Biomedical Engineering Reference
In-Depth Information
Although the excess surface free energy contributes to the
high electroactivity toward Li storage, it also results in several
disadvantages. First, nanoparticles have low thermodynamic
stability, therefore tend to agglomerate due to their high surface
energy, and this makes them difficult to be dispersed or mixed with
carbon black and binder to produce electrodes. It is also noted that
the high electrolyte/electrode surface area may raise the risk of
secondary reactions involving electrolyte decomposition between
electrode and electrolyte, and this may be responsible for the low
coulombic efficiency and poor cycle life of the battery and even
lead to serious safety problems. In addition, nanoparticles are
often difficult to synthesize, and the uniformity of their particle
sizes may also be difficult to control. Moreover, since the density of
nanopowder is always less than that of the same material formed
from micrometer-sized particles, a decrease in energy density
may happen during the nanostructuring process of electrode
materials. In view of all problems in the use of nanomaterials, it
is necessary to find a solution to overcome the shortcomings of
nanosized materials while retaining their merits. In this context,
the construction of hierarchically nanostructured electrode
materials has been provided to be a solution to such problem.
6.5 HIERARCHICALLY NANOSTRUCTURED ELECTRODE
MATERIALS
It is known that nanostructured electrode materials, compared
with its micro-sized counterparts, have a more enhanced kinetics
for both Li ions and electrons due to a shorter diffusion length,
a better accommodation of the strain caused by Li insertion/
extraction and some new lithium storage mechanisms [14];
therefore, it can surpass the micro-sized materials in many
electrochemical properties such as capacity, charge/discharge rate,
and cycling performance. However, micro-sized materials are easy
to operate, and the cost of their production is usually affordable,
whereas for nanomaterials, a lot of problems limit their practical
applications, such as low thermodynamic stability, high activity
toward surface reactions, and difficulties in handling. Besides,
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