4.2 2D Transition Metal Oxides
63
To solve the problem of poor rate capability and cycling stability of Fe 3 O 4 anode
materials in LIBs, Zhang et al. (2016) reported a clean, simple one-step method for
synthesis on a large scale of ultrafine Fe 3 O 4 nanoparticles (∼3 nm) homogeneously
embedded in 2D carbon nanonetworks through the thermolysis of iron(III) acetylacetonate (Fe(C 5 H 7 O 2 ) 3 ) precursors at 350 °C under vacuum (designated as 2D Fe 3 O 4 /C
nanonetworks). This simple method, based on low-cost precursors, offered a clean
and low-cost method to synthesize the Fe 3 O 4 /carbon composites. Benefitting from
the excellent electroconductive nanonetworks, uniform distribution and the ultrafine
size of Fe 3 O 4 particles, high contact surface area and the efficient protection of the
carbon shell, the resultant delivered outstanding cycling properties with excellent
Coulombic efficiency (∼100%), a large reversible capacity of 1534 mA h g
−1 at
1 A g
−1 after 500 cycles, and superior rate capability of 845 mA h g
−1 at 5 °C. The
fabricated 2D Fe 3 O 4 /carbon nanonetwork can meet almost all the kinetic requirements to achieve fast discharging and charging of ideal electrode materials and long
cycle life.
4.2.4 Mixed Oxide
Compared to pure metal oxides, mixed oxides have attracted great interest due to
their excellent electronic conductivity. This is a result of the existence of multiple
valence states for contributing metals and the synergistic effect of various metallic
species (Kaneti et al. 2017). Among various mixed oxides, metal cobaltates
(MCo 2 O 4 , M = Mn, Zn, Ni, etc.) are widely studied for energy storage applications due to their superior electrical conductivity, layered structure, and low cost
(Wei et al. 2009).
Zhu et al. (2015) reported the high-quality 2D ultrathin ZnCo 2 O 4 nanosheets
synthesized by microwave-assisted liquid-phase growth and post-annealing procedures. Different from conventional heating methods, the microwave dielectric irradiation features ultrafast, selective, and volumetric heating (Baghbanzadeh et al.
2011). Polar molecules and ions are forced to orderly orientate with the constantly
changing electric field caused by microwave activation (Zhu and Chen 2014). The
microwave dielectric irradiation is favorable for the 2D anisotropic growth of inorganic nanocrystals. The independent and well-defined nanosheets show ultrathin
thickness and a micron-level planar area, indicating a high surface atomic ratio with
electronic structure and a special surface, thereby promoting the charge transfer to
improve the overall properties of the electrochemical reaction. The ultrathin ZnCo 2 O 4
nanosheets used as anode materials in LIBs show an excellent reversible lithium
storage capacity of 930–980 mAh g
−1 at 200 mA g
−1 during 200 cycles with a
good cyclic stability and high-rate capability. More importantly, they have expanded
the convenient approaches for forming other similar nanosheets, including binary
and ternary transition metal oxides (Co 3 O 4 , NiO, CuCo 2 O 4 , and NiCo 2 O 4 ), and to
explore more unique performance and promising commercial application offers the
possibility.
63
To solve the problem of poor rate capability and cycling stability of Fe 3 O 4 anode
materials in LIBs, Zhang et al. (2016) reported a clean, simple one-step method for
synthesis on a large scale of ultrafine Fe 3 O 4 nanoparticles (∼3 nm) homogeneously
embedded in 2D carbon nanonetworks through the thermolysis of iron(III) acetylacetonate (Fe(C 5 H 7 O 2 ) 3 ) precursors at 350 °C under vacuum (designated as 2D Fe 3 O 4 /C
nanonetworks). This simple method, based on low-cost precursors, offered a clean
and low-cost method to synthesize the Fe 3 O 4 /carbon composites. Benefitting from
the excellent electroconductive nanonetworks, uniform distribution and the ultrafine
size of Fe 3 O 4 particles, high contact surface area and the efficient protection of the
carbon shell, the resultant delivered outstanding cycling properties with excellent
Coulombic efficiency (∼100%), a large reversible capacity of 1534 mA h g
−1 at
1 A g
−1 after 500 cycles, and superior rate capability of 845 mA h g
−1 at 5 °C. The
fabricated 2D Fe 3 O 4 /carbon nanonetwork can meet almost all the kinetic requirements to achieve fast discharging and charging of ideal electrode materials and long
cycle life.
4.2.4 Mixed Oxide
Compared to pure metal oxides, mixed oxides have attracted great interest due to
their excellent electronic conductivity. This is a result of the existence of multiple
valence states for contributing metals and the synergistic effect of various metallic
species (Kaneti et al. 2017). Among various mixed oxides, metal cobaltates
(MCo 2 O 4 , M = Mn, Zn, Ni, etc.) are widely studied for energy storage applications due to their superior electrical conductivity, layered structure, and low cost
(Wei et al. 2009).
Zhu et al. (2015) reported the high-quality 2D ultrathin ZnCo 2 O 4 nanosheets
synthesized by microwave-assisted liquid-phase growth and post-annealing procedures. Different from conventional heating methods, the microwave dielectric irradiation features ultrafast, selective, and volumetric heating (Baghbanzadeh et al.
2011). Polar molecules and ions are forced to orderly orientate with the constantly
changing electric field caused by microwave activation (Zhu and Chen 2014). The
microwave dielectric irradiation is favorable for the 2D anisotropic growth of inorganic nanocrystals. The independent and well-defined nanosheets show ultrathin
thickness and a micron-level planar area, indicating a high surface atomic ratio with
electronic structure and a special surface, thereby promoting the charge transfer to
improve the overall properties of the electrochemical reaction. The ultrathin ZnCo 2 O 4
nanosheets used as anode materials in LIBs show an excellent reversible lithium
storage capacity of 930–980 mAh g
−1 at 200 mA g
−1 during 200 cycles with a
good cyclic stability and high-rate capability. More importantly, they have expanded
the convenient approaches for forming other similar nanosheets, including binary
and ternary transition metal oxides (Co 3 O 4 , NiO, CuCo 2 O 4 , and NiCo 2 O 4 ), and to
explore more unique performance and promising commercial application offers the
possibility.