Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New 'designer carbon' from Stanford boosts battery performance

01.06.2015

Stanford University scientists have created a new carbon material that significantly boosts the performance of energy-storage technologies. Their results are featured on the cover of the journal ACS Central Science.

"We have developed a 'designer carbon' that is both versatile and controllable," said Zhenan Bao, the senior author of the study and a professor of chemical engineering at Stanford. "Our study shows that this material has exceptional energy-storage capacity, enabling unprecedented performance in lithium-sulfur batteries and supercapacitors."


This image shows designer carbon improving energy storage.

Credit: John To and Zheng Chen, Stanford University

According to Bao, the new designer carbon represents a dramatic improvement over conventional activated carbon, an inexpensive material widely used in products ranging from water filters and air deodorizers to energy-storage devices.

"A lot of cheap activated carbon is made from coconut shells," Bao said. "To activate the carbon, manufacturers burn the coconut at high temperatures and then chemically treat it."

The activation process creates nanosized holes, or pores, that increase the surface area of the carbon, allowing it to catalyze more chemical reactions and store more electrical charges.

But activated carbon has serious drawbacks, Bao said. For example, there is little interconnectivity between the pores, which limits their ability to transport electricity.

"With activated carbon, there's no way to control pore connectivity," Bao said. "Also, lots of impurities from the coconut shells and other raw starting materials get carried into the carbon. As a refrigerator deodorant, conventional activated carbon is fine, but it doesn't provide high enough performance for electronic devices and energy-storage applications."

3-D networks

Instead of using coconut shells, Bao and her colleagues developed a new way to synthesize high-quality carbon using inexpensive - and uncontaminated - chemicals and polymers.

The process begins with conducting hydrogel, a water-based polymer with a spongy texture similar to soft contact lenses.

"Hydrogel polymers form an interconnected, three-dimensional framework that's ideal for conducting electricity," Bao said. "This framework also contains organic molecules and functional atoms, such as nitrogen, which allow us to tune the electronic properties of the carbon."

For the study, the Stanford team used a mild carbonization and activation process to convert the polymer organic frameworks into nanometer-thick sheets of carbon.

"The carbon sheets form a 3-D network that has good pore connectivity and high electronic conductivity," said graduate student John To, a co-lead author of the study. "We also added potassium hydroxide to chemically activate the carbon sheets and increase their surface area."

The result: designer carbon that can be fine-tuned for a variety of applications.

"We call it designer carbon because we can control its chemical composition, pore size and surface area simply by changing the type of polymers and organic linkers we use, or by adjusting the amount of heat we apply during the fabrication process," To said.

For example, raising the processing temperature from 750 degrees Fahrenheit (400 degrees Celsius) to 1,650 F (900 C) resulted in a 10-fold increase in pore volume.

Subsequent processing produced carbon material with a record-high surface area of 4,073 square meters per gram - the equivalent of three American football fields packed into an ounce of carbon. The maximum surface area achieved with conventional activated carbon is about 3,000 square meters per gram.

"High surface area is essential for many applications, including electrocatalysis, storing energy and capturing carbon dioxide emissions from factories and power plants," Bao said.

Supercapacitors

To see how the new material performed in real-world conditions, the Stanford team fabricated carbon-coated electrodes and installed them in lithium-sulfur batteries and supercapacitors.

"Supercapacitors are energy-storage devices widely used in transportation and electronics because of their ultra-fast charging and discharging capability," said postdoctoral scholar Zheng Chen, a co-lead author. "For supercapacitors, the ideal carbon material has a high surface area for storing electrical charges, high conductivity for transporting electrons and a suitable pore architecture that allows for the rapid movement of ions from the electrolyte solution to the carbon surface."

In the experiment, a current was applied to supercapacitors equipped with designer-carbon electrodes.

The results were dramatic. Electrical conductivity improved threefold compared to supercapacitor electrodes made of conventional activated carbon.

"We also found that our designer carbon improved the rate of power delivery and the stability of the electrodes," Bao added.

Batteries

Tests were also conducted on lithium-sulfur batteries, a promising technology with a serious flaw: When lithium and sulfur react, they produce molecules of lithium polysulfide, which can leak from the electrode into the electrolyte and cause the battery to fail.

The Stanford team discovered that electrodes made with designer carbon can trap those pesky polysulfides and improve the battery's performance.

"We can easily design electrodes with very small pores that allow lithium ions to diffuse through the carbon but prevent the polysulfides from leaching out," Bao said. "Our designer carbon is simple to make, relatively cheap and meets all of the critical requirements for high-performance electrodes."

###

Other Stanford co-authors of the study are graduate student Jiajun He; postdoctoral scholars Hongbin Yao, Kwanpyo Kim and Ho-Hsiu Chou; visiting scholar Lijia Pan, and professors Jennifer Wilcox and Yi Cui.

Media Contact

Mark Shwartz
mshwartz@stanford.edu
650-723-9296

 @stanford

http://news.stanford.edu/ 

Mark Shwartz | EurekAlert!

More articles from Materials Sciences:

nachricht Scientists channel graphene to understand filtration and ion transport into cells
11.12.2017 | National Institute of Standards and Technology (NIST)

nachricht Successful Mechanical Testing of Nanowires
07.12.2017 | Helmholtz-Zentrum Geesthacht - Zentrum für Material- und Küstenforschung

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

Im Focus: Virtual Reality for Bacteria

An interdisciplinary group of researchers interfaced individual bacteria with a computer to build a hybrid bio-digital circuit - Study published in Nature Communications

Scientists at the Institute of Science and Technology Austria (IST Austria) have managed to control the behavior of individual bacteria by connecting them to a...

Im Focus: A space-time sensor for light-matter interactions

Physicists in the Laboratory for Attosecond Physics (run jointly by LMU Munich and the Max Planck Institute for Quantum Optics) have developed an attosecond electron microscope that allows them to visualize the dispersion of light in time and space, and observe the motions of electrons in atoms.

The most basic of all physical interactions in nature is that between light and matter. This interaction takes place in attosecond times (i.e. billionths of a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

PhoxTroT: Optical Interconnect Technologies Revolutionized Data Centers and HPC Systems

11.12.2017 | Information Technology

Large-scale battery storage system in field trial

11.12.2017 | Power and Electrical Engineering

See, understand and experience the work of the future

11.12.2017 | Event News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>