Capacitors are widely used, in large quantities, and irreplaceable electronic components. Their output accounts for approximately 40% of the total output of electronic components. Among them, 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 components that have developed relatively rapidly in China over the past decade. Currently, the annual total production of electrolytic capacitors in China is close to 25 billion pieces, with an average annual growth rate as high as 28%, accounting for one-third of the global output of electrolytic capacitors.

During the development process, aluminum electrolytic capacitors are also affected by the improvements in integrated circuits and complete machine circuits, as well as the mutual penetration of other capacitors (such as multilayer monolithic ceramic capacitors, metallized film capacitors, tantalum electrolytic capacitors, etc.) in the application fields of high voltage, high frequency, long lifespan, and small capacitance. Aluminum electrolytic capacitors themselves are also constantly being improved, perfected, and innovated.

Especially with the development of science and technology, the increase in social demands, the improvement of the environment, and the emergence of new types of complete machines, the application fields of miniaturized, chip-type, and medium-high voltage large-capacity aluminum electrolytic capacitors are constantly expanding, and the demand is increasing. Therefore, aluminum electrolytic capacitors will not only not shrink, but also have stronger vitality, a broader development space, and a faster growth rate.

1 Structure and Performance Characteristics of Aluminum Electrolytic Capacitors

An aluminum electrolytic capacitor is made by winding an anodized aluminum foil (which has been etched and formed with an oxide film), an etched cathode aluminum foil, with an electrolytic paper in between, then impregnating it with a working electrolyte, and finally sealing it in an aluminum shell. Its performance characteristics are described as follows.

1.1 Extremely Large Capacitance per Unit Volume

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

1.2 Very Large Rated Capacitance

Since electrolytic capacitors adopt a winding structure, it is very easy to increase their volume. Therefore, it is possible to easily achieve a rated capacitance of tens of thousands of microfarads or even hundreds of thousands of microfarads.

1.3 Self-healing Function

Due to the presence of the electrolyte inside the capacitor, during operation, once the dielectric on the anode aluminum foil of the capacitor is locally damaged, the O2－,OH－or acid radical ions in the electrolyte will quickly reach the damaged position under the action of the electric field force, block the damaged position, and repair the damaged oxide film, restoring the capacitor to its normal state.

1.4 High Working Electric Field Strength

Since the anodic oxide film grows about 1.4nm per volt during the formation process, that is, the electric field strength during the growth of the anodic oxide film is about 7×107V/cm，and the electric field strength in its working state is about 5×107V/cm，This value is much larger than the working electric field strength of ceramic capacitors and film capacitors.

1.5 Price Advantage

Since the main raw materials used in the manufacture of aluminum electrolytic capacitors are all common industrial materials, the equipment used belongs to general industrial equipment, and the degree of automation is relatively high, the manufacturing cost is relatively low. Especially, the manufacturing cost per unit capacitance has an overwhelming advantage over other types of capacitors.

2 Disadvantages of Aluminum Electrolytic Capacitors

2.1 Polarity and the Possibility of Leakage

Since electrolytic capacitors have polarity, when using them, attention must be paid to the correct connection of the positive and negative poles. Otherwise, not only will the capacitor not function properly, but the leakage current will be very large. The inside of the capacitor will heat up in a short time, damaging the oxide film and then the capacitor. Aluminum electrolytic capacitors are sealed with an aluminum shell and a rubber plug. When the working electrolyte vaporizes due to heat, it is likely to seep out from the root of the lead wire. After the capacitor works 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 Larger Dissipation Factor (tanδ) and Relatively Poor Temperature and Frequency Characteristics

The working electrolyte plays the role of the cathode in an aluminum electrolytic capacitor. Since the working electrolyte is an ionic conductor, and the movement speed of ions is much slower than that of electrons, the conductivity of the working electrolyte is lower than that of an electronic conductor. After being impregnated with the electrolytic paper, its conductivity decreases further. Therefore, the equivalent series resistance caused by the working electrolyte is larger than that caused by the metal electrodes of other capacitors, resulting in a larger dissipation factor (tanδ) of aluminum electrolytic capacitors and relatively poor frequency characteristics. In addition, since the conductivity of the liquid material 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, base and salt as the electrolyte and water and organic solvents as the solvent, it still has a certain degree of corrosiveness and has a certain erosive effect on the anodic oxide film and the rubber plug of the capacitor. In addition, a certain chemical reaction will also occur between the electrolyte salt and the solvent over time. These phenomena will lead to the deterioration of the electrical performance of the capacitor.

