Research On High Frequency Characteristics Of Cathode Capacity Of Solid Aluminum Capacitors

Solid aluminum capacitors are widely used in high-frequency electronics fields such as 5G communications,multimedia equipment,new energy systems and frequency conversion equipment due to their higher impedance frequency characteristics and good temperature characteristics.Electrode foil and conductive polymer materials are the key materials that constitute solid aluminum capacitors.Especially the frequency characteristics of the cathode foil determine the high frequency characteristics of solid aluminum capacitors.So to ensure the high-frequency response of solid aluminum capacitors,both the specific capacity and the good frequency characteristics of the cathode foil are required.In recent years,although a method of attaching carbon powder to aluminum foil to increase the surface area of the cathode foil has been developed to prepare a high specific capacity cathode foil.But the contact resistance between the carbon material and the aluminum foil is large and the capacity attenuation increases at high frequencies,which seriously restricts the high frequency characteristics of solid aluminum capacitors.Therefore,it is necessary to in-depth study of the high-frequency characteristics of the cathode foil's specific capacity,breakthrough the methods and key technologies of high-frequency and high-capacity aluminum/carbon cathode foils and realize the high-frequency application of solid aluminum capacitors.In this paper,the slurry coating carbon coating process is used to prepare aluminum/carbon cathode foil and it will bring about some problems such as high surface resistance,low carbon layer adhesion and high-frequency specific capacity attenuation.But the method of adding composite conductive agent graphite powder to the carbon slurry,pressing,high temperature degummingand forming a metallurgical structure on the surface of the composite foil can effectively solve these problems.When using composite carbon materials(activated carbon,acetylene black,graphite powder)to prepare aluminum/carbon composite foil,the influence of different process conditions on the specific volume and carbon layer adhesion of the composite foil was studied and the specific capacity and carbon under different frequency conditions were measured and the microstructure of the composite foil is studied by SEM,XRD and other test methods.Finally under the best process conditions,two methods were used to prepare aluminum/carbon composite cathode foils with high frequency characteristics and high specific volume.One method is to add tin powder to the carbon paste and the other method is to coat a layer of ruthenium oxide on the surface of the aluminum foil and then coat the carbon layer.Draw the following conclusion:1.The influence of various factors in the process of preparing aluminum/carbon composite foil using composite carbon materials is studied.The experimental results show that the aluminum/carbon composite foil prepared by the slurry coating method combining press rolling,high temperature degumming and adding composite conductive materials has the carbon layer with well-developed pores and Al₄C₃phase with high bonding strength carbon layer structure is formed at the interface of aluminum/carbon composite foil.When the mass ratio of the carbon paste is activated carbon:acetylene black:graphite powder:adhesive=15:2:1:2,the carbon-aluminum layer has a good bonding degree and under the condition of 1kHz-0.3V,its specific capacity reaches 2950?F/cm².2.The test results show that different adhesives have a greater impact on the specific capacity and adhesion of the cathode foil.By studying the influence of different binder materials on the specific capacity and carbon layer adhesion of aluminum/carbon composite foils,the following conclusions can be drawn.At low and intermediate frequencies,the composite cathode foil made with PVDF binder has a higher specific capacity.Under high frequency conditions,the specific capacity attenuation of LA132and epoxy resin binder cathode composite foil is small.Throughout the frequency stage,the specific volume of the cathode foil prepared with epoxy resin or LA132 binder is relatively stable and the adhesion of the carbon layer can reach up to 97.5%.3.The aluminum/carbon composite cathode foil with high frequency characteristics,high specific capacity and excellent interfacial bonding was prepared by two methods.One method is to add tin powder to the carbon paste and then coat the surface of the aluminum foil with a carbon layer.The other method is to first coat the surface of the aluminum foil with a ruthenium oxide layer and then coat the carbon layer.The composite cathode foil is prepared by adding tin powder to the binder epoxy resin carbon slurry.Under the condition of 1kHz-0.3V,its specific volume is as high as about3189.2?F/cm²and the adhesion of carbon layer is 98.4%and the attenuation of the specific volume is less than 650?F/cm²for every 1kHz increase in frequency at high frequency.The composite foil that are prepared by using LA132 as binder and coating ruthenium oxide layer has a specific volume of about 3264.2?F/cm²at 1kHz-0.3V,which is closer to the specific volume of Japan's cathode foil of 3400?F/cm²,the adhesion of the carbon layer is 98.5%and the attenuation of the specific volume is less than 760?F/cm² for every 1kHz increase in frequency at high frequency.