Low-Dose Nanoscale Visualization of Crystal Phases in Epitaxial Cathodes via Cepstral Matching of Scanning Nanobeam Electron Diffraction

Layered cathodes are essential for achieving a high energy density in rechargeable lithium-ion batteries, but they suffer from capacity fade due to local crystal phase transitions during charge-discharge cycles. Understanding these phase transitions is essential to minimizing their effects, but their nanometer size and sensitivity to experimental conditions make observation difficult. Here, we visualized nanometer-scale crystal phases within an epitaxial LiCoO₂ cathode after 100 charge-discharge cycles by matching experimental and simulated cepstra derived from scanning nanobeam electron diffraction. While the LiCoO₂ bulk remained a layered structure, spinel- and rocksalt-type phases were observed within 3 nm of the cathode-electrolyte interface. The developed method achieved a spatial resolution of 1.5 nm across a field of view of several hundred nanometers with minimal electron beam damage. The cepstral matching analysis offers valuable insights into the interfacial phase transitions and will aid in the design of high-performance lithium-ion batteries.