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Perspectives and Challenges
9.3.4 Composite Electrode Materials
The technical challenges associated with electric double-layer carbon
and psuedocapacitive material development have been addressed innovatively by several techniques as discussed in the previous section.
However, while advances in the energy storage capabilities of these materials have been marginal over recent years, breakthroughs in energy
storage techniques are necessities. Compositing carbons with psuedocapacitive materials emerged as promising approaches to realize significantly higher energy storage capabilities and successfully bridge the gap
between batteries and traditional capacitor materials. This method capitalizes on specific charge storage mechanisms that can complement each
other in new ES designs.
As previously discussed, the poor cyclability of conductive polymer materials may hinder their application as stand-alone electrode materials in ESs.
Compositing conductive polymers with carbon-based active materials may
overcome these challenges while also increasing the electronic conductivity
of the active layer. For example, combining psuedocapacitive polymer materials with CNTs [41–43] and graphene [44–46] are currently the most extensively investigated composite formulations for ES applications.
While CNTs possess limited surface areas compared to other microporous
carbon blacks, they maintain rigid mechanically robust structures that can
result in favorable three-dimensional electrode architectural configurations.
The network arrangement can provide a porous structure that can readily
facilitate the transport of electrolyte species and provide highly electronically conductive pathways to the redox centers of the active materials. The
structure, porosity, and pore size distribution of this scaffold-like architecture can also be tailored by using CNTs with varying diameters, surface
properties, and wall thicknesses or by modifying preparation techniques.
These unique electrode structures can effectively serve to increase the
utilization of the redox centers present throughout the bulk of conductive
polymer materials. Moreover, a flexible CNT network structure can cater to
the volumetric changes resulting from charging and discharging processes.
This structure can maintain the mechanical integrity of the active material
layer, improving the cyclabilities of the materials [47]. The surfaces of CNTs
can also interact favorably with many conjugated conductive polymer structures and these composites can readily form charge transfer complexes [48].
The exact nature of these interactions and the polymer–CNT interface are
still unknown and should be investigated further.
Overcoming the low electronic conductivity and irreversibility of metal
oxide species can also be achieved by developing carbon–metal oxide
composites including manganese oxide–carbon nanotube thin films [49],
graphene nanoplatelet-supported manganese oxide nanoparticles [50], manganese oxide coated carbon nanofoams [51], manganese oxide nanosheets
dispersed on functionalized graphene [52], and nickel oxide nanoparticles
Perspectives and Challenges
9.3.4 Composite Electrode Materials
The technical challenges associated with electric double-layer carbon
and psuedocapacitive material development have been addressed innovatively by several techniques as discussed in the previous section.
However, while advances in the energy storage capabilities of these materials have been marginal over recent years, breakthroughs in energy
storage techniques are necessities. Compositing carbons with psuedocapacitive materials emerged as promising approaches to realize significantly higher energy storage capabilities and successfully bridge the gap
between batteries and traditional capacitor materials. This method capitalizes on specific charge storage mechanisms that can complement each
other in new ES designs.
As previously discussed, the poor cyclability of conductive polymer materials may hinder their application as stand-alone electrode materials in ESs.
Compositing conductive polymers with carbon-based active materials may
overcome these challenges while also increasing the electronic conductivity
of the active layer. For example, combining psuedocapacitive polymer materials with CNTs [41–43] and graphene [44–46] are currently the most extensively investigated composite formulations for ES applications.
While CNTs possess limited surface areas compared to other microporous
carbon blacks, they maintain rigid mechanically robust structures that can
result in favorable three-dimensional electrode architectural configurations.
The network arrangement can provide a porous structure that can readily
facilitate the transport of electrolyte species and provide highly electronically conductive pathways to the redox centers of the active materials. The
structure, porosity, and pore size distribution of this scaffold-like architecture can also be tailored by using CNTs with varying diameters, surface
properties, and wall thicknesses or by modifying preparation techniques.
These unique electrode structures can effectively serve to increase the
utilization of the redox centers present throughout the bulk of conductive
polymer materials. Moreover, a flexible CNT network structure can cater to
the volumetric changes resulting from charging and discharging processes.
This structure can maintain the mechanical integrity of the active material
layer, improving the cyclabilities of the materials [47]. The surfaces of CNTs
can also interact favorably with many conjugated conductive polymer structures and these composites can readily form charge transfer complexes [48].
The exact nature of these interactions and the polymer–CNT interface are
still unknown and should be investigated further.
Overcoming the low electronic conductivity and irreversibility of metal
oxide species can also be achieved by developing carbon–metal oxide
composites including manganese oxide–carbon nanotube thin films [49],
graphene nanoplatelet-supported manganese oxide nanoparticles [50], manganese oxide coated carbon nanofoams [51], manganese oxide nanosheets
dispersed on functionalized graphene [52], and nickel oxide nanoparticles