Potassium-ion batteries (PIBs) have been considered as promising alternatives to lithium-ion batteries due to the rich natural abundance of potassium (K) and similar redox potential with Li+/Li.
|However, due to the large K ion radius and slow reaction dynamics, the previously reported PIB anode materials (carbon-based materials, alloy-based anodes such as tin and antimony, metal oxides, etc.) suffer from a low capacity and fast capacity decay.|
|In order to achieve a high capacity and excellent cycle stability for K storage process, rational design of the electrode materials and proper selection of the electrolytes should be considered simultaneously.|
|Recently, two research teams led by Prof. Chunsheng Wang and Prof. Michael R. Zachariah from the University of Maryland, College Park, have designed and fabricated a novel antimony (Sb) carbon composite PIB anode via a facile and scalable electrospray-assisted strategy and found that this anode delivered super high specific capacities as well as cycling stability in a highly concentrated electrolyte (4M KTFSI/EC+DEC).|
|This work has been published in Energy and Environmental Science (“Super Stable Antimony-carbon composite anodes for potassium-ion batteries”).
|Figure 1. Schematic illustration of electrospray-assisted strategy for fabricating antimony @carbon sphere network electrode materials. (© Royal Society of Chemistry)|
|We have successfully fabricated a novel antimony carbon composite with small Sb nanoparticles uniformly confined in the carbon sphere network (Sb@CSN) via a facile and scalable electrospray-assisted strategy.|
|Such a unique nanostructure can effectively mitigate the deleteriously mechanical damage from large volume changes and provide a highly conductive framework for fast electron transport during alloy/de-alloy cycling process.|
|Alongside the novel structural design of the anode material, formation of a robust solid-electrolyte-interphase (SEI) on the anode is crucially important to achieve its long-term cycling stability.|
|The formation of a robust SEI on the anode material is determined by both the surface chemistries of active electrode materials as well as electrolyte compositions such as salt anion types and concentrations.|
|Therefore, designing a proper electrolyte is extremely important for the anode to achieve a high cycling stability.|
|In our study, we have for the first time developed a stable and safe electrolyte of highly concentrated 4M KTFSI/EC+DEC for PIBs to promote the formation of a stable and robust KF-rich SEI layer on an Sb@CSN anode, which guarantees stable electrochemical alloy/de-alloy reaction dynamics during long-time cycling process.|
|Figure 2. Cycling performance of antimony carbon sphere network electrode materials at 200mA/g current density in the highly concentrated electrolyte (4M KTFSI/EC+DEC). (© Royal Society of Chemistry)|
|In the optimized 4M KTFSI/EC+DEC electrolyte, the Sb@CSN composite delivers excellent reversible capacity of 551 mAh/g at 100 mA/g over 100 cycles with a capacity decay of 0.06% per cycle from the 10st to 100th cycling and 504 mAh/g even at 200 mA/g after 220 cycling. This demonstrates the best electrochemical performances with the highest capacity and longest cycle life when compared with all K-ion batteries anodes reported to date.|
|The electrochemical reaction mechanism was further revealed by density functional theory (DTF) calculation to support such excellent Potassium-storage properties.|
|Figure 3. Capacity comparison of Sb@CSN anode with previous reported anodes in potassium ion batteries. (© Royal Society of Chemistry)|
|In conclusion, these outstanding performances should be attributed to the novel nanostructure of Sb nanoparticles uniformly encapsulated into conductive carbon network and the formation of a more stable and robust KF-rich SEI layer on Sb@CSN in the optimized 4M KTFSI electrolyte.|
|These encouraging results will significantly promote the deep understanding of the fundamental electrochemistry in Potassium-ion batteries as well as rational development of efficient electrolyte systems for next generation high-performance Potassium-ion batteries.|
|Yong Yang, Research Associate, Prof. Zachariah Research Group, Department of Chemical and Environmental Engineering, University of California, Riverside|
Building at the nanoscale is not like building a house. Scientists often start with two-dimensional molecular layers and combine them to form complex three-dimensional architectures.
And instead of nails and screws, these structures are joined together by the attractive van der Waals forces that exist between objects at the nanoscale.
