120
9 Materials Near the Layered Boundary
Electrochemical tests were carried out on some samples as described in Sect. 2.5.
Two identical cells were made for each sample. All cycling was performed at a
specific current of 10 mA/g. For samples A 9 and B 9 , made by regular cooling after
heating in the 2 % oxygen mixture, inductively coupled plasma (ICP) was used as
elemental analysis to determine the metal molar fractions of the final products (these
values were used in generating Fig. 9.1). The XRD patterns from all samples were
measured in either a JD-2000 diffractometer or a Siemens D-5000 diffractometer.
The resulting scans were then analyzed using Rietveld refinement.
A series of samples Li 1+x [Ni 0.5 Mn 0.5 ] 1−x O 2 was also synthesized at 900
◦ C in air
with regular cooling (by Jing Li who performed all measurements on these samples).
This composition line was previously studied by Myung et al. [64] over the range
0 ≤ x ≤ 0.06 and capacity was found to increase with x when cycled up to 4.6 V.
Here, the wider composition range 0 ≤ x ≤ 0.24 was studied and the upper cutoff
was 4.4 V in order to avoid the high voltage plateau [2]. Samples A 9 , B 9 and C 9
in Fig. 9.1 have nominal compositions given by x = 0, 0.04, and 0.08, respectively.
Samples with x = 0.12, 0.16, 0.20, and 0.24 were also prepared.
Finally, to better understand the consequences of the layered–layered phase separation on the structure, a Monte Carlo simulation of a material of composition A 9
in Fig. 9.1 was performed. The details of this simulation are given in Sect. 2.12.
The temperature scale was set by the parameter ,β T and previous results suggest that
β T = 1 corresponds to a temperature near and below 800
◦ C, such that the value of
β T = 2 used here is near 250
◦ C, and is therefore well below the critical temperature
above which solid solutions are favored due to a higher entropy. Two compositions
were simulated: Li 0.9 Ni 0.1 [Ni 0.4 Mn 0.5 Li 0.1 ]O 2 (stoichiometric LiNi 0.5 Mn 0.5 O 2 with
10 % nickel on the lithium layer, consistent with Ref. [2]) and Li[Ni 0.4 Mn 0.5 Li 0.1 ]O 2
simulated in order to determine the role played by nickel on the lithium layer. The
fact that there was nickel on the lithium layer in the first simulation meant that the
model required out-of-plane interactions. Therefore, two layers were simulated: one
lithium layer and one TM layer. It was assumed that these two layers stack alternately and the only out-of-plane interactions included in the calculations were for
nearest neighbors, such that every atom had six in-plane and six out-of-plane nearest
neighbor interactions. Periodic boundary conditions were used.
9.3 Structural Results
The results of the elemental analysis for composition A 9 were Li 0.48 Ni 0.26 Mn 0.26 and
that point was positioned accordingly in Fig. 9.1. This composition suggests that the
material, if single phase, would be Li 0.96 Ni 0.52 Mn 0.52 O 2 assuming no metal/oxygen
vacancies and can therefore be considered a slightly lithium-poor layered material.
Figure 9.2 shows XRD scans of samples at composition A 9 made under various
conditions. The scan of the sample made in pure oxygen and regular cooled shows
three phases (three peaks visible near 44
◦ ) consistent with the R, N, and M phases
discussed at length in previous chapters. Since broadening of the Bragg peak near
9 Materials Near the Layered Boundary
Electrochemical tests were carried out on some samples as described in Sect. 2.5.
Two identical cells were made for each sample. All cycling was performed at a
specific current of 10 mA/g. For samples A 9 and B 9 , made by regular cooling after
heating in the 2 % oxygen mixture, inductively coupled plasma (ICP) was used as
elemental analysis to determine the metal molar fractions of the final products (these
values were used in generating Fig. 9.1). The XRD patterns from all samples were
measured in either a JD-2000 diffractometer or a Siemens D-5000 diffractometer.
The resulting scans were then analyzed using Rietveld refinement.
A series of samples Li 1+x [Ni 0.5 Mn 0.5 ] 1−x O 2 was also synthesized at 900
◦ C in air
with regular cooling (by Jing Li who performed all measurements on these samples).
This composition line was previously studied by Myung et al. [64] over the range
0 ≤ x ≤ 0.06 and capacity was found to increase with x when cycled up to 4.6 V.
Here, the wider composition range 0 ≤ x ≤ 0.24 was studied and the upper cutoff
was 4.4 V in order to avoid the high voltage plateau [2]. Samples A 9 , B 9 and C 9
in Fig. 9.1 have nominal compositions given by x = 0, 0.04, and 0.08, respectively.
Samples with x = 0.12, 0.16, 0.20, and 0.24 were also prepared.
Finally, to better understand the consequences of the layered–layered phase separation on the structure, a Monte Carlo simulation of a material of composition A 9
in Fig. 9.1 was performed. The details of this simulation are given in Sect. 2.12.
The temperature scale was set by the parameter ,β T and previous results suggest that
β T = 1 corresponds to a temperature near and below 800
◦ C, such that the value of
β T = 2 used here is near 250
◦ C, and is therefore well below the critical temperature
above which solid solutions are favored due to a higher entropy. Two compositions
were simulated: Li 0.9 Ni 0.1 [Ni 0.4 Mn 0.5 Li 0.1 ]O 2 (stoichiometric LiNi 0.5 Mn 0.5 O 2 with
10 % nickel on the lithium layer, consistent with Ref. [2]) and Li[Ni 0.4 Mn 0.5 Li 0.1 ]O 2
simulated in order to determine the role played by nickel on the lithium layer. The
fact that there was nickel on the lithium layer in the first simulation meant that the
model required out-of-plane interactions. Therefore, two layers were simulated: one
lithium layer and one TM layer. It was assumed that these two layers stack alternately and the only out-of-plane interactions included in the calculations were for
nearest neighbors, such that every atom had six in-plane and six out-of-plane nearest
neighbor interactions. Periodic boundary conditions were used.
9.3 Structural Results
The results of the elemental analysis for composition A 9 were Li 0.48 Ni 0.26 Mn 0.26 and
that point was positioned accordingly in Fig. 9.1. This composition suggests that the
material, if single phase, would be Li 0.96 Ni 0.52 Mn 0.52 O 2 assuming no metal/oxygen
vacancies and can therefore be considered a slightly lithium-poor layered material.
Figure 9.2 shows XRD scans of samples at composition A 9 made under various
conditions. The scan of the sample made in pure oxygen and regular cooled shows
three phases (three peaks visible near 44
◦ ) consistent with the R, N, and M phases
discussed at length in previous chapters. Since broadening of the Bragg peak near