Two-dimensional lithiated nanosheets usually show excellent electrochemical performance due to an increase in surface area and shorter diffusion paths. However, processing techniques, such as shear mixing or liquid phase exfoliation could induce phase changes or knock out some of the structural lithium (Li) ions, what in turn might result in poor electrochemical performance. Here different lithiated layered compounds mainly LiCoO₂, LiMn₂O₄, and Li₅Ti₄O₁₂ were chemically exfoliated and investigated using electron energy loss spectroscopy (EELS) for their Li-K edge. Further analyses were carried out, looking at the oxygen (O) K edge with their respective transition metal core loss peak (Mn, Co and Ti) which revealed changes in the Energy loss near edge structures (ELNES) when compared to the unlithiated compounds. STEM-EELS analyses confirmed uneven distribution of lithium within the lithiated layered materials. In this work, EELS was used for the first time to detect and to probe the chemical environment of the lithium in liquid phase exfoliated material. 

Figures:

(a, b) shows O K-edge and Co L-edge of LiCoO2 respectively. (c,d) Li-K edge and Ti-L/O-K edge respectively for Li4Ti5O12, (e and f) O-K edge and Mn-L edge respectively of LiMn2O4.

(a) Bright field TEM image of a flake of LiCoO2. The TEM beam was condensed to a diameter of approximately 10nm and EELS spectra were collected from regions marked A and B. (b) EELS spectra collected from the regions marked A and B in (a). The lithium signal is clearly present in the spectrum collected from the centre of the flake, while it is absent from the spectrum collected from the edge. (c) The percentage of flakes in which a lithium signal was detected for each centrifugation speed. (e) The EELS spectrum collected from a LiCoO2 flake (d) as the flake remains illuminated by the beam over a period of four minutes. The lithium signal is clearly visible in the first spectrum and decreases over time until it is completely absent.

The EELS signals of all the materials examined showing the presence lithium (red arrows). Other reference spectra of MnO2, cobalt oxide and titanium oxide

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EMC Abstracts - https://emc-proceedings.com/abstract/eels-probing-of-lithium-based-2-d-battery-compounds-processed-by-liquid-phase-exfoliation/