Tag Archives: Po-Chun Hsu

No more kevlar-wrapped lithium-ion batteries?

Current lithium-ion batteries present a fire hazard, which is why, last, year a team of researchers at the University of Michigan came up with a plan to prevent fires by wrapping the batteries in kevlar. My Jan. 30, 2015 post describes the research and provides some information about airplane fires caused by the use of lithium-ion batteries.

This year, a team of researchers at Stanford University (US) have invented a lithium-ion (li-ion) battery that shuts itself down when it overheats, according to a Jan. 12, 2016 news item on Nanotechnology Now,

Stanford researchers have developed the first lithium-ion battery that shuts down before overheating, then restarts immediately when the temperature cools.

The new technology could prevent the kind of fires that have prompted recalls and bans on a wide range of battery-powered devices, from recliners and computers to navigation systems and hoverboards [and on airplanes].

“People have tried different strategies to solve the problem of accidental fires in lithium-ion batteries,” said Zhenan Bao, a professor of chemical engineering at Stanford. “We’ve designed the first battery that can be shut down and revived over repeated heating and cooling cycles without compromising performance.”

Stanford has produced a video of Dr. Bao discussing her latest work,

A Jan. 11, 2016 Stanford University news release by Mark Schwartz, which originated the news item, provides more detail about li-ion batteries and the new fire prevention technology,

A typical lithium-ion battery consists of two electrodes and a liquid or gel electrolyte that carries charged particles between them. Puncturing, shorting or overcharging the battery generates heat. If the temperature reaches about 300 degrees Fahrenheit (150 degrees Celsius), the electrolyte could catch fire and trigger an explosion.

Several techniques have been used to prevent battery fires, such as adding flame retardants to the electrolyte. In 2014, Stanford engineer Yi Cui created a “smart” battery that provides ample warning before it gets too hot.

“Unfortunately, these techniques are irreversible, so the battery is no longer functional after it overheats,” said study co-author Cui, an associate professor of materials science and engineering and of photon science. “Clearly, in spite of the many efforts made thus far, battery safety remains an important concern and requires a new approach.”

Nanospikes

To address the problem Cui, Bao and postdoctoral scholar Zheng Chen turned to nanotechnology. Bao recently invented a wearable sensor to monitor human body temperature. The sensor is made of a plastic material embedded with tiny particles of nickel with nanoscale spikes protruding from their surface.

For the battery experiment, the researchers coated the spiky nickel particles with graphene, an atom-thick layer of carbon, and embedded the particles in a thin film of elastic polyethylene.

“We attached the polyethylene film to one of the battery electrodes so that an electric current could flow through it,” said Chen, lead author of the study. “To conduct electricity, the spiky particles have to physically touch one another. But during thermal expansion, polyethylene stretches. That causes the particles to spread apart, making the film nonconductive so that electricity can no longer flow through the battery.”

When the researchers heated the battery above 160 F (70 C), the polyethylene film quickly expanded like a balloon, causing the spiky particles to separate and the battery to shut down. But when the temperature dropped back down to 160 F (70 C), the polyethylene shrunk, the particles came back into contact, and the battery started generating electricity again.

“We can even tune the temperature higher or lower depending on how many particles we put in or what type of polymer materials we choose,” said Bao, who is also a professor, by courtesy, of chemistry and of materials science and engineering. “For example, we might want the battery to shut down at 50 C or 100 C.”

Reversible strategy

To test the stability of new material, the researchers repeatedly applied heat to the battery with a hot-air gun. Each time, the battery shut down when it got too hot and quickly resumed operating when the temperature cooled.

“Compared with previous approaches, our design provides a reliable, fast, reversible strategy that can achieve both high battery performance and improved safety,” Cui said. “This strategy holds great promise for practical battery applications.”

Here’s a link to and a citation for the paper,

Fast and reversible thermoresponsive polymer switching materials for safer batteries by Zheng Chen, Po-Chun Hsu, Jeffrey Lopez, Yuzhang Li, John W. F. To, Nan Liu, Chao Wang, Sean C. Andrews, Jia Liu, Yi Cui, & Zhenan Bao. Nature Energy 1, Article number: 15009 (2016) doi:10.1038/nenergy.2015.9 Published online: 11 January 2016

This paper appears to be open access.

A new approach to heating: warm the clothing not the room

A Jan. 7, 2015 news item on ScienceDaily describes a new type of textile which could change the way we use heat (energy),

To stay warm when temperatures drop outside, we heat our indoor spaces — even when no one is in them. But scientists have now developed a novel nanowire coating for clothes that can both generate heat and trap the heat from our bodies better than regular clothes. They report on their technology, which could help us reduce our reliance on conventional energy sources, in the ACS journal Nano Letters.

