Biomedical Engineering Reference
In-Depth Information
nanostructuring process often requires more time and more
complicated procedures, which will then raise the cost of
manufacture [8, 14]. Since the properties of nanomaterials
and properties of micro-sized materials are complementary to
each other, if a material can integrate all merits of the both it will
be highly possible to obtain an electrode material with superior
performance. Concerning factors in all the aspects, nano/micro
hierarchical structured materials become the best choice for novel
structures of electrodes.
Nano/micro hierarchical structures often consist of
nanometer-sized building blocks and micro- or submicrometer-
sized assemblies, and as stated above, they have been chosen as
the best system for lithium-ion batteries because they can take
advantages of both the components of nano and micro. The former
can greatly shorten diffusion times and provide possible new
Li storage mechanisms, while the latter guarantees good stability
and makes the materials easy to handle [14, 62]. On the basis of
their morphology, commonly reported nano/micro hierarchical
structured materials include sphere-like nano/micro hierarchical
structures, flower-like nano/micro hierarchical structures, and
hierarchical 3D mixed conducting networks. The following part
will discuss these structures.
6.5.1 Sphere-Like Nano/Micro Hierarchical Structures for
Electrode Materials
Sphere-like nano/micro hierarchical structures are often at
micro-scale or submicron-scale, and they can be synthesized from
various nanometer-sized building blocks such as nanoparticles and
nanorods. As one of the most promising hierarchical structures
for lithium-ion batteries, its large quantity of nanochannels
and nanopores will enable a fast migration for both Li ions and
electrons, whereas the sphere-like microstructure can enhance
its stability and bring about a better dispersivity. For example,
through a mediated polyol process, highly ordered superstructures
of V
can be self-assembled, in which nanoparticles interconnect
to form nanorods, which will then circle around to form hollow
O
2
5
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