Understanding the origins of the voltage fade of Li- and Mn-rich cathode materials is crucial to future high-capacity battery material design with improved stability. The redox of lattice O2- ions has opened avenues to increase the energy densities of Li-rich layered transition metal (TM) oxides beyond cationic redox. Accessing the O-redox capacities of these Li-rich oxides is accompanied by the challenging problem of voltage fading which can be caused by the oxygen vacancy formation, reduction of TMs, TM migration and irreversible O-lattice distortions of the materials in cycling. 

For Li ion battery cathode materials, the challenges of TEM investigation include the beam sensitivity of the materials and the low contrast of Li and O in the lattice due to their low atomic number. In our previous work [1], we have demonstrated the power of simultaneous annular dark-field (ADF) imaging and ptychography in the scanning TEM (STEM). The ADF image unambiguously identifies the transition metal (TM) locations while ptychography, being a phase imaging technique, offers an electron-efficient imaging mode for detecting Li and O. Importantly, ptychography makes efficient use of transmitted electrons, allowing lower doses to be used when detecting Li and O, and also allows for correction of residual aberrations thereby improving contrast and precision in images.

[1] Song, W. X. et al. Direct imaging of oxygen shifts associated with the oxygen redox of Li-rich layered oxides. Joule 6, 1049-1065, (2022).