174
Electrochemical Supercapacitors for Energy Storage and Delivery
0
200
400
Specific Capacitance (F/g)
600
800
1000
1200
1400
0.25 mg/cm
2
0.28 mg/cm
2
0.44 mg/cm
2
0.67 mg/cm
2
0.99 mg/cm
2
1
10
100
Scan Rate (mV/s)
FIGURE 4.25
Specific capacitance for vanadium nitride nanocrystals synthesized at 400°C and tested at varying scan rates and mass loadings onto collector in 1 M KOH. (Source: Choi, D. G. E. Blomgren,
and P. N. Kumta. 2006. Advanced Materials, 18, 1178–1182. With permission.)
to generate particles of specific size and shape [97]. The conducting polymer
storage mechanism involves accumulation of charge via proton doping interactions throughout the materials backbone (Figure 4.26).
However, as a result of direct charge uptake and fast discharge inherent to
an ES, conductive polymers are subject to swelling and cracking over time.
The relaxation of the polymer matrix can result in a large amount of irreversible reduction over the first few hundred cycles. To reduce this relaxation effect, slower charging must be used. The upside is that high specific
capacitance values of 400 F.g –1 can be achieved throughout the material and
not just at the material surface [99].
Conducting polymers, like most other pseudocapacitive materials, limit
the potential range of the electrode to regions where reversible redox reactions occur for that particular material. In the case of polymers, a lack of
oxidation states limits the potential window and also a physical polymer
breakdown caused by over-oxidation occurs when charges cannot redistribute quickly enough within the polymer matrix [100]. The poor stability
during oxidation and the irreversible capacitance challenges highlight conductive polymers as interesting materials for composite cathodes.
Work by Yan et al. on PANI and graphene composites showed an electrode
capacitance as high as 1000 F.g –1 in an aqueous electrolyte [101]. The same
research also showed that incorporation of CNT additives helped enhance
percolation and mechanical strength during the doping process, enabling
the electrode to retain 94% of the original capacitance after 1000 cycles compared to retention below 50% without the CNT additive [101].
Electrochemical Supercapacitors for Energy Storage and Delivery
0
200
400
Specific Capacitance (F/g)
600
800
1000
1200
1400
0.25 mg/cm
2
0.28 mg/cm
2
0.44 mg/cm
2
0.67 mg/cm
2
0.99 mg/cm
2
1
10
100
Scan Rate (mV/s)
FIGURE 4.25
Specific capacitance for vanadium nitride nanocrystals synthesized at 400°C and tested at varying scan rates and mass loadings onto collector in 1 M KOH. (Source: Choi, D. G. E. Blomgren,
and P. N. Kumta. 2006. Advanced Materials, 18, 1178–1182. With permission.)
to generate particles of specific size and shape [97]. The conducting polymer
storage mechanism involves accumulation of charge via proton doping interactions throughout the materials backbone (Figure 4.26).
However, as a result of direct charge uptake and fast discharge inherent to
an ES, conductive polymers are subject to swelling and cracking over time.
The relaxation of the polymer matrix can result in a large amount of irreversible reduction over the first few hundred cycles. To reduce this relaxation effect, slower charging must be used. The upside is that high specific
capacitance values of 400 F.g –1 can be achieved throughout the material and
not just at the material surface [99].
Conducting polymers, like most other pseudocapacitive materials, limit
the potential range of the electrode to regions where reversible redox reactions occur for that particular material. In the case of polymers, a lack of
oxidation states limits the potential window and also a physical polymer
breakdown caused by over-oxidation occurs when charges cannot redistribute quickly enough within the polymer matrix [100]. The poor stability
during oxidation and the irreversible capacitance challenges highlight conductive polymers as interesting materials for composite cathodes.
Work by Yan et al. on PANI and graphene composites showed an electrode
capacitance as high as 1000 F.g –1 in an aqueous electrolyte [101]. The same
research also showed that incorporation of CNT additives helped enhance
percolation and mechanical strength during the doping process, enabling
the electrode to retain 94% of the original capacitance after 1000 cycles compared to retention below 50% without the CNT additive [101].