| La première
génération de batteries rechargeables au lithium utilisait
une anode en lithium sous sa forme métallique. Cette technologie
a été rapidement abandonnée car l'anode en lithium
pouvait atteindre accidentellement son point de fusion (180°C) lors
d'une décharge trop rapide. Le lithium liquide ainsi formé
produisait une réaction violente et l'émission de gaz brûlants
en entrant en contact avec la cathode.
Ce problème a par la suite été contourné en utilisant le lithium sous sa forme ionique et en l'incluant dans l'électrolyte des batteries au lieu d'en constituer l'anode. Cependant, la densité d'énergie des batteries lithium-ion est en théorie plus faible que celle des batteries
lithium-metal, d'où l'intérêt de revenir à l'ancienne génération d'accumulateurs en résolvant le problème de sécurité.
| C'est dans le cadre de ces
recherches que Daiichi Kougyou Seiyaku a développé avec l'AIST
(National Institute of Advanced Industrial Science and Technology) un liquide
ionique (un imide bisfluorosulfonyle) qui, utilise en tant qu'électrolyte,
permet d'assurer une décharge contrôlée de la batterie.
Ce liquide ionique possédant une haute conductivité, des propriétés ignifuges et une faible volatilité, il est un candidat prometteur pour la réintroduction sur le marché des accumulateurs lithium-metal.
Pour en savoir plus, contacts:
Site de Daichi Kougyou Seiyaku
Source: Japan Chemical Week - 16/02
| Researchers at MIT have developed a
new type of lithium battery that could become a cheaper alternative to
the batteries that now power hybrid electric cars.
Until now, lithium batteries have not had the rapid charging capability or safety level needed for use in cars. Hybrid cars now run on nickel metal hydride batteries, which power an electric motor and can rapidly recharge while the car is decelerating or standing still.
But lithium nickel manganese oxide, described in a paper to be published in Science on Feb. 17, could revolutionize the hybrid car industry -- a sector that has "enormous growth potential," says Gerbrand Ceder, MIT professor of materials science and engineering, who led the project.
"The writing is on the wall. It's clearly happening," said Ceder, who said that a couple of companies are already interested in licensing the new lithium battery technology.
The new material is more stable (and thus safer) than lithium cobalt oxide batteries, which are used to power small electronic devices like cell phones, laptop computers, rechargeable personal digital assistants (PDAs) and such medical devices as pacemakers.
The small safety risk posed by lithium cobalt oxide is manageable in small devices but makes the material not viable for the larger batteries needed to run hybrid cars, Ceder said. Cobalt is also fairly expensive, he said.
The MIT team's new lithium battery contains manganese and nickel, which are cheaper than cobalt.
Scientists already knew that lithium nickel manganese oxide could store a lot of energy, but the material took too long to charge to be commercially useful. The MIT researchers set out to modify the material's structure to make it capable of charging and discharging more quickly.
| Lithium nickel manganese oxide consists of layers
of metal (nickel and manganese) separated from lithium layers by oxygen.
The major problem with the compound was that the crystalline structure
was too "disordered," meaning that the nickel and lithium were drawn to
each other, interfering with the flow of lithium ions and slowing down
the charging rate.
Lithium ions carry the battery's charge, so to maximize the speed at which the battery can charge and discharge, the researchers designed and synthesized a material with a very ordered crystalline structure, allowing lithium ions to freely flow between the metal layers.
A battery made from the new material can charge or discharge in about 10 minutes -- about 10 times faster than the unmodified lithium nickel manganese oxide. That brings it much closer to the timeframe needed for hybrid car batteries, Ceder said.
Before the material can be used commercially, the manufacturing process needs to be made less expensive, and a few other modifications will likely be necessary, Ceder said.
Other potential applications for the new lithium battery include power tools, electric bikes, and power backup for renewable energy sources.
The lead author on the research paper is Kisuk Kang, a graduate student in Ceder's lab. Ying Shirley Meng, a postdoctoral associate in materials science and engineering at MIT, and Julien Breger and Clare P. Grey of the State University of New York at Stony Brook are also authors on the paper.
The research was funded by the National Science Foundation and the U.S. Department of Energy.
Contact: Elizabeth Thomson
Massachusetts Institute of Technology
|Batteries could soon replace standard
nickel-metal hydride batteries in hybrid vehicles
ALBUQUERQUE, N.M. - As part of the Department of Energy-funded FreedomCAR program, Sandia National Laboratories' Power Sources Technology Group is researching ways to make lithium-ion batteries work longer and safer. The research could lead to these batteries being used in new hybrid electric vehicles (HEVs) in the next five to ten years.
"Batteries are a necessary part of hybrid electric-gasoline powered vehicles and someday, when the technology matures, will be part of hybrid electric-hydrogen fuel cell powered vehicles," says Dan Doughty, manager of Sandia's Advanced Power Sources Research and Development Department. "Current hybrid vehicles use nickel-metal hydride batteries, but a safe lithium-ion battery will be a much better option for the hybrids."
He notes a lithium-ion battery has four times the energy density of lead-acid batteries and two to three times the energy density of nickel-cadmium and nickel-metal hydride batteries. It also has the potential to be one of the lowest-cost battery systems.
Doughty's department receives about $1.5 million a year from the FreedomCAR program to improve the safety, lengthen the lifetime, and reduce costs of lithium-ion batteries.
The FreedomCAR program, initiated by President Bush in 2002, focuses on developing hydrogen-powered electric vehicles to help free the U.S. from dependence on foreign oil supplies. Five national laboratories - Sandia, Argonne, Lawrence Berkeley, Idaho, and Brookhaven - are involved in the program, each researching different aspects of making hybrid electric-hydrogen vehicles a reality.
Sandia's FreedomCAR work centers on the areas of battery abuse tolerance and accelerated lifetime prediction, with abuse tolerance receiving most of the focus.
"We want to develop a battery that has a graceful failure - meaning that if it's damaged, it won't cause other problems," Doughty says. "We have to understand how batteries fail and why they fail."
The technical goal is to comprehend mechanisms that lead to poor abuse tolerance, including heat- and gas-generating reactions. Understanding the chemical response to abuse can point the way to better battery materials. But, Doughty says, there is no "magic bullet" for completely stable lithium-ion cells.
| "Fixing the problem will
come from informed choices on improved cell materials, additives, and cell
design, as well as good engineering practices."
Work in abuse tolerance is beginning to shed light on mechanisms that control cell response, including effects of the anode and cathode, electrolyte breakdown, and battery additives.
The other area of work, accelerated life test, involves developing a method to predict lithium-ion battery life.
"We have two approaches in our research - the empirical model and the mechanistic model," Doughty says. "The empirical model generates life prediction from accelerated degradation test data, while the mechanistic model relates life prediction to changes in battery materials. Our approach provides an independent measure of battery life so we don't have to rely on what battery manufacturers tell us."
Improved abuse test procedures developed at Sandia have led to lithium-ion test standards that the battery team has developed and recently published in a Sandia research report. Doughty anticipates that the Society of Automotive Engineers will soon adopt these test procedures as national standards, just as they adopted in 1999 the abuse test procedures Sandia developed for electric vehicle batteries.
"There has been substantial progress in making batteries more tolerant to abusive conditions," Doughty says. "It won't be long before these batteries will be used in gasoline-electric hybrid vehicles. And the great thing is this technology will be able to transfer over to the electric-hydrogen fuel cell powered hybrid vehicles of the future."
Sandia is a National Nuclear Security Administration
Release and image are available on the web site of Sandia