How Batteries Grow Old

There should be an image here!In a laboratory at Ohio State University, an ongoing experiment is studying why batteries lose their ability to hold a charge as they age — specifically lithium-ion batteries, which have generated a lot of buzz for their potential to power the electric cars of the future.

Preliminary results presented today at the AVS 57th International Symposium & Exhibition, taking place this week at the Albuquerque Convention Center in New Mexico, suggest that the irreversible changes inside a dead battery start at the nanoscale.

Yann Guezennec and Giorgio Rizzoni of OSU developed new experimental facilities and procedures to charge and discharge commercially available Li-ion batteries thousands of times over many months in a variety of conditions designed to mimic how these batteries are actually used by hybrid and all-electric vehicles. Some of the batteries were run in hot temperatures like those in Arizona; others in colder conditions similar to those in Alaska.

To understand the results of this testing, Bharat Bhushan, Suresh Babu, and Lei Raymond Cao studied the materials inside of the batteries to help determine how this aging manifests itself in the structure of the electrode materials.

When the batteries died, the scientists dissected them and used a technique called infrared thermal imaging to search for problem areas in each electrode, a 1.5-meter-long strip of metal tape coated with oxide and rolled up like a jelly roll. They then took a closer look at these problem areas using a variety of techniques with different length scale resolutions (e.g. scanning electron microscopy, atomic force microscope, scanning spreading resistance microscopy, Kelvin probe microscopy, transmission electron microscopy) and discovered that the finely-structured nanomaterials on these electrodes that allow the battery rapidly charge and discharge had coarsened in size.

Additional studies of the aged batteries, using neutron depth profiling, revealed that a fraction of the lithium that is responsible, in ion form, for shuttling electric charge between electrodes during charging and discharging, was no longer available for charge transfer, but was irreversibly lost from the cathode to the anode.

“We can clearly see that an aged sample versus and unaged sample has much lower lithium concentration in the cathode,” said Rizzoni, director of the Center for Automotive Research at OSU. “It has essentially combined with anode material in an irreversible way.”

This research is being performed by Center for Automotive Research at OSU in collaboration with Oak Ridge National Laboratory and the National Institute of Standards Technology.

The researchers suspect, but cannot yet prove, that the coarsening of the cathode may be behind this loss of lithium. If this theory turns out to be correct, it could point battery manufacturers in the right direction for making durable batteries with longer lifetimes.

[Photo above by Dean Johnson / CC BY-ND 2.0]

Jason Socrates Bardi @ American Institute of Physics


Batteries Smaller Than A Grain Of Salt

There should be an image here!Lithium-ion batteries have become ubiquitous in today’s consumer electronics — powering our laptops, phones, and iPods. Research funded by DARPA is pushing the limits of this technology and trying to create some of the tiniest batteries on Earth, the largest of which would be no bigger than a grain of sand.

These tiny energy storage devices could one day be used to power the electronics and mechanical components of tiny micro- to nano-scale devices.

Jane Chang, an engineer at the University of California, Los Angeles, is designing one component of these batteries: the electrolyte that allows charge to flow between electrodes. She presents her results today at the AVS 57th International Symposium & Exhibition, which takes place this week at the Albuquerque Convention Center in New Mexico.

“We’re trying to achieve the same power densities, the same energy densities as traditional lithium ion batteries, but we need to make the footprint much smaller,” says Chang.

To reach this goal, Chang is thinking in three dimensions in collaboration with Bruce Dunn other researchers at UCLA. She’s coating well-ordered micro-pillars or nano-wires — fabricated to maximize the surface-to-volume ratio, and thus the potential energy density — with electrolyte, the conductive material that allows current to flow in a battery.

Using atomic layer deposition — a slow but precise process that allows layers of material only an atom thick to be sprayed on a surface — she has successfully applied the solid electrolyte lithium aluminosilicate to these nanomaterials.

The research is still in its early stages: other components of these 3D microbatteries, such as the electrodes, have also been developed, but they have yet to be assembled and integrated to make a functioning battery.

[Photo above by Kevin Dooley / CC BY-ND 2.0]

Jason Socrates Bardi @ American Institute of Physics

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Have You Got The Power?

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Yes, the name is horrible. But this is an awesome product. I use it. I was shocked a few days ago. I needed to use my iPhone and ran out of battery. I plugged this in and used it for more than twenty-four hours while connected to this device.

I don’t think you’ll find another external battery that connects via USB. 5000MaH is a LOT. It can charge any number of devices, making sure you are connected all the time.

Electron Switch Between Molecules Points Way To New High-Powered Organic Batteries

There should be an image here!The development of new organic batteries — lightweight energy storage devices that work without the need for toxic heavy metals — has a brighter future now that chemists have discovered a new way to pass electrons back and forth between two molecules.

The research is also a necessary step toward creating artificial photosynthesis, where fuel could be generated directly from the sun, much as plants do.

University of Texas at Austin chemists Christopher Bielawski and Jonathan Sessler led the research, which was published in Science.

When molecules meet, they often form new compounds by exchanging electrons. In some cases, the electron transfer process creates one molecule with a positive charge and one molecule with a negative charge. Molecules with opposite charges are attracted to each other and can combine to form something new.

In their research, the chemists created two molecules that could meet and exchange electrons but not unite to form a new compound.

“These molecules were effectively spring-loaded to push apart after interacting with each other,” says Bielawski, professor of chemistry. “After electron transfer occurs, two positively charged molecules are formed which are repelled by each other, much like magnets held in a certain way will repel each other. We also installed a chemical switch that allowed the electron transfer process to proceed in the opposite direction.”

Sessler adds, “This is the first time that the forward and backward switching of electron flow has been accomplished via a switching process at the molecular scale.” Sessler is the Roland K. Pettit Centennial Chair in Chemistry at The University of Texas at Austin and a visiting professor at Yonsei University.

Bielawski says this system gives important clues for making an efficient organic battery. He says understanding the electron transfer processes in these molecules provides a way to design organic materials for storing electrical energy that could then be retrieved for later use.

“I would love it if my iPhone was thinner and lighter, and the battery lasted a month or even a week instead of a day,” says Bielawski. “With an organic battery, it may be possible. We are now starting to get a handle on the fundamental chemistry needed to make this dream a commercial reality.”

The next step, he says, is to demonstrate these processes can occur in a condensed phase, like in a film, rather than in solution.

Organic batteries are made of organic materials instead of heavy metals. They could be lightweight, could be molded into any shape, have the potential to store more energy than conventional batteries and could be safer and cheaper to produce.

The molecular switch could also be a step toward developing a technology that mimics plants’ ability to harvest light and convert it to energy. With such a technology, fuel could be produced directly from the sun, rather than through a plant mediator, such as corn.

“I am excited about the prospect of coupling this kind of electron transfer ‘molecular switch’ with light harvesting to go after what might be an improved artificial photosynthetic device,” says Sessler. “Realizing this dream would represent a big step forward for science.”

[Photo above by oskay / CC BY-ND 2.0]

Dr. Christopher Bielawski @ University of Texas at Austin

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