Disordered lithium-based compounds could yield better batteries
14.00
In today’s lithium batteries, those cathodes are usually made of an orderly crystalline material, sometimes in a layered structure. When slight deviations from that perfect order are introduced, the battery’s efficiency generally goes down, so disordered materials have mostly been ignored in the search for improved battery materials.
But researchers from MIT have just find out that certain kinds of disorder can provide a significant boost in cathode performance. The results achieved through a combination of computer modelling and laboratory experiments are reported in the journal Science, in a paper by MIT graduate student Jinhyuk Lee, professor of materials science and engineering Gerbrand Ceder, and four others.
Ceder describes the materials that can release and then reabsorb the lithium ions as a kind of “reversible sponge.” In today’s batteries, the cathodes are striated materials, made up of lithium layers alternating with oxides of transition metals. Scientists had thought the layering was necessary to provide a pathway for lithium to pass in and out of the cathodes without bumping into the transition metal oxide layer.
Moreover, disorder “usually significantly reduces the lithium ion mobility,” Ceder says, and high mobility is essential for an efficient rechargeable battery.
Conventional layered lithium and transition metal cathode material (top) and the new disordered material studied by researchers at MIT (bottom) as seen through a scanning tunneling electron microscope. Inset images show diagrams of the different structures in these materials. (In the disordered material, the blue lines show the pathways that allow lithium ions to traverse the material.) Image courtesy of the researchers
However, MIT’s computer modelling and lab experiments have shown that a significant excess of lithium in the material changes things dramatically. In the traditional ordered structure, there is an exact balance between the number of lithium and metal atoms, but with enough of a lithium excess, new channels can take over from the channels that are closed off by the disorder.
While the disordered material with excess lithium produces irregular pathways, it turns out that these nevertheless can still act as efficient channels for the lithium ions. Another benefit of such a material is that the lithium ions don’t push the layers out of shape.
The new material tested in MIT’s experiments, lithium molybdenum chromium oxide, exhibits a very high dimensional stability, which reduces battery fatigue. While the dimensional changes in layered materials can be as much as 5 to 10 percent, according to Ceder, in the new disordered material it is only about 0.1 percent.
This finding opens up a new route to search for even better materials. Many new materials take decades to move from the laboratory to useful applications, but the researcher hopes that using computational tools such as the Materials Project, this transition could be reduced to a couple of years.
Normal
0
false
false
false
EN-GB
X-NONE
X-NONE
/* Style Definitions */
table.MsoNormalTable
{mso-style-name:”Table Normal”;
mso-tstyle-rowband-size:0;
mso-tstyle-colband-size:0;
mso-style-noshow:yes;
mso-style-priority:99;
mso-style-parent:””;
mso-padding-alt:0cm 5.4pt 0cm 5.4pt;
mso-para-margin:0cm;
mso-para-margin-bottom:.0001pt;
mso-pagination:widow-orphan;
font-size:10.0pt;
font-family:”Calibri”,”sans-serif”;}
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
