Electrochemical Li Intercalation in Black Phosphorus: In Situ and Ex Situ Studies
Manthila Rajapakse, Rajib khan Musa, Usman O. Abu, Bhupendra Karki, Ming Yu, Gamini Sumanasekera, Jacek B. Jasiński
Abstract
A systematic study on electrochemical charge transfer in Li-doped black phosphorus (BP) was carried out by both in situ and ex situ Raman scattering. Galvanostatic discharge of dedicated in situ electrochemical cell for Raman spectroscopy was used to study time evolution of vibrational modes under lithiation. In addition to the peak broadening, which is a result of structural expansion, peaks corresponding to all three atomic vibrational modes A1g, B2g, and A2g were found to redshift as a result of lithiation. Peaks B2g and A2g were shifted about 1.6 times more toward lower wavenumbers in comparison to A1g. Further characterizations using optical and electron microscopy showed that the intercalation of BP is highly anisotropic, where channels along the zigzag direction were found to be the easy direction for intercalation. X-ray diffraction on intercalated samples confirmed a reduction of thickness as lithiation weakens interlayer bonding, thus resulting in a partial exfoliation of BP flakes. Furthermore, first principle studies using density functional theory were used to develop a theoretical model for the intercalation mechanism. The discrepancy between the experimental and the theoretical results was also addressed.