The Preparation And Application Of Manganese Dioxide/Carbon Catalysts In Lithium Air Batteries

With the rapid development of economy, the growing social problems such as the world energy crisis, greenhouse effect and environmental pollution are rapidly becoming outstanding. So the whole world attaches great importance to the development of new energy industry to cope with them. Lithium air batteries can provide 11140Wh/kg usable energy density rivaling that of gasoline combustion(13200Wh/kg). And their power storage capacity is even more 10 times than the best performing lithium-ion batteries. Therefore lithium air batteries are considered as one of the most potential and promising new energy batteries in the future.At present, lithium air batteries’ research is still in early stages. There are many core problems seriously constraining their superior performance to be resolved, such as low power density,high polarization of air electrode and poor cycle life. Among numerous problems of lithium air batteries,high polarization of air electrode is the most remarkable. Some research showed that catalysts could reduce overvoltage and low polarization of air electrode in order to improve cathodic oxygenreductionreactionrate and enhance energyconversionefficiency.Traditionalcatalysts(such as platinum, gold, their alloy and CoPC, ect) have high catalytic activity, but they are expensive. Transitional metal oxidemanganese dioxide hasrelatively low catalytic activity, but it has theadvantages of rich rawmaterials,low cost, simple preparation method andeasy realization oflarge-scale production.Carbon nanomaterials have their unique superiority in good conductivity, huge specific surface area and flourishing hole structure, andthey have caused extensive concern in the field of batteries. In this paper, we chose three typical carbon materials(Super P, Graphene and Mesoporous Carbon) and doped them into manganese dioxide to obtain composite catalysts-manganese dioxide/carbon. At the same time, we discussed how hydrothermal synthesis method of the reaction temperature, time, ratio of raw materials, carbon content and temperature of heat treatment had effect on catalysts.We estimated catalyst activity by linear sweep voltammetry, and excellent catalysts’ synthetic technological conditions were determined. At last, we studied how these catalysts influenced on charge and discharge properties and impedance of lithium air batteries.With temperature rising and time increasing, MnO2/Super P had more completer structure, and higher purity, specific surface area, and conductivity, and their activity was enhanced. Excellent MnO2/Super P catalysts were obtained when reaction temperature was more 150 and reaction time was more 5 h.℃When the ratio of KMnO4 and MnSO4 ranged from 1:1 to 5:2 and the quality of grapheme was increasing from 5 mg to100 mg, the structure and morphology of MnO2/Graphene remained unchanged constantly. But their specific surface area and conductivity were increased obviously. Especially, when the ratio of KMnO4 and MnSO4 was 5:2, MnO2/Graphene’s specific surface area was 81.34m2/g, their conductance was 12.83 S/m, and their activity was the better. When the quality of grapheme was100 mg, MnO2/ Graphene’s specific surface area was 130.04m2/g, their conductance was 46.70 S/m. At this time their activity was the best and polarization of air electrode was the lowest.With increased temperature of heat treatment ranging from 250 ℃to 380℃, MnO2/Mesoporous Carbon’s structure and morphology have not been changed, which just showed they had high thermal stability. But their specific surface area and conductivity were on the move again. High activity of MnO2/Mesoporous Carbon played an important role in reducing effectively polarization of air electrode.When lithium air batteries were in the oxygen atmosphere and charged or discharged at current density of 0.20mA/cm2, the first discharge capacities of lithium air batteries with MnO2/carbon prepared by hydrothermal synthesis method were more than 1000mAh/g.Among them, MnO2/Mesoporous Carbon’s first discharge capacity was up to 1326.80 mAh/g, which was maximum. With recycle number increasing, capacities of lithium air batteries faded sharply, their capacities decreased quickly until extinction after recycling 3 times. Moreover, their impedance expanded significantly. Compared with impedance before the first discharge, impedance after recycling 3 times amostly increased 5 times.