New design points a path to the ‘ultimate’ battery

ultimate-battery-lithium-oxygen
Many of the technologies we use every day have been getting smaller, faster and cheaper each year — with the notable exception of batteries. Apart from the possibility of a smartphone which lasts for days without needing to be charged, the challenges associated with making a better battery are holding back the widespread adoption of two major clean technologies: electric cars and grid-scale storage for solar power. Credit: © Eyematrix / Fotolia

Scientists have developed a working laboratory demonstrator of a lithium-oxygen battery which has very high energy density, is more than 90% efficient, and, to date, can be recharged more than 2000 times, showing how several of the problems holding back the development of these devices could be solved.

Lithium-oxygen, or lithium-air, batteries have been touted as the ‘ultimate’ battery due to their theoretical energy density, which is ten times that of a lithium-ion battery. Such a high energy density would be comparable to that of gasoline — and would enable an electric car with a battery that is a fifth the cost and a fifth the weight of those currently on the market to drive from London to Edinburgh on a single charge.

However, as is the case with other next-generation batteries, there are several practical challenges that need to be addressed before lithium-air batteries become a viable alternative to gasoline.

Now, researchers from the University of Cambridge have demonstrated how some of these obstacles may be overcome, and developed a lab-based demonstrator of a lithium-oxygen battery which has higher capacity, increased energy efficiency and improved stability over previous attempts.

Their demonstrator relies on a highly porous, ‘fluffy’ carbon electrode made from graphene (comprising one-atom-thick sheets of carbon atoms), and additives that alter the chemical reactions at work in the battery, making it more stable and more efficient. While the results, reported in the journal Science, are promising, the researchers caution that a practical lithium-air battery still remains at least a decade away.

“What we’ve achieved is a significant advance for this technology and suggests whole new areas for research — we haven’t solved all the problems inherent to this chemistry, but our results do show routes forward towards a practical device,” said Professor Clare Grey of Cambridge’s Department of Chemistry, the paper’s senior author.

Many of the technologies we use every day have been getting smaller, faster and cheaper each year — with the notable exception of batteries. Apart from the possibility of a smartphone which lasts for days without needing to be charged, the challenges associated with making a better battery are holding back the widespread adoption of two major clean technologies: electric cars and grid-scale storage for solar power.

“In their simplest form, batteries are made of three components: a positive electrode, a negative electrode and an electrolyte,” said Dr Tao Liu, also from the Department of Chemistry, and the paper’s first author.

In the lithium-ion (Li-ion) batteries we use in our laptops and smartphones, the negative electrode is made of graphite (a form of carbon), the positive electrode is made of a metal oxide, such as lithium cobalt oxide, and the electrolyte is a lithium salt dissolved in an organic solvent. The action of the battery depends on the movement of lithium ions between the electrodes. Li-ion batteries are light, but their capacity deteriorates with age, and their relatively low energy densities mean that they need to be recharged frequently.

Over the past decade, researchers have been developing various alternatives to Li-ion batteries, and lithium-air batteries are considered the ultimate in next-generation energy storage, because of their extremely high energy density. However, previous attempts at working demonstrators have had low efficiency, poor rate performance, unwanted chemical reactions, and can only be cycled in pure oxygen.

What Liu, Grey and their colleagues have developed uses a very different chemistry than earlier attempts at a non-aqueous lithium-air battery, relying on lithium hydroxide (LiOH) instead of lithium peroxide (Li2O2). With the addition of water and the use of lithium iodide as a ‘mediator’, their battery showed far less of the chemical reactions which can cause cells to die, making it far more stable after multiple charge and discharge cycles.

By precisely engineering the structure of the electrode, changing it to a highly porous form of graphene, adding lithium iodide, and changing the chemical makeup of the electrolyte, the researchers were able to reduce the ‘voltage gap’ between charge and discharge to 0.2 volts. A small voltage gap equals a more efficient battery — previous versions of a lithium-air battery have only managed to get the gap down to 0.5 — 1.0 volts, whereas 0.2 volts is closer to that of a Li-ion battery, and equates to an energy efficiency of 93%.

The highly porous graphene electrode also greatly increases the capacity of the demonstrator, although only at certain rates of charge and discharge. Other issues that still have to be addressed include finding a way to protect the metal electrode so that it doesn’t form spindly lithium metal fibres known as dendrites, which can cause batteries to explode if they grow too much and short-circuit the battery.

