Foreword for Eric McCalla’s Thesis-prepared
by Jeff Dahn
Given the large number of attractive and useful materials in the Li–Ni–Mn–O system
and given the confusion about the structure and properties of many of them, Eric
McCalla decided to undertake a complete determination of the Li–Ni–Mn–O phase
diagram as the major portion of his Ph.D. thesis. Eric adopted combinatorial and
high throughput materials science methods for the synthesis of these materials and
used X-ray diffraction as the main characterization tool. Eric learned how to control
lithium loss during heating of the small combinatorial samples and studied the effects
of oxygen partial pressure, heating temperature, and cooling rate on the obtained
materials.
The phase diagrams presented in this thesis have all been determined with great
care. Analysis of multiphase regions using the lever rule gave phase boundaries
that agree very well with direct determinations of phase boundaries by inspection
of X-ray patterns for single phase or hints of other phases. The dramatic effect of
cooling rate on the three phase regions in the phase diagrams was a huge surprise. In
addition, the identification of a solid solution phase, Li[Li 1/3−x P x/2 Ni x/2 Mn 2/3 ]O 2 ,
where Ni and a vacancy (P) replace two Li atoms in Li[Li 1/3 Mn 2/3 ]O 2 , showed that
lithium-deficient layered materials incorporate vacancies, not Mn
3+ .
The thesis shows that “layered-layered” nanocomposites and the “layeredlayered-spinel” three phase composites do exist in certain regions of the phase
diagram. However, these materials do not incorporate LiNi 1/2 Mn 1/2 O 2 and Li 2 MnO 3
as the two layered components. Instead, the Mn-rich component contains some Ni
and vacancies and the Ni-rich component is not LiNi 1/2 Mn 1/2 O 2 . Furthermore, Eric
shows in the thesis that materials which are “layered-layered” nanocomposites yield
inferior electrochemical performance to those which are single-phase solid solutions.
The thesis also explains why rock-salt structure so-called “impurity” phases occur
in many samples in the literature and that these rock-salt phases are not impurities
but are expected based on the Li–Ni–Mn–O phase diagram. There are many more
gems in the thesis that the reader can discover.
The thesis was examined and approved by Dr. Shirley Meng of the University
of California at San Diego. Dr. Meng was impressed by the gap that Eric’s thesis
helped fill in the cathode materials research community. Meng believes that Eric’s
methodology was unique and the information Eric presented in his thesis will be
critical to researchers in the future.
vii
by Jeff Dahn
Given the large number of attractive and useful materials in the Li–Ni–Mn–O system
and given the confusion about the structure and properties of many of them, Eric
McCalla decided to undertake a complete determination of the Li–Ni–Mn–O phase
diagram as the major portion of his Ph.D. thesis. Eric adopted combinatorial and
high throughput materials science methods for the synthesis of these materials and
used X-ray diffraction as the main characterization tool. Eric learned how to control
lithium loss during heating of the small combinatorial samples and studied the effects
of oxygen partial pressure, heating temperature, and cooling rate on the obtained
materials.
The phase diagrams presented in this thesis have all been determined with great
care. Analysis of multiphase regions using the lever rule gave phase boundaries
that agree very well with direct determinations of phase boundaries by inspection
of X-ray patterns for single phase or hints of other phases. The dramatic effect of
cooling rate on the three phase regions in the phase diagrams was a huge surprise. In
addition, the identification of a solid solution phase, Li[Li 1/3−x P x/2 Ni x/2 Mn 2/3 ]O 2 ,
where Ni and a vacancy (P) replace two Li atoms in Li[Li 1/3 Mn 2/3 ]O 2 , showed that
lithium-deficient layered materials incorporate vacancies, not Mn
3+ .
The thesis shows that “layered-layered” nanocomposites and the “layeredlayered-spinel” three phase composites do exist in certain regions of the phase
diagram. However, these materials do not incorporate LiNi 1/2 Mn 1/2 O 2 and Li 2 MnO 3
as the two layered components. Instead, the Mn-rich component contains some Ni
and vacancies and the Ni-rich component is not LiNi 1/2 Mn 1/2 O 2 . Furthermore, Eric
shows in the thesis that materials which are “layered-layered” nanocomposites yield
inferior electrochemical performance to those which are single-phase solid solutions.
The thesis also explains why rock-salt structure so-called “impurity” phases occur
in many samples in the literature and that these rock-salt phases are not impurities
but are expected based on the Li–Ni–Mn–O phase diagram. There are many more
gems in the thesis that the reader can discover.
The thesis was examined and approved by Dr. Shirley Meng of the University
of California at San Diego. Dr. Meng was impressed by the gap that Eric’s thesis
helped fill in the cathode materials research community. Meng believes that Eric’s
methodology was unique and the information Eric presented in his thesis will be
critical to researchers in the future.
vii