventually); the synergy between EVs, solar, and grid storage; the growth of solar power and grid storage; blah blah blah.
I know, I actually love all that stuff as much as the rest of you — it’s what I read, edit, & write about every day(!) — but it’s basically all general history and trends we know all about. But then JB dropped the awesome-bomb:
“I think we’re at the beginning of a new cost-decline curve, and, you know, this is something where there’s a lot of similarities to what happened with photovoltaics. Almost no one [would have predicted] that photovoltaic prices would have dropped as fast as they have, and storage is right at the cliff, heading down that price curve. It’s soon going to be cheaper to drive a car on electricity — a pure EV on electricity — than it is to drive a gasoline car. And as soon as we see that kind of shift in the actual cost of operation in a car that you can actually use for your daily driver, you know, from all manufacturers I believe we’re going to see electric vehicles come to dominate the whole transportation fleet.
“Also, that same battery cost decrease is going to drive batteries in the grid. There’s going to be much faster growth of grid energy storage than I think most people expected. You suddenly get to have energy that’s 100% firm and buffered from photovoltaics that’s cheaper than fossil energy. And we’re within sort of grasping distance of that goal, which is very, very exciting.
“Because once we get to that, and there really is no going back, it will make sense to do this economically without any environmental consideration whatsoever. So that’s the amazing tipping point that’s going to happen within I’m quite certain the next 10 years.”
The next 10 years!
(Though, he didn’t actually drop the mic.)
You can watch the highlights via Intersolar on YouTube — video below:
Another great quote, however, was this gem: “It’s not going to be many years before Tesla will have a million cars, or 70 gigawatt-hours of storage.” (That quote wasn’t in the highlight video above for some reason!)
| Solar energy is the world’s most plentiful and ubiquitous energy source, and researchers around the world are pursuing ways to convert sunlight into a useful form.
Most people are aware of solar photovoltaics that generate electricity and solar panels that produce hot water. But there is another thrust of solar research: turning sunlight into liquid fuels.
|Research in solar-derived liquid fuels, or solar fuels, aims to make a range of products that are compatible with our energy infrastructure today, such as gasoline, jet fuel and hydrogen. The goal is to store sunlight in liquid form, conveniently overcoming the transient nature of sunlight. I am among the growing number of researchers focused on this field.|
|How can this be done? And what scientific challenges remain before one can fill up a car on solar-generated fuel?|
|Packing heat: concentrating sunlight into a reactor to split H2O and CO2 – a step toward making liquid fuels. (Courtesy of Professor David Hahn, University of Florida, Author provided)|
|Speeding up nature|
|The production of solar fuels is particularly attractive because it addresses both the conversion and storage problem endemic to sunlight; namely, the sun is available for only one-third of the day. This is a distinct advantage compared to other solar conversion technologies. Solar photovoltaic panels, for instance, must be coupled to a complex distribution and storage network, such as batteries, when production of electric power doesn’t equal demand.|
|The term “solar fuel” is a bit of a misnomer. In fact, all fossil fuels are technically solar-derived. Solar energy drives photosynthesis to form plant matter through the reaction of carbon dioxide (CO2) and water (H2O) and, over millions of years, the decay of plant matter creates the hydrocarbons we use to power our society.|
|One thermochemical approach strips oxygen from steam and carbon dioxide gas using the sun’s heat. Then, the resulting gases are combined chemically in a separate process to make liquid fuels. (Image: Jonathan Scheffe, Author provided)|
|The downside of this process is that nature’s efficiency at producing hydrocarbons is excruciatingly low, and humankind’s hunger for energy has never been greater. The result is that the current rate of fossil fuel consumption is much larger than the rate they are produced by nature alone, which provides the motivation to increase nature’s efficiencies and speed up the process of solar fuel production through artificial means.|
|This is the true meaning of “solar fuel” as it is used today, but the ultimate goal is the same: namely, the conversion of solar energy, CO2 and H2O to chemical forms such as gasoline.|
|To the lab|