Additionally, the demonstrator can only be cycled in pure oxygen, while the air around us also contains carbon dioxide, nitrogen and moisture, all of which are generally harmful to the metal electrode.

“There’s still a lot of work to do,” said Liu. “But what we’ve seen here suggests that there are ways to solve these problems — maybe we’ve just got to look at things a little differently.”

“While there are still plenty of fundamental studies that remain to be done, to iron out some of the mechanistic details, the current results are extremely exciting — we are still very much at the development stage, but we’ve shown that there are solutions to some of the tough problems associated with this technology,” said Grey.


Story Source:

The above post is reprinted from materials provided by University of Cambridge. Note: Materials may be edited for content and length.


Journal Reference:

  1. T. Liu, M. Leskes, W. Yu, A. J. Moore, L. Zhou, P. M. Bayley, G. Kim, C. P. Grey. Cycling Li-O2 batteries via LiOH formation and decomposition. Science, 2015; 350 (6260): 530 DOI: 10.1126/science.aac7730

Making batteries with portabella mushrooms

Diagram showing how mushrooms are turned into a material for battery anodes. Credit: Image courtesy of University of California - Riverside
Diagram showing how mushrooms are turned into a material for battery anodes.
Credit: Image courtesy of University of California – Riverside

Can portabella stop cell phone batteries from degrading over time?

Researchers at the University of California, Riverside Bourns College of Engineering think so.

They have created a new type of lithium-ion battery anode using portabella mushrooms, which are inexpensive, environmentally friendly and easy to produce. The current industry standard for rechargeable lithium-ion battery anodes is synthetic graphite, which comes with a high cost of manufacturing because it requires tedious purification and preparation processes that are also harmful to the environment.

With the anticipated increase in batteries needed for electric vehicles and electronics, a cheaper and sustainable source to replace graphite is needed. Using biomass, a biological material from living or recently living organisms, as a replacement for graphite, has drawn recent attention because of its high carbon content, low cost and environmental friendliness.

UC Riverside engineers were drawn to using mushrooms as a form of biomass because past research has established they are highly porous, meaning they have a lot of small spaces for liquid or air to pass through. That porosity is important for batteries because it creates more space for the storage and transfer of energy, a critical component to improving battery performance.

In addition, the high potassium salt concentration in mushrooms allows for increased electrolyte-active material over time by activating more pores, gradually increasing its capacity.

A conventional anode allows lithium to fully access most of the material during the first few cycles and capacity fades from electrode damage occurs from that point on. The mushroom carbon anode technology could, with optimization, replace graphite anodes. It also provides a binderless and current-collector free approach to anode fabrication.

“With battery materials like this, future cell phones may see an increase in run time after many uses, rather than a decrease, due to apparent activation of blind pores within the carbon architectures as the cell charges and discharges over time,” said Brennan Campbell, a graduate student in the Materials Science and Engineering program at UC Riverside.

The research findings were outlined in a paper, “Bio-Derived, Binderless, Hierarchically Porous Carbon Anodes for Li-ion Batteries,” published in the journal Scientific Reports. It was authored by Cengiz Ozkan and Mihri Ozkan, both professors in the Bourns College of Engineering, and three of their current or former graduate students: Campbell, Robert Ionescu and Zachary Favors.

Nanocarbon architectures derived from biological materials such as mushrooms can be considered a green and sustainable alternative to graphite-based anodes, said Cengiz Ozkan, a professor of mechanical engineering and materials science and engineering.

The nano-ribbon-like architectures transform upon heat treatment into an interconnected porous network architecture which is important for battery electrodes because such architectures possess a very large surface area for the storage of energy, a critical component to improving battery performance.

One of the problems with conventional carbons, such as graphite, is that they are typically prepared with chemicals such as acids and activated by bases that are not environmentally friendly, said Mihri Ozkan, a professor of electrical and computer engineering. Therefore, the UC Riverside team is focused on naturally-derived carbons, such as the skin of the caps of portabella mushrooms, for making batteries.

It is expected that nearly 900,000 tons of natural raw graphite would be needed for anode fabrication for nearly six million electric vehicle forecast to be built by 2020. This requires that the graphite be treated with harsh chemicals, including hydrofluoric and sulfuric acids, a process that creates large quantities of hazardous waste. The European Union projects this process will be unsustainable in the future.

The Ozkan’s research is supported by the University of California, Riverside.