Van der Waals forces are critical in constructing materials for energy storage, biochemical sensors and electronics, although they are weak when compared to chemical bonds. They also play a crucial role in drug delivery systems, determining which drugs bind to the active sites in proteins.
In new research that could help inform development of new materials, Cornell chemists have found that the empty space (“pores”) present in two-dimensional molecular building blocks fundamentally changes the strength of these van der Waals forces, and can potentially alter the assembly of sophisticated nanostructures.
The findings represent an unexplored avenue toward governing the self-assembly of complex nanostructures from porous two-dimensional building blocks.
“We hope that a more complete understanding of these forces will aid in the discovery and development of novel materials with diverse functionalities, targeted properties, and potentially novel applications,” said Robert A. DiStasio Jr., assistant professor of chemistry in the College of Arts and Sciences.
In a paper titled “Influence of Pore Size on the van der Waals Interaction in Two-Dimensional Molecules and Materials,” published Jan. 14 in Physical Review Letters, DiStasio, graduate student Yan Yang and postdoctoral associate Ka Un Lao describe a series of mathematical models that address the question of how void space fundamentally affects the attractive physical forces which occur over nanoscale distances.
In three prototypical model systems, the researchers found that particular pore sizes lead to unexpected behavior in the physical laws that govern van der Waals forces.
Further, they write, this behavior “can be tuned by varying the relative size and shape of these void spaces … [providing] new insight into the self-assembly and design of complex nanostructures.”
While strong covalent bonds are responsible for the formation of two-dimensional molecular layers, van der Waals interactions provide the main attractive force between the layers. As such, van der Waals forces are largely responsible for the self-assembly of the complex three-dimensional nanostructures that make up many of the advanced materials in use today.
The researchers demonstrated their findings with numerous two-dimensional systems, including covalent organic frameworks, which are endowed with adjustable and potentially very large pores.
“I am surprised that the complicated relationship between void space and van der Waals forces could be rationalized through such simple models,” said Yang. “In the same breath, I am really excited about our findings, as even small changes in the van der Waals forces can markedly impact the properties of molecules and materials.”
Explore further: Researchers refute textbook knowledge in molecular interactions
More information: Yan Yang et al, Influence of Pore Size on the van der Waals Interaction in Two-Dimensional Molecules and Materials, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.122.026001
2019 is an exciting year for renewable energy. More and more countries and cities are adopting ambitious renewable energy targets and the technology is evolving rapidly. Many of these technologies, such as microgrids and energy storage, could become mainstream technology in the coming years. At this speed of innovation, it is difficult to keep track of all the changes!
This selection of TED Talks covers some of the most fascinating and promising energy topics for 2019. Be sure to read the 2018 Climate Change Overview and list of Energy Trends To Watch In 2019 before diving into these talks to better understand the impact of these new developments.
1. Accelerating The Shift To Clean Energy, Bill Nussey
Topic: Building local, consumer-driven electricity markets, such as the Brooklyn Microgrid, with renewable energy resources. (2017).
Nussey is an entrepreneur, investor, speaker, clean tech CEO and founder of the Freeing Energy Project.
“Solar and batteries are governed by something called Swanson‘s law, which states the more product you manufacture, the cheaper it gets. If we want to unleash society’s most powerful force for change, the irresistible economics of a lower price, we just need to make more and more solar panels and batteries. This is where you come in. For the first time in energy history, each of us can play a role in creating the future. All we have to do is embrace clean, local energy ourselves. Install solar panels. Purchase community solar. Buy an electric vehicle to drive up the battery volumes. Do business with companies powered by clean energy. Every little thing we do adds up.”
2. Batteries Not Included, Marek Kubik
Topic: How energy storage technologies are transforming our approach to electricity generation with renewables. (2018).
Kubik is an energy and sustainability futurist, Forbes 30 Under 30 Honouree and TEDx speaker.
“Solar and wind are already cost-competitive today. The cost of these technologies has fallen to a point where, in many countries, they are already the cheapest forms of electricity generation. And that trend is set to continue.”
3. Ground Zero For Global Energy Transition, Justin Locke
Topic: The role of leadership that small islands are taking in developing sustainable energy solutions. (2017).
Locke is a writer and speaker on sustainable energy and the director for the Islands Energy Program at the Rocky Mountain Institute. (See also: Electric Vehicles in Barbados).
