Page 383 - Handbook of Battery Materials

354 12 Lithium Intercalation Cathode Materials for Lithium-Ion Batteries

Layered material

AIPO 4
coating

5 nm

Figure 12.9 TEM image of 4 wt% nano AlPO 4 modified
Li[Li 0.2 Mn 0.54 Ni 0.13 Co 0.13 ]O 2 cathode.

−1
the surface-modified samples exhibit a high discharge capacity, ∼280 mAh g ,
which is twice that of LiCoO 2 . This improvement in surface-modified samples
has been explained on the basis of the retention of a higher number of oxygen
vacancies in the layered lattice after the first charge compared to that in the
unmodified samples. The bonding of the nano-oxides to the surface of the layered
oxide lattice suppresses the diffusion of oxygen vacancies and their elimination.
A careful analysis of the first charge and discharge capacity values of the pristine
sample also reveals that part of the oxygen vacancies are retained in the material
after the first charge [57]. Moreover, the surface-modified cathodes have been
found to exhibit higher rate capability than the unmodified samples despite the
electronically insulating nature of the coating materials like Al 2 O 3 and AlPO 4 [57].
This is believed to be due to the suppression of the formation of thick SEI layers,
as the coating material minimizes the direct reaction of the cathode surface with
the electrolyte at the high charging voltages.
However, these high-capacity layered oxide cathodes have to be charged up to
about 4.8 V, so more stable, compatible electrolytes need to be developed to fully
exploit their potential as high-energy-density cathodes. Moreover, oxygen is lost
irreversibly from the lattice during first charge, and it may have to be vented
appropriately during cell manufacture. Also, the long-term cyclability of these
high-capacity cathodes at elevated temperatures needs to be fully assessed.

12.9
Other Layered Oxides

LiVO 2 is isostructural with LiCoO 2 and has the O3 layered structure. However,
in de-lithiated Li 1−x VO 2 with (1 – x) < 0.67, the vanadium ions migrate from
the octahedral sites of the vanadium layer into the octahedral sites of the lithium
layer because of the low OSSE of the vanadium ions [58]. Therefore, the kinetics
of lithium transport and the electrochemical performance is very poor with LiVO 2 ,