Research On The Synthesis And Properties Of Spinel LiMn₂O₄ And LiM_xMn_2-xO₄

Lithium ion battery is a new type of rechargeable battery. In the beginning of 1990s, SONY coporation declared that they found a practicable battery system which used carbon and lithium cobalt oxide as negative material and