In general, although aluminum electrolytic capacitors have certain disadvantages that limit their application in some situations, due to their significant advantages such as high capacitance and price advantage, they firmly occupy more than 30% of the market share in the competition with ceramic capacitors, film capacitors, and tantalum electrolytic capacitors. And with the development of power electronics technologies such as automotive electronics and frequency conversion technology, the proportion it occupies is likely to increase significantly.

3 The Vitality of Aluminum Electrolytic Capacitors

With the development of science and technology, especially the development of integrated circuits (IC) and very large scale integrated circuits (VLSI), there are doubts about whether the entire capacitor industry can continue to develop or even has room for survival. However, since 1987, the global production of capacitors has increased at a rate of more than 20% per year, which has dispelled such doubts. Practice has proved that aluminum electrolytic capacitors have extremely strong vitality.

3.1 The Development of ICs Cannot Replace Aluminum Electrolytic Capacitors

On the one hand, the emergence of ICs has integrated some small-capacitance capacitors into the circuit. On the other hand, the development of ICs has greatly increased the working frequency of the circuit system, resulting in aluminum electrolytic capacitors being replaced by other capacitors in some circuits. However, the power supply part of the IC circuit always cannot do without electrolytic capacitors. In addition, the improvement of the performance of aluminum electrolytic capacitors themselves has also expanded into the application fields of other capacitors.

3.2 Changes in the Complete Machine Circuit Only Change the Model of Aluminum Electrolytic Capacitors

The volume of switching power supplies is constantly shrinking, and the energy conversion efficiency is constantly increasing, which makes the working frequency of switching power supplies continuously increase (from 20 kHz to 500 kHz, and even up to more than 1 MHz), resulting in an increase in high-frequency noise in the output part. In order to effectively filter, capacitors with ultra-low high-frequency impedance or low equivalent series resistance (ESR) must be used.

3.3 Mutual Complementation between Other Capacitors and Aluminum Electrolytic Capacitors

The continuous development of the ceramic dielectric used in multilayer monolithic ceramic capacitors and the continuous increase of the dielectric constant, together with their good high-frequency performance and chip form, give them certain advantages in low-voltage and small-capacitance application scenarios.

The continuous improvement of the preparation technology of metallized films has greatly improved the voltage resistance of the films. In addition, film capacitors have the advantages of high reliability and small ESR, giving them certain advantages in the use of medium-high voltage and small capacitance.

Tantalum electrolytic capacitors not only have excellent temperature and frequency characteristics but also have the advantage of being in chip form, and have a certain growth in the application field of low-voltage and medium-small capacitance.

The continuous progress of the materials and preparation technology of double-layer capacitors has greatly reduced their ESR, making them competitive in the application field of low-voltage and large capacitance.

It can be seen that medium-high voltage and large-capacitance aluminum electrolytic capacitors have not been impacted by other capacitors and have their unique advantages. In addition, although there is certain competition in the low-voltage and small-capacitance field, the way out lies in accelerating the research and development of relevant technologies, strengthening and continuing to expand the existing advantages of aluminum electrolytic capacitors, and overcoming their own disadvantages. Especially in recent years, aluminum electrolytic capacitors have made great breakthroughs in many aspects and achieved a qualitative leap. Not only has their market share not shrunk, but on the contrary, their application fields have been continuously expanded, showing rapid growth and ushering in many unprecedented development opportunities.

4 Aluminum Electrolytic Capacitors Usher in a Rare Opportunity

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 achieved unprecedented development.