“Islands have been determined as victims of colonization, occupation and now climate change. But now they are flipping that script and actually providing the solutions to the world’s most difficult challenge: how to combat climate change.”
4. A Printable, Flexible, Organic Solar Cell, Hannah Bürckstümmer
Topic: Efficient, flexible organic solar cells that can be printed in any shape to allow the facades of buildings to capture solar from every exposed surface. (2017).
Bürckstümmer has a background in chemistry and a curiosity about our environment, which she has translated into research into third-generation solar cells and work on the strategy and marketing for organic photovoltaics.
“This is pointing towards a future where buildings are no longer energy consumers, but energy providers. I want to see solar cells seamlessly integrated into our building shells to be both resource-efficient and a pleasure to look at. To exploit the potential of all facades and other areas, organic photovoltaics can offer a significant contribution, and they can be made in any form architects and planners will want them to.”
5. The Thrilling Potential For Off-Grid Solar Energy, Amar Inamdar
Topic: How the factors of distributed generation- lower costs, infrastructure and decentralization- are revolutionizing the energy market, to the benefit of the environment. (2017).
Inamdar works with businesses and entrepreneurs to imagine, create and grow markets that address our biggest social and environmental challenges.
“We aspire towards energy access for everybody, and we aspire towards a fully-functioning low-carbon economy. And we’re getting to the point where we’re seeing the fully-functioning low-carbon economy is not just about getting people onto the grid, it’s about getting people onto electricity and doing it in a way that’s really dignified.”
To learn more about the latest energy trends, you should read the 2018 Climate Change Overview and list of Energy Trends To Watch In 2019. Stay tuned for another selection of TED Talks in February with a focus on the latest science and action combating global climate change. Presented by James Ellsmoor is a Forbes 30 Under 30 entrepreneur.
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In a bid to help scale renewable energy, many companies are working on new ways to store energy long-term. But the plain old battery is still king. Can ultra-cold liquid air make all the difference?
Elon Musk’s Tesla took less than 100 days to install its Hornsdale Power Reserve – the world’s largest lithium ion battery – in dusty, sunny South Australia, following a Twitter bet. UK-based Highview Power has been a bit slower than that. After years of delays, its Liquid Air Energy Storage (LAES) plant near Manchester has come online.
It’s the world’s first grid-scale liquid air energy storage plant – and with off-the-shelf components, it’s relatively easy and cheap to build and to scale. Air is cooled down, made liquid, and stored in tanks for weeks until you need electricity again. Sounds pretty cool, doesn’t it?
While it’s certainly a moment of success for alternative energy storage, don’t break out the confetti yet: lithium ion isn’t about to give up its crown, says Dan Finn-Foley, a senior analyst at GTM Research. In the US alone, li-ion battery technology accounts for more than 95 per cent of annual storage deployments. But batteries, even the most efficient ones, fail to store energy for longer than a few hours.
So where does it leave solar and wind power, with their need to smooth out the supply peaks and troughs?
“Alternative energy storage could be a holy grail for the grid, a missing link that could get us towards renewables much faster,” explains Ravi Manghani, the director of the energy storage section of GTM Research.
One thing is certain: without reliable energy storage technology, the world will struggle to wean itself off dirty coal and other fossil fuels. If an economy and society wants to rely on renewables on a massive scale, it needs a backup solution. Renewables are growing fast – last year, 29 per cent of all electricity in the UK was generated by renewable energy plants; in Germany, it was 33 per cent.
But the sun doesn’t shine at night, and wind doesn’t always blow. Right now, the storage market is dominated by lithium ion battery technology, but despite Tesla’s worldwide total of one gigawatt-hour of energy storage, the available batteries can last about eight hours tops. “We absolutely must install multiple days worth of energy storage – we can’t get away with four to six hours only,” says Manghani.
Storing electricity for longer
Hornsdale Power Reserve 100 MW storage system can provide 129 megawatt-hours of electricity and is connected to the Hornsdale Wind Farm. Its primary aim is to increase grid stability during system contingencies events like extremely hot summer afternoons, or when a large gas plant will trip – it improves the grid’s ability to cope with small blips in energy generation, which typically means replacing about one to one and half hour of energy supply.