|The first step in creating manmade solar fuels is to break down CO2 and/or H2O molecules, often to carbon monoxide (CO) or carbon and hydrogen (H2). This is no easy feat, as both of these molecules are very stable (H2 does not form spontaneously from H2O!) and therefore this step requires a substantial amount of energy supplied from sunlight, either directly in the form of photons or indirectly as electricity or heat.|
|This step is often the most crucial component of the process and represents the greatest roadblock to commercialization of solar fuel technologies today, as it largely defines the efficiency of the overall fuel production process and therefore the cost.|
|Downstream of this step, the resulting molecules – in this case, a mixture of CO and hydrogen called synthesis gas – may be converted through a variety of existing technologies depending on the final product desired. This step of converting hydrocarbon gases to liquid form is already performed at an industrial scale, thanks to large corporations such as Shell Global Solutions and Sasol that use these technologies to leverage to low cost of today’s natural gas to make more valuable liquid fuels.|
|Recently, a European Union-sponsored project called SOLAR-JET (Solar chemical reactor demonstration and Optimization for Long-term Availability of Renewable JET fuel) demonstrated the first-ever conversion of solar energy to jet fuel, or kerosene. Researchers coupled the solar-driven production of synthesis gas, also called syngas, from CO2 and H2O with a downstream gas-to-liquids reactor – in this case a Fischer-Tropsch reactor at Shell’s Headquarters in Amsterdam.|
|The production of liquid fuels is especially important for the aviation industry that relies on energy-dense fuels and represents another important advantage of solar fuel production compared to solar electricity.|
|The SOLAR-JET project, which I worked on with several other researchers, utilized a process called solar thermochemical fuel production, in which solar energy is concentrated using optics – mirrors and lenses – much the way a magnifying glass can start a fire. The resulting heat is then absorbed in a chamber that acts as a chemical reactor. The absorbed heat is then used to dissociate H2O and/or CO2 through a catalytic-type process – one of the most technically challenging steps for all solar fuel conversion processes. The resulting products (hydrogen or synthesis gas) can then be captured and further converted to liquid fuels downstream.|
|There are numerous other strategies to drive these reactions needed for the first step of solar fuel production, including those that utilize light – photons – directly or indirectly in the form of electricity.|
|For example, so-called artificial photosynthesis utilizes photons directly in a catalytic process, rather than absorbing them as heat, to break down H2O and CO2 molecules.|
|Former Energy Secretary Steven Chu visiting the Joint Center for Artificial Photosynthesis, which received an additional US$75 million in funding earlier this year. The lab is pursuing converting light (not heat) directly into fuels. (Image: Lawrence Berkeley National Laboratory)|
|Electrochemical approaches utilize electricity that could be generated from a photovoltaic cell to drive the separation of H2O and CO2 through a process known as electrolysis.|
|To date, the key barriers to commercialization of all of these technologies are primarily related to their low efficiencies – that is related to the amount of energy needed to produce a liquid fuel – and overall robustness. For example, the efficiency of the SOLAR-JET thermochemical conversion project discussed above is still less than 2%, but for this technology to become commercially viable, efficiencies greater than 10% will need to be achieved.|
|A team working at the University of Florida funded by research agency ARPA-E is working toward these efficiency goals using another thermochemical process that uses optics to generate heat. Yet robustness because of extreme temperatures (greater than 1200 Celsius or over 2000 Farenheit) is still a major concern that is being addressed.|
|Furthermore, for solar fuel production to truly reduce greenhouse gas levels, it must be coupled with methods to capture CO2 from the air. This is still a relatively immature technology, but companies such as Climeworks are working to make this a reality.|
|Add in the complexity of integrating a temporally varying energy input (the sun) with a chemical reactor and the overall scope of the challenge can appear large. Nevertheless, advances are being made daily that give hope that solar fuels at higher efficiencies will soon be a reality.|
|Source: By Jonathan Scheffe, Associate Professor Department of Mechanical and Aerospace Enginering at University of Florida, via The Conversation|
22 Jun 2015
Aiming to completely overhaul the lithium-ion battery industry, MIT-based scientist Yet-Ming Chiang on Monday publicly unveiled his latest startup, called 24M.
