104
7 Investigations of Bulk Li–Mn–Ni–O Samples to Confirm the Combinatorial Studies
in the region directly above point G 7 in Fig. 7.5. During slow cooling, the upper
boundary of the layered region moves downward. This implies that the layered–
layered region also moves downward as the M and N points move. A sample made
near the composition of LiNi 0.5 Mn 0.5 O 2 (point G 7 ) would be single phase if quenched
from high temperature and would transform toward a layered–layered composite
when regular cooled. The endpoints of the phase separation would lie along the
boundary between N and M. Since the N phase contains a large amount of nickel on
the lithium layer, the formation of nano-composites in this composition space would
involve the clustering of nickel on the lithium layer which could interfere with lithium
diffusion. This well-known composition, LiNi 0.5 Mn 0.5 O 2 , therefore warrants further
study and will be discussed from this new point of view in Chap. 9.
7.5 Conclusions Based on Bulk Li–Mn–Ni–O Samples
The key features in the Li–Mn–Ni–O pseudo-ternary phase diagrams, as determined
using combinatorial samples, were confirmed with bulk samples synthesized under
various conditions via two different synthesis routes. The four-phase equilibrium
was observed and transformations were found to be reversible, thereby confirming
that two three-phase regions exist and transform during slow cooling. The primary
importance of this work is a better understanding of how the phase boundaries and
coexisting regions transform when cooled at rates typically used commercially. It
is also important to recognize that a small amount of transformation occurred even
for samples quenched on a copper or steel plate. These changes cannot be avoided
entirely without quenching in liquid nitrogen or avoiding the compositions where the
transformations occur. Understanding the phase diagrams should have a significant
impact on research focused on composite electrodes in the Li–Mn–Ni–O system,
since this work identified the compositions and conditions required to obtain layered–
layered nano-composites and layered–spinel composites.
The lattice parameter contour plots developed here also showed that some samples
made with excess lithium retain most of the excess, even after heating to high temperatures. Elemental analysis on a sample in the layered region is therefore mandatory
in order to be confident of the composition of the final product.
7 Investigations of Bulk Li–Mn–Ni–O Samples to Confirm the Combinatorial Studies
in the region directly above point G 7 in Fig. 7.5. During slow cooling, the upper
boundary of the layered region moves downward. This implies that the layered–
layered region also moves downward as the M and N points move. A sample made
near the composition of LiNi 0.5 Mn 0.5 O 2 (point G 7 ) would be single phase if quenched
from high temperature and would transform toward a layered–layered composite
when regular cooled. The endpoints of the phase separation would lie along the
boundary between N and M. Since the N phase contains a large amount of nickel on
the lithium layer, the formation of nano-composites in this composition space would
involve the clustering of nickel on the lithium layer which could interfere with lithium
diffusion. This well-known composition, LiNi 0.5 Mn 0.5 O 2 , therefore warrants further
study and will be discussed from this new point of view in Chap. 9.
7.5 Conclusions Based on Bulk Li–Mn–Ni–O Samples
The key features in the Li–Mn–Ni–O pseudo-ternary phase diagrams, as determined
using combinatorial samples, were confirmed with bulk samples synthesized under
various conditions via two different synthesis routes. The four-phase equilibrium
was observed and transformations were found to be reversible, thereby confirming
that two three-phase regions exist and transform during slow cooling. The primary
importance of this work is a better understanding of how the phase boundaries and
coexisting regions transform when cooled at rates typically used commercially. It
is also important to recognize that a small amount of transformation occurred even
for samples quenched on a copper or steel plate. These changes cannot be avoided
entirely without quenching in liquid nitrogen or avoiding the compositions where the
transformations occur. Understanding the phase diagrams should have a significant
impact on research focused on composite electrodes in the Li–Mn–Ni–O system,
since this work identified the compositions and conditions required to obtain layered–
layered nano-composites and layered–spinel composites.
The lattice parameter contour plots developed here also showed that some samples
made with excess lithium retain most of the excess, even after heating to high temperatures. Elemental analysis on a sample in the layered region is therefore mandatory
in order to be confident of the composition of the final product.