Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > Silicon-carbon electrodes snap, swell, don't pop: Nanocomposite electrodes being charged with electricity reveal performance advantages that could lead to longer-lasting, cheaper vehicle batteries

This composite image shows a silicon-carbon nanofiber electrode before (left) and after (right) being charged with lithium ions.
This composite image shows a silicon-carbon nanofiber electrode before (left) and after (right) being charged with lithium ions.

Abstract:
A study that examines a new type of silicon-carbon nanocomposite electrode reveals details of how they function and how repeated use could wear them down. The study also provides clues to why this material performs better than silicon alone. With an electrical capacity five times higher than conventional lithium battery electrodes, silicon-carbon nanocomposite electrodes could lead to longer-lasting, cheaper rechargeable batteries for electric vehicles.

Silicon-carbon electrodes snap, swell, don't pop: Nanocomposite electrodes being charged with electricity reveal performance advantages that could lead to longer-lasting, cheaper vehicle batteries

Richland, WA | Posted on March 14th, 2012

Published online in the journal Nano Letters last week, the study includes videos of the electrodes being charged at nanometer-scale resolution. Watching them in use can help researchers understand the strengths and weaknesses of the material.

"The electrodes expand as they get charged, and that shortens the lifespan of the battery," said lead researcher Chongmin Wang at the Department of Energy's Pacific Northwest National Laboratory. "We want to learn how to improve their lifespan, because silicon-carbon nanofiber electrodes have great potential for rechargeable batteries."

Plus & Minus

Silicon has both advantages and disadvantages for use as a battery material. It has a high capacity for energy storage, so it can take on a hefty charge. Silicon's problem, though, is that it swells up when charged, expanding up to 3 times its discharged size. If silicon electrodes are packed tightly into a battery, this expansion can cause the batteries to burst. Some researchers are exploring nano-sized electrodes that perform better in such tight confines.

A multi-institution group led by PNNL's Wang decided to test nano-sized electrodes consisting of carbon nanofibers coated with silicon. The carbon's high conductivity, which lets electricity flow, nicely complements silicon's high capacity, which stores it.

Researchers at DOE's Oak Ridge National Laboratory in Oak Ridge, Tenn., Applied Sciences Inc. in Cedarville, Ohio, and General Motors Global R&D Center in Warren, Mich. created carbon nanofibers with a thin layer of silicon wrapped around. They provided the electrodes to the team at PNNL to probe their behavior while functioning.

First, Wang and colleagues tested how much lithium the electrodes could hold and how long they lasted by putting them in a small testing battery called a half-cell. After 100 charge-discharge cycles, the electrodes still maintained a very good capacity of about 1000 milliAmp-hours per gram of material, five to 10 times the capacity of conventional electrodes in lithium ion batteries.

Although they performed well, the team suspected that the expansion and contraction of the silicon could be a problem for the battery's longevity, since stretching tends to wear things out. To determine how well the electrodes weather the repeated stretching, Wang popped a specially designed, tiny battery into a transmission electron microscope, which can view objects nanometers wide, in DOE's EMSL, the Environmental Molecular Sciences Laboratory on the PNNL campus.

They zoomed in on the tiny battery's electrode using a new microscrope that was funded by the Recovery Act. This microscope allowed the team to study the electrode in use, and they took images and video while the tiny battery was being charged and discharged.

Not Crystal Glass

Previous work has shown that charging causes lithium ions to flow into the silicon. In this study, the lithium ions flowed into the silicon layer along the length of the carbon nanofiber at a rate of about 130 nanometers per second. This is about 60 times faster than silicon alone, suggesting that the underlying carbon improves silicon's charging speed.

As expected, the silicon layer swelled up about 300 percent as the lithium entered. However, the combination of the carbon support and the silicon's unstructured quality allowed it to swell evenly. This compares favorably to silicon alone, which swells unevenly, causing imperfections.

In addition to swelling, lithium is known to cause other changes to the silicon. The combination of lithium and silicon initially form an unstructured, glassy layer. Then, when the lithium to silicon ratio hits 15 to 4, the glassy layer quickly crystallizes, as previous work by other researchers has shown.

Wang and colleagues examined the crystallization process in the microscope to better understand it. In the microscope video, they could see the crystallization advance as the lithium filled in the silicon and reached the 15 to 4 ratio.

They found that this crystallization is different from the classic way that many substances crystallize, which builds from a starting point. Rather, the lithium and silicon layer snapped into a crystal all at once when the ratio hit precisely 15 to 4. Computational analyses of this crystallization verified its snappy nature, a type of crystallization known as congruent phase transition.

But the crystallization wasn't permanent. Upon discharging, the team found that the crystal layer became glassy again, as the concentration of lithium dropped on its way out of the silicon.

To determine if repeated use left its mark on the electrode, the team charged and discharged the tiny battery 4 times. Comparing the same region of the electrode between the first and fourth charging, the team saw the surface become rough, similar to a road with potholes.

The surface changes were likely due to lithium ions leaving a bit of damage in their wake upon discharging, said Wang. "We can see the electrode's surface go from smooth to rough as we charge and discharge it. We think as it cycles, small defects occur, and the defects accumulate."