The company uses a novel battery composition based on a semi-solid material that eliminates much of the bulk of conventional lithium-ion batteries—which are typically made up mostly of inactive, non-energy-storing materials—while dramatically increasing the energy density. Chiang and 24M CEO Throop Wilder also say that they can reduce the time needed to make a battery by 80 percent and the cost by 30 to 50 percent.
After five years of research and development, 24M has raised $50 million in funding from Charles River Ventures, North Bridge Venture Partners, and its strategic partners, along with a $4.5 million grant from the U.S. Department of Energy. It has strategic partnerships with the Japanese heavy-industry giant IHI and from PTT, the formerly state-owned Thai oil and gas company, which is increasingly moving into alternative energy.
Since a 2011 paper in the journal Advanced Energy Materials previewed 24M’s technology, the company has received a large amount of press coverage for a stealth-mode startup, including articles in this publication as well as a long, adulatory profile on the website Quartz. The company calls its new battery “the most significant advancement in lithium-ion technology since its debut more than 20 years ago.”
That would be a remarkable accomplishment, with the potential to drive the electric-vehicle market to a new level and accelerate the spread of renewable energy. But 24M faces a challenge that many previous companies with promising technology have failed to solve: how to revolutionize a manufacturing industry with huge amounts of capital sunk into extensive existing capacity.
Yet-Ming Chiang is personally familiar with this quandary: he was one of the founders of A123, the lithium-ion startup that received nearly a quarter of a million dollars in funding from the U.S. government, went public in the largest IPO of 2009, and filed for bankruptcy in 2012. A123 was done in by an EV market that grew slower than expected and by its close relationship with EV maker Fisker, which itself failed in 2013 and was purchased by the Chinese auto parts company Wanxiang Group. But it also stumbled in trying to compete with more established battery makers such as LG and Panasonic.
Chiang acknowledges the dilemma: “In the last decade, there have been a lot of new lithium-ion plants built, and the EV market has not materialized to fill these factories.”
Now, energy storage demand is soaring—for vehicles, for power grids, and for residences with distributed renewable generation, such as rooftop solar arrays. Capacity in the United States is expected to more than triple this year, and rapid growth will continue through the end of the decade, according to GTM Research.
That means that demand for a less expensive, more efficient technology should be robust. But the building boom of the previous decade means there’s also excess manufacturing capacity available to supply that market. LG Chem’s plant in Holland, Michigan, which makes batteries for the Chevrolet Volt and the Cadillac ELR, currently operates at about 30 percent of capacity, according to CEO Prabhakar Patil.
And established players are already increasing their output. Mercedes-Benz parent company Daimler, for instance, announced late last year it will invest 100 million euros ($113 million) to expand its lithium-ion manufacturing capacity through its subsidiary Deutsche ACCUmotive.
Then there’s the Gigafactory. Tesla’s giant Nevada plant will produce 35 gigawatt-hours’ worth of batteries a year, dwarfing any previous manufacturing ventures for lithium-ion batteries.
Meanwhile, improvements in the manufacturing of conventional lithium-ion batteries are reducing the cost per kilowatt-hour of existing systems—even as research into next-generation chemistries, such as lithium-sulfur and lithium-air, continues at institutions around the world.
In short, 24M is attempting to transform a worldwide manufacturing industry in which established players with deep pockets are investing hundreds of millions in the expansion of existing processes. That’s a tough road even for a startup with a novel and exciting technology.
Chiang and CEO Wilder are undeterred. “This is the next great mega-market,” says Wilder. “To quote Elon Musk, the world is going to need multiple gigafactories.”
Extremely small batteries built inside nanopores show that properly scaled structures can use the full theoretical capacity of the charge storage material. The batteries are part of assessing the basics of ion and electron transport in nanostructures for energy storage. These nanobatteries delivered their stored energy efficiently at high power (fast charge and discharge) and for extended cycling.
