The performance of the capacitor cathode material (ie, electrolyte) largely determines the performance of the capacitor. Solid electrolytes have much higher electrical conductivity than liquid electrolytes (depending on materials, conductivity up to 0.1-100 S/cm), and have excellent temperature characteristics and chemical stability, precisely because of the excellent properties of solid electrolytes. Solid aluminum capacitors outperform liquid aluminum capacitors. The performance between different solid electrolytes varies widely. From the initial use of manganese dioxide to the PEDOT currently used, the conductivity is hundreds of times different. Therefore, the performance of solid aluminum capacitors in different development periods varies greatly. The following is an introduction to the development of solid aluminum capacitors.

1. Manganese dioxide type solid aluminum capacitor

Manganese dioxide as a solid electrolyte has been successful in the application of tantalum capacitors. At the beginning, some people tried to use manganese dioxide as the electrolyte of solid aluminum capacitors, but the Al2O3 dielectric oxide film is easily corroded at high temperatures, resulting in increased leakage current of the capacitor. Large, therefore, the use of manganese dioxide as an aluminum capacitor electrolyte technology is very difficult, and the yield is low.

2. TCNQ type solid aluminum capacitor

TCNQ was first synthesized by DuPont researchers in 1959. In 1961, ROSS Company of the United States first used TCNQ composite salt to prepare capacitors. In 1983, Sanyo Electric Company of Japan developed organic semiconductor TCNQ type solid aluminum capacitors, which is true. The first generation of solid aluminum capacitors in the sense is called OS-Con type aluminum electrolytic capacitors. The conductivity of TCNQ is about 1 S/cm, which is much higher than 0.01 S/cm of liquid electrolyte. Therefore, TCNQ type solid aluminum capacitor has much lower ESR than liquid aluminum capacitor, and has good high frequency characteristics. Its service life and environmental stability are also greatly improved. There is no doubt that OS-Con capacitors are a big step forward over traditional liquid aluminum capacitors.

A series of studies have shown that the direct heating and melting of TCNQ composite salt, followed by impregnation and cooling solidification is a better method for preparing TCNQ type solid aluminum capacitors. However, since the hot working property of the TCNQ composite salt is not so good, it can only maintain a molten stable state in a very narrow temperature range, and the stabilization time is also short. Therefore, the manufacturing process of the TCNQ type solid aluminum capacitor (especially impregnation) Process) requirements are very strict. In addition, TCNQ's soldering heat stability is not good enough, which restricts the further development of TCNQ type solid aluminum capacitor to a certain extent.

3. Polypyrrole type solid aluminum capacitor

Since the successful research of conductive polypyrrole films, great efforts have been devoted to the research of polypyrrole type solid aluminum capacitors. In 1973, Showa Denko of Japan applied for a basic patent for polypyrrole type solid aluminum capacitors. This type of capacitor is called a functional polymer type solid aluminum electrolytic capacitor (SP-Cap) and is a second generation solid aluminum capacitor. SP-Cap has a lower ESR than OS-Con, has better frequency characteristics, and can maintain a very low ESR over a wide temperature range. In addition, polypyrrole has higher temperature and chemical stability than TCNQ. Therefore, SP-Cap is a big improvement over OS-Con.

Since polypyrrole type solid aluminum capacitors generally adopt electrochemical polymerization methods, it is necessary to first form a thin conductive layer on the surface of the aluminum oxide film, but this method generally can only produce a stacked aluminum capacitor, which is not suitable for winding. Aluminum capacitors.

4. Polyaniline solid aluminum capacitor

Conductive polyaniline research provides a new class of electrolytes for solid aluminum capacitors. Polyaniline has good environmental stability, cheap raw materials, easy to dissolve and melt, and has certain advantages in the use and preparation of solid aluminum capacitors, but because Aniline has environmental pollution problems, which limits its application.

5. PEDOT type solid aluminum capacitor

In 1988, Bayer (Germany) first developed a new generation of conductive polymer material PEDOT (Eur. Patent 339340 (1988)), and applied for the basic application patent of PEDOT type solid aluminum capacitor.

Compared to other solid electrolytes, PEDOT has the following outstanding properties:

u high conductivity, can reach 100S / cm;

u works in a thin layer of less than 1mm on the surface of the substrate, so it can be used at a lower cost to obtain good results;

u Very good resistance to hydrolysis, light stability and thermal stability, will not cause environmental pollution;

u Simple process and easy to use;

u Conductivity does not decrease at high pH;

u Good electrochemical performance.

The successful application of PEDOT in aluminum capacitors marks the birth of the third generation of solid aluminum capacitors. The industry generally believes that PEDOT aluminum solid capacitors have the most promising and application value. At present, PEDOT type solid aluminum capacitors have been recognized by well-known international electronics manufacturers, and are considered to be the most advanced solid aluminum capacitors, and are put into mass production.

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