84
2.50
2.50E+04
Specific Power Density, W/kg
2.00E+04
Maximum specific power density
Half of maximum cell voltage
2.00
1.50E+04
1.50
1.00E+04
1.00
Cell Voltage, V
5.00E+03
0.50
0.00E+00
0.00
0.00
0.02
0.04
0.06
0.08
0.10
Current Density, A/cm 2
Electrochemical Supercapacitors for Energy Storage and Delivery
FIGURE 2.18
Calculated specific power density and cell voltage as function of cell current density at discharging moment at 10 sec. R p = 10000 Ω.cm 2 , C T
dl = 0.4 F.cm –2 , V 0
SC = 2.5 V, and R esr = 0.05 Ω.cm 2 ,
respectively.
position of the maximum power density is half way through the discharging
cell voltage.
Figure 2.19 shows the effects of ESR, leakage resistance, and discharging time on maximum specific power density. Note that ESR has a much
stronger effect on maximum power density, in particular at the starting
moment of discharge. Leakage resistance has an insignificant effect unless
its magnitude is small. In practice, leakage is normally large, so its effect on
maximum power density may be negligible during discharging. However, to
achieve a long shelf-life for a device, this leakage may be significant.
The matched impedance case for power density assumes that one half the
discharge energy is electricity and the other half is lost through resistive
heating. The 50% efficiency makes the operating condition unsuitable for
most applications. As a result, the matched impedance case largely overestimates the usable maximum power density, which is a much more important
consideration for industry in applying ES technologies than it is for materials
research. The United States Advanced Battery Consortium (USABC) specifies operating efficiency for electrochemical capacitors at 95% [38]. This value
is a more useful estimate of the practical output power available. By using
the adjusted efficiency (EF), peak power density becomes:
9
2
( )
P
= ( 1− E F )( V
o
m
s c ) R esr
(2 .75)
max
16
2.50
2.50E+04
Specific Power Density, W/kg
2.00E+04
Maximum specific power density
Half of maximum cell voltage
2.00
1.50E+04
1.50
1.00E+04
1.00
Cell Voltage, V
5.00E+03
0.50
0.00E+00
0.00
0.00
0.02
0.04
0.06
0.08
0.10
Current Density, A/cm 2
Electrochemical Supercapacitors for Energy Storage and Delivery
FIGURE 2.18
Calculated specific power density and cell voltage as function of cell current density at discharging moment at 10 sec. R p = 10000 Ω.cm 2 , C T
dl = 0.4 F.cm –2 , V 0
SC = 2.5 V, and R esr = 0.05 Ω.cm 2 ,
respectively.
position of the maximum power density is half way through the discharging
cell voltage.
Figure 2.19 shows the effects of ESR, leakage resistance, and discharging time on maximum specific power density. Note that ESR has a much
stronger effect on maximum power density, in particular at the starting
moment of discharge. Leakage resistance has an insignificant effect unless
its magnitude is small. In practice, leakage is normally large, so its effect on
maximum power density may be negligible during discharging. However, to
achieve a long shelf-life for a device, this leakage may be significant.
The matched impedance case for power density assumes that one half the
discharge energy is electricity and the other half is lost through resistive
heating. The 50% efficiency makes the operating condition unsuitable for
most applications. As a result, the matched impedance case largely overestimates the usable maximum power density, which is a much more important
consideration for industry in applying ES technologies than it is for materials
research. The United States Advanced Battery Consortium (USABC) specifies operating efficiency for electrochemical capacitors at 95% [38]. This value
is a more useful estimate of the practical output power available. By using
the adjusted efficiency (EF), peak power density becomes:
9
2
( )
P
= ( 1− E F )( V
o
m
s c ) R esr
(2 .75)
max
16