Precise structures can be constructed to assess the fundamentals of ion and electron transport in nanostructures for energy storage and to test the limits of three-dimensional nanobattery technologies.
Nanostructured batteries, when properly designed and built, offer promise for delivering their energy at much higher power and longer life than conventional technology. To retain high energy density, nanostructures (such as nanowires) must be arranged as dense “nanostructure forests,” producing three-dimensional nanogeometries in which ions and electrons can rapidly move. Researchers have built arrays of nanobatteries inside billions of ordered, identical nanopores in an alumina template to determine how well ions and electrons can do their job in such ultrasmall environments.
The nanobatteries were fabricated by atomic layer deposition to make oxide nanotubes for ion storage inside metal nanotubes for electron transport, all inside each end of the nanopores. The tiny nanobatteries work extremely well: they can transfer half their energy in just a 30 second charge or discharge time, and they lose only a few percent of their energy storage capacity after 1000 cycles. Researchers attribute this performance to rational design and well-controlled fabrication of nanotubular electrodes to accommodate ion motion in and out and close contact between the thin nested tubes to ensure fast transport for both ions and electrons.
This work was performed at the University of Maryland and was supported by the Nanostructures for Electrical Energy Storage (NEES) Center, an Energy Frontier Research Center funded by the DOE Office of Science, Office of Basic Energy Sciences.
- Chanyuan Liu, Eleanor I. Gillette, Xinyi Chen, Alexander J. Pearse, Alexander C. Kozen, Marshall A. Schroeder, Keith E. Gregorczyk, Sang Bok Lee, Gary W. Rubloff. An all-in-one nanopore battery array. Nature Nanotechnology, 2014; 9 (12): 1031 DOI: 10.1038/nnano.2014.247
- Paul V. Braun, Ralph G. Nuzzo. Batteries: Knowing when small is better. Nature Nanotechnology, 2014; 9 (12): 962 DOI: 10.1038/nnano.2014.263
A new semiliquid battery developed by researchers at The University of Texas at Austin has exhibited encouraging early results, encompassing many of the features desired in a state-of-the-art energy-storage device. In particular, the new battery has a working voltage similar to that of a lithium-ion battery, a power density comparable to that of a supercapacitor, and it can maintain its good performance even when being charged and discharged at very high rates.
The researchers, led by Assistant Professor Guihua Yu, along with Yu Ding and Yu Zhao, at UT Austin, have published their paper on the new membrane-free, semiliquid battery in a recent issue of Nano Letters. The researchers explain that the battery is considered “semiliquid” because it uses a liquid ferrocene electrolyte, a liquid cathode, and a solid lithium anode.
“The greatest significance of our work is that we have designed a semiliquid battery based on a new chemistry,” Yu told Phys.org. “The battery shows excellent rate capability that can be fully charged or discharged almost within one minute while maintaining good energy efficiency and reasonable energy density, representing a promising prototype liquid redox battery with both high energy density and power density for energy storage.”
The battery is designed for applications in two of the biggest areas of battery technology: hybrid electric vehicles and energy storage for renewable energy resources.
As shown in the figure above, the battery’s high power density (1400 W/L) and good energy density (40 Wh/L) put it in the uniquely favorable position of combining a power density that is as high as that of current supercapacitors with an energy density on par with those of state-of-the-art redox flow batteries and lead-acid batteries, though slightly lower than that of lithium-ion batteries. This combination is especially attractive for electric vehicles, where the power density corresponds to top speed and the energy density to the vehicle’s range per charge.
The researchers also report in their paper that the new battery has a high capacity (137 mAh/g) and a high capacity retention of 80% for 500 cycles.
The researchers attribute the battery’s good performance in large part to its liquid electrode design that enables its high rate capability, which is basically a measure of how fast the battery operates. The ions can move through the liquid battery very rapidly compared to in a solid battery, and the redox reactions in which the electrons are transferred between electrodes also occur at very high rates in this particular battery. For comparison, the values used to measure these rates (the diffusion coefficient and the reaction constant) are orders of magnitude greater in the new battery than in most conventional flow batteries.
