Capacitors are the most widely used, largest, and irreplaceable electronic components. Their output accounts for about 40% of electronic components, and aluminum electrolytic capacitors account for 36.8% of the output of the three major types of capacitors (electrolytic capacitors, ceramic capacitors, and organic film capacitors). %. Electrolytic capacitors have been one of the fastest growing components in my country over the past 10 years. At present, the total annual production volume of domestic electrolytic capacitors is close to 25 billion units, with an average annual growth rate of 28%, accounting for 1/3 of global electrolytic capacitor production. In the process of development, aluminum electrolytic capacitors have also come from improvements in integrated circuits, complete circuits, and other capacitors in high-voltage, high-frequency, long-life, and small-capacity applications (such as multilayer monolithic ceramic capacitors, metallized film capacitors, tantalum electrolytic capacitors, etc.). Aluminum electrolytic capacitors themselves are constantly improving, improving and innovating. Especially with the development of science and technology, the increase of social needs, the improvement of the environment, and the birth of new complete machines, the application fields of miniaturization, chip type, and medium- and high-voltage large-capacity aluminum electrolytic capacitors are constantly expanding, and the demand is increasing. big. Therefore, aluminum electrolytic capacitors will not only not shrink, but also have stronger vitality and broader development space, and will have a faster growth rate.

1.Structure and Performance Characteristics of Aluminum Electrolytic Capacitors Aluminum electrolytic capacitors are made of anode aluminum foil that has been corroded and formed an oxide film, and corroded cathode aluminum foil, separated by electrolytic paper, is rolled up, then impregnated with the working electrolyte, and then sealed in an aluminum shell. Made from. Its performance characteristics are described below.

1.1 The capacitance per unit volume is very large

 The capacitance of the capacitor C=ε0εrS/d, where ε0 is the vacuum permittivity (constant), εr is the relative dielectric constant of the dielectric material, S is the effective area of the electrode, and d is the thickness of the dielectric material. For aluminum electrolytic capacitors, εr=8~10. The surface area of anode aluminum foil and cathode aluminum foil can be increased by dozens to hundreds of times through corrosion. d=αVf, α≈1.4nm/V, Vf=10V~600V, then d is about 0.014μm~0.9μm, which is several to hundreds of times smaller than other capacitors. Therefore, the capacitance per unit volume of electrolytic capacitors is several to dozens of times larger than other capacitors.

1.2 The rated capacity is very large. Since the electrolytic capacitor adopts a winding structure, it is easy to expand the volume. Therefore, the rated capacitance of tens of thousands of microfarads or even hundreds of thousands of microfarads can be easily achieved.

1.3 It has a self-healing effect. Since there is electrolyte inside the capacitor, once the dielectric on the anode aluminum foil of the capacitor is partially damaged during operation, the O2- or OH- or acid ions in the electrolyte will quickly arrive under the action of the electric field force. Block the damaged location, repair the damaged oxide film, and return the capacitor to its normal state.

1.4 High working electric field intensity Since the anodic oxide film grows about 1.4nm per volt during the formation process, that is, the electric field intensity when the anodic oxide film grows is about 7×107V/cm, and the electric field intensity under its working state is about 5×107V/ cm, this value is much greater than the working electric field strength of ceramic capacitors and film capacitors.

1.5 Price advantage Since the main raw materials used in manufacturing aluminum electrolytic capacitors are ordinary industrial materials, the equipment used is general industrial equipment, and the degree of automation is high, so the manufacturing cost is relatively low, especially the manufacturing cost per unit capacity is higher than other types. Capacitors have overwhelming advantages.

2 Disadvantages of aluminum electrolytic capacitors

2.1 Polarity and possibility of leakage Since electrolytic capacitors have polarity, you must pay attention to the correct connection of the positive and negative poles when using them. Otherwise, not only will the capacitor not be able to play its role, but the leakage current will be very large, and the inside of the capacitor will become damaged in a short period of time. It will generate heat, destroy the oxide film, and then be damaged. Aluminum electrolytic capacitors are sealed with an aluminum shell and a rubber plug. When the working electrolyte is heated and vaporized, it easily seeps out from the root of the lead. After the capacitor has been working for a long time, the electrolyte will dry up, causing the capacitor to fail. This is one of the main failure modes of aluminum electrolytic capacitors.

