Preparation And Performance Of Al/C Composite Foil

Aluminum foil is electrode material of aluminum electrolytic capacitor, and important collector material of lithium ion battery and super capacitor. It has obvious influence on performances of above electronic devices. Modification on it is an important way to improve the related device performance. In recent years, research show that Al/C composite foil, which is made by forming carbon layer on both sides of aluminum foil, can effectively reduce the interface resistance of aluminum foil with active material, and increase the aluminum foil’s surface area and affinity to active material, thus provide greatly performance improvement of electronic devices. Solid aluminum electrolytic capacitor shows better performances such as temperature stability, equivalent series resistance (ESR), dissipation factor(DF), frequency characteristic and operating life than traditional aluminum electrolytic capacitor, and has become the future direction of traditional aluminum electrolytic capacitor. Al/C composite foil has become key material of solid aluminum electrolytic capacitor for the special characteristics of conductive polymer, and has significant influence on development of solid aluminum electrolytic capacitor industry. Existing technique employ chemical vapor deposition to form carbon layer on aluminum foil, but there are problems of complicated equipment and high cost.In present paper, aluminum foil coated by organic precursor and conductive carbon materials were heat treated to carbonize the organic precursor and to generate aluminum carbide in interface of aluminum foil and carbon layer. Al/C composite foil was thus produced.Efforts was made to investigate influence of composition of carbon layer, conditions of heat treatment and activating treatment, on the properties of Al/C composite foil. Properties of sheet resistance, adhesive strength of carbon layer and specific surface area were measured to evaluate the performance Al/C composite foil. Microstructure of Al/C composite foil was investigated by TEM and SEM. Main conclusions are listed as follows:(1) Discussion on factors in the process of preparing of Al/C composite foil offered an optimum preparation technology of Al/C composite foil:the best ratio of flake graphite, organic resin, surface active agent in carbon layer is80:18:2; The optimal heat treatment condition is550℃-6h; The best activating treatment condition is400℃-4h in air atmosphere.(2) Several analysis were used to investigate the relevance of composition and structure of carbon layer and interface to performance of Al/C composite foil. Results show that:carbon layer of prepared of Al/C composite foil consists of ordered sp2graphite, disordered sp2、sp3pyrolysis carbon; organic resin pyrolysis carbon content can be improved to acquire a carbon layer structure with large specific surface area, high conductivity and high bonding strength in the premise of graphite flake conductive network can be formed. Carbon layer and aluminum foil of Al/C composite foil composite foil were combined closely, and short rod-shaped Al4C3phase formed in the interface of carbon layer and aluminum foil. It’s confirmed that the formation of Al4C3phase is necessary to achieve a low sheet resistance in close proximity to aluminum foil. The dense carbon layer and metallurgical bonding in the interface also give Al/C composite foil high thermostability, which can maintain stable at400℃.(3) conditions and rules of reaction of Al and C in Al/C composite foil were discussed in thermodynamics and kinetics, result shows the reaction is controlled by diffusion and thus can be accelerated by shorten the diffusion distance of C and Al.(4) Al/C composite foil was used as cathode foil to prepared4v,560μF solid aluminum electrolytic capacitor, the best performance can reach a capacity of615μF, ESR of4.6m Ω., dissipation factor of0.98%, leakage current of17.7μ.A, which are all superior to the commercial performance standards. Solid aluminum electrolytic capacitors made by Al/C composite foil show lower equivalent series resistance and dissipation factor compared with the traditional etched aluminum foil.Research show that carbon layer of Al/C composite foil can modify interface combination status of conductive polymer layer and cathode foil. Solid aluminum electrolytic capacitors prepared showed excellent performance under a life test of145℃,250h. It proved the excellent stability of Al/C composite foil developed in this paper. Bending times is also an important performance parameter of Al/C composite foil, which will directly affect the riveting effect.