This paper involving mushrooms is published just over a year after the Ozkan’s labs developed a lithium-ion battery anode based on nanosilicon via beach sand as the natural raw material. Ozkan’s team is currently working on the development of pouch prototype batteries based on nanosilicon anodes.

The UCR Office of Technology Commercialization has filed patents for the inventions above.


Story Source:

The above post is reprinted from materials provided by University of California – Riverside. The original item was written by Sean Nealon. Note: Materials may be edited for content and length.


Journal Reference:

  1. Brennan Campbell, Robert Ionescu, Zachary Favors, Cengiz S. Ozkan, Mihrimah Ozkan. Bio-Derived, Binderless, Hierarchically Porous Carbon Anodes for Li-ion Batteries. Scientific Reports, 2015; 5: 14575 DOI: 10.1038/srep14575

Trees are source for high-capacity, soft batteries

A closeup of the soft battery, created with wood pulp nanocellulose. Credit: Courtesy of Max Hamedi and Wallenberg Wood Science Center
A closeup of the soft battery, created with wood pulp nanocellulose.
Credit: Courtesy of Max Hamedi and Wallenberg Wood Science Center

A method for making elastic high-capacity batteries from wood pulp was unveiled by researchers in Sweden and the US. Using nanocellulose broken down from tree fibres, a team from KTH Royal Institute of Technology and Stanford University produced an elastic, foam-like battery material that can withstand shock and stress.

“It is possible to make incredible materials from trees and cellulose,” says Max Hamedi, who is a researcher at KTH and Harvard University. One benefit of the new wood-based aerogel material is that it can be used for three-dimensional structures.

“There are limits to how thin a battery can be, but that becomes less relevant in 3D, ” Hamedi says. “We are no longer restricted to two dimensions. We can build in three dimensions, enabling us to fit more electronics in a smaller space.”

A 3D structure enables storage of significantly more power in less space than is possible with conventional batteries, he says.

“Three-dimensional, porous materials have been regarded as an obstacle to building electrodes. But we have proven that this is not a problem. In fact, this type of structure and material architecture allows flexibility and freedom in the design of batteries,” Hamedi says.

The process for creating the material begins with breaking down tree fibres, making them roughly one million times thinner. The nanocellulose is dissolved, frozen and then freeze-dried so that the moisture evaporates without passing through a liquid state.

Then the material goes through a process in which the molecules are stabilised so that the material does not collapse.

“The result is a material that is both strong, light and soft,” Hamedi says. “The material resembles foam in a mattress, though it is a little harder, lighter and more porous. You can touch it without it breaking.”

The finished aerogel can then be treated with electronic properties. “We use a very precise technique, verging on the atomic level, which adds ink that conducts electricity within the aerogel. You can coat the entire surface within.”

In terms of surface area, Hamedi compares the material to a pair of human lungs, which if unfurled could be spread over a football field. Similarly, a single cubic decimeter of the battery material would cover most of a football pitch, he says.

“You can press it as much as you want. While flexible and stretchable electronics already exist, the insensitivity to shock and impact are somewhat new.”

Hamedi says the aerogel batteries could be used in electric car bodies, as well as in clothing, providing the garment has a lining.

The research has been carried out at the Wallenberg Wood Science Center at KTH. KTH Professor Lars Wågberg also has been involved, and his work on aerogels is in the basis for the invention of soft electronics. Another partner is leading battery researcher, Professor Yi Cui from Stanford University.


Story Source:

The above story is based on materials provided by KTH The Royal Institute of Technology. Note: Materials may be edited for content and length.


Journal Reference:

  1. Gustav Nyström, Andrew Marais, Erdem Karabulut, Lars Wågberg, Yi Cui & Mahiar M. Hamedi. Self-Assembled Three-Dimensional And Compressible Interdigitated Thin Film Supercapacitors And Batteries. Nature Communications, May 29, 2015 DOI:10.1038/ncomms8259

Ultra-fast charging batteries that can be 70% recharged in just two minutes

NTU Assoc Prof Chen holding the ultrafast rechargable batteries in his right hand, with the battery test station to his left. Credit: Image courtesy of Nanyang Technological University
NTU Assoc Prof Chen holding the ultrafast rechargable batteries in his right hand, with the battery test station to his left.
Credit: Image courtesy of Nanyang Technological University

Scientists from Nanyang Technological University (NTU Singapore) have developed a new battery that can be recharged up to 70 per cent in only 2 minutes. The battery will also have a longer lifespan of over 20 years.

