Basic Research On Compatibilization Technology Of Anode Foil For Aluminum Electrolytic Capacitor

Aluminum electrolytic capacitor is widely employed in the communications market,electrical applications and industrial field for its superior performance,low price and reliable quality.Simultaneously,the rapid development of electronic products brings forward higher requirements for miniaturization and high specific capacitance of aluminum electrolytic capacitor.However,the key technology for miniaturization and high specific capacitance is to improve the capacitance of anodic aluminum foil effectively.The capacitance formula of anodic aluminum foil is C =(εε0S)/d,where the vacuum permittivity ε0 is equal to 8.85×10-12 F·m-1,S denotes the specific surface area of anodic foil,d is the thickness of oxide film.Whether Al2O3 is amorphous or crystalline,its relative dielectric constant ε is fixed about 8-10.The thickness of oxide film d can be expressed as:d=Ea·K.Where Eais the forming voltage,K is formation constant of oxide film.Therefore,d is a constant while the forming voltage is unchangeable.Based on the above analysis,in this paper,ultrasound was introduced in etching process to improve the pitting state by strengthening mass transfer and then enhance the S of aluminum foil;Furthermore,TiO2-Al2O3 composite coating was applied in forming process to enlarge e and then increase the capacitance of anodic aluminum foil.The main research contents and results are as follows:(1)Etching aluminum foil was prepared by electrochemical DC etching under ultrasonic superimposition.Specifically,the relationship of electrochemical behavior,interface behavior and mass transfer enhancement from ultrasound was investigated intensively by chronopotentiometry,potentiodynamic polarization,cyclic voltarmmetry and electrochemical impedance spectra.Meanwhile,the etching specimens were characterized by SEM,N2 adsorption and XRD patterns measurements.The results showed that ultrasonic agitation inhibited the growth of aluminum oxide film and facilitated pit initiation effectively via increasing the Cl-adsorption on electrolyte/aluminum oxide film interface,and strengthened the inward/outward migration of Cl-and AICl3 within tunnels by thinning the thickness of diffusion layer and decreasing the electrolyte resistance.Moreover,the double layer capacitance Cdl,pit density,average pit size/tunnel length and its homogeneity are all enhanced under ultrasonic superimposition.(2)Etching aluminum specimens were covered with titanium dioxide film by sol-gel coating using titanium alkoxide,and then anodized in ammonium borate solution.The cross section morphology and its titanium-distribution map,element and crystalline phase of specimens were characterized by SEM,EDS and XRD patterns respectively.Subsequently,the distribution characteristics of titanium element were analyzed.Furthermore,the anodization-time curve,potentiodynamic polarization curve,and electrochemical impedance spectra was investigated intensively.It found that the antase titanium dioxide was obtained successfully by annealing at 550 ℃.With the increase of cycle time of coating,the pitting diameter decreased and the blocked probability of pits and the defects of coating layer were increased.While the Ti content on unit area of etching aluminum is 4.4 mg·cm-2,the consumptions of electric quantity in anodizing process were minimal.Specifically,the degradation of consumptions is 85%,the capacitance decreased to 25.84%compared with etching specimen without coating.