A Study on the Preparation of LixMn2O4 Cathode Materials and Their Charge/Discharge Behaviors

• Main Authors: Wu, Fu-Chi, 吳富其
• Other Authors: Ho, Kuo-Chuan
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/80528171222898890255

碩士 === 國立臺灣大學 === 化學工程學研究所 === 87 === This study is about the preparation and characterization of LixMn2O4 cathode for lithium ion batteries. The preparation conditions were determined from the thermal properties of lithium nitride (LiNO3) and manganese dioxide (MnO2). The row materials were sintered in different atmospheres (air, nitrogen, oxygen and argon) with different mix ratios in a temperature programmable furnace. The LixMn2O4 electrodes were made by using the PVDF binder. The testing cells or coin-type cells were assembled by using the prepared electrodes as the cathode, 1M LiPF6＋EC/DMC(1:1 in vol.) as the electrolyte, and the lithium foil as the anode. The cells were tested using various electrochemical methods (ac impedance, cyclic voltammetry, and cyclic charge/discharge testing). It was found experimentally that the sintering temperature, atmosphere, gas flow rate, mix ratio and the particle sizes of the row materials do affect the results of preparation. When copper foil was used as the current collector, the dissolution, electromigration and electrodeposition of Cu prevented the reaction when cell was charged. When aluminum foil was used as the collector, the reaction was still prevented if the aluminum oxide on the surface was not properly removed. The passivation phenomena on the metallic lithium were detected by the ac impedance analysis. Besides, we first discussed the charge/discharge behaviors of the LixMn2O4 material from the viewpoint of structural change. Attempts were made to relate the cyclic voltammograms, charge/discharge curves and the structures of LixMn2O4 material. The behaviors can be reasonably explained by using the formation of three stable structures under three different potentials. Finally, cyclic charge/discharge testing of the coin cells, which were assembled by LixMn2O4 prepared under different conditions, revealed that, when sintered in nitrogen, the capacities increased with the sintering temperature. When sintered in O2 by using the non-milled MnO2 mixed with LiNO3 at the ratio of Li/Mn=0.6, the capacity was about 105 mAh/g on average discharging at 0.5 mA/cm2 for the first 20 cycles and reached the highest value of 125 mAh/g.