Expected to be the next big thing in battery technology, this breakthrough has a wide-ranging impact on many industries, especially for electric vehicles which are currently inhibited by long recharge times of over 4 hours and the limited lifespan of batteries.

This next generation of lithium-ion batteries will enable electric vehicles to charge 20 times faster than the current technology. With it, electric vehicles will also be able to do away with frequent battery replacements. The new battery will be able to endure more than 10,000 charging cycles — 20 times more than the current 500 cycles of today’s batteries.

NTU Singapore’s scientists replaced the traditional graphite used for the anode (negative pole) in lithium-ion batteries with a new gel material made from titanium dioxide, an abundant, cheap and safe material found in soil. It is commonly used as a food additive or in sunscreen lotions to absorb harmful ultraviolet rays.

Naturally found in a spherical shape, NTU Singapore developed a simple method to turn titanium dioxide particles into tiny nanotubes that are a thousand times thinner than the diameter of a human hair.

This nanostructure is what helps to speeds up the chemical reactions taking place in the new battery, allowing for superfast charging.

Invented by Associate Professor Chen Xiaodong from the School of Materials Science and Engineering at NTU Singapore, the science behind the formation of the new titanium dioxide gel was published in the latest issue of Advanced Materials, a leading international scientific journal in materials science.

NTU professor Rachid Yazami, who was the co-inventor of the lithium-graphite anode 34 years ago that is used in most lithium-ion batteries today, said Prof Chen’s invention is the next big leap in battery technology.

“While the cost of lithium-ion batteries has been significantly reduced and its performance improved since Sony commercialised it in 1991, the market is fast expanding towards new applications in electric mobility and energy storage,” said Prof Yazami.

“There is still room for improvement and one such key area is the power density — how much power can be stored in a certain amount of space — which directly relates to the fast charge ability. Ideally, the charge time for batteries in electric vehicles should be less than 15 minutes, which Prof Chen’s nanostructured anode has proven to do.”

Prof Yazami, who is Prof Chen’s colleague at NTU Singapore, is not part of this research project and is currently developing new types of batteries for electric vehicle applications at the Energy Research Institute at NTU (ERI@N).

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Commercialisation of technology

Moving forward, Prof Chen’s research team will be applying for a Proof-of-Concept grant to build a large-scale battery prototype. The patented technology has already attracted interest from the industry.

The technology is currently being licensed to a company and Prof Chen expects that the new generation of fast-charging batteries will hit the market in two years’ time. It holds a lot of potential in overcoming the longstanding power issues related to electro-mobility.

“With our nanotechnology, electric cars would be able to increase their range dramatically with just five minutes of charging, which is on par with the time needed to pump petrol for current cars,” added Prof Chen.

“Equally important, we can now drastically cut down the waste generated by disposed batteries, since our batteries last ten times longer than the current generation of lithium-ion batteries.”

The long-life of the new battery also means drivers save on the cost of a battery replacement, which could cost over USD$5,000 each.

Easy to manufacture

According to Frost & Sullivan, a leading growth-consulting firm, the global market of rechargeable lithium-ion batteries is projected to be worth US$23.4 billion in 2016.

Lithium-ion batteries usually use additives to bind the electrodes to the anode, which affects the speed in which electrons and ions can transfer in and out of the batteries.

However, Prof Chen’s new cross-linked titanium dioxide nanotube-based electrodes eliminate the need for these additives and can pack more energy into the same amount of space.

“Manufacturing this new nanotube gel is very easy,” Prof Chen added. “Titanium dioxide and sodium hydroxide are mixed together and stirred under a certain temperature. Battery manufacturers will find it easy to integrate our new gel into their current production processes.”

This battery research project took the team of four NTU Singapore scientists three years to complete and is funded by Singapore’s National Research Foundation.

Last year, Prof Yazami was awarded the Draper Prize by the National Academy of Engineering for his ground-breaking work in developing the lithium-ion battery with three other scientists.


Story Source:

The above story is based on materials provided by Nanyang Technological University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Yuxin Tang, Yanyan Zhang, Jiyang Deng, Jiaqi Wei, Hong Le Tam, Bevita Kallupalathinkal Chandran, Zhili Dong, Zhong Chen, Xiaodong Chen. Nanotubes: Mechanical Force-Driven Growth of Elongated Bending TiO2-based Nanotubular Materials for Ultrafast Rechargeable Lithium Ion Batteries (Adv. Mater. 35/2014). Advanced Materials, 2014; 26 (35): 6046 DOI:10.1002/adma.201470238