A Jan. 7, 2015 American Chemical Society (ACS) news release (also on EurekAlert), which originated the news item, provides more information about energy consumption and the researchers’ proposed solution,

Yi Cui [Stanford University] and colleagues note that nearly half of global energy consumption goes toward heating buildings and homes. But this comfort comes with a considerable environmental cost – it’s responsible for up to a third of the world’s total greenhouse gas emissions. Scientists and policymakers have tried to reduce the impact of indoor heating by improving insulation and construction materials to keep fuel-generated warmth inside. Cui’s team wanted to take a different approach and focus on people rather than spaces.

The researchers developed lightweight, breathable mesh materials that are flexible enough to coat normal clothes. When compared to regular clothing material, the special nanowire cloth trapped body heat far more effectively. Because the coatings are made out of conductive materials, they can also be actively warmed with an electricity source to further crank up the heat. The researchers calculated that their thermal textiles could save about 1,000 kilowatt hours per person every year — that’s about how much electricity an average U.S. home consumes in one month.

Here’s a link to and a citation for the paper,

Personal Thermal Management by Metallic Nanowire-Coated Textile by Po-Chun Hsu, Xiaoge Liu, Chong Liu, Xing Xie, Hye Ryoung Lee, Alex J. Welch, Tom Zhao, and Yi Cui. Nano Lett., Article ASAP DOI: 10.1021/nl5036572 Publication Date (Web): November 30, 2014
Copyright © 2014 American Chemical Society

This paper is behind a paywall.

How is an eggshell like a lithium-ion battery?

How is an eggshell like a lithium-ion battery? It’s all about the yolk. Some days I can’t resist the urge for some wordplay, even if it isn’t the best fit, and the Jan. 9, 2013 news item by Mike Ross on phys.org proved irresistible,

SLAC [Stanford National Accelerator Laboratory] and Stanford [University] scientists have set a world record for energy storage, using a clever “yolk-shell” design to store five times more energy in the sulfur cathode of a rechargeable lithium-ion battery than is possible with today’s commercial technology. The cathode also maintained a high level of performance after 1,000 charge/discharge cycles, paving the way for new generations of lighter, longer-lasting batteries for use in portable electronics and electric vehicles.

The study has been published in Nature Communications where this explanatory image amongst others can be viewed,

[downloaded from Nature Communications: http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2327.html]

[downloaded from Nature Communications: http://www.nature.com/ncomms/journal/v4/n1/full/ncomms2327.html]

You can find out more about the research here,

Sulphur–TiO2 yolk–shell nanoarchitecture with internal void space for long-cycle lithium–sulphur batteries by Zhi Wei Seh, Weiyang Li, Judy J. Cha,    Guangyuan Zheng, Yuan Yang, Matthew T. McDowell, Po-Chun Hsu & Yi Cui in Nature Communications 4, Article number: 1331 doi:10.1038/ncomms2327

The Jan. 8, 2013 SLAC news release, which originated the news item, provides more details about the lithium-ion batteries in general and this attempt to improve their energy storage capacity,

Lithium-ion batteries work by moving lithium ions back and forth between two electrodes, the cathode and anode. Charging the battery forces the ions and electrons into the anode, creating an electrical potential that can power a wide range of devices. Discharging the battery – using it to do work – moves the ions and electrons to the cathode.

Today’s lithium-ion batteries typically retain about 80 percent of their initial capacity after 500 charge/discharge cycles.

For some 20 years, researchers have known that sulfur could theoretically store more lithium ions, and thus much more energy, than today’s cathode materials…

Cui’s innovation is a cathode made of nanoparticles, each a tiny sulfur nugget surrounded by a hard shell of porous titanium-oxide, like an egg yolk in an eggshell. Between the yolk and shell, where the egg white would be, is an empty space into which the sulfur can expand. During discharging, lithium ions pass through the shell and bind to the sulfur, which expands to fill the void but not so much as to break the shell. The shell, meanwhile, protects the sulfur-lithium intermediate compound from electrolyte solvent that would dissolve it.

Each cathode particle is only 800 nanometers (billionths of a meter) in diameter, about one-hundredth the diameter of a human hair.

“After 1,000 charge/discharge cycles, our yolk-shell sulfur cathode had retained about 70 percent of its energy-storage capacity. This is the highest performing sulfur cathode in the world, as far as we know,” he [Cui] said. “Even without optimizing the design, this cathode cycle life is already on par with commercial performance. This is a very important achievement for the future of rechargeable batteries.”

Over the past seven years, Cui’s group has demonstrated a succession of increasingly capable anodes that use silicon rather than carbon because it can store up to 10 times more charge per weight. Their most recent anode also has a yolk-shell design that retains its energy-storage capacity over 1,000 charge/discharge cycles.

The group’s next step is to combine the yolk-shell sulfur cathode with a yolk-shell silicon anode to see if together they produce a high-energy, long-lasting battery.

I have posted a number of recent pieces about lithium-ion (li-ion) batteries including a Dec. 12, 2012 piece about using the Madder plant to develop a greener li-ion battery, a Dec. 10, 2012 piece about the break-up of 123 Systems, a manufacturer of li-ion batteries, and a Nov. 27, 2012 piece about a project in Québec to combine lithium iron phospate with graphene for improved li-ion batteries.