| The development of pulsed power technology demands a miniaturized and light power system. It is very important to increase the energy density of energy storage devices that occupy the largest proportion of volume and weight in the power system. Nowadays, capacitors are most widely used among all kinds of energy storage devices due to their comparatively reliable technology. Pulsed energy storage capacitors have a wide range of operating voltage depending on different applied conditions. Because it is difficult to produce a very thin (eg. Thinner than 3μm) organic film which has high breakdown electric field Eb, such kind of film can't be used to make high energy storage density capacitors for medium volgate application. The medium voltage capacitors may use ceramic as the dielectric material due to its high dielectric constant εr and low Eb, while high voltage products often use organic films because of their high Eb and low εr. This dissertation researches on some new methods to improve these two kinds of capacitors. The dissertation first researches on the ceramic capacitors in the aspects of theory and experiments. The results indicate that the ferroelectric ceramic uesd to produce based multilayer ceramic capacitors (MLC), which has a X7R temperature characteristic, can reach a high energy density of several hundred J/L. After formulation improvement,and optimization of construction and technical process, some capacitors of 1 -10μF/500-1000V were produced with energy density of several hundred J/L. The inverse coefficients in the tests were between 70% and 80%, and repeat frequency of charge/discharge ranged from 100Hz to 1000Hz. Under such conditions, the capacitors had a very long time of 107 shots. On the other hand, the capacitors have some disadvantages including the distortion of discharge current waveform, the limitation of discharge current and the large amount of heat resulting from the nonline character of ferroelectric ceramic, which should be modificated in further research. The dissertation also studies on the reliability of high energy density MLC. Two kinds of ways were adopted including destructive accelerating lifetime test and nondestructive ultrasonic scan. The accelerating life test took the voltage as the accerelating factor. The experimental results show that the discharge voltage and lifetime meet the exponential rules. The results of ultrasonic scan indicated that all of the flawless samples could pass the lifetime test at the rated voltage, while the severely defective samples could not. The breakdown positions in the samples were coincident with the site shown in the ultrasonic scan photos. In a conclusion, the accelerating lifetime test are available for the type approval test, and the ultrasonic scan test are suitable for acceptable end-products. Theconclusion provides a test method for high energy storage density MLC products. For metallized film capacitors, there are three methods to increase the energy density that are new dielectric materials, new electrode structures and process technology. There have been many researches on the frontal two methods in the world, while the third means is just underway. A new process technology, which is named non-thermal equilibrium plasma surface treatment, was used to improve the electrtic breakdown field of the film. Glow discharge plasma was produced in a low gas pressure in a cylindrical chamber. Different kinds of gas including O2, N2 and Ar were used to treat PP film in different treatment intensity, and the treated film were analyzed by detect techniques. The experimental results show that the kind of gas is the most important factor affecting the result. The Vb of the film decreased apparently after they were exposed in the O2 plasma. There existed a best point for the treatment intensity. Infrared spectra showed that under appropriate treatment conditions, some polarity groups such as –COOH and -OH were produced on the surface of film. However, the energy spectrum presented that the mole and weight percent of C, N and O on the surface changed little, indicating that the amount of polarity groups is very small, leading to little improvement of the characteristics for bulk of film. The photographs from SEM show that the corrosion on the film surface was very serious. Amorphous phases were removed, while crystal phases were exposed on the surface. The corrosion was uniform on the surface. This phenomenon indicates an obvious coarsen effect, which may lead to more sufficient impregnating progress. In order to study farther the experimental phenomenon, the dissertation analyses the chemical and physical mechanism of plasma surface treatment. The process of plasma treatment can produce free radicals, polarity groups and form cross linkage lays. These chemical reactions may change the structures of the film surface, and bring about the reduction of initial charge carrier and decrease of electron conductivity in the bulk, leading to increase of the breakdown voltage Vb of the film. Some parts of experimental result are consistent with the theory analyses, while the results about the change of Vb of film need a further study. In summary, the work described in the dissertation have provided a foundation for the development of high energy density capacitors of medium voltage, and have made some useful researches on the improvement of the energy storage density of the mentalize film capacitors.
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