FTIR and Raman Study of the LixTiyMn1-yO2 (y=0, 0.11) Cathodes in Methylpropyl Pyrrolidinium Bis(fluoro-sulfonyl)imide, LiTFSI Electrolyte

This work demonstrates the protective effect of partial titanium substitution in LixTi0.11Mn0.89O2 against surface decomposition in room-temperature ionic liquid (RTILs) cells. Raman microscopy and reflectance Fourier transform IR (FTIR) spectroscopy were used to analyze electrodes recovered from cycled Li/LixTiyMn1-yO2 (y=0, 0.11) cells containing the 0.5 mol/kg LiTFSI in P13FSI RTIL electrolyte. [TFSI=bis(trifluoromethanesulfonyl)imide.] Raman and FTIR spectra of cycled LixMnO2 cathodes showed many distinct bands that can be attributed to both the electrolyte and electrode decomposition products. The thickness of the amorphous porous layer on the LixMnO2 cathode increased during cycling. The surface degradation of LixMnO2 and precipitation of electrolyte decomposition products contributed to the film growth. Improved cycling behavior was observed in cells containing LixTi0.11Mn0.89O2, yet Raman spectroscopy also showed possible surface degradation. The FTIR spectra of cycled LixMnO2 and LixTi0.11Mn0.89O2 cathodes displayed bands characteristic for LiSO3CF3 and Li2NSO2CF3, which originate from the reaction of the TFSI anion with traces of water present in the cell.