New material for inexpensive batteries advancing the large-scale storage of renewable energies

via Engineering News – GlobalSpec

A new conductor material and a new electrode material could pave the way for inexpensive batteries and therefore the large-scale storage of renewable energies.

The energy transition depends on technologies that allow the inexpensive temporary storage of electricity from renewable sources. A promising new candidate is aluminium batteries, which are made from cheap and abundant raw materials (see box).

Scientists from ETH Zurich and Empa – led by Maksym Kovalenko, Professor of Functional Inorganic Materials – are among those involved in researching and developing batteries of this kind. The researchers have now identified two new materials that could bring about key advances in the development of aluminium batteries. The first is a corrosion-resistant material for the conductive parts of the battery; the second is a novel material for the battery’s positive pole that can be adapted to a wide range of technical requirements.

Aggressive electrolyte fluid

As the electrolyte fluid in aluminium batteries is extremely aggressive and corrodes stainless steel, and even gold and platinum, scientists are searching for corrosion-resistant materials for the conductive parts of these batteries. Kovalenko and his colleagues have found what they are looking for in titanium nitride, a ceramic material that exhibits sufficiently high conductivity. “This compound is made up of the highly abundant elements titanium and nitrogen, and it’s easy to manufacture,” explains Kovalenko.

The scientists have successfully made aluminium batteries with conductive parts made of titanium nitride in the laboratory. The material can easily be produced in the form of thin films, also as a coating over other materials such as polymer foils. Kovalenko believes it would also be possible to manufacture the conductors from a conventional metal and coat them with titanium nitride, or even to print conductive titanium nitride tracks on to plastic. “The potential applications of titanium nitride are not limited to aluminium batteries. The material could also be used in other types of batteries; for example, in those based on magnesium or sodium, or in high-voltage lithium-ion batteries,” says Kovalenko.

An alternative to graphite

The second new material can be used for the positive electrode (pole) of aluminium batteries. Whereas the negative electrode in these batteries is made of aluminium, the positive electrode is usually made of graphite. Now, Kovalenko and his team have found a new material that rivals graphite in terms of the amount of energy a battery is able to store. The material in question is polypyrene, a hydrocarbon with a chain-like (polymeric) molecular structure. In experiments, samples of the material – particularly those in which the molecular chains congregate in a disorderly manner – proved to be ideal. “A lot of space remains between the molecular chains. This allows the relatively large ions of the electrolyte fluid to penetrate and charge the electrode material easily,” Kovalenko explains.

One of the advantages of electrodes containing polypyrene is that scientists are able to influence their properties, such as the porosity. The material can therefore be adapted perfectly to the specific application. “In contrast, the graphite used at present is a mineral. From a chemical engineering perspective, it cannot be modified,” says Kovalenko.

As both titanium nitride and polypyrene are flexible materials, the researchers believe they are suitable for use in “pouch cells” (batteries enclosed in a flexible film).

Batteries for the energy transition

An increasing amount of electricity is generated from solar and wind energy. However, as electricity is needed even when the sun is not shining and the wind is not blowing, new technologies will be needed, such as new types of batteries, to store this electricity in a cost-effective manner. Although existing lithium-ion batteries are ideal for electromobility due to their low weight, they are also quite expensive and therefore unsuitable for economical large-scale, stationary power storage.

Furthermore, lithium is a relatively rare metal and is hard to extract – unlike aluminium, magnesium or sodium. Batteries based on one of the latter three elements are thus seen as a promising option for stationary power storage in the future. However, such batteries are still at the research stage and have not yet entered industrial use.

Learn more: New materials for sustainable, low-cost batteries

 

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Aluminum battery from Stanford offers safe alternative to conventional batteries

Stanford postdoc Yingpen Wu and colleagues have developed the first rechargeable aluminum-ion battery that's inexpensive, long-lasting and safe. (Mark Shwartz / Precourt Institute for Energy)

Stanford postdoc Yingpen Wu and colleagues have developed the first rechargeable aluminum-ion battery that’s inexpensive, long-lasting and safe. (Mark Shwartz / Precourt Institute for Energy)

The new aluminum-ion battery could replace many of the lithium-ion and alkaline batteries in wide use today

Stanford University scientists have invented the first high-performance aluminum battery that’s fast-charging, long-lasting and inexpensive. Researchers say the new technology offers a safe alternative to many commercial batteries in wide use today.

“We have developed a rechargeable aluminum battery that may replace existing storage devices, such as alkaline batteries, which are bad for the environment, and lithium-ion batteries, which occasionally burst into flames,” said Hongjie Dai, a professor of chemistry at Stanford. “Our new battery won’t catch fire, even if you drill through it.”

Dai and his colleagues describe their novel aluminum-ion battery in “An ultrafast rechargeable aluminum-ion battery,” which will be published in the April 6 advance online edition of the journal Nature.

Aluminum has long been an attractive material for batteries, mainly because of its low cost, low flammability and high-charge storage capacity. For decades, researchers have tried unsuccessfully to develop a commercially viable aluminum-ion battery.  A key challenge has been finding materials capable of producing sufficient voltage after repeated cycles of charging and discharging.

Graphite cathode

An aluminum-ion battery consists of two electrodes: a negatively charged anode made of aluminum and a positively charged cathode.

“People have tried different kinds of materials for the cathode,” Dai said. “We accidentally discovered that a simple solution is to use graphite, which is basically carbon. In our study, we identified a few types of graphite material that give us very good performance.”

For the experimental battery, the Stanford team placed the aluminum anode and graphite cathode, along with an ionic liquid electrolyte, inside a flexible polymer- coated pouch.

“The electrolyte is basically a salt that’s liquid at room temperature, so it’s very safe,” said Stanford graduate student Ming Gong, co-lead author of the Nature study.

Aluminum batteries are safer than conventional lithium-ion batteries used in millions of laptops and cell phones today, Dai added.

“Lithium-ion batteries can be a fire hazard,” he said.

As an example, he pointed to recent decisions by United and Delta airlines to ban bulk lithium-battery shipments on passenger planes.

“In our study, we have videos showing that you can drill through the aluminum battery pouch, and it will continue working for a while longer without catching fire,” Dai said. “But lithium batteries can go off in an unpredictable manner  – in the air, the car or in your pocket. Besides safety, we have achieved major breakthroughs in aluminum battery performance.”

One example is ultra-fast charging. Smartphone owners know that it can take hours to charge a lithium-ion battery. But the Stanford team reported “unprecedented charging times” of down to one minute with the aluminum prototype.

Read more: Aluminum battery from Stanford offers safe alternative to conventional batteries

 

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