Preface
The improvement of volumetric energy density remains a key area of research to
optimize Li-ion batteries for applications such as extending the range of electric
vehicles. There is still improvement to be made in the energy density in the positive
electrode materials. The current thesis deals with determining the phase diagrams
of the Li–Mn–Ni–O and Li–Co–Mn–O systems in order to better understand the
structures and the electrochemistry of these materials. The phase diagrams were made
through careful analysis of hundreds of X-ray diffraction patterns taken of milligramscale combinatorial samples. A number of bulk samples were also investigated.
The Li–Mn–Ni–O system is of particular interest as avoiding cobalt lowers the
cost of the material. However, this system is very complex: there are two large
solid-solution regions separated by three two-phase regions as well as two threephase regions. Comparing quenched and slow cooled samples shows that the system
transforms dramatically when cooled at rates typically used to make commercial
materials. The consequences of these results are that much of the system must be
avoided in order to guarantee that the materials remain single phase during cooling.
This work should therefore impact significantly researchers working on composite
electrodes.
Two new structures were found. The first was Li-Ni-Mn oxide rocksalt structures with vacancies and ordering of manganese which were previously mistakenly
identified as Li x Ni 2−x O 2 . The other new structure was a layered oxide with metal
site vacancies allowing manganese to order on two
√
3 ×
√
3 superlattices. The
electrochemistry of both these materials is presented here.
Finally, the region where layered-layered composites form during cooling has
been determined. These materials were long looked for along the composition line
from Li 2 MnO 3 to LiNi 0.5 Mn 0.5 O 2 and the most significant consequence of the actual
locations of the end-members is that one of the structures contains a high concentration of nickel on the lithium layer. Layered-layered nano-composites formed in this
system are therefore not ideal positive electrode materials and it will be demonstrated
that single-phase layered materials lead to better electrochemistry.
ix
The improvement of volumetric energy density remains a key area of research to
optimize Li-ion batteries for applications such as extending the range of electric
vehicles. There is still improvement to be made in the energy density in the positive
electrode materials. The current thesis deals with determining the phase diagrams
of the Li–Mn–Ni–O and Li–Co–Mn–O systems in order to better understand the
structures and the electrochemistry of these materials. The phase diagrams were made
through careful analysis of hundreds of X-ray diffraction patterns taken of milligramscale combinatorial samples. A number of bulk samples were also investigated.
The Li–Mn–Ni–O system is of particular interest as avoiding cobalt lowers the
cost of the material. However, this system is very complex: there are two large
solid-solution regions separated by three two-phase regions as well as two threephase regions. Comparing quenched and slow cooled samples shows that the system
transforms dramatically when cooled at rates typically used to make commercial
materials. The consequences of these results are that much of the system must be
avoided in order to guarantee that the materials remain single phase during cooling.
This work should therefore impact significantly researchers working on composite
electrodes.
Two new structures were found. The first was Li-Ni-Mn oxide rocksalt structures with vacancies and ordering of manganese which were previously mistakenly
identified as Li x Ni 2−x O 2 . The other new structure was a layered oxide with metal
site vacancies allowing manganese to order on two
√
3 ×
√
3 superlattices. The
electrochemistry of both these materials is presented here.
Finally, the region where layered-layered composites form during cooling has
been determined. These materials were long looked for along the composition line
from Li 2 MnO 3 to LiNi 0.5 Mn 0.5 O 2 and the most significant consequence of the actual
locations of the end-members is that one of the structures contains a high concentration of nickel on the lithium layer. Layered-layered nano-composites formed in this
system are therefore not ideal positive electrode materials and it will be demonstrated
that single-phase layered materials lead to better electrochemistry.
ix