“It’s designed to handle very short duration contingency needs,” says Finn-Foley. That’s why batteries simply can’t provide peak power, or compete with and replace so-called ‘peaker’ plants – power plants like natural gas power stations that are only switched on to fill the gap at times of peak energy demand. They also can’t help extend the use of solar power to later in the day. “You’ll need 10 to 12 hours of continuous discharge duration, which means you’ll need four times the battery or more,” says Finn-Foley.
That’s where alternative energy storage technologies could change things.
Currently, the best long-duration energy storage solutions are thermal storage, pumped hydro, compressed air energy storage – and the newest kid on the block, liquid air energy storage. There are also alternative battery technologies such as flow batteries, which researchers believe may one day scale up to discharge energy for longer than lithium ion.
At the end of the day, though, it all comes down to cost. And developing and operating novel tech is not cheap. The cost of lithium ion batteries, meanwhile, keeps on plummeting, thanks to the ever-surging demand for consumer electronics and electric cars, with all the giga and megafactories mushrooming around the globe. Over the past few years, li-ion battery prices dropped by more than 60 per cent – and are expected to fall by another 40 per cent by 2022.
These cost drops are impressive – but while batteries are good for providing power over short timescales, they quickly get very expensive for storing large amounts of energy over hours and days.
What is liquid air energy storage?
Enter LAES. First dreamt up in the 1970s in the UK and then toyed with in the 1980s and 90s by Hitachi and Mitsubishi (without any proper pilot plants though), this tech has the potential to scale up at low cost, says professor Yulong Ding at the University of Birmingham, who together with Highview developed the technology.
LAES works by using electricity from the grid to cool atmospheric air until it liquifies, and then storing it in big tanks at low pressure at –196C – at a fraction of the air’s original volume. “The working principle is quite similar to a domestic fridge – just the temperature and pressure ranges are different,” says Ding. The air can stay in the tanks for weeks and even months, dissipating slowly – and the better the insulation, the slower it will vanish. “It can easily be kept in tanks for about two months,” adds Ding.
When you need to generate electricity, you just have to heat the air to ambient temperature. In the process it will expand a whopping 700 times, creating a lot of air pressure that can be used to spin a turbine in the same way that, say, steam would in conventional generators – and produce electricity.
Because it’s so similar to a traditional fridge, the individual components of LAES for cooling, storing, and re-pressurising gases can be bought quite cheaply off the shelf. “These are well-understood, decades and centuries-old processes that are highly cost-efficient,” says Finn-Foley. The only novel bit here, says Ding, is the integration of the different parts in the most-optimised way.
LAES is not that efficient, though: Tesla’s battery in Australia is 88 per cent efficient, while LAES is 60 to 70 per cent, says Manghani. But as batteries can only store energy for a few hours, if they need to supply energy for longer, they quickly get very costly.
LAES also cannot respond to grid signals in a matter of milliseconds like batteries do. On the upside, the liquid air project can provide energy in bulk, around a day’s worth of it (although the pilot can store just 5 MW of electricity – enough to power roughly 5,000 homes for about three hours; on a commercial scale, Manchester’s LAES plant could have the capacity of 50 MW).
Still, as the liquid air energy storage is so cheap and can scale easily, it could, potentially, fill a crucial gap in the successful energy ecosystem geared towards renewables. Why, then, is it just the UK looking into it? Jonathan Radcliffe, an energy researcher at the University of Birmingham, has a simple answer: because of the UK’s ambitious plans for electricity generation from offshore wind in the 2020s. Also, he adds, “as an island, we have fewer connections to other electricity networks that could help balance supply and demand”.
Manghani is even more prosaic: the world isn’t ready for LAES just yet. Even at the scale of current use of renewables in countries like Germany and Australia, “there is no market out there that needs such longer duration of storage solutions,” he says – experimental plants like LAES are looking for a problem that doesn’t yet exist. But in a decade from now, once solar panel arrays and wind turbines produce more than 60 or 70 per cent of our energy, long-duration storage will be crucial. And we can’t wait a decade to start finding a viable solution, says Manghani – we have to get ready now.
De-Throning the king?
