Comparison of Supercapacitors and Energy Storage Devices
Their primary characteristics are as follows.
- Can be charged and discharged over several hundred cycles (long service life)
- Few losses during charge/discharge (low internal resistance)
- Constituent materials do not include heavy metals
- Capable of rapid charge/discharge with large currents (high output density)
- Capable of full discharge (no limit to depth of discharge)
- High degree of safety during abnormalities, and not damaged by external shorts
When compared to the performance of rechargeable batteries, the energy storage device that most people are familiar with, supercapacitors fall behind in terms of energy density (the amount of energy that can be stored per unit of mass or volume). However, they excel in output density (the volume of electricity that can be instantaneously produced per unit of mass or volume). And they have other superior characteristics as well, such as extremely low degradation in performance over repeated charge/discharge cycles, and long life.
Expressing the relationship between typical energy storage devices based on energy density and output density, gives the characteristics above. Supercapacitors have properties that complement the characteristics of rechargeable batteries such as lithium-ion batteries, and the components that we normally call "capacitors", namely aluminum electrolytic capacitors and ceramic capacitors. Rechargeable batteries are suited to applications that require more energy. While supercapacitors are suited to applications requiring instantaneous charging/discharging, charging/discharging at larger currents, and durability over repeated cycles.
In addition, supercapacitors are capable of discharging completely. Compared to rechargeable batteries, which cannot discharge completely, supercapacitors feature a large energy output to storage capacity ratio. The change in voltage proportional to change in energy retained is the same as for rechargeable batteries. However, because they can discharge all the way to 0V, depending on the load, supercapacitors may require a power converter (DC/DC converter) to stabilize voltage. On the other hand, they have the benefit of being able to use this characteristic to measure the terminal voltage and accurately ascertain remaining charge.
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