What are Ultracapacitors?

Super capacitor refers to a new type of energy storage device between traditional capacitors and rechargeable batteries. It has both the characteristics of fast charging and discharging of capacitors and the energy storage characteristics of batteries.

Supercapacitors are new types of components that store energy through an interface double layer formed between an electrode and an electrolyte. When the electrode is in contact with the electrolyte, due to the Coulomb force, intermolecular force, and intermolecular force, the solid-liquid interface has a stable double-layer charge with the opposite sign, which is called the interface double-layer. Think of the electric double layer supercapacitor as two inactive porous plates suspended in the electrolyte, and the voltage is applied to the two plates. The potential applied to the positive plate attracts negative ions in the electrolyte, and the negative plate attracts positive ions, thereby forming an electric double layer capacitor on the surfaces of the two electrodes. Electric double layer capacitors can be divided into carbon electrode double layer supercapacitors, metal oxide electrode supercapacitors and organic polymer electrode supercapacitors according to the electrode materials. ^[1]

Compared with batteries and traditional physical capacitors, the characteristics of supercapacitors are mainly reflected in:

(1) High power density. It can reach 102 ~ 104 W / kg, which is much higher than the power density level of the battery.

(2) Long cycle life. After 500,000 to 1 million high-speed deep charge-discharge cycles in a few seconds, the characteristics of the supercapacitors change little, and the capacity and internal resistance are only reduced by 10% to 20%.

(3) Wide working temperature limit. Since the adsorption and desorption speed of ions in the supercapacitor does not change much at low temperature, its capacity change is much smaller than that of the battery. Commercial supercapacitors can operate at temperatures ranging from -40 ° C to + 80 ° C.

(4) Maintenance-free. Supercapacitors have high charge and discharge efficiency, have a certain tolerance for overcharge and overdischarge, can be repeatedly charged and discharged stably, and theoretically do not require maintenance.

(5) Environmental protection. Super capacitors do not use heavy metals and other harmful chemicals in the production process, and have a long life span, so they are a new type of green environmental protection power supply. ^[1]

For supercapacitors, there are different classification methods based on different contents.

First, according to different energy storage mechanisms, supercapacitors can be divided into two categories: electric double layer capacitors and Faraday quasi capacitors. Among them, electric double-layer capacitors generate storage energy mainly through the adsorption of pure electrostatic charges on the electrode surface. Faraday quasi-capacitors mainly generate Faraday quasi-capacitance through reversible redox reactions on and near the surface of Faraday quasi-capacitive active electrode materials (such as transition metal oxides and polymer polymers), thereby achieving energy storage and conversion.

Secondly, according to the type of electrolyte, it can be divided into two categories: aqueous supercapacitors and organic supercapacitors.

In addition, depending on whether the types of active materials are the same, they can be divided into symmetric supercapacitors and asymmetric supercapacitors.

Finally, according to the state of the electrolyte, supercapacitors can be divided into two categories: solid electrolyte supercapacitors and liquid electrolyte supercapacitors. ^[2]

1) Lifetime: If the internal resistance of the supercapacitor is increased, the capacity will be reduced within the specified parameter range, and its effective use time can be extended, which is generally related to its characteristics as specified in Article 4. What affects the life is the active dryness, increased internal resistance, and the ability to store electrical energy drops to 63.2% is called the end of life.

2) Voltage: Super capacitors have a recommended voltage and an optimal working voltage. If the used voltage is higher than the recommended voltage, the life of the capacitor will be shortened, but the capacitor can work continuously for a long time in an over-voltage state, and the activated carbon inside the capacitor will decompose to form a gas It is beneficial to store electrical energy, but it cannot exceed 1.3 times the recommended voltage, otherwise the super capacitor will be damaged due to the excessive voltage.

3) Temperature: The normal operating temperature of the super capacitor is -40 ~ 70 . Temperature and voltage are important factors affecting the life of supercapacitors. Every 5 ° C increase in temperature will reduce the life of the capacitor by 10%. At low temperatures, increasing the working voltage of the capacitor will not increase the internal resistance of the capacitor, which can improve the efficiency of the capacitor.

4) Discharge: In the pulse charging technology, the internal resistance of the capacitor is an important factor; in the small current discharge, the capacity is an important factor.

5) Charging: There are many ways to charge capacitors, such as

Precautions for using super capacitors include:

1) Super capacitors have a fixed polarity. Before use, confirm the polarity.

2) Super capacitors should be used at nominal voltage. When the capacitor voltage exceeds the nominal voltage, it will cause the electrolyte to decompose, at the same time the capacitor will heat up, the capacity will decrease, and the internal resistance will increase, and the life will be shortened.

3) Super capacitors should not be used in high-frequency charging and discharging circuits. High-frequency fast charge and discharge will cause the capacitor to heat up, the capacity will decrease, and the internal resistance will increase.

4) The ambient temperature has an important effect on the life of the super capacitor. Therefore, super capacitors should be kept as far away from heat sources as possible.

5) When a super capacitor is used as a backup power source, because the super capacitor has a large internal resistance, there is a voltage drop at the moment of discharge.

6) Super capacitors should not be placed in an environment with relative humidity greater than 85% or containing toxic gases. These environments will lead to corrosion of the leads and the capacitor case, resulting in disconnection.

7) Super capacitors should not be placed in high temperature and high humidity environments. They should be stored in an environment with a temperature of -30 to 50 ° C and a relative humidity of less than 60% as much as possible. Avoid sudden temperature rises and falls, as this will cause product damage .

8) When a super capacitor is used on a double-sided circuit board, it should be noted that the connection cannot pass through the capacitor's reach. Due to the way the super capacitor is installed, it will cause a short circuit.

9) When the capacitor is soldered on the circuit board, the capacitor case must not be contacted with the circuit board, otherwise the solder will penetrate into the capacitor through hole and affect the performance of the capacitor.

10) After installing a super capacitor, do not forcibly tilt or twist the capacitor. This will cause the capacitor leads to loosen and cause performance degradation.

11) Avoid overheating capacitors during soldering. If the capacitor is overheated during welding, it will reduce the service life of the capacitor.

12) After the capacitor is soldered, the circuit board and capacitor need to be cleaned, because some impurities may cause the capacitor to short circuit.

13) When supercapacitors are used in series, there is a problem of voltage balance between the cells. A simple series connection will cause one or more of the individual capacitors to overvoltage, which will damage these capacitors and affect the overall performance. , Need technical support from the manufacturer.

14) In the process of using supercapacitors, there are other application problems. You should consult the manufacturer or refer to the relevant technical data of the supercapacitor's instructions. ^[4]