3.4 Conclusions Regarding Synthesis of Combinatorial Samples
47
in crystallites that were considerably larger than the rocksalt structure with which
it was reacting (Fig. 3.7 (b)). Furthermore, the lithium carbonate crystallites were
small with little strain when heated in oxygen.
Figure 3.7 (b) shows that nickel oxide crystallites grew steadily over the entire temperature range and the strain stayed small. By contrast, when lithium was
present, crystallites remained small until all the lithium was done reacting. Figure 3.7
(c) shows that in oxygen, the strain increased dramatically while the lithium entered
the structure (500–700
◦ C) indicative of an increase in the number of defects as well
as variations in lithium content within each crystallite [62]. In air, the results were
similar with the crystallites only growing rapidly once most of the lithium was reacted. The higher strain was also present over a greater temperature range. Figure 3.7
(c) suggests that heating to 800
◦ C ensures that the crystallites obtained are relatively
homogeneous and have few defects.
3.4 Conclusions Regarding Synthesis of Combinatorial Samples
Mechanisms for lithium loss during and after the formation of combinatorial samples
of lithium nickel oxide were identified. During synthesis in air, the main source of
lithium loss was the decomposition of lithium carbonate that failed to react with the
nickel oxide structure. The fact that the formation of LiNiO 2 was hindered significantly in air was attributed to the presence of constituents in air other than oxygen
and nitrogen, the likeliest candidates being carbon dioxide and water vapor. The
second mechanism for lithium loss was the thermal decomposition of Li x Ni 2−x O 2 .
TGA was used to confirm that both lithium oxide and oxygen were lost when the
samples were heated in either air or oxygen. In both cases, the loss of lithium from
the samples was attributed to the conversion of lithium oxide to lithium peroxide
vapor. Synthesizing the samples in dry, carbon dioxide free air would therefore result in lithium content very close to that seen in oxygen, the only difference being
attributed to a slight increase in the rate of decomposition of lithium nickel oxide
as seen in the TGA. Combinatorial samples of Li x Ni 2−x O 2 cannot be made with
x > 0.77 at 700
◦ C in air. In a flow of oxygen, excess lithium was used to react a
sufficient amount of lithium into the material to form Li 0.95 Ni 1.05 O 2 at 800
◦ C on an
alumina substrate. These conditions allow the simultaneous synthesis of the layered
and spinel structures in the Li–Mn–Ni–O system.
Alumina, the least desirable substrate in air, performed comparably to the others in
oxygen. Magnesia required large amounts of stearic acid in order to bead the solutions
and the subsequent decomposition of the stearic acid was found to interfere with the
samples. The third substrate tested was alumina treated with lithium hydroxide and
it was difficult to treat it uniformly enough to get consistent results. The substrate
selected for further combinatorial studies was therefore alumina in a flow of oxygen.
Two precipitators were tested: ammonium bicarbonate and ammonium hydroxide.
Little difference can be found in the lithium content of the final samples, but only
47
in crystallites that were considerably larger than the rocksalt structure with which
it was reacting (Fig. 3.7 (b)). Furthermore, the lithium carbonate crystallites were
small with little strain when heated in oxygen.
Figure 3.7 (b) shows that nickel oxide crystallites grew steadily over the entire temperature range and the strain stayed small. By contrast, when lithium was
present, crystallites remained small until all the lithium was done reacting. Figure 3.7
(c) shows that in oxygen, the strain increased dramatically while the lithium entered
the structure (500–700
◦ C) indicative of an increase in the number of defects as well
as variations in lithium content within each crystallite [62]. In air, the results were
similar with the crystallites only growing rapidly once most of the lithium was reacted. The higher strain was also present over a greater temperature range. Figure 3.7
(c) suggests that heating to 800
◦ C ensures that the crystallites obtained are relatively
homogeneous and have few defects.
3.4 Conclusions Regarding Synthesis of Combinatorial Samples
Mechanisms for lithium loss during and after the formation of combinatorial samples
of lithium nickel oxide were identified. During synthesis in air, the main source of
lithium loss was the decomposition of lithium carbonate that failed to react with the
nickel oxide structure. The fact that the formation of LiNiO 2 was hindered significantly in air was attributed to the presence of constituents in air other than oxygen
and nitrogen, the likeliest candidates being carbon dioxide and water vapor. The
second mechanism for lithium loss was the thermal decomposition of Li x Ni 2−x O 2 .
TGA was used to confirm that both lithium oxide and oxygen were lost when the
samples were heated in either air or oxygen. In both cases, the loss of lithium from
the samples was attributed to the conversion of lithium oxide to lithium peroxide
vapor. Synthesizing the samples in dry, carbon dioxide free air would therefore result in lithium content very close to that seen in oxygen, the only difference being
attributed to a slight increase in the rate of decomposition of lithium nickel oxide
as seen in the TGA. Combinatorial samples of Li x Ni 2−x O 2 cannot be made with
x > 0.77 at 700
◦ C in air. In a flow of oxygen, excess lithium was used to react a
sufficient amount of lithium into the material to form Li 0.95 Ni 1.05 O 2 at 800
◦ C on an
alumina substrate. These conditions allow the simultaneous synthesis of the layered
and spinel structures in the Li–Mn–Ni–O system.
Alumina, the least desirable substrate in air, performed comparably to the others in
oxygen. Magnesia required large amounts of stearic acid in order to bead the solutions
and the subsequent decomposition of the stearic acid was found to interfere with the
samples. The third substrate tested was alumina treated with lithium hydroxide and
it was difficult to treat it uniformly enough to get consistent results. The substrate
selected for further combinatorial studies was therefore alumina in a flow of oxygen.
Two precipitators were tested: ammonium bicarbonate and ammonium hydroxide.
Little difference can be found in the lithium content of the final samples, but only