Highview claims that overall, LAES plants will be cheaper than lithium ion; if that’s confirmed at scale: “I expect the technology to go global quickly,” says Finn-Foley. But first, it has to start competing in multiple markets and applications, and existing regulations, as well as incentives to invest in energy storage, are a challenge.
The LAES plant “will need to operate for some time to demonstrate that they have truly worked out the kinks, says Finn-Foley. It also has to prove viability, which is tricky for a project that is supposed to run for decades. “Batteries degrade and must be replaced – but proving a forty-year lifetime is hard to do until you’ve run it for 40 years,” he adds.
But in the end of the day, alternative technologies aren’t trying to usurp li-ion’s throne, but “carve out their own kingdom, with applications and use cases that they think they can do better,” he says. “So far they have been unsuccessful, but a pilot project proving cost-effectiveness is a crucial step.” For the next five years though, he says, “lithium ion will keep the crown”.
“Charge Up in as little as 17 minutes.”
To say Volkswagen has ambitious plans for electric vehicles may be an understatement.
The automaker projects it will produce 15 million vehicles on its new MEB platform in the first wave of its EV assault, and it plans to invest 9 billion euros in the new VW I.D. familythrough 2023.
The marque will have 20 electric models in its lineup by 2025, up from just two entries now. To support this barrage of new EVs, Volkswagen is getting ready to introduce mobile quick-charging stations.
The charging columns are based on the battery pack used with the automaker’s MEB platform.
These stations can be set up in public parking lots, at a company building, or at large events, then removed when no longer needed. VW says the charging process takes an average of 17 minutes.
With a battery storage capacity of 360 kilowatt-hours, each station can charge up to 15 electric vehicles before themselves needed to be recharged.
As many as four vehicles can be charged at the same time, two with DC quick-charging connections and two with AC connections.
Charging stations that have depleted their energy storage would be exchanged for full ones.
When linked up to a power supply, however, the mobile station can be recharged constantly. The charging stations can be juiced up via solar or wind energy, providing C02 neutrality.
Furthermore, VW suggests reusing batteries from electric vehicles to power the stations.
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Tiny, disordered particles of magnesium chromium oxide may hold the key to new magnesium battery energy storage technology, which could possess increased capacity compared to conventional lithium-ion batteries, find UCL and University of Illinois at Chicago researchers.
The study, published today in Nanoscale, reports a new, scalable method for making a material that can reversibly store magnesium ions at high-voltage, the defining feature of a cathode.
While it is at an early stage, the researchers say it is a significant development in moving towards magnesium-based batteries. To date, very few inorganic materials have shown reversible magnesium removal and insertion, which is key for the magnesium battery to function.
“Lithium-ion technology is reaching the boundary of its capability, so it’s important to look for other chemistries that will allow us to build batteries with a bigger storage capacity and a slimmer design,” said co-lead author, Dr. Ian Johnson (UCL Chemistry).
“Magnesium battery technology has been championed as a possible solution to provide longer-lasting phone and electric car batteries, but getting a practical material to use as a cathode has been a challenge.”
One factor limiting lithium-ion batteries is the anode. Low-capacity carbon anodes have to be used in lithium-ion batteries for safety reasons, as the use of pure lithium metal anodes can cause dangerous short circuits and fires.
In contrast, magnesium metal anodes are much safer, so partnering magnesium metal with a functioning cathode material would make a battery smaller and store more energy.
Previous research using computational models predicted that magnesium chromium oxide (MgCr2O4) could be a promising candidate for Mg battery cathodes.
Inspired by this work, UCL researchers produced a ~5 nm, disordered magnesium chromium oxide material in a very rapid and relatively low temperature reaction.
Collaborators at the University of Illinois at Chicago then compared its magnesium activity with a conventional, ordered magnesium chromium oxide material ~7 nm wide.
They used a range of different techniques including X-ray diffraction, X-ray absorption spectroscopy and cutting-edge electrochemical methods to see the structural and chemical changes when the two materials were tested for magnesium activity in a cell.
The two types of crystals behaved very differently, with the disordered particles displaying reversible magnesium extraction and insertion, compared to the absence of such activity in larger, ordered crystals.
