4
1 Introduction
properties have emerged due to the well-known quantum size effects (Zalfani et al.
2016). In addition, nanomaterials can provide a larger specific surface area, which
is advantageous to energy devices compared with their bulk masses, as the reaction/interaction between the device and the interaction medium can be significantly
enhanced (Lü et al. 2014; Gao et al. 2013). As a result, people have made tremendous
efforts to exploit the unique properties of nanomaterials and have made tremendous
progress in developing high-performance energy conversion and storage devices as
shown in Fig. 1.1.
In the past two decades, there have been many scientific efforts devoted to
the design and preparation of nanomaterials with controlled morphology and
tailored anisotropic nanostructures such as one-dimensional (1D) nanowires (NWs),
nanorods (NRs), and nanotubes (NTs), two-dimensional (2D) nanoplates, and threedimensional (3D) hierarchical structures have exhibited new fundamental (Shen et al.
2017; Qu et al. 2018; Wu et al. 2017; Guo et al. 2017; Lee et al. 2017; Xin et al.
2018). 0D structures have a short diffusion length and a minimal surface area, so
agglomeration tends to occur during the cycle. 1D nanomaterials have attracted wide
attention from the academic and industrial world due to their low cost, controllable
size, and large-scale manufacturing capabilities (Liu et al. 2014; Ma et al. 2016;
Wang et al. 2018). These nanomaterials have a unique, versatile, tunable structure
with a nano interface, a high surface to volume ratio, and a large surface area, which
can improve the performance of energy devices (Lin et al. 2017; Wei et al. 2017; Li
et al. 2018). 1D structure has a fast electron transport in one dimension and a short
ion diffusion length in the radial direction, but the static structure and fixed size limit
the non-adjustable specific surface area and porosity properties (Mao et al. 2018). In
contrast, 2D nanomaterials with high aspect ratios are very attractive materials for
energy storage applications due to their unique electronic, mechanical and optical
properties, quantum confinement, large surface area, and surface orientation properties (Wu et al. 2014; Peng et al. 2017). With the thickness of atoms or molecules and
the infinite plane length, 2D nanomaterials have different atomic structures from their
bulk counterparts including atomic arrangements, chemical valences, coordination
numbers, and bond length differences. In addition, their more exposed internal atoms
inevitably induce the formation of various defects, which will have a non-negligible
effect on their chemical and physical properties. In fact, 2D nanomaterials have
shown fascinating properties in the energy storage field including good mechanical
flexibility, short ion diffusion length, and a large exposed surface electrochemical
process (Pomerantseva and Gogotsi 2017; Tan et al. 2017). In addition, 2D nanomaterials have been extensively studied as active or supporting materials for various
energy storage applications such as lithium ions, sodium ions, lithium sulfur, and
metal-air batteries (Ji et al. 2016; Agubra et al. 2016; Ji et al. 2011). In general,
3D structures have the following advantages: (1) The large specific surface area of
nanoplatelets can be maintained because the restacking of nanoplatelets is effectively
suppressed. Therefore, a large number of electrochemically active sites are exposed
to the electrolyte so that sufficient electrochemical reactions can be performed. (2) In
the preparation of 3D structures, the use of nanosized 2D nanoplatelets as building
blocks can result in a large number of pores or channels, thereby effectively reducing
1 Introduction
properties have emerged due to the well-known quantum size effects (Zalfani et al.
2016). In addition, nanomaterials can provide a larger specific surface area, which
is advantageous to energy devices compared with their bulk masses, as the reaction/interaction between the device and the interaction medium can be significantly
enhanced (Lü et al. 2014; Gao et al. 2013). As a result, people have made tremendous
efforts to exploit the unique properties of nanomaterials and have made tremendous
progress in developing high-performance energy conversion and storage devices as
shown in Fig. 1.1.
In the past two decades, there have been many scientific efforts devoted to
the design and preparation of nanomaterials with controlled morphology and
tailored anisotropic nanostructures such as one-dimensional (1D) nanowires (NWs),
nanorods (NRs), and nanotubes (NTs), two-dimensional (2D) nanoplates, and threedimensional (3D) hierarchical structures have exhibited new fundamental (Shen et al.
2017; Qu et al. 2018; Wu et al. 2017; Guo et al. 2017; Lee et al. 2017; Xin et al.
2018). 0D structures have a short diffusion length and a minimal surface area, so
agglomeration tends to occur during the cycle. 1D nanomaterials have attracted wide
attention from the academic and industrial world due to their low cost, controllable
size, and large-scale manufacturing capabilities (Liu et al. 2014; Ma et al. 2016;
Wang et al. 2018). These nanomaterials have a unique, versatile, tunable structure
with a nano interface, a high surface to volume ratio, and a large surface area, which
can improve the performance of energy devices (Lin et al. 2017; Wei et al. 2017; Li
et al. 2018). 1D structure has a fast electron transport in one dimension and a short
ion diffusion length in the radial direction, but the static structure and fixed size limit
the non-adjustable specific surface area and porosity properties (Mao et al. 2018). In
contrast, 2D nanomaterials with high aspect ratios are very attractive materials for
energy storage applications due to their unique electronic, mechanical and optical
properties, quantum confinement, large surface area, and surface orientation properties (Wu et al. 2014; Peng et al. 2017). With the thickness of atoms or molecules and
the infinite plane length, 2D nanomaterials have different atomic structures from their
bulk counterparts including atomic arrangements, chemical valences, coordination
numbers, and bond length differences. In addition, their more exposed internal atoms
inevitably induce the formation of various defects, which will have a non-negligible
effect on their chemical and physical properties. In fact, 2D nanomaterials have
shown fascinating properties in the energy storage field including good mechanical
flexibility, short ion diffusion length, and a large exposed surface electrochemical
process (Pomerantseva and Gogotsi 2017; Tan et al. 2017). In addition, 2D nanomaterials have been extensively studied as active or supporting materials for various
energy storage applications such as lithium ions, sodium ions, lithium sulfur, and
metal-air batteries (Ji et al. 2016; Agubra et al. 2016; Ji et al. 2011). In general,
3D structures have the following advantages: (1) The large specific surface area of
nanoplatelets can be maintained because the restacking of nanoplatelets is effectively
suppressed. Therefore, a large number of electrochemically active sites are exposed
to the electrolyte so that sufficient electrochemical reactions can be performed. (2) In
the preparation of 3D structures, the use of nanosized 2D nanoplatelets as building
blocks can result in a large number of pores or channels, thereby effectively reducing