New Cathode Material For Lithium-Ion Batteries

Between charges, an electric vehicle can travel only as far as its rechargeable lithium-ion battery allows it. And those batteries can only pack so much energy into a given volume. Making the batteries bigger would add weight to cars and be counterproductive. Now researchers have demonstrated a new battery cathode material that could potentially pack more charge into the same mass (Chem. Mater. 2013, DOI: 10.1021/cm402567e).

Peter G. Khalifah, a chemist at the State University of New York, Stony Brook, and Brookhaven National Laboratory, and his colleagues wanted to develop a cathode material that had good electrochemical properties and did not contain rare-earth elements, which are expensive and limited in supply. They started with an iron nitridophosphate, a compound of sodium, iron, phosphorous, oxygen, and nitrogen—all earth-abundant elements. They ground the material into a powder, mixed it with a powder of lithium bromide, and heated the mixture under a flow of nitrogen gas. During the heating, the lithium ions replaced the sodium ions. The researchers used the resulting material as a cathode in a battery and measured the material’s energy capacity as 125 mAh/g. Today’s lithium-ion batteries top out around 150 mAh/g.

Khalifah says this is just a first step in demonstrating this new material system for battery cathodes. Altering the structure of phosphorus groups in the material could produce a cathode material with a theoretical energy density upwards of 200 mAh/g, he says.