But the fact that the silicon layer is very thin makes it more durable than thicker silicon. In thick silicon, the holes that lithium ions leave behind can come together to form large cavities. "In the current design, because the silicon is so thin, you don't get bigger cavities, just like little gas bubbles in shallow water come up to the surface. If the water is deep, the bubbles come together and form bigger bubbles."

In future work, researchers hope to explore the thickness of the silicon layer and how well it bonds with the underlying carbon to optimize the performance and lifetime of the electrodes.

####

About DOE/Pacific Northwest National Laboratory
EMSL, the Environmental Molecular Sciences Laboratory, is a national scientific user facility sponsored by the Department of Energy's Office of Science. Located at Pacific Northwest National Laboratory in Richland, Wash., EMSL offers an open, collaborative environment for scientific discovery to researchers around the world. Its integrated computational and experimental resources enable researchers to realize important scientific insights and create new technologies.

Interdisciplinary teams at Pacific Northwest National Laboratory address many of America's most pressing issues in energy, the environment and national security through advances in basic and applied science. PNNL employs 4,700 staff, has an annual budget of nearly $1.1 billion, and has been managed for the U.S. Department of Energy by Ohio-based Battelle since the laboratory's inception in 1965.

For more information, please click here

Contacts:
Mary Beckman

509-375-3688

Copyright © DOE/Pacific Northwest National Laboratory

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Reference: Chong-Min Wang, Xiaolin Li, Zhiguo Wang, Wu Xu, Jun Liu, Fei Gao, Libor Kovarik, Ji-Guang Zhang, Jane Howe, David J. Burton, Zhongyi Liu, Xingcheng Xiao, Suntharampillai Thevuthasan, and Donald R. Baer, 2012. In situ TEM investigation of congruent phase transition and structural evolution of nanostructured silicon/carbon anode for lithium ion batteries, Nano Letters March 2, doi: 10.1021/nl204559u.:

MORE VIDEO: Late in this video, reflections change when the lithium-silicon crystallizes in the left-hand screen and dots flicker in the X-ray diffraction in the right-hand screen:

Related News Press

News and information

Researchers develop artificial building blocks of life March 8th, 2024

How surface roughness influences the adhesion of soft materials: Research team discovers universal mechanism that leads to adhesion hysteresis in soft materials March 8th, 2024

Two-dimensional bimetallic selenium-containing metal-organic frameworks and their calcinated derivatives as electrocatalysts for overall water splitting March 8th, 2024

Curcumin nanoemulsion is tested for treatment of intestinal inflammation: A formulation developed by Brazilian researchers proved effective in tests involving mice March 8th, 2024

Laboratories

A battery’s hopping ions remember where they’ve been: Seen in atomic detail, the seemingly smooth flow of ions through a battery’s electrolyte is surprisingly complicated February 16th, 2024

NRL discovers two-dimensional waveguides February 16th, 2024

Catalytic combo converts CO2 to solid carbon nanofibers: Tandem electrocatalytic-thermocatalytic conversion could help offset emissions of potent greenhouse gas by locking carbon away in a useful material January 12th, 2024

Three-pronged approach discerns qualities of quantum spin liquids November 17th, 2023

Govt.-Legislation/Regulation/Funding/Policy

What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024

Researchers’ approach may protect quantum computers from attacks March 8th, 2024

The Access to Advanced Health Institute receives up to $12.7 million to develop novel nanoalum adjuvant formulation for better protection against tuberculosis and pandemic influenza March 8th, 2024

Optically trapped quantum droplets of light can bind together to form macroscopic complexes March 8th, 2024

Discoveries

What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024

Researchers’ approach may protect quantum computers from attacks March 8th, 2024

High-tech 'paint' could spare patients repeated surgeries March 8th, 2024

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Announcements

What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024

Curcumin nanoemulsion is tested for treatment of intestinal inflammation: A formulation developed by Brazilian researchers proved effective in tests involving mice March 8th, 2024

The Access to Advanced Health Institute receives up to $12.7 million to develop novel nanoalum adjuvant formulation for better protection against tuberculosis and pandemic influenza March 8th, 2024

Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024

Automotive/Transportation

Researchers’ approach may protect quantum computers from attacks March 8th, 2024

New designs for solid-state electrolytes may soon revolutionize the battery industry: Scientists achieve monumental improvements in lithium-metal-chloride solid-state electrolytes November 3rd, 2023

Previously unknown pathway to batteries with high energy, low cost and long life: Newly discovered reaction mechanism overcomes rapid performance decline in lithium-sulfur batteries September 8th, 2023

Tests find no free-standing nanotubes released from tire tread wear September 8th, 2023

Battery Technology/Capacitors/Generators/Piezoelectrics/Thermoelectrics/Energy storage

What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024

Two-dimensional bimetallic selenium-containing metal-organic frameworks and their calcinated derivatives as electrocatalysts for overall water splitting March 8th, 2024

Discovery of new Li ion conductor unlocks new direction for sustainable batteries: University of Liverpool researchers have discovered a new solid material that rapidly conducts lithium ions February 16th, 2024

A battery’s hopping ions remember where they’ve been: Seen in atomic detail, the seemingly smooth flow of ions through a battery’s electrolyte is surprisingly complicated February 16th, 2024

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project