Exfoliation of LiNiMnCoO into Nanosheets Using Electrochemical Oxidation and Reassembly with Dialysis or Flocculation.

Two-dimensional (2D) materials such as nanosheets are increasingly attracting attention for applications in energy storage and conversion. Many conventional battery compounds have layered structures, which can facilitate the exfoliation of these materials into nanosheet morphologies. In this work, LiNiMnCoO (NMC) particles were exfoliated into nanosheets using an electrochemical oxidation method enabled by the intercalation of tetraethylammonium cations into the interlayer space. The exfoliated materials were monolayer or double-layer nanosheets with hexagonal shapes and sizes of <50 nm. Two different methods were used to reassemble the nanosheets into NMC particles: (1) a slow, dialysis-based approach and (2) direct flocculation. Characterization of the NMC materials at different stages in the exfoliation and reassembly processes was performed using compositional analysis, X-ray diffraction, electron microscopy, and electrochemical methods. The dialysis reassembly method allowed for the restacking of the nanosheets into faceted, hexagonally shaped nanoplatelets, and the flocculation approach yielded only ill-defined particles. The differences in the observed potential-dependent redox behavior and electrochemical cycling characteristics are attributed to the role of the reassembly method in the formation of phase-segregated domains, with the particles reassembled using the dialysis approach displaying the best performance.