Study On Synthesis And Electrochemical Characteristics Of λ-MnO₂ Cathode Material For Li/MnO₂ Batteries

Li/MnO₂ battery has some merits as follow: high working voltage and specific energy, wide working temperature range, low self discharge rate, good leaking resistance, no pollution, and so on. So it’s the most familiar one of primary lithium batteries and having the most output, and it is widely used in military and civil domain. EMD is the most widely used cathode material in the present-day Li/MnO₂ batteries. Technology’s development demand batteries with high energy-density and safety. Improving the performance of MnO₂ has always been an important research work for the battery scientist and material scientist. Theλ-MnO₂ has the spinel-type structure which like three-dimensional net, and can afford bigger space for lithium ion thanγ-manganese dioxide （EMD） with one-dimensional tunnel structure. Soλ-MnO₂ is an excellent cathode material for lithium battery. In this dissertation, the studies on the synthesis, morphology, structure and electrochemical performance ofλ-MnO₂ as cathode materials for lithium batteries were carried out systemically.In this paper, the LiMn₂O₄ precursor with uniform spinel structure was prepared by melt-impregnation method. The effects of pre-treatment technique, reaction temperature and time on the physical and chemical properties of the LiMn₂O₄ precursor were studied in detail. The results indicated that the optimum conditions for preparing spinel LiMn₂O₄ were that the starting materials were mixed and pressed to pellet, the pellet was sintered for 12h at 650℃and followed a sintering process which was for 24h at 850℃.λ-MnO₂ powders were successfully synthesized by acidifying spinel LiMn₂O₄ with 6mol·L^-1 H₂SO₄. The effects of reaction temperature and time, dryness temperature and time on the electrochemical properties and structure of theλ-MnO₂ were characterized by the Rietveld refinement associated with electrochemical studies. The results showed that the optimum process for the preparation ofλ-MnO₂ was to acidify treatment for 20h at 25℃, then drying in vacuum for 24h at 80℃.Finally, the morphology, tap-density, structure and electrochemical performance of the as-preparedλ-MnO₂ are further studied. The as-preparedλ-MnO₂ has the same uniform spinel structure like LiMn₂O₄. The corresponding tap-density was approximately 2.383g·cm^-3. The results revealed that the Li/MnO₂ battery usingλ-MnO₂ could work at -45 to 50℃, and had excellent storage characteristics and electrochemical properties.