| With the arriva l of energy crisis in the 21 st century, lithium-air batteries which have high energy density attract people’s attention and research. However, effic ient catalysts must be added to reduce the potential energy of oxygen reduction reaction at the cathode. Common catalysts such as platinum and its alloys are expensive, which is not uneconomical for commercial production of lithium- air batteries, but α-Mn O2 is a kind of low-cast and efficient catalyst. In addition, the breathable waterproof membrane used outside the cathode is prepared and the research is carried out in the ambient air condition in order to speed up the practical use of lithium- air batteries. The preparation of α-Mn O2 catalysts, doping rare earth elements to Mn O2, electrochemical performance of different carbon surpports and the mechanis m of charge-discharge in ambient air condit ion are researched in the test, and then the model of electron transfer failure is proposed and established first in the field of lithium- air battery research.The nanorods α-Mn O2, which has suitable micro and meso structure porous and large surface area, can be obtained through the reaction of KMn O4 and Mn SO4 under 180 ℃ conditions for 12 h.The battery will have a better performance only if the cathode materials ha ve the properties of suitable micro and meso structure porous, better catalysis for O RR, and small charge transfer resistance. The specific capacity increases, while the cycling performance decreases with the increase of surface area and pore volume of cathode materials. However, the specific capacity and cycling performance d on’t change regularly with the average size of pores of cathode materials. Among graphite, ks6 graphite, Super P, acetylene black and CN Ts, Mn O2/CN Ts shows the largest capacity of 2200 m A h/g(car bon + cat alyst).CexMn1-xO2 materials which have the O RR/O ER catalys is are obtained through doping rare earth elements to Mn O2. In the test of limited capacity discharge, Ce0.1Mn0.9O2 which has the best catalytic ability, shows the lowest charge and discharge potential of 700 m V, which is third of the charge and discharge potential of Mn O2(2100 m V). The method of doping rare earth elements to the transit ion metal oxide provides a new method for preparation of cathode catalyst for lithium- air battery.The poor performance of lithium- air batteries is mainly caused by the type of electrolyte instead of the breathable waterproof membrane and the impurit ies in the air. The lithium-air battery with ether-based(CN Ts/TEGDME) electrolyte has 60 times cycles in the limited capacity charge and discharge test, while the ester-based lithium- air battery(CN Ts/PC/EC/EMC) only has 12 times. The catalysis will reduce when the surface of the catalyst is covered with the discharge products during the charge and discharge process. And the accumulation of Li2CO3, Li F due to the decomposition of ester-based electrolyte leads to the battery failure. However, the ether-based electrolyte only leads to generate the desired products of Li2O2 and a small amount of Li2CO3 during discharge process.It is confirmed that the charge-discharge process has the largest effect on the charge transfer impedance of the cathode reaction through the results of DC, EIS, XRD and SEM tests, and then the model of electron transfer failure is proposed and established first in the field of lithium- air battery research. The model gives a reasonable explanation for the inva lid of different cathode materials and discharge curves, and then provides the practical guidance for lithium-air batteries. |
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