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n
OO
Li or carbon
anode
separator
Radical cathode
N
•
O
1
1
µ
m
Carbon fiber
(Vapor Grown
Carbon Fiber)
Radial polymer/carbon
composite electrode
Figure 14.5
A typical fabrication method of the prototype ''organic radical battery''. A full-colour version of
thisfigureappearsintheColourPlatesectionof this topic.
was obtained from cyclic voltammetry. The charge/discharge capacities were about 110 mAh/g (Coulomb
efficiency
100 %), which was close to 100 % utilization of the loaded amount of radical polymer, based
on theoretical capacity of
1
(111 mAh/g).
21
The battery exhibited a surprisingly high current capability,
allowing rapid charging within about one minute and large discharge currents (50 C, where 1 C is defined as
the current density at which the charging and discharging of the battery takes one hour) without substantial
loss of output voltages (Figure 14.6), which was in contrast to conventional lithium ion batteries. The
cycle performance during charging and discharging of the battery was extremely stable, and no significant
deterioration in the capacity was observed for more than 1000 cycles. This surprisingly high current
capability and long cyclability can be attributed to the rapid and reversible one-electron transfer reaction of
the radical, no significant structural change of the radical upon electron transfer, and to the nanometer-sized,
amorphous electrode structure.
The battery performance based on the polymer
1
cathode is presented on an energy/power density dia-
gram (Ragone plot) in Figure 14.7, along with data for conventional secondary batteries (lithium ion, nickel
metal hydride batteries) and electric double layer capacitor (EDLC). The radical battery is characterized
∼
1 C
4
5
10
20
50
3.5
3
3 C
1 C
0.5 C
2.5
0 0 0 0 0 0
Capacity (%)
Figure14.6
Currentrateperformanceoftheorganicradicalbattery(solidline,1-50Crate)andaconventional
lithiumionbattery(dashedline,0.5-3Crate).
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