button cell battery cr2025.Research and analysis on the application of supercapacitors and lithium batteries in ships

　　In most cases, the ship's electric propulsion system uses an internal combustion engine to drive a generator set to provide power to the system. Due to the complex and changeable marine environment, the load changes. When the load deviates from the optimal load point, the fuel will not be fully burned, the fuel utilization rate will drop significantly, and a large amount of nitrogen oxides and sulfur will be produced. oxides, causing pollution to the environment. Energy storage technology is one solution to this problem.

　　The energy storage unit is used to store excess energy when the system is lightly loaded to prevent the impact of this energy on the power grid. When the system is overloaded, the energy storage unit releases energy to meet the load's needs. Energy storage technology is already well used in the electric vehicle industry. The development of large-capacity energy storage technology has made it possible for energy storage units to be used in ship electric propulsion systems. Using energy storage units to overcome the impact of power fluctuations on ship electric propulsion systems will be a new direction for the development of ship propulsion technology in the future.

　　1Supercapacitor technology

　　1.1 Structure of supercapacitor

　　Supercapacitors, sometimes called electric double-layer capacitors, or double-layer capacitors, are electrochemical capacitors with high energy density. A standard battery-sized electrolytic capacitor has a capacitance of tens of microfarads, but a supercapacitor of the same size can Up to several farads, the difference can be five orders of magnitude. A capacitor stores energy through the capacitance effect. Its capacity is directly proportional to the surface area of the electrodes and the dielectric constant of the electrolyte, and inversely proportional to the distance between the electrodes. Supercapacitors use high dielectric constant electrolytes, and their electrodes use porous activated carbon materials that can greatly increase their surface area. This is the main reason why supercapacitors can store huge amounts of energy. Typically, the two electrodes are separated by a porous activated carbon membrane in the middle, with water or organic electrolyte on both sides. Figure 1 shows the structural principles of double-layer capacitors and ordinary capacitors.

　　1.2 Advantages and Disadvantages of Supercapacitors

　　Advantages of supercapacitors:

　　1) High current capacity. Supercapacitors are designed with a low equivalent series resistance, so the capacitor can send and sink very high currents. The low equivalent series resistance of supercapacitors allows the capacitors to charge quickly. The characteristics of the capacitors themselves allow the capacitors to charge and discharge at the same speed, which is not possible with batteries.

　　2) Long service life. The energy storage mechanism of supercapacitors is a highly reversible process. This process only moves charges and ions without creating or destroying chemical bonds, so the number of charge and discharge cycles can reach hundreds of thousands of times. Neither small cycle charge and discharge nor deep cycle charge and discharge will damage the performance of supercapacitors, making the use of supercapacitors more flexible. In addition, supercapacitors are easy to store and their performance will not be affected by long-term placement.

　　3)Wide temperature range. Because supercapacitors work without resorting to chemical reactions, they can operate over a wide range of temperatures. Supercapacitors can operate normally within the temperature range of -40°C to +65°C.

　　4) Environmentally friendly. The materials used in supercapacitors are environmentally friendly and will not produce toxic or harmful substances during operation.

　　5) Easy maintenance. Supercapacitors basically require no maintenance, have no storage performance, no excessive discharge, and can work at any rated voltage or lower than the rated voltage.

　　6) Status monitoring is easy. Since the energy stored in a capacitor is only a function of capacitance and voltage, and the capacitance is relatively constant, a single open circuit voltage measurement can determine the state of charge.

　　7) Extend the service life of other energy sources. Energy sources like batteries, specialized engines, and fuel cells do not perform well under transient conditions. For some components, transient processes can significantly shorten the service life of the component. Combined with the use of supercapacitors and these energy sources, many of these transients can be unloaded from the primary energy source.

　　Disadvantages of supercapacitors:

　　1) Low energy density. The energy density of supercapacitors is 1~10Wh/kg, which is 1/10 of lithium batteries.

　　2) The terminal voltage changes greatly. The terminal voltage of the supercapacitor constantly changes during the charging and discharging process, so a voltage regulating device needs to be installed between the energy storage component and the load to maintain load-side voltage stability, which increases the cost of the energy storage system.

　　3) Expensive. The price of a supercapacitor cell is dozens of times that of a lithium battery.

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