Researchers power up new lithium battery for hybrid cars
February 16th, 2006
The structure of lithium nickel manganese oxide consists of layersof transition metal (nickel and manganese, blue layer) separatedfrom lithium layers (green) by oxygen (red). Image courtesy / CederLaboratory
Researchers at MIT have developed a new type of lithium batterythat could become a cheaper alternative to the batteries that nowpower hybrid electric cars.
Until now, lithium batteries have not had the rapid chargingcapability or safety level needed for use in cars. Hybrid cars nowrun on nickel metal hydride batteries, which power an electricmotor and can rapidly recharge while the car is decelerating orstanding still.
But lithium nickel manganese oxide, described in a paper to bepublished in Science on Feb. 17, could revolutionize thehybrid car industry -- a sector that has "enormous growthpotential," says Gerbrand Ceder, MIT professor of materials scienceand engineering, who led the project.
An electron micrograph of lithium nickel manganese oxide. The whitelayers are composed of nickel manganese oxide, and the dark layersrepresent lithium. Image courtesy / Ceder Laboratory
"The writing is on the wall. It's clearly happening," said Ceder,who said that a couple of companies are already interested inlicensing the new lithium battery technology.
The new material is more stable (and thus safer) than lithiumcobalt oxide batteries, which are used to power small electronicdevices like cell phones, laptop computers, rechargeable personaldigital assistants (PDAs) and such medical devices aspacemakers.
The small safety risk posed by lithium cobalt oxide is manageablein small devices but makes the material not viable for the largerbatteries needed to run hybrid cars, Ceder said. Cobalt is alsofairly 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 couldstore a lot of energy, but the material took too long to charge tobe commercially useful. The MIT researchers set out to modify thematerial's structure to make it capable of charging and dischargingmore quickly.
Lithium nickel manganese oxide consists of layers of metal (nickeland manganese) separated from lithium layers by oxygen. The majorproblem with the compound was that the crystalline structure wastoo "disordered," meaning that the nickel and lithium were drawn toeach other, interfering with the flow of lithium ions and slowingdown the charging rate.
Lithium ions carry the battery's charge, so to maximize the speedat which the battery can charge and discharge, the researchersdesigned and synthesized a material with a very ordered crystallinestructure, allowing lithium ions to freely flow between the metallayers.
A battery made from the new material can charge or discharge inabout 10 minutes -- about 10 times faster than the unmodifiedlithium nickel manganese oxide. That brings it much closer to thetimeframe needed for hybrid car batteries, Ceder said.
Before the material can be used commercially, the manufacturingprocess needs to be made less expensive, and a few othermodifications will likely be necessary, Ceder said.
Other potential applications for the new lithium battery includepower tools, electric bikes, and power backup for renewable energysources.