4.2 2D Transition Metal Oxides
65
representative samples and found that they showed a specific capacitance of 6–20
times and greatly improved capacitance retention compared to NiCo 2 O 4 nanospheres
obtained by directly calcining Ni–Co glycerate nanospheres. This indicates another
advantage of the method that is used to enhance the electrochemical properties of
mixed oxide products in supercapacitor applications. In addition, the asymmetric
supercapacitor (ASC) assembled using the 2D NiCo 2 O 4 nanosheets//GO shows a
superior capacitance retention (91%) at 5 A g
−1 after 2000 cycles and a maximum
energy density (38.53 W h kg
−1 ). It is hoped that this method can be extended to
other transition metal elements to produce 2D mixed oxide nanosheets with enhanced
electrochemical properties and increased surface area.
NiO and Co 3 O 4 have also been selected to construct the hybrid nanocomposite.
Zhang et al. (2015) develop a simple hydrothermal reaction to prepare the 2D/0D
(NiO–Co 3 O 4 ) hybrid nanocomposite. The scheme of the formation process of NiO–
Co 3 O 4 nanocomposite is displayed in Fig. 4.3b. Figure 4.3c is the SEM image of
NiO–Co 3 O 4 nanocomposite, which clearly reveals numerous Co 3 O 4 nanoparticles
uniformly distributed on the surface of each NiO nanoplate. Quantitative EDS analysis in SEM shows a weight ratio of Co to Ni is about 1:2.8. The hybrid NiO–Co 3 O 4
nanostructure in Fig. 4.3d remains the hexagonal structure. As shown in Fig. 4.3e,
the high-density Co 3 O 4 nanoparticles (3 ~ 5 nm) have been finely anchored on
the surface of NiO nanoplate. As an anode material of LIB, the nanocomposite
exhibits greatly improved specific capacities and stable cyclability of 633 mA h g
−1
at 100 mA g
−1 after 70 cycles, much higher than the corresponding building block
alone. The outstanding properties of the NiO/Co 3 O 4 composite are ascribed to the
synergistic effect of various components and the hybrid structure. This large-scale
and cost-efficient synthesis can be extended for the synthesis of TMOs composite
for high-performance electrochemical energy storage.
2D perovskite-type metal oxides have the ultrathin characteristics of nanosheets
and have a broad application prospect in the field of electrochemical energy storage.
The synthesis of 2D perovskite-type LaNiO 3 (LNO) nanosheets materials with high
conductivity and rich porous structure was firstly reported via a sol-gel method and
following heating treatment by Li et al. (2017b). By adjusting the heating temperature
and time, the electrochemical properties, crystal structure and morphology of LaNiO 3
can be easily adjusted. The FESEM images of the optimized sample at different
magnifications were exhibited in Fig. 4.3f, g. As displayed in low-magnification
SEM images, a large micron-scale interconnected agglomerates to form an openpore network structure. It is apparent that the 2D sheet-like morphology is uniform
and the average thickness is ~50 nm (insert in Fig. 4.3g). These materials with
richly porous morphology and microstructure are very favorable for applications in
aspect of energy storage, which are not only beneficial to the electron/ion diffusion
and transmission, but also increase the specific surface area of the material, and
then provide more reaction sites. When the current density of the optimized sample
is 1.0 A g
−1 , the specific capacitance reaches 139.2 mAh g
−1 , which has good
65
representative samples and found that they showed a specific capacitance of 6–20
times and greatly improved capacitance retention compared to NiCo 2 O 4 nanospheres
obtained by directly calcining Ni–Co glycerate nanospheres. This indicates another
advantage of the method that is used to enhance the electrochemical properties of
mixed oxide products in supercapacitor applications. In addition, the asymmetric
supercapacitor (ASC) assembled using the 2D NiCo 2 O 4 nanosheets//GO shows a
superior capacitance retention (91%) at 5 A g
−1 after 2000 cycles and a maximum
energy density (38.53 W h kg
−1 ). It is hoped that this method can be extended to
other transition metal elements to produce 2D mixed oxide nanosheets with enhanced
electrochemical properties and increased surface area.
NiO and Co 3 O 4 have also been selected to construct the hybrid nanocomposite.
Zhang et al. (2015) develop a simple hydrothermal reaction to prepare the 2D/0D
(NiO–Co 3 O 4 ) hybrid nanocomposite. The scheme of the formation process of NiO–
Co 3 O 4 nanocomposite is displayed in Fig. 4.3b. Figure 4.3c is the SEM image of
NiO–Co 3 O 4 nanocomposite, which clearly reveals numerous Co 3 O 4 nanoparticles
uniformly distributed on the surface of each NiO nanoplate. Quantitative EDS analysis in SEM shows a weight ratio of Co to Ni is about 1:2.8. The hybrid NiO–Co 3 O 4
nanostructure in Fig. 4.3d remains the hexagonal structure. As shown in Fig. 4.3e,
the high-density Co 3 O 4 nanoparticles (3 ~ 5 nm) have been finely anchored on
the surface of NiO nanoplate. As an anode material of LIB, the nanocomposite
exhibits greatly improved specific capacities and stable cyclability of 633 mA h g
−1
at 100 mA g
−1 after 70 cycles, much higher than the corresponding building block
alone. The outstanding properties of the NiO/Co 3 O 4 composite are ascribed to the
synergistic effect of various components and the hybrid structure. This large-scale
and cost-efficient synthesis can be extended for the synthesis of TMOs composite
for high-performance electrochemical energy storage.
2D perovskite-type metal oxides have the ultrathin characteristics of nanosheets
and have a broad application prospect in the field of electrochemical energy storage.
The synthesis of 2D perovskite-type LaNiO 3 (LNO) nanosheets materials with high
conductivity and rich porous structure was firstly reported via a sol-gel method and
following heating treatment by Li et al. (2017b). By adjusting the heating temperature
and time, the electrochemical properties, crystal structure and morphology of LaNiO 3
can be easily adjusted. The FESEM images of the optimized sample at different
magnifications were exhibited in Fig. 4.3f, g. As displayed in low-magnification
SEM images, a large micron-scale interconnected agglomerates to form an openpore network structure. It is apparent that the 2D sheet-like morphology is uniform
and the average thickness is ~50 nm (insert in Fig. 4.3g). These materials with
richly porous morphology and microstructure are very favorable for applications in
aspect of energy storage, which are not only beneficial to the electron/ion diffusion
and transmission, but also increase the specific surface area of the material, and
then provide more reaction sites. When the current density of the optimized sample
is 1.0 A g
−1 , the specific capacitance reaches 139.2 mAh g
−1 , which has good