2.2 The loss tangent value is large and the temperature and frequency characteristics are relatively poor. The working electrolyte plays the role of the cathode in the aluminum electrolytic capacitor. Since the working electrolyte is an ionic conductor, the movement speed of ions is much slower than the movement speed of electrons. , causing the conductivity of the working electrolyte to be lower than that of the electron conductor. After the electrolytic paper is dipped again, its conductivity further decreases. Therefore, the equivalent series resistance caused by the working electrolyte is larger than the equivalent series resistance caused by the metal electrodes of other capacitors, resulting in a larger loss tangent value of the aluminum electrolytic capacitor. , and the frequency characteristics are relatively poor. In addition, since the conductivity of liquid materials is greatly affected by temperature, the temperature characteristics of aluminum electrolytic capacitors are also relatively poor.

2.3 Easy to age. Although the working electrolyte uses weak acid/weak alkali salts as electrolytes and water and organic solvents as solvents, it is still corrosive to a certain extent and has a certain corrosive effect on the anodized film and rubber plug of the capacitor. In addition, certain chemical reactions will also occur between the electrolyte salt and the solvent over time. These phenomena will cause the electrical performance of the capacitor to deteriorate. In short, although aluminum electrolytic capacitors have certain shortcomings that limit their application in certain situations, due to their significant advantages such as high capacity and price advantage, they compete with ceramic capacitors, film capacitors, and tantalum electrolytic capacitors. China firmly occupies more than 30% share. And with the development of power electronics technologies such as automotive electronics and frequency conversion technology, its proportion will increase significantly.

3. The vitality of aluminum electrolytic capacitors. With the development of science and technology, especially the development of integrated circuits (ICs) and very large scale integrated circuits (VLSI), people have doubted whether the entire capacitor industry can continue to develop or even have room for survival. However, since 1987, global capacitor production has grown at a rate of more than 20% every year, making this suspicion self-defeating. Practice has proved that aluminum electrolytic capacitors have extremely strong vitality.

3.1 The development of IC cannot replace aluminum electrolytic capacitors. On the one hand, due to the emergence of IC, some small-capacity capacitors are integrated into the circuit; on the other hand, the development of IC has greatly increased the operating frequency of circuit systems, resulting in aluminum electrolytic capacitors being used in some applications. replaced by other capacitors in the circuit. However, the power supply part of the IC circuit is always inseparable from electrolytic capacitors. In addition, the improvement of the performance of aluminum electrolytic capacitors has also expanded to the application fields of other capacitors.

3.2 Changes in the overall circuit only change the model of the aluminum electrolytic capacitor. The size of the switching power supply continues to shrink and the energy conversion efficiency continues to increase, causing the operating frequency of the switching power supply to continue to increase (from 20kHz to 500kHz, even reaching more than 1MHz), resulting in its output Part of the high-frequency noise increases, and in order to effectively filter it, capacitors with ultra-low high-frequency impedance or low equivalent series resistance (ESR) must be used.

3.3 Other capacitors and aluminum electrolytic capacitors complement each other. The continuous development of ceramic dielectric used in multilayer monolithic ceramic capacitors and the continuous improvement of dielectric constant, coupled with its good high-frequency performance and chip-type and other favorable conditions, make it suitable for low voltage applications. Small capacity applications have certain advantages. The preparation technology of metallized films continues to improve, which greatly improves the voltage resistance of the film. In addition, film capacitors have the advantages of high reliability and low ESR, which make film capacitors have certain specialties in the use of medium, high, and small capacities. Tantalum electrolytic capacitors not only have excellent temperature and frequency characteristics, but also have the advantage of chip type. They have certain growth in the application fields of low voltage, medium and small capacity. The continuous advancement of materials and preparation technology of electric double layer capacitors has greatly reduced their ESR, making them competitive in low-voltage and large-capacity applications. It can be seen that medium and high-voltage large-capacity aluminum electrolytic capacitors have not been impacted by other capacitors and have their own unique advantages. In addition, although there is some competition in the field of low voltage and small capacity, the way out lies in accelerating the research and development of related technologies, strengthening and continuing to expand the existing advantages of aluminum electrolytic capacitors, and overcoming its own shortcomings. Especially in recent years, aluminum electrolytic capacitors have made great breakthroughs in many aspects and achieved a qualitative leap. Not only has its market share not shrunk, on the contrary, its application fields have continued to expand, showing rapid growth and ushering in many unprecedented development opportunities.

4. Aluminum electrolytic capacitors usher in rare opportunities

 The advent of the information age and the emergence of the knowledge economy have not only brought good news to the global economy, but also brought unprecedented prosperity to the electronics industry. Similarly, aluminum electrolytic capacitors have also experienced unprecedented development.