LNMO batteries

Print edition : August 07, 2015

A 3D X-ray image showing how defects move around inside the LNMO spinel as a battery is charged to higher voltages. Photo: UCSD

WHILE the cathode materials in most of today’s lithium-ion batteries operate at a maximum of 4.2 volts, the cathode material called LNMO spinel (composed of lithium, nickel, manganese and oxygen atoms) functions at up to 4.9 V. Why this material performs well at high voltages had remained a mystery. In a new study, a multi-institutional team of researchers, led by scientists at the University of California, San Diego (UCSD), has offered an answer. The insights, published in a recent issue of Science, could help battery developers design rechargeable lithium-ion batteries that operate at higher voltages, an attribute that is crucial for batteries used in high-power applications such as electric cars.

The researchers used a powerful 3D X-ray imaging technique combined with new data analysis algorithms to gain insights, at the nanoscale level, into the material’s mechanical properties. They identified and located defects within the material, which are irregularities in its otherwise highly ordered atomic structure. The team imaged the cathode material while it was inside a charging lithium-ion battery. Analyses of the images revealed that the defects were stationary when the battery was at rest but moved around within the cathode material when the battery was charged to a high voltage. This is a significant finding because “materials typically respond to strain by cracking. Our experiments show that this material handles strain by moving the defects around while the battery is charging,” said Shirley Meng of UCSD, a corresponding author on the study. “From the perspective of a battery materials researcher, this study also points to the exciting possibility of “defect engineering” for battery materials. This would involve designing new battery materials that have specific ‘defects’ that improve performance.”