Characteristics and advantages of supercapacitors

Characteristics and advantages of supercapacitors

With the development of social economy, people are paying more and more attention to green energy and the natural environment. As a new type of energy storage device, supercapacitors are receiving more and more attention due to their irreplaceable advantages. In some designs that require high power and efficiency solutions, engineers have started using supercapacitors to replace traditional batteries.

Defects in battery technology

New types of batteries such as Li Li and NiMH can provide a reliable energy storage solution and have been widely used in many fields. As is well known, chemical batteries store charges through electrochemical reactions that generate Faraday charge transfer, resulting in a shorter lifespan and greater susceptibility to temperature. This is also a challenge faced by designers of lead-acid batteries (batteries). Meanwhile, high current directly affects the lifespan of these batteries. Therefore, for certain applications that require long lifespan and high reliability, these chemical reaction based batteries exhibit various shortcomings.

The characteristics and advantages of supercapacitors

The principle of supercapacitors is not based on new technologies. Common supercapacitors are mostly double layer structures, similar to electrolytic capacitors. These supercapacitors have high energy density and power density. Compared with traditional capacitors and secondary batteries, supercapacitors can store charges in the same way as ordinary capacitors. They are characterized by fast charging and discharging, high efficiency, environmental pollution, long cycle life, wide temperature range and safety.

In addition to being able to charge and discharge quickly, another major feature of supercapacitors is their low impedance. So, when a supercapacitor is fully discharged, it will exhibit high resistance characteristics, and if there is no restriction, it will pull the possible source current. Therefore, it is necessary to use a constant current or constant voltage charger.

Ten years ago, supercapacitors could only be sold in small quantities each year, and the price was very expensive, about 1-2 US dollars per farad. Now, supercapacitors have been supplied to the market in bulk as standard products, and the price has also been decreasing, averaging 0.01 to 0.02 US dollars per farad. In the past few years, supercapacitors have begun to enter many application fields, such as consumer electricity, manufacturing, and transportation.

The structure of supercapacitors

Although there are many supercapacitor manufacturers around the world who can provide various types of supercapacitor products, most of their products are based on a similar double layer structure. Supercapacitors are often similar in structure to electrolytic capacitors, and their main difference lies in electrode materials.

The electrodes of early supercapacitors were made of carbon, and the surface area of the carbon electrode material was very large. The size of the capacitor depends on the surface area and the distance between the electrodes. The surface area of this carbon electrode, combined with a very large electrode distance, allows the capacitance of the supercapacitor to be constant. Most supercapacitors can achieve Faraday level, with a general capacitance range of 1-5000F.

Using supercapacitors

Supercapacitors have a wide range of applications. Combined with materials with high energy density such as fuel cells, supercapacitors can provide rapid energy release and meet the power demand, allowing fuel cells to function solely as energy sources. Recently, the energy density of supercapacitors can reach 20kW/kg, and they have begun to seize this market share between traditional capacitors and batteries.

In applications that require high reliability but do not require high energy, supercapacitors can be used to replace batteries, or supercapacitors can be combined with batteries. In applications that require high energy, larger and more economical batteries can be adopted.

The ESR value of supercapacitors is very low, and they can output high current and quickly absorb high current. Similar to the principle of chemical charging, the working principle of supercapacitors makes the performance of this product more stable, therefore, the lifespan of supercapacitors is longer. For devices like electric tools and toys that require fast charging, supercapacitors are undoubtedly an ideal power source.

Some products are suitable for hybrid systems using batteries/supercapacitors. The use of supercapacitors can avoid using large batteries to obtain more energy. For example, digital cameras in consumer electronics products are an example, and the use of supercapacitors allows digital cameras to use inexpensive alkaline batteries (rather than batteries)

Pool. For example, digital cameras in consumer electronics products are an example, and the use of supercapacitors allows digital cameras to use inexpensive alkaline batteries (rather than expensive Li ion batteries).

The rated voltage range of supercapacitor units (cells) is 2.5-2.7V, so many applications need to use multiple supercapacitor units. When connecting these units in series, the design engineer needs to consider the balance and charging situation between the units.

Any supercapacitor will discharge through an internal parallel resistor when energized, and this discharge current is called leakage current, which will affect the discharge of the supercapacitor unit. Similar to some advanced battery technologies, the voltage of supercapacitors needs to be balanced when used in series because there is leakage current, and the internal parallel resistance will determine the voltage distribution on the connected supercapacitor units. When the voltage on the supercapacitor stabilizes, the voltage on each unit will vary with different leakage currents, rather than with different capacitance values. The higher the leakage current, the higher the rated voltage. Conversely, the higher the leakage current, the higher the rated voltage. This is because leakage current can cause discharge of supercapacitor units, resulting in a decrease in voltage. This voltage will then affect the voltage of other units connected in series with it (assuming that these connected units are powered by the same constant voltage).

To compensate for changes in leakage current, a common method is to parallel a resistor next to each unit to control the leakage current of the entire unit. This method effectively reduces the corresponding changes in parallel resistance between units.

Another recommended method is active cell balancing, where each unit is actively monitored and balanced when there is a voltage change. This method can reduce any additional load on the unit, making work efficiency higher.

If the voltage exceeds the rated voltage of the unit, it will shorten the service life of the unit. For highly reliable supercapacitors, maintaining voltage within the required range is a crucial point, and the charging voltage must be controlled to ensure that it does not exceed the rated voltage of each unit.