“This suggests the future of batteries might lie in disordered and unconventional structures, which is an exciting prospect and one we’ve not explored before as usually disorder gives rise to issues in battery materials. It highlights the importance of seeing if other structurally defective materials might give further opportunities for reversible battery chemistry” explained Professor Jawwad Darr (UCL Chemistry).
“We see increasing the surface area and including disorder in the crystal structure offers novel avenues for important chemistry to take place compared to ordered crystals.
Conventionally, order is desired to provide clear diffusion pathways, allowing cells to be charged and discharged easily—but what we’ve seen suggests that a disordered structure introduces new, accessible diffusion pathways that need to be further investigated,” said Professor Jordi Cabana (University of Illinois at Chicago).
These results are the product of an exciting new collaboration between UK and US researchers. UCL and the University of Illinois at Chicago intend to expand their studies to other disordered, high surface area materials, to enable further gains in magnesium storage capability and develop a practical magnesium battery.
More information: Linhua Hu et al, Tailoring the Electrochemical Activity of Magnesium Chromium Oxide Towards Mg Batteries Through Control of Size and Crystal Structure, Nanoscale (2018). DOI: 10.1039/C8NR08347A
Figure 1: Structure of the newly developed ionic crystal. The pathway in which the ions can travel is highlighted in yellow. (Image: Osaka University)
A research team at Osaka University has reported a new advance in the design of materials for use in rechargeable batteries, under high humidity conditions. Using inspiration from living cells that can block smaller particles but let larger particles pass through, the researchers were able to create a material with highly mobile potassium ions that can easily migrate in response to electric fields (Chemical Science, “Mobility of hydrated alkali metal ions in metallosupramolecular ionic crystals”).
|This work may help make rechargeable batteries safe and inexpensive enough to drastically reduce the cost of electric cars and portable consumer electronics.|
|Link to Osaka University’s Joint Research Programs|
|Rechargeable lithium-ion batteries are widely used in laptops, cell phones, and even electric and hybrid cars. Unfortunately, these batteries are expensive, and have even been known to burst into flames on occasion.|
|New materials that do not use lithium could reduce the cost and improve the safety of these batteries, and have the potential to greatly accelerate the adoption of energy-efficient electric cars. Both sodium and potassium ions are potential candidates that can be used to replace lithium, as they are cheap and in high supply.|
|However, sodium and potassium ions are much larger ions than lithium, so they move sluggishly through most materials. These positive ions are further slowed by the strong attractive forces to the negative charges in crystalline materials.|
|“Potassium ions possess low mobility in the solid state due to their large size, which is a disadvantage for constructing batteries,” explains corresponding author Takumi Konno.|
|To solve this problem, the researchers used the same mechanism your cells employ to allow the large potassium ions to pass through their membranes while simultaneously keeping out smaller particles. Living systems achieve this seemingly impossible feat by considering not just the ion themselves, but also the surrounding water molecules, called the “hydration layer,” that are attracted to the ion’s positive charge.|
|In fact, the smaller the ion, the larger and more tightly bound its associated hydration layer will be. Specialized potassium channels in cell membranes are just the right size to allow hydrated potassium ions to pass through, but block the large hydration layers of smaller ions.|
|The researchers developed an ionic crystal using rhodium, zinc, and oxygen atoms. Just as with the selective biological channels, the mobility of the ions in the crystal was found to be higher for the bigger potassium ions, compared with the smaller lithium ions.|
|In fact, the potassium ions moved so easily, the crystal was classified as a “superionic conductor.” The researchers found that the current material had the largest hydrated potassium ion mobility ever seen to date.|
Figure 2: Conductivities of lithium (Li , red), sodium (Na , green), and potassium (K , blue) ions inside the crystal at different temperatures. The conductivities increase even as the sizes of the ions increase. (Image: Osaka University)
|“Remarkably, the crystal exhibited a particularly high ion conductivity due to the fast migration of hydrated potassium ions in the crystal lattice” lead author Nobuto Yoshinari says. “Such superionic conductivity of hydrated potassium ions in the solid state is unprecedented, and may lead to both safer and cheaper rechargeable batteries.”|
|Source: Osaka University|
October 25, 2018
Rice University scientists are counting on films of carbon nanotubes to make high-powered, fast-charging lithium metal batteries a logical replacement for common lithium-ion batteries.
