Chapter 1
Introduction
1.1 Motivation: Li–Co–Mn–Ni Oxide Materials
Improving the energy density of lithium (Li)-ion batteries remains important for a
number of applications. In particular, high energy densities are required to extend
the range of electric vehicles and minimize the space and mass of the battery pack. In
the ongoing search for means to increase the energy of Li-ion batteries, the discovery
of new positive electrode materials is of critical importance. The positive electrode
is synthesized with lithium in it, some of which is removed during charging of the
cell along with electrons that travel through the external circuit. The lithium is then
reinserted into the material while the battery is discharged, which is accompanied by
electrons traveling through the external circuit to do work. There are many challenges
with respect to finding better positive electrode materials, the primary of which are
increasing the volumetric energy density, lowering the cost, and improving the safety.
Though safety is a very important issue with respect to Li-ion batteries, the focus of
this thesis will be to maximize energy while trying to minimize cost.
Table 1.1 shows the volumetric energy density of the most competitive positive
electrode materials, calculated from data from Ref. [1]. The most common commercially used positive electrode, LiCoO 2 , has an energy density of 3.05 Wh/cm
3 while
the material with the highest energy density, Li[Li 1/9 Ni 1/3 Mn 5/9 ]O 2 , is a lithium-rich
layered oxide material that has roughly 25 % more energy than LiCoO 2 . The lithiumrich layered structures are very promising as possible next-generation high energy
positive electrodes. They exist over wide composition ranges within the Li–Co–Mn–
Ni–O system [2, 3] and will be discussed in detail throughout this thesis. Despite the
potentially very high energy density, there remain challenges with respect to these
materials and this will be discussed throughout the thesis. The primary motivation
for studying the Li–Co–Mn–Ni–O system is, therefore, that many promising materials have already been found in this system. For example, all the materials listed
in Table 1.1 lie within this system except for the last two, one of which is LiFePO 4
with the lowest energy density of those listed. It must be emphasized here that the
primary objective here is maximizing volumetric energy density. For applications
where gravimetric energy density and particularly power are more critical materials
such as LiFePO 4 are of greater importance. Table 1.1, therefore, demonstrates why
1
E. McCalla, Consequences of Combinatorial Studies of Positive Electrodes
for Li-ion Batteries, Springer Theses, DOI 10.1007/978-3-319-05849-8_1,
© Springer International Publishing Switzerland 2014
Introduction
1.1 Motivation: Li–Co–Mn–Ni Oxide Materials
Improving the energy density of lithium (Li)-ion batteries remains important for a
number of applications. In particular, high energy densities are required to extend
the range of electric vehicles and minimize the space and mass of the battery pack. In
the ongoing search for means to increase the energy of Li-ion batteries, the discovery
of new positive electrode materials is of critical importance. The positive electrode
is synthesized with lithium in it, some of which is removed during charging of the
cell along with electrons that travel through the external circuit. The lithium is then
reinserted into the material while the battery is discharged, which is accompanied by
electrons traveling through the external circuit to do work. There are many challenges
with respect to finding better positive electrode materials, the primary of which are
increasing the volumetric energy density, lowering the cost, and improving the safety.
Though safety is a very important issue with respect to Li-ion batteries, the focus of
this thesis will be to maximize energy while trying to minimize cost.
Table 1.1 shows the volumetric energy density of the most competitive positive
electrode materials, calculated from data from Ref. [1]. The most common commercially used positive electrode, LiCoO 2 , has an energy density of 3.05 Wh/cm
3 while
the material with the highest energy density, Li[Li 1/9 Ni 1/3 Mn 5/9 ]O 2 , is a lithium-rich
layered oxide material that has roughly 25 % more energy than LiCoO 2 . The lithiumrich layered structures are very promising as possible next-generation high energy
positive electrodes. They exist over wide composition ranges within the Li–Co–Mn–
Ni–O system [2, 3] and will be discussed in detail throughout this thesis. Despite the
potentially very high energy density, there remain challenges with respect to these
materials and this will be discussed throughout the thesis. The primary motivation
for studying the Li–Co–Mn–Ni–O system is, therefore, that many promising materials have already been found in this system. For example, all the materials listed
in Table 1.1 lie within this system except for the last two, one of which is LiFePO 4
with the lowest energy density of those listed. It must be emphasized here that the
primary objective here is maximizing volumetric energy density. For applications
where gravimetric energy density and particularly power are more critical materials
such as LiFePO 4 are of greater importance. Table 1.1, therefore, demonstrates why
1
E. McCalla, Consequences of Combinatorial Studies of Positive Electrodes
for Li-ion Batteries, Springer Theses, DOI 10.1007/978-3-319-05849-8_1,
© Springer International Publishing Switzerland 2014