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Batteries Microscope Image of Yolk-Shell Battery Nanostructures

Published on January 8th, 2013 | by SLAC National Accelerator Laboratory

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World-Record Battery Performance Achieved With Egg-Like Nanostructures

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January 8th, 2013 by  

SLAC and Stanford 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.

Microscope Image of Yolk-Shell Battery Nanostructures

The research was led by Yi Cui, a Stanford associate professor of materials science and engineering and a member of the Stanford Institute for Materials and Energy Sciences, a SLAC/Stanford joint institute. The team reported its results Jan. 8 in Nature Communications.

The Sulfur Cathode Problem

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. But two critical disadvantages prevented its commercial use: When lithium ions enter a sulfur cathode during discharging, they bond with sulfur atoms to create an intermediate compound that’s important for the cathode’s performance; but this compound kept dissolving, limiting the cathode’s energy-storage capacity. At the same time, the influx of ions caused the cathode to expand by about 80 percent. When scientists applied protective coatings to keep the intermediate compound from dissolving, the cathode would expand and crack the coating, rendering it useless.

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An Egg-cellent Solution

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.

Diagram showing how Lithium/Titanium-Oxide yolk-shells work

The yolk-shell nanoparticles are made by coating sulfur with a nanoporous layer of hard titanium dioxide, and then using a solvent to dissolve away some of the sulfur while leaving the shell in place. Each cathode particle is only 800 nanometers (billionths of a meter) in diameter, about one-hundredth the diameter of a human hair.

“It basically worked the first time we tried it,” Cui said. “The sulfur cathode stored up to five times more energy per sulfur weight than today’s commercial materials.

“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 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.”

3-part diagram explaining yolk-shell cathode design

Previous attempts to make sulfur cathodes using bare sulfur or simply coated particles could not prevent the dramatic reduction of energy-storage capacity as the lithium-sulfur intermediate compounds (polysulfides) created during charging broke free and dissolved away.

Funding for the project came from the DOE Office of Basic Energy Sciences through SLAC’s Laboratory Directed Research and Development Program, which directs a percentage of the lab’s funding to high-risk, high-payoff research that, if successful, can lead to future program opportunities.

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.

Source: Mike Ross, SLAC National Accelerator Laboratory
Images & Diagrams: Zhi Wei She et al., Stanford University

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About the Author

programs explore the ultimate structure and dynamics of matter and the properties of energy, space and time -- at the smallest and largest scales, in the fastest processes and at the highest energies -- through robust scientific programs, excellent accelerator-based user facilities and valuable partnerships. Located in Menlo Park, California, SLAC is operated by Stanford University for the U.S. Department of Energy Office of Science.



  • http://soltesza.wordpress.com/ sola

    This really sounds brilliant.

    If the silicone-anode/sulfur-cathode battery works-out, the resulting battery would be really big advancement.

    I hope they make it in a couple of months and we learn about the new cell’s other important parameters (wh/kg, wh/l, maximum tolerated charge/discharge ratios, calendar life…etc)

  • CaptD

    Another side benefit would be to get “rid” of lots of sulfur and the process does not require any rare earth materials which are in ever shorter supply

    • Bob_Wallace

      The “rare” in rare earth minerals does not mean that there is a shortage in the Earth’s crust.

      A short supply of a specific material usually means that there isn’t currently a lot of unused production capacity. If demand for something increases then more mines are opened and processing plants are built.

      The world is well-supplied with lithium (which is a metal, not a REM).

  • Amanda

    I am interested in knowing the process it would take to make these at a commercial level. What kind of resources does it take to make these? Is this process/processes sustainable?

  • anderlan

    This is actually exciting.

    • Bob_Wallace

      Sure is. Points the way toward a lighter, cheaper 200 mile range EV. 1,000 cycles would make for 200,000 mile batteries.

    • http://zacharyshahan.com/ Zachary Shahan

      Insanely exciting. :D

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