The Rice lab of chemist James Tour showed thin nanotube films effectively stop dendrites that grow naturally from unprotected lithium metal anodes in batteries. Over time, these tentacle-like dendrites can pierce the battery’s electrolyte core and reach the cathode, causing the battery to fail.
That problem has both dampened the use of lithium metal in commercial applications and encouraged researchers worldwide to solve it.
Rice University graduate student Gladys López-Silva holds a lithium metal anode with a film of carbon nanotubes. Once the film is attached, it becomes infiltrated by lithium ions and turns red. Photo by Jeff Fitlow
Lithium metal charges much faster and holds about 10 times more energy by volume than the lithium-ion electrodes found in just about every electronic device, including cellphones and electric cars.
“One of the ways to slow dendrites in lithium-ion batteries is to limit how fast they charge,” Tour said. “People don’t like that. They want to be able to charge their batteries quickly.”
The Rice team’s answer, detailed in Advanced Materials, is simple, inexpensive and highly effective at stopping dendrite growth, Tour said.
“What we’ve done turns out to be really easy,” he said. “You just coat a lithium metal foil with a multiwalled carbon nanotube film. The lithium dopes the nanotube film, which turns from black to red, and the film in turn diffuses the lithium ions.”
“Physical contact with lithium metal reduces the nanotube film, but balances it by adding lithium ions,” said Rice postdoctoral researcher Rodrigo Salvatierra, co-lead author of the paper with graduate student Gladys López-Silva. “The ions distribute themselves throughout the nanotube film.”
An illustration shows how lithium metal anodes developed at Rice University are protected from dendrite growth by a film of carbon nanotubes. Courtesy of the Tour Group
When the battery is in use, the film discharges stored ions and the underlying lithium anode refills it, maintaining the film’s ability to stop dendrite growth.
The tangled-nanotube film effectively quenched dendrites over 580 charge/discharge cycles of a test battery with a sulfurized-carbon cathode the lab developed in previous experiments.
The researchers reported the full lithium metal cells retained 99.8 percent of their coulombic efficiency, the measure of how well electrons move within an electrochemical system.
Rice University scientists have discovered that a film of multiwalled carbon nanotubes quenches the growth of dendrites in lithium metal-based batteries. Courtesy of the Tour Group
Co-authors of the paper are Rice alumni Almaz Jalilov of the King Fahd University of Petroleum and Minerals, Saudi Arabia; Jongwon Yoon, a senior researcher at the Korea Basic Science Institute; and Gang Wu, an instructor, and Ah-Lim Tsai, a professor of hematology, both at the McGovern Medical School at the University of Texas Health Science Center at Houston.
Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of computer science and of materials science and nanoengineering at Rice.
The research was supported by the Air Force Office of Scientific Research, the National Institutes of Health, the National Council of Science and Technology, Mexico; the National Council for Scientific and Technological Development, Ministry of Science, Technology and Innovation and Coordination for the Improvement of Higher Education Personnel, Brazil; and Celgard, LLC.
Rice University chemist James Tour, left, graduate student Gladys López-Silva and postdoctoral researcher Rodrigo Salvatierra use a film of carbon nanotubes to prevent dendrite growth in lithium metal batteries, which charge faster and hold more power than current lithium-ion batteries. Photo by Jeff Fitlow.
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From 2019, every new car that Volvo launches is set to be electrified. The business wants fully-electric cars to account for 50 percent of overall global sales by the year 2025.
“To support wider consumer adoption of electric cars, society needs to make charging an electric car as simple as filling up your tank,” Zaki Fasihuddin, the Volvo Cars Tech Fund CEO, said in a statement. “Our investment in FreeWire is a firm endorsement of the company’s ambitions in this area.”
In 2017, there were more than 3 million electric and plug-in hybrid cars on the planet’s roads, according to the International Energy Agency’s (IEA) Global Electric Vehicles Outlook. This represents an increase of 54 percent compared to 2016.
Almost 580,000 electric cars were sold in China last year, according to the IEA, while around 280,000 were sold in the U.S.
In terms of charging infrastructure, the IEA says that, globally, there were an estimated 3 million private chargers at homes and workplaces in 2017. The number of “publicly accessible” chargers amounted to roughly 430,000.