Carbon Nanotubes Supercapacitors

Supercapacitor is a new type of energy storage equipment which combines theadvantages of conventional capacitors and rechargeable batteries. It has higher energydensity than conventional capacitors and higher power density than rechargeablebatteries，the promising application of supercapacitors in the fields such as mobiletelecommunication，consumer electronics，electric vehicle， and military force，havebeen attracting more and more attention through out the world. Studies onsupercapacitors are mainly focused on the preparation of electrode material.In thisdissertation, CNT electrode, MnO₂electrode, CNT/MnO₂composite electrode andCNT/NiO composite electrode were fabricated. The microstructures and morphologiesof these materials were investigated by scanning electron microscopy （SEM） and X-raydiffraction （XRD）, and their electrochemical properties were investigated. Through aseries of experiments, the following conclusions were drawn：CNT electrode was fabricated by chemical vapor deposition, super capacitor withCNT electrode was assembled. The electrochemical properties of the material wasstudied. The results indicated that the CNT electrode showed ideal characteristic ofdouble layer capacitance，CNT electrode provided specific capacitance of7.81mF/cm²with Equivalent Series Resistance（ESR） of1.3.MnO₂electrode was fabricated by chemical deposition，super capacitor withMnO₂electrode was assembled. The electrochemical property of the material wasstudied. The results indicated that the MnO₂electrode provided specific capacitance of573.41mF/cm², with Equivalent Series Resistance （ESR） of63.5, showedcharacteristic of pseudo capacitanceCNT/MnO₂electrodes were fabricated by solid phase synthesis, super capacitorwith CNT/MnO₂electrode was assembled. The effect of CNT/MnO₂weight ratio oncapacitive behavior was studied. CNT/MnO₂electrodes with80:20,70:30,60:40weightratio of MnO₂:CNT had specific capacitance of2.23F/cm²,0.955F/cm²and0.566F/cm²at1.89mA, with Equivalent Series Resistance（ESR） of48.6,39.5and30.2Therefore, by adding CNT, the capacitance of MnO₂electrode was evidently increased and the Equivalent Series Resistance was reduced. The results also indicated thatCNT/MnO₂electrodes with higher MnO₂weight ratio had higher specific capacitanceand higher Equivalent Series Resistance.CNT/MnO₂electrodes were fabricated by chemical deposition, super capacitor withCNT/MnO₂electrode was assembled. The effect of deposition time of MnO₂oncapacitive behavior was studied. CNT/MnO₂electrodes with60min and120mindeposition time of MnO₂had specific capacitance of91.21mF/cm²and127.5mF/cm².As a consequence, extremely long deposition time provide higher capacitance，butcritically reduce the adhesion of CNT and MnO₂.CNT/NiO electrodes synthesized by magnetron sputtering had had specificcapacitance of5.04mF/cm², CNT/NiO electrodes prepared by liquid deposition hadspecific capacitance of11.2mF/cm². CNT/NiO electrodes fabricated by liquiddeposition showed higher capacitance.