X-ray imaging pinpoints improved battery performance at high voltages

June 22, 2015 // By Paul Buckley
A multi-institution team is led by physicists and nanoengineers at the University of California, San Diego could help battery developers design rechargeable lithium-ion batteries that operate at higher voltages.

In a study, described in the 19 June issue of the journal Science, the researchers explain why one particular cathode material works well at high voltages, while most other cathodes do not.

The researchers used X-ray imaging techniques combined with new data analysis algorithms to gain insights — at the nanoscale level — on the mechanical properties of a cathode material called an LNMO spinel (composed of lithium, nickel, manganese and oxygen atoms). The study reveals how the cathode material behaves while the battery charges and offers a possible explanation for why this particular cathode material works well at high voltage levels, an attribute that is crucial for batteries used in high-power applications such as electric cars.

In addition, the imaging and data analysis techniques described in this study provide new strategies for discovering how other cathode materials behave at the nanoscale level while batteries are charging.

X-ray imaging experiments were performed at Argonne National Laboratory’s Advanced Photon Source.

“Understanding why this cathode material works well at high voltage can help us understand how to make other battery materials also work better at high voltages,” said Andrew Ulvestad, the first author of the Science paper.

The 3D X-ray imaging technique used in this study shows how defects move around inside the LNMO spinel as the battery is charged to higher voltages.

While the cathode materials in most of today’s lithium-ion batteries operate at 4.2 Volts maximum, the LNMO spinel is robust at higher voltages and functions at up to 4.9 Volts. Reasons for why this material performs well at high voltages have remained a mystery. Through imaging and data analysis techniques, the researchers have identified and located defects within the cathode material. The defects are irregularities in the material’s otherwise highly ordered atomic structure.