Better LithiumIon Batteries Are On The Way From Berkeley Lab …

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A revolutionary conducting polymer the use of low-cost, high-energy silicon for the generation of lithium-ion battery

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At left, the approach to composite anodes silicon (blue spheres) for energy capacity has a polymer such as PVDF (light plus added particles of to conduct electricity (dark spheres). Silicon swells and while acquiring and releasing ions, and repeated swelling and eventually break contacts the conducting carbon particles. At the new Berkeley Lab polymer (purple) is conductive and continues to bind to the silicon particles despite swelling and shrinking.

Lithium-ion are everywhere, in smart phones, an array of other consumer and the newest electric cars. as they are, they be much better, especially it comes to lowering the cost and the range of electric cars. To do batteries need to store a lot energy.

The anode is a critical for storing energy in lithium-ion A team of scientists at the U.S. of Energy’s Lawrence Berkeley Laboratory (Berkeley Lab) has a new kind of anode that can eight times the lithium of designs, and has maintained its greatly energy capacity after a year of testing and many of charge-discharge cycles.

The secret is a polymer that conducts and binds closely to lithium-storing particles, even as they to more than three their volume during and then shrink again discharge. The new anodes are made low-cost materials, compatible standard lithium-battery manufacturing The research team reports its in Advanced Materials . now available

High-capacity expansion

“High-capacity anode materials have confronted the challenge of volume – swelling – when electrodes lithium,” says Gao Liu of Berkeley Environmental Energy Technologies (EETD), a member of the BATT (Batteries for Advanced Transportation managed by the Lab and supported by DOE’s of Vehicle Technologies.

Says “Most of today’s lithium-ion have anodes made of which is electrically conducting and only modestly when the ions between its graphene Silicon can store 10 times – it has by far the highest capacity among storage materials – but it swells to than three times its when fully charged.”

kind of swelling quickly the electrical contacts in the anode, so have concentrated on finding ways to use silicon while anode conductivity. Many have been proposed; are prohibitively costly.

At top, of a series of polymers obtained soft x-ray absorption at ALS beamline 8.0.1 show a “lowest unoccupied molecular for the new Berkeley Lab polymer, PFFOMB than other polymers indicating better potential Here the peak on the absorption reveals the lower key electronic At bottom, simulations disclose the complete, two-stage electron transfer when lithium bind to the new polymer.

One less-expensive approach has been to mix particles in a flexible polymer with carbon black to the mix to conduct electricity. Unfortunately, the swelling and shrinking of the silicon as they acquire and release ions eventually push the added carbon particles. needed is a flexible binder can conduct electricity by itself, the added carbon.

“Conducting aren’t a new idea,” says “but previous efforts worked well, because haven’t taken into the severe reducing environment on the side of a lithium-ion battery, renders most conducting insulators.”

One such experimental called PAN (polyaniline), has positive it starts out as a conductor but quickly conductivity. An ideal conducting should readily acquire rendering it conducting in the anode’s environment.

The signature of a promising would be one with a low value of the called the “lowest unoccupied orbital,” where electrons can reside and move freely. electrons would be acquired the lithium atoms during the charging process. Liu and his postdoctoral Shidi Xun in EETD designed a of such polyfluorene-based conducting – PFs for short.

When Liu discussed the performance of the PFs with Wanli of Berkeley Lab’s Advanced Source (ALS), a scientific emerged to understand the new materials. suggested conducting soft absorption spectroscopy on Liu and Xun’s polymers using ALS beamline to determine their key electronic

Says Yang, “Gao to know where the ions and are and where they move. x-ray spectroscopy has the power to exactly this kind of information.”

Compared with the structure of PAN, the absorption Yang obtained for the PFs stood out The differences were greatest in PFs a carbon-oxygen functional group

“We had the experimental evidence,” says “but to understand what we seeing, and its relevance to the conductivity of the we needed a theoretical explanation, from first principles.” He Lin-Wang Wang of Berkeley Materials Sciences Division to join the research collaboration.

and his postdoctoral fellow, Nenad conducted ab initio calculations of the polymers at the Lab’s National Research Scientific Computing (NERSC). Wang says, calculation tells you what’s going on – including precisely how the ions attach to the polymer, and why the carbonyl functional group the process. It was quite impressive the calculations matched the experiments so

The simulation did indeed reveal really going on” with the of PF that includes the carbonyl group, and showed why the system so well. The lithium ions with the polymer first, and bind to the silicon particles. a lithium atom binds to the through the carbonyl group, it its electron to the polymer  – a doping that significantly improves the electrical conductivity, facilitating and ion transport to the silicon particles.

Transmission electron microscopy the new conducting polymer’s improved properties. At left, silicon embedded in the binder are shown cycling through charges and (closer view at bottom). At after 32 charge-discharge cycles, the is still tightly bound to the particles, showing why the energy of the new anodes remains much than graphite anodes more than 650 charge-discharge during testing.

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Having through one cycle of material at EETD, experimental analysis at the and theoretical simulation at MSD, the results triggered a new cycle of Almost as important as its electrical are the polymer’s physical properties, to Liu now added another functional producing a polymer that can tightly to the silicon particles as acquire or lose lithium and undergo repeated changes in

Scanning electron microscopy and electron microscopy at the National for Electron Microscopy (NCEM), the anodes after 32 charge-discharge confirmed that the modified adhered strongly throughout the operation even as the silicon repeatedly expanded and contracted. at the ALS and simulations confirmed that the mechanical properties did not affect the superior electrical properties.

“Without the input from our at the ALS and in MSD, what can be modified and should not be modified in the next of polymers would not have obvious,” says Vince Program Manager of EETD’s Energy Technologies Department.

achievement provides a rare showcase, combining advanced of synthesis, characterization, and simulation in a approach to materials development,” Zahid Hussain, the ALS Division for Scientific Support and Scientific Group Leader. “The approach can lead to the discovery of new materials with a fundamental of their properties.”

The icing on the cake is that the new PF-based is not only superior but economical. commercial silicon particles and any conductive additive, our composite exhibits the best performance so says Gao Liu. “The manufacturing process is low cost and with established manufacturing The commercial value of the polymer has been recognized by major and its possible applications extend silicon anodes.”

Anodes are a key of lithium-ion battery technology, but far the only challenge. Already the collaboration is pushing to the next studying other battery including cathodes.

###

“Polymers Tailored Electronic Structure for Capacity Lithium Battery by Gao Liu, Shidi Xun, Vukmirovic, Xiangyun Song, Olalde-Velasco, Honghe Zheng, S. Battaglia, Lin-Wang Wang, and Yang, appears in Advanced and is available online at http://onlinelibrary.wiley.com/doi/10.1002/adma.201102421/abstract .

Materials research for this in the BATT program was supported by the Department of Energy’s Office of Efficiency and Renewable Energy. The NCEM, and NERSC are national user facilities supported by Office of Science.

The Office of is the single largest supporter of research in the physical sciences in the States, and is working to address of the most pressing challenges of our For more information, please http://science.energy.gov .

Lawrence Berkeley Laboratory addresses the world’s urgent scientific challenges by sustainable energy, protecting health, creating new materials, and the origin and fate of the universe. in 1931, Berkeley Lab’s expertise has been recognized 12 Nobel prizes. The University of manages Berkeley Lab for the U.S.

of Energy’s Office of Science. For visit www.lbl.gov .

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