Shulou(Shulou.com)11/24 Report--

Chen Yuanzhen, a professor at Xi'an Jiaotong University, a scientist of Changan Energy Storage Research Institute, has published more than 70 articles in international first-class journals and presided over two national natural science projects. Long-term engaged in energy storage and conversion, low-temperature waste heat recovery and power generation system research.

On the competition field, people feel the beauty of power brought by different events! Some people are good at exploding, such as the 100-meter flying man race, and the burst muscle bullets make people's blood swell; others are good at enduring, like a marathon, with a steady stream of energy output that people admire from the bottom of their hearts; and there are others who are gentle and firm, slow in fast and slow, and show their sports charm.

In the field of energy storage, there is also a "beauty of power". Energy-based devices are like long-distance runners in the field of track and field, with the ability to output energy for a long time; power-based devices, like a 100-meter flying man, have amazing explosive power and can output energy quickly in a short time. At present, in practical applications, energy-based devices have been more popular. Especially such as power battery, 3C battery, energy storage battery and so on, the main reason is that most application places belong to medium power or low power application places, so the battery can meet its application conditions. However, for the battery, its power output is not high. From figure 1, we can see that energy and power seem to be the relationship between one and the other. if the energy density is high, the power density is low, and vice versa. Therefore, for the requirement of high power output, another kind of power supply equipment-supercapacitor is needed.

Fig. 1 Energy and power density diagrams of different devices

In the current energy storage applications, although supercapacitors are not as widely used as batteries, they also have their irreplaceable fields. Before introducing its application, we first introduce its three core features:

High power density. The electric energy can be filled or released in a short time (seconds-minutes), and the highest power density can usually reach more than 10 kW / kg, which is mainly determined by its energy storage principle. At present, it is mainly based on two fast energy storage principles, namely physical adsorption and Faraday pseudo-capacitive electrochemical reaction. Physical adsorption is easy to understand. Ions are adsorbed quickly and released quickly. The other is the Faraday pseudo-capacitive electrochemical reaction, which can be understood as the electrochemical reaction in the shallow layer of the surface. When it comes to electrochemical energy storage, ion diffusion is involved. The diffusion of ions from the surface to the material core is relatively slow, which is the main reason for the low power of the battery. The diffusion of ions from the surface to the shallow area near the surface is relatively fast, so the ion diffusion path is short, so the power density is high. However, most of the energy stored under these two energy storage mechanisms is relatively small, so their energy density is small.

It has a long life. Supercapacitors based on physical adsorption are generally more than 1 million times, and supercapacitors based on pseudo-capacitors can reach more than tens of thousands of times. However, the average battery life is only 2000-4000 cycles. The main reason is that physical adsorption does not damage the structure of the material, while Faraday pseudo-capacitive electrochemical reaction only occurs near the surface of the material, and does not cause much damage to the material structure, so it has a long life. For example, for lithium-ion batteries, the diffusion of ions from the surface to the core will cause a large lattice distortion of the material as a whole, and the ion will undergo some distortion during the ion detachment, so that the lattice will be tired and destroyed, thus reducing the ion storage capacity and energy density.

The efficiency of energy recovery is high. Because the supercapacitor is "open to all" for both large and small currents, it is more resistant to high current charging, so it is very beneficial for braking energy recovery. At present, the highest known energy recovery efficiency can reach 45%. At the same time, this feature also creates conditions for its use in conjunction with the battery. For example, in the energy storage battery, the impact of unstable new energy power on the battery can be mitigated by supercapacitors to protect the battery.

Because the supercapacitor has the above three characteristics, it shows unique advantages in some scenes.

Scene 1: frequent start-up and braking scenarios. Such as subway, bus, driving and so on. Take the subway as an example, it will efficiently recover the energy when entering the station and store it in the supercapacitor system, and start the subway with capacitors when leaving the station, which can effectively save electricity. According to the report [1], Guangzhou Metro uses this capacitor system, the integrated energy storage power of the station saves an average of 1400 kWh / day station, reduces the annual emission of 490 tons of carbon dioxide, and saves about 510000 yuan per year. According to the consideration of 20 stations, one subway line can reduce the emission of 9800 tons of carbon dioxide every year and save 10.2 million yuan in electricity charges every year.

Fig. 2 Super capacitor subway application system

In addition, supercapacitors will also have a good application prospect in high-speed rail. Its energy recovery will be more significant. In addition, the capacitive bus has been running in Shanghai for many years, although the energy density is low, but it has fast charging and long life, so it is very suitable for this short-distance, frequent start / brake scene.

Scenario 2: high-power short-time output scene. In the research and development of the latest generation of high-end weapons, high-power devices are one of the indispensable core equipment, such as laser weapons, electromagnetic pulse weapons and so on. This kind of weapons need power to output huge energy in a short time to achieve the purpose of destroying the target. Supercapacitors have become the best choice for this kind of power supply. Continuous high power output can be achieved through reasonable power management design.

Fig. 4 shipborne laser gun

Scene 3: fixed charging pile / mobile charging robot. When charging automobile power battery, the future development direction must be fast charging technology. whether it is fixed charging pile or mobile charging robot, the challenge is high power charging technology. and supercapacitors have undoubtedly become an important choice to break through this technology, especially for mobile charging robots, the combination of "battery and capacitor" High energy density "big portable battery" + ultra-high power density supercapacitors can achieve this goal well and make the fast charging technology further.

Fig. 5 Mobile charging robot [2]

Supercapacitor has the unique characteristics of high power, long life and efficient energy recovery, which makes it an irreplaceable power supply system in some occasions. How to expand the application field of supercapacitors, in addition to the improvement of supercapacitor cells in power and energy output, supercapacitor power management systems also need to be developed synchronously. In the aspect of large-scale energy storage, it has great potential to become an auxiliary device of energy storage battery. Through the co-construction of "double electricity" mode, the goal of improving pulse charging capacity and prolonging battery life can be achieved.

Author's statement: this content only represents the author's personal views and has no conflict of interest with others.

Reference content:

(1) excerpt of ten typical cases of double-carbon scientific and technological innovation-- the project "Super Capacitor Integrated Energy Storage Power supply Technology promotes Metro Energy Saving and Emission reduction"

(2) you can find your own electric car, Aichi car, research and development of mobile charging robot-tram resources

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