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■Principle of the electric double layer capacitor
When an electrode such as carbon is immersed in electrolyte, solvents and ions are orderly arranged on its surface, and layers having an ion concentration different from that of an electrolyte far from the electrode are created simultaneously on the positive and negative side. These layers are called the electric double layer, which can be regarded as extremely thin capacitors from a different point of view. For example, in the microscopic world, the condition of the surface of spherical fat granules in milk is similar to this.
The electric double layer capacitor can be regarded as two capacitors connected in series having an anode and a cathode. When an external power supply is connected to this capacitor, an increase in the density of ions forming double layers in these anodes and cathodes results in an electric charge of the capacitor elements.
Excessive increase of voltage between the electrodes (over charge) causes transfer of electrons between the electrode and the electrolyte, leading to degradation of the capacitor. Voltage range in this stable operation is called rated voltage and depends on the ambient temperature as well.
Diagram for explaining the principle of the electric double layer capacitor
As stated above, the electric double layer capacitor physically stores an electric charge in contrast to the general rechargeable batteries that store an electric charge in chemical reaction. Therefore, the capacitor has the great advantage that the cycle life of charge and discharge is very long and can effectively handle rapid charge and discharge.
By the way, most capacitors as electronic parts have a construction where a dielectric, such as ceramic or polymer film is put between both metal electrodes. On the other hand, the electric double layer capacitor consists of a capacitor formed on the solid-liquid interface at an interval as extremely thin as several atomic layers, thus providing an enormously high electrostatic capacitance and energy density generally as high as 100 to 1,000 times that of other capacitors.
| In comparison with other rechargeable batteries : |
| Globally environmentally friendly |
Not contain any hazardous substances, such as heavy metals and acids |
| Excellent safety performance |
No occurrence of dangerous explosion, combustion, or natural ignition |
| Capable of rapid charge and discharge |
Capable of rapid charge and discharge |
| Long cycle life |
Charge and discharge life of more than ten thousand (10,000) cycles |
| High charge and discharge efficiency |
Large depth of discharge and in/out energy efficiency of more than 90% |
| Capable of operation in low-temperature environments |
Capable of operation under freezing temperatures |
| Accurate measurement of remaining energy |
Remaining energy simply and accurately is determined only by voltage measurement |
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