New phases and phase transitions observed in Li1-xCoO2 during charge: in situ synchrotron X-ray diffraction studies

We have utilized synchrotron X-ray radiation to perform an `in situʹ X-ray diffraction study on a Li1-xCoO2 cathode in a Li|Li1-xCoO2 cell. The cell was charged at a C/10 rate from 3.5 to 5.2 V. In the composition range of x=0 to x=0.5, a new intermediate phase H2a was observed in addition to the two expected hexagonal phases, H1 and H2. In the region very close to x=0.5, some spectral signatures for the formation of a monoclinic phase M1 were also observed. Furthermore, in the x=0.8 to x=1 region, the formation of a CdI2 type hexagonal phase has been confirmed. However, this new phase originates from a CdCl2 type hexagonal phase, rather than from a monoclinic phase M2 as previously reported in the literature.