|The structure of lithium nickel manganese oxide consists of layers of transition metal (nickel and manganese, blue layer) separated from lithium layers (green) by oxygen (red). Image: Ceder Laboratory|
Hybrid Electric Vehicles require rechargeable batteries that combine high energy density with high charge and discharge rate capability. Researchers at MIT have now developed lithium nickel manganese oxide electrodes for a new type of lithium battery that offers unexpectedly high rate-capability—considerably better than lithium cobalt oxide (LiCoO2), the current battery electrode material of choice.
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 standard compound is that the crystalline structure is too disordered—the nickel and lithium are 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 unmodified lithium nickel manganese oxide technology, according to Gerbrand Ceder, MIT professor of materials science and engineering, who led the project. That brings it much closer to the timeframe needed for hybrid car batteries.
The lithium nickel manganese oxide [Li(Ni0.5Mn0.5)O2] batteries would also be less expensive and more stable than lithium cobalt oxide cells. 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.
The research was funded by the National Science Foundation and the US Department of Energy.
“Electrodes with High Power and High Capacity for Rechargeable Lithium Batteries”; Kisuk Kang, Ying Shirley Meng, Julien Bréger, Clare P. Grey, Gerbrand Ceder; Science 17 February 2006: Vol. 311. no. 5763, pp. 977–980; DOI: 10.1126/science.1122152