BCDI 3-D X-ray imaging reveals how the defects move around inside the LNMO spinel nanoparticle as the battery is charged. Credit: Andrew Ulvestad / Department of Physics, Jacobs School of Engineering / UC San Diego
Tiny defects in nanostructured materials called dislocations typically cause capacity loss in lithium-ion (Li-ion) batteries as they induce stress and strain. But the same dislocations can also relieve strain during phase changes, preventing cracking and undesirable reactions (Sci., doi: 10.1126/science.aaa1313).
It’s difficult to track the nuanced properties of these nanoscale defects in bulk materials as they operate, but doing so could help engineers design better materials and devices. So to study these properties, an interdisciplinary team led by physics professor Oleg Shpyrko at the University of California-San Diego (USA) used a powerful technique called Bragg coherent diffraction imaging (BCDI) to create 3-D images of the atomic displacement fields in a disordered spinel material called LiNi0.5Mn1.5O4 (LNMO).
A promising cathode material, LMNO works well at high voltages, which makes it ideal for batteries in high-power applications like electric vehicles. To image the tiny displacement fields of an LMNO cathode nanoparticle, the BCDI technique focuses a powerful beam of coherent X-rays onto the 800 nm nanoparticle.
In this case, the team used the ultra-bright, high-energy X-ray beams generated at the Advanced Photon Source at Argonne National Laboratory (USA). The highly coherent X-rays required for the BCDI method are diffracted by a dislocation in the particle, which is then mapped in 3-D at three different charge states.
Shpyrko’s Ph.D. candidate Andrew Ulvestad, first author on the study, said, “For the first time, we can see these battery dislocations in 3-D, which might enable design of a new cathode material for high-voltage, high-power electric vehicles.”