| As a high efficient energy conversion device (convert chemical energy into electric energy), chemical power sources received much attention. Among those devices, supercapacitors are a kind of intermediate systems between conventional capacitors and rechargeable batteries which have many advantages over conventional capacitors,such as possessing higher capacities and energy, higher specific power compared to batteries, and fast charge-discharge speed, extremely long cycle life and wide operating temperature range. Supercapacitors are widely used in many areas such as military aerospace, mobile telecommunication and information technology, consumer electronics, fuel cells, electric vehicles and urban transports, solar and wind energy. Some of the aeras are often irreplaceable. When the supercapacitors combined with rechargeable batteries formed the hybrid power system, which can meet the high power out-put need, and play an significant role in electric vehicles in condition of instantly starting, acceletating and braking. Consequently, it is significant to do research and development on a new kinds of electrode materials of supercapacitors.Graphite (MCMB) and hard carbon with good electrochemical performance and high conductivity are most uaually used as negative electrode materials in lithium-ion battery. Especially hard carbon has a "card" layered structure and its theoretical lithium insertion capacity higher than graphite. We consider using hard carbon and activated carbon as anode and cathode respecitively for a new type of asymmetric supercapacitor. In this dissertation, MCMB material and activated carbon have been researched in the former section. The second part will focus on the hybrid capacitor. The conclusions can be drawn as follows by doing a series of experiments:1. The CV results of graphite(MCMB) in a three-electrode using 1.3 mol/L LiPF6/EC+DMC show:the SEI formation potential range in the first cathodic process was 0.75-0.2 V, and the de-intercalation potential range was 0.2-0.01 V. The SEI film was formed mostly in the first cycle. However, the high rate performance of the MCMB electrode was not so satisfactory. The electrochemical tests of activated carbon electrode indicated its good power and capacitance characteristics. And the electrode was very stable during the whole process.2. The layer spacing of hard carbon in this paper was relatively large and its corresponding lithium intercalated capacity was high. The lithium intercalation experiments and CV tests of hard carbon using 1.3 mol/L LiPF6/EC+ DMC demonstrate:the SEI formation potential range in the first cathodic process was 1.0-0.5 V, and the de-intercalation potential range was 0.5-0 V. In addition, the SEI film was formed mostly in the first cycle. And the discharge capacity of hard carbon was 284.7 mAh/g at the current density of 25 mA/g. Morever, hard carbon can intercalate lithium at a fast speed, which made it suitable to work at high rate. So it can be used as electrode for supercapacitors.3. The AC/HC asymmetric capacitor was characterized by galvanostatic charge/discharge, cyclic voltammetry and EIS tests. The results indicate:The specific capacity of the hybrid capacitor can reach to the best value when the mass ratio of cathode to anode was 1:1. And the EIS value was lower than AC symmetric capacitor. Besides, the unipolar specific capacity was 80.1 F/g and 78.9 F/g when the current density was 25 mA/g and 100 mA/g, respectively, retained 98.5%. Finally, the cycle performance tests for the hybrid supercapacitor showed:afer 1000 cycles, the specific capacitance retained 70.4%, while the charge/discharge efficiency was 98%, and the electrochemical performance of the hybrid capacitor needs to be improved. |
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