Study On The Electrochemical Performances Of Hybrid Supercapacitor In MnO₂//AC And LiMn₂O₄//AC System

Hybrid supercapacitor （HESC） combines the advantages of high energy densityof batteries and high power density of the supercapacitors and has broad applicationprospects. In this thesis, the electrochemical performances of hybrid supercapacitor inMnO₂//activated carbon （AC） and LiMn₂O₄//AC system were studied.MnO₂was synthesized by KMnO4and MnSO₄as raw materials and FeSO₄asmodification. The structure and morphology of Fe-MnO₂was characterized by XRDand SEM.The results showed that the Fe-MnO₂pocessed the better electrochemicalproperties when the bath temperature was30C and the dopant of Fe was2wt.%. Itsspecific capacitance was210F/g at the current density of0.2A/g, improved up to12.7%when compared to that of pure MnO₂. After assemble into the hybridsupercapacitor with activated carbon, the potential window with0-1.8V was high,and the maximum specific capacitance was43F/g at the current density of0.2A/g. Itshowed an energy density of19.4Wh/kg at a power density of180W/kg. When thepower density increased to1800W/kg, the energy density is still14Wh/kg.The LiMn₂O₄//AC hybrid supercapacitor consisted of a LiMn₂O₄positiveelectrode and AC negative electrode was assembled in1mol/L Li2SO4. The effect ofspecific surface area of the activated carbon, the mass ratio of anode and cathode,operating voltage range on the electrochemical performance of LiMn₂O₄//AC wereinvestigated. The result showed that the optimal experimental conditions wereoperating voltage range at0¹.8V, the surface area of the activated carbon with2000m2/g, the mass ratio of anode to cathode at1:2. Carbon nanotubes were introducedinto the positive electrode to make effective elctric-contact between LiMn₂O₄particlesand improve the LiMn₂O₄activity and utilization. The maximum specificcapacitanceof LiMn₂O₄//AC was85.9F/g with addition of1%CNT into positiveelectrode. It showed an energy density of38.26Wh/kg at a power density of2640.72W/kg. With the increase of the content of CNT, the specific capacitance of hybridsupercapacitor decreased, however, the power density improved compared withLiMn₂O₄//AC.