Visualizing nanoscale 3D compositional fluctuation of lithium in advanced lithium-ion battery cathodes

摘要

The distribution of cations in Li-ion battery cathodes as a function of cycling is a pivotal characteristic of battery performance. The transition metal cation distribution has been shown to affect cathode performance; however, Li is notoriously challenging to characterize with typical imaging techniques. Here laser-assisted atom probe tomography (APT) is used to map the three-dimensional distribution of Li at a sub-nanometre spatial resolution and correlate it with the distribution of the transition metal cations ( M ) and the oxygen. As-fabricated layered Li_1.2Ni_0.2Mn_0.6O₂ is shown to have Li-rich Li₂ M O₃ phase regions and Li-depleted Li(Ni_0.5Mn_0.5)O₂ regions. Cycled material has an overall loss of Li in addition to Ni-, Mn- and Li-rich regions. Spinel LiNi_0.5Mn_1.5O₄ is shown to have a uniform distribution of all cations. APT results were compared to energy dispersive spectroscopy mapping with a scanning transmission electron microscope to confirm the transition metal cation distribution.