Evaluation of Chemical and Structural Homogeneity in Single Particles of Li_1–xNi_0.33Mn_0.33Co_0.33O₂

Abstract

Identifying irreversible phenomena at single particles of battery cathode materials is an important step to understanding degradation pathways upon cycling. Li-Ni 0.33 Mn 0.33 Co 0.33 O 2 (LiNMC(111)) single particles of size 200 × 300 nm were studied before and after cycling using Scanning Xray Diffraction Microscopy (SXDM) and ptychographic microscopy. With resolutions of 30 and 5 nm, respectively, it was possible to map the (003) reflection and nickel oxidation state changes in single particles at different states of charge. While the compositions measured by the c lattice parameter from SXDM were found to be homogeneous, mapping at higher resolution using ptychography revealed that Ni oxidation states decrease sharply 0−25 nm from the edge, then trail into a steady oxidation state toward the interior of the particle. Within the 30 nm length scale, we conclude that LiNi 0.33 Mn 0.33 Co 0.33 O 2 single particles are highly structurally reversible.