Biomedical Engineering Reference
In-Depth Information
6.3.3 Olivine Structured Oxide
) with an olivine structure have
attracted extensive interests as potential cathode materials for
lithium-ion batteries. In the crystalline structure, phosphorous
occupies tetrahedral sites, while the transition metal (M) occupies
octahedral
Lithium phosphates (LiMPO
4
sites
and
lithium
forms
one-dimensional
chains
along
the
[010]
direction
[51].
The
most
widely
studied
phosphate is LiFePO
. Owing to its high power density and
long cycle life, LiFePO
4
has a great potential in manufacturing
lithium-ion batteries to power the next-generation EVs and HEVs.
However, the electronic conductivity of LiFePO
4
is relatively low
4
(ca. 10
). In order to overcome this
shortcoming, many methods have been used, among which the
introduction of hierarchical 3D mixed conducting networks is one
of the best choices in enhancing the power and rate performance
of LiFePO
-
9
S cm
-
1
for the pure LiFePO
4
[52], and this work will be further discussed in
Section 6.5.3.
4
6.4 NANOSTRUCTURED ELECTRODE MATERIALS
Although lithium-ion batteries have achieved great commercial
success, further application of these batteries is now limited by
their performance (e.g., charge/discharge rate) due to the fact that
most lithium-ion batteries are based on micrometer-sized electrode
materials, thus poor in their kinetics, lithium-ion intercalation
capacities, and structural stability; limits will always exist if no
improvement is made on the intrinsic diffusivity of Li ions in
the solid state (ca. 10
) or other material properties
[8]. Therefore, in order to meet the demands of next-generation
HEVs and clean energy storage, people may still face challenges
in developing new electrode materials with high power density
(viz. high rates), high energy density, longer cycle life, and
improved safety [14]. As a result, people naturally turn to
nanomaterials, for the sake of size effects, ultrahigh specific
surface areas and other attractive features they possess. For
example, reduced dimensions of nanomaterials may accelerate
-
8
cm
2
s
-
1
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