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SECONDARY ELECTROCHEMICAL ACCUMULATORS 825
Voltage
[V]
4.5
4.0
3.5
3.0
2 C
Charge: 1 C (4.1 V cccv)
Temperature: 20°C
0.2 C
2.5
1 C
2.0 0 500 1000 1500
Capacity
[mAh]
Figure 18.8 Voltage during discharge of a Li-ion battery with C 5 = 1350 mAh capacity as a
function of the discharged capacity at different discharge currents and a temperature of 20 ◦ C. The
charging is done with the constant current–constant voltage (cccv or IU, see Sub-section 18.4.7.6.1)
regime with a charge current of 1 C and an end-of-charge voltage of 4.1 V [14]
Voltage
[V]
4.5
4.0
3.5
3.0
2.5
−10°C
−20°C
Charge: 1 C (4.1 V cccv)
Discharge: 0.2 C
60°C
20°C
2.0 0 500 1000 1500
Capacity
[mAh]
Figure 18.9 Voltage during discharge of a Li-ion battery with C 5 = 1350 mAh capacity as a
function of the discharged capacity at different battery temperatures at a discharge current of 0.2 C.
The charging is done as in Figure 18.8 [14]
only depends on the electrostatic effect. However, in contrast to classical capacitors in
which in the dielectric only electrons are moved, in double-layer capacitors a movement
of ions and therefore a significant mass movement occurs. This results in diffusion-time
constants during charging and discharging in the double-layer capacitor.
Depending on the electrode material, the capacity is approximately 20 to 40 µF/cm 2 .
The electrode materials are typically made of carbon with very high surface areas of
approximately 2000 m 2 /g. The number of charge carriers in the double layer is limited
because with increasing charge-carrier density the potential increases. If the potential is
too high, the charge carriers are forced to penetrate the electrode/electrolyte interface
resulting in electrochemical reactions like in secondary batteries. However, in this case