Research On High Capacitance Aluminum Foil For Electrolytic Capacitor With Electrochemical Machining

With the rapid development of electronic products,the demand for aluminum electrolytic capacitors is increasing quickly,and there has been higher requirements for their specific capacitances.Electrode aluminum foil is an important component of electrolytic capacitors,and increasing the true surface area of aluminum foils is an effective way to improve the specific capacitance of electrolytic capacitors.Therefore,it is of great importance to increase surface area and capacitance of aluminum foils.However,the current methods to expand surface area tend to involve strong acid,strong alkali,and heavy metal solutions,and can only construct microstructures on the surface,thus restraining further increase of the surface area.This thesis employs electrochemical etching and anodization to build micro-nano composite structures on aluminum foil surfaces,and can obviously expand their surface area,thereby increasing the specific capacitances.The main research work can be summarized as follows:Electrochemical etching was carried out using environmental-friendly sodium chloride solution as electrolyte to prepare microscale rough structures on the aluminum foil surfaces.Electrochemical machining parameters were optimized to reduce weight loss rate and increase specific capacitance of the aluminum foils.According to the results,when the current density was 0.5A/cm²,25s electrochemical etching in 0.1 mol/L sodium chloride solution resulted in the increase of the specific capacitance from 13?F/cm² to 63?F/cm²,and the weight loss rate was just 7%.The micromorphology of electrochemically-etched surfaces was observed using scanning electron microscope.The results showed that step-like microscale rough structures were formed,and the surface area and specific capacitance were therefore increased.According to the analysis results of X-ray interferometer and energy spectrum analyzer,no new material appeared on the aluminum foil surfaces after electrochemical etching.In order to further increase the specific capacitance of the aluminum foil,on the basis of anodization technology,nanostructures we re constructed on the microstructures of the aluminum foil surfaces after electrochemical etching.Using single-factor tests,the effects of electrolyte type,processing voltage,and anodizing time on the surface morphology and the specific capacitance of the aluminum foil were investigated.It was found that when oxalic acid solution was used as the electrolyte,the oxide film was uniform,the corrosion was less,and the weight loss rate was relatively lower.Furthermore,using 0.3 mol/L oxalic acid solution as the electrolyte,when the processing voltage was 50 V,and anodization time was10 min,the specific capacitance could be increased from 63?F/cm² to 243?F/cm²,and the weight loss rate was only 6.3%.The chemical composition analysis of the obtained aluminum foil surface revealed that a large amount of oxides appeared after anodization,and the main components were alumina and boehmite.Based on anodic oxidation technology,nanostructures were formed on the surface of aluminum foil after electrochemical etching.O n the basis of single factor,different processing parameters were studied to determine suitable electrolyte types,processing voltage and anodizing time.The morphology analysis showed that when 0.3mol/L oxalic acid was used as the oxidizing solution,the oxide film was homogeneous and self corrosion was less.Increasing the anodizing voltage within a certain range,the size of the oxide holes on the aluminum foil surface increases and the pores are uniform.With the increase of anodization time,the nanopores on the surface of aluminum foil will expand.Finally,the adjacent holes will break down and form nanowire structure.By analyzing the chemical composition of the surface of aluminum foil,a large number of oxygen elements appeared after anodizing relative to the unprocessed surface.The oxide film was formed on the surface by the analysis of the morphology.The test results shows that when in the 0.3 mol/L H₂C₂O₄ solution uses50 V voltage anodic oxygen 10 min,the weight loss rate of aluminum foil is 6.3%,and the specific capacitance can reach 243?F/cm².