A powerful tool for fast charging and discharging: Supercapacitor technology explained in detail

"Supercapacitor" often sounds like something very impressive. As a new type of electrical energy storage component, supercapacitor can make up for the shortcomings of lithium-ion batteries in terms of power density. At present, it has been used in military, new energy vehicles and various electromechanical equipment. When it forms a "crossfire" with lithium-ion batteries, it can greatly improve the technical indicators of energy storage components to meet the almost harsh and complex use environment.

● Basic structure of supercapacitor

Supercapacitors are also called double-layer capacitors. From a structural point of view, they are very similar to electrolytic capacitors. Simply put, if two electrodes are inserted into an electrolyte and a voltage is applied, the positive and negative ions in the electrolyte will quickly move toward the two poles under the action of the electric field, and eventually form a compact charge layer on the surface of the two electrodes, namely a double layer.

The size of the capacitor depends on the size of the electrode surface area and the distance between the two electrodes. The electrode surface area of ​​a traditional capacitor is the flat surface area of ​​the conductor. In order to obtain a larger capacity, the conductor material is usually rolled very long, and sometimes a special structure is used to increase its surface area. At the same time, traditional capacitors use insulating materials to separate its two electrodes, generally plastic films, paper, etc., and these materials are also required to be as thin as possible.

The surface area of ​​the supercapacitor's electrodes is based on porous carbon materials. The porous structure of the material makes its surface area very large, and the distance between the electrodes of the supercapacitor is determined by the size of the electrolyte ions attracted to the charged electrodes, which is smaller than the distance that can be achieved by the film materials of traditional capacitors. This huge surface area, coupled with the very small electrode spacing, makes the supercapacitor have an amazing electrostatic storage capacity compared to traditional capacitors, which is also an important reason why it is called "super".

The basic function of capacitors is charging and discharging, but many circuit phenomena derived from the basic charging and discharging functions make capacitors have more diverse uses. In general electronic circuits, capacitors are often used to achieve bypass, coupling, filtering, oscillation, phase shift, and waveform transformation, etc. These functions are the evolution of charging and discharging functions. Due to the various characteristics of supercapacitors, they are more widely used in the energy field and are usually used as batteries.

● Advantages and disadvantages of supercapacitors

Compared with lead-acid batteries, nickel-cadmium batteries, and lithium-ion batteries, supercapacitors have the advantages of energy saving, ultra-long service life, safety, environmental protection, wide temperature range, and no need for manual maintenance. Since supercapacitors use physical methods to store energy, one of their most important characteristics is their high power density, which can be understood as rapid charging and discharging and the ability to absorb or release extremely high energy instantly, which is something that no battery can do at present.

Perhaps everything is imperfect, and supercapacitors are no exception. One of its relatively fatal weaknesses is its low energy density. The so-called energy density refers to the amount of energy stored in a certain space or mass of matter. For example, the larger the mAh of the No. 5 rechargeable battery we often use, the higher its energy density. It can be said that the lower energy density of supercapacitors compared to lithium-ion batteries limits their application in many fields.

● Application fields of supercapacitors

After understanding some of the general information about supercapacitors, let's take a look at the fields in which they are currently applied. First of all, the emergence and development of any new technology is often first applied to the military field. We don't know whether the original intention of the research and development of supercapacitors is also the same, but in a complex battlefield environment, supercapacitors do have special advantages. The wide temperature range (usually between -40℃-65℃) and high power density mentioned above can ensure the smooth start of high-horsepower military vehicles such as tanks and armored vehicles, especially in the cold winter, and its high power density can also be used as a pulse energy source for laser weapons.

In the civilian field, supercapacitors also play a huge role. For example, they can be used to power camera flashlights, which can enable the flashlights to achieve continuous use performance, thereby improving the camera's ability to shoot continuously. At the same time, supercapacitors can also be used to control the camera shutter. In addition, with the development of the electronics and energy industries, supercapacitors play an irreplaceable role in maintenance-free systems such as short-term UPS systems and solar power systems.

Since supercapacitors can charge and discharge at high power, they can be used in some transportation vehicles to store the braking energy of trains or large buses and provide peak power output during acceleration. Since the charging and discharging speed is very fast, the supercapacitor can be fully charged in a short time when the vehicle enters the station and passengers get on and off, and it is enough to run to the next station. In this way, the vehicle does not need to carry a pantograph, and there is no need to set up high-voltage lines along the way, which undoubtedly reduces construction costs.

Since the energy density of supercapacitors is much lower than that of lithium-ion batteries, it is difficult to use them alone as energy storage devices in passenger vehicles, but they can form a hybrid system with traditional internal combustion engines. Toyota has applied supercapacitor technology to its Le Mans racing car. Since the energy of the racing car is very large at the moment of braking, the high power density of supercapacitors can more efficiently recover and store energy. At the same time, when the racing car needs to overtake and other instantaneous high power situations, supercapacitors can also meet such requirements.

In the current mainstream battery technology, lithium battery and supercapacitor technology have their own strengths and weaknesses. Lithium-ion batteries have high energy storage density, while supercapacitors have high power storage density. A lot of research work is focused on improving the power density of lithium-ion batteries or increasing the energy storage density of supercapacitors, but the challenges are huge. But when we combine the two, such a battery becomes more perfect.

Especially in large buses, since more energy is generated during braking than in small cars, supercapacitors can absorb this energy very well. When the vehicle starts or accelerates suddenly, supercapacitors can quickly release this energy. In normal low-power energy conversion, lithium-ion batteries can be used to complete it. Therefore, this "mixed" battery technology has broken through the technical bottleneck of a certain type of battery at this stage, and it is perfect.

Summary of the full text:

Although supercapacitors have many advantages, their low energy density still limits their use in the field of new energy vehicles. According to the current level of technological development, the combination of supercapacitors and lithium-ion batteries can be said to complement each other and basically meet people's needs for high energy density and high power density of batteries. Personally, I think that based on the basic physical structure of capacitors, it is difficult for them to make breakthroughs in energy density, but this does not prevent them from forming hybrid systems with internal combustion engines and playing their own advantages and specialties in other fields.