Thread Content
New Trends in the Development of Aluminum Electrolytic Foil Technology in China – China Alumium Industry Network. Within the family of electrolytic capacitors, aluminum electrolytic capacitors have seen significant growth worldwide over the past 20 years, thanks to their excellent performance, low cost, and wide range of applications. Taking Japan alone as an example, the production of aluminum foil for electrolytic capacitors was around 3,000 tons in 1995; by 2001 it had risen to 70,000–80,000 tons, showing an astonishing rate of increase. The development of aluminum electrolytic capacitors in our country is also progressing rapidly. According to statistics, the production volume in 1997 was around 15 billion units, and it is estimated that this figure may have now exceeded 20 billion units. Judging from the development of China’s electronics industry, the production of aluminum electrolytic capacitors is set to see further significant increases in the coming years. At present, some of the aluminum foil used for electrolytic capacitors in our country is domestically produced, while a considerable amount still relies on imports. To change this situation, domestic manufacturers have done a lot of work in terms of localization. Not long ago, the research project on high-voltage aluminum foil for electrolytic capacitors at Southwest Aluminum was successfully completed; the quality of these products has reached international advanced levels, making them fully capable of replacing imported products. It can be said that, after more than 10 years of development, especially in the past five to six years, the quality of electronic aluminum foil in our country has improved significantly. The aluminum foil used in electrolytic capacitors falls under the category of electronic aluminum foil, which is a corrosion-resistant material that functions under polar conditions. Electron aluminum foils with different polarities require different types of corrosion. High-pressure anode foil exhibits columnar pore corrosion, low-pressure anode foil shows sponge-like corrosion, while anode foil in the medium-pressure range displays worm-eaten corrosion. Before the 1980s, electrolytic capacitors mostly used manual chemical etching; after the 1980s, automated electrochemical etching was adopted. The purity of aluminum foil used for manual corrosion is relatively low (99.3%–99.7%), and the requirements regarding the processing quality of such aluminum foil are not high either. The coupling electrochemical corrosion process requires increasingly higher purity of aluminum foil, as well as greater precision in its processing quality. In terms of aluminum purity, it was 99.99% in the 1980s, and today it has reached 99.993%. These are the requirements for electrode foil, and they reflect the technological advancements in the aluminum processing industry. An increase in the purity of aluminum foil certainly has a positive effect on the quality of electrode foil, but on the other hand it increases costs. At the same time, the corrosive agents are also constantly changing; the concentration of some of these agents is increasing, and the types of agents are changing as well. All of this is detrimental to environmental protection efforts, placing a heavy burden on manufacturers in terms of environmental compliance, which may lead to a reduction in the purity of aluminum. Recent compositional analyses of Japanese aluminum foil have revealed a trend in this regard. The improvement in the quality of corroded foil is inseparable from the advancement in the quality of aluminum foil. According to Japanese patents, the peak period for patents related to cathode foil was in the 1980s, while there were two peak periods for patents related to anode foil: one around 1977–1978, and another around 1983. These peaks in patents indicate that technology is advancing at a rapid pace. Globally, the development trends of electronic aluminum foil are roughly as follows: High-voltage anode foil. High-voltage anode foil can be divided into two categories; one is high-quality high-voltage foil ； One type is ordinary high-voltage foil. High-quality high-voltage anode foil is characterized by \"two highs and one thinness\", namely high purity, high cubic texture, and a thin surface oxide film. These products are of high quality, but their cost is high. Aluminum purity > 99.99%, cubic texture 96%. Vacuum heat treatment is carried out under conditions of 10–3 Pa to 10–5 Pa. Conventional high-voltage anode foil is an economical and practical type of high-voltage anode foil, with an aluminum purity of >99.98% and a cubic texture degree of >92%; it is vacuum-treated under conditions of 10–1 Pa to 10–2 Pa. Low-voltage anode foil: The manufacturing process for low-voltage anode foil is relatively complex. We believe it is impossible to use a single method to meet the voltage requirements at different stages; it can roughly be divided as follows. For low-voltage foils with a voltage of less than 35 Vf, it is necessary to develop methods for corroding hard-pure aluminum foil; the advantage of the hard state is that it allows for the formation of numerous small corrosion cores and corrosion channels. It is necessary to study whether direct current or alternating current is a better power source for corrosion. Industry experts believe that the specific capacity of this method can be increased by 5 μF/cm2 compared to the soft-state method. Low-voltage foils with a value of Vf greater than 50V, namely soft high-purity aluminum foils, provide numerous conditions for differences in crystal plane orientations, enabling the production of corroded foils with larger pores. Negative electrode foil: Negative electrode foils are also divided into soft and hard types. Japan is characterized by soft electrochemical corrosion, while Western Europe is characterized by hard chemical corrosion. Each has its own advantages and disadvantages; the soft type uses aluminum foil with high purity (>99.85%), free of copper, offering excellent quality but at a higher cost ； For rigid applications, aluminum foil containing copper with low purity is used; it is cost-effective and easier to improve. To develop copper-free or low-copper anode foils with moderate electrostatic capacitance and low cost, alloys such as AL-Fe and AL-Mg can be used. Among them, the high-purity low-copper aluminum foil uses high-purity aluminum as a base with trace amounts of copper added as the corrosion core; its specific volume is comparable to that of the aluminum foil produced by high-purity soft electrochemical corrosion methods. Due to its low cost, it is likely to be well received in the market.