Although the battery looks very promising so far, the researchers note that more work still needs to be done, in particular regarding the lithium anode.
“The potential weakness of this battery is the lithium anode in terms of long-term stability and safety,” Yu said. “More advanced lithium anode protection is required to fully suppress self-discharge. We suppose that other metals like zinc and magnesium may also function as the anode for such a battery as long as the electrolyte compatibility is resolved. We also expect that other organometallic compounds with multi-valence-state metal centers (redox centers) may also function as the anode, which eventually would make the battery fully liquid.”
In the future, the researchers plan to test the long-term durability of the battery, especially its lithium anode, under realistic operating conditions. In addition, the researchers want to find a way to increase the solubility of ferrocene in order to further increase the energy density to compete with current lithium-ion batteries while maintaining its very high power density.
More information: Yu Ding, et al. “A Membrane-Free Ferrocene-Based High-Rate Semiliquid Battery.” Nano Letters. DOI: 10.1021/acs.nanolett.5b01224
Tesla is launching the home battery business partly because it’s already making vehicle batteries—and as a result it can benefit from the economies of scale that come from making both. Another reason is that the market for storage is expected to grow in concert with the use of solar power. Tesla needs both electric vehicles and solar power to boom if it hopes to fulfill the projected output from a vast $5 billion battery “gigafactory” it’s building in Nevada.
“The obvious problem with solar power is that the sun does not shine at night,” Tesla CEO Elon Musk said at the unveiling of the new batteries at the company’s design studio in Hawthorne, California, yesterday. “We need to store the energy that is generated during the day so you can use it at night.”
A number of solar companies now offer batteries to accompany their solar panels (see “Solar Power, and Somewhere to Store It”). Although just a tenth of a percent of U.S. homes now get power from rooftop solar panels combined with energy storage, such systems could account for 3 percent of homes by 2018, according to Greentech Media Research.
Tesla’s residential battery, called Powerwall, will be available in several months and will come in two sizes, a seven-kilowatt-hour battery system that costs $3,000 and a slightly larger 10-kilowatt-hour system for $3,500. The larger battery would keep an average-sized home running for a day. It is unclear what the cost of installation would be.
Tesla expects that many sales will come from commercial customers who pay a variable rate of electricity over the course of a day based on demand. Such customers already see significant reductions in their energy bills by drawing on stored electricity during periods of peak energy demand.
In the near term, the market for home energy storage will depend on how states regulate homeowners’ ability to buy and sell electricity. Net metering, currently available in 43 states, allows residential customers to sell excess generation back to their utility company at retail rates. The policies are being challenged by utility companies that say it undermines their ability to recoup grid infrastructure costs. But as long as net metering continues, consumers will have little need to buy an energy storage system because they can sell the excess solar power they generate rather than store it, says Jay Stein, an analyst with energy consulting company E Source. “I don’t see any financial payoff for them to buy batteries,” he says.
Most utilities that offer net metering, however, also allow residential customers to buy and sell electricity at rates that vary throughout the day based on demand. Battery storage would allow such people to maximize the value of the electricity they sell back to the utility.
“There are some arbitrage values emerging,” says Karl Rábago, executive director of the Pace Energy and Climate Center in White Plains, New York. “If I could export selectively, using a storage device, I might beget higher value for my generation.”
Home energy storage will make more sense in the years to come. Residential and commercial solar-plus-storage systems will offer a clear cost advantage over electricity from the grid throughout the United States by 2030, according to a recent report by the Rocky Mountain Institute, an energy research and consulting group.
Tesla’s Nevada gigafactory, which it’s building with Panasonic, will have an annual production capacity of 35 gigawatt-hours by 2020, more than all the lithium-ion batteries produced globally in 2013.
Such a large investment in what is still a niche market is risky, but Tesla claims that the new factory will cut battery costs by 30 percent when it begins operations, as early as 2016. Tesla’s biggest challenge will likely be filling enough orders for the output. By 2020, the plant will be able to produce enough batteries for half a million electric vehicles per year. Last year, Tesla sold around 20,000 cars.