Chapter 9
Materials Near the Layered Boundary
9.1 Motivation for Studying LiNi 0.5 Mn 0.5 O 2
As previously discussed, LiNi 0.5 Mn 0.5 O 4 lies near the upper boundary of the layered
region. Figure 9.1 shows the phase boundaries of the layered region when heated in air
to either 800 or 900
◦ C as determined in previous chapters. The effect of synthesis
atmosphere and cooling rate will be studied for two compositions in the current
chapter, labeled A 9 and B 9 . The single-phase layered boundary moves downward
in the Gibbs triangle when samples are cooled more slowly such that sample A 9 ,
which is single-phase if quenched, lies in the layered–layered two phase coexistence
region when cooled more slowly. A higher oxygen partial pressure also lowers the
upper layered boundary in the Gibbs triangle, since more oxygen favors the spinel
structures over the relatively oxygen-poor layered structures. Thus, for lower oxygen
partial pressures, sample A 9 will lie very close to the layered boundary when regular
cooled. The main objective of this chapter is to find conditions that produce a sample
showing the first signs of layered–layered phase separation in order to study the
consequences of this on the performance of the electrode material.
In the literature, there is considerable debate over whether or not lithium-rich
layered materials form solid solutions [2, 3, 46] or layered–layered nano-composites
[43, 44]. In the combinatorial study, the compositions where one can expect layered–
layered materials when synthesized in oxygen were determined. The fact that these
materials can transform dramatically during slow cooling has been known for quite
some time [11, 54]. Kang and Amine [11] observed that a single-phase sample of
Li 1.17 Ni 0.25 Mn 0.58 O 2 had a first cycle capacity of 175 mAh/g when quenched and
showed phase separation in the X-ray diffraction (XRD) pattern when slow cooled
giving a first charge capacity as low as 55 mAh/g and never exceeding 85 mAh/g.
It is difficult to identify the phases present based on the XRD shown in Ref. [11].
However, based on the phase diagrams from Chaps. 5–7, their sample was made
up of a monoclinic phase near M, a rocksalt phase and/or a layered phase near
Data in this chapter are included in Ref. [92], published in the Journal of the Electrochemical
Society.
117
E. McCalla, Consequences of Combinatorial Studies of Positive Electrodes
for Li-ion Batteries, Springer Theses, DOI 10.1007/978-3-319-05849-8_9,
© Springer International Publishing Switzerland 2014
Materials Near the Layered Boundary
9.1 Motivation for Studying LiNi 0.5 Mn 0.5 O 2
As previously discussed, LiNi 0.5 Mn 0.5 O 4 lies near the upper boundary of the layered
region. Figure 9.1 shows the phase boundaries of the layered region when heated in air
to either 800 or 900
◦ C as determined in previous chapters. The effect of synthesis
atmosphere and cooling rate will be studied for two compositions in the current
chapter, labeled A 9 and B 9 . The single-phase layered boundary moves downward
in the Gibbs triangle when samples are cooled more slowly such that sample A 9 ,
which is single-phase if quenched, lies in the layered–layered two phase coexistence
region when cooled more slowly. A higher oxygen partial pressure also lowers the
upper layered boundary in the Gibbs triangle, since more oxygen favors the spinel
structures over the relatively oxygen-poor layered structures. Thus, for lower oxygen
partial pressures, sample A 9 will lie very close to the layered boundary when regular
cooled. The main objective of this chapter is to find conditions that produce a sample
showing the first signs of layered–layered phase separation in order to study the
consequences of this on the performance of the electrode material.
In the literature, there is considerable debate over whether or not lithium-rich
layered materials form solid solutions [2, 3, 46] or layered–layered nano-composites
[43, 44]. In the combinatorial study, the compositions where one can expect layered–
layered materials when synthesized in oxygen were determined. The fact that these
materials can transform dramatically during slow cooling has been known for quite
some time [11, 54]. Kang and Amine [11] observed that a single-phase sample of
Li 1.17 Ni 0.25 Mn 0.58 O 2 had a first cycle capacity of 175 mAh/g when quenched and
showed phase separation in the X-ray diffraction (XRD) pattern when slow cooled
giving a first charge capacity as low as 55 mAh/g and never exceeding 85 mAh/g.
It is difficult to identify the phases present based on the XRD shown in Ref. [11].
However, based on the phase diagrams from Chaps. 5–7, their sample was made
up of a monoclinic phase near M, a rocksalt phase and/or a layered phase near
Data in this chapter are included in Ref. [92], published in the Journal of the Electrochemical
Society.
117
E. McCalla, Consequences of Combinatorial Studies of Positive Electrodes
for Li-ion Batteries, Springer Theses, DOI 10.1007/978-3-319-05849-8_9,
© Springer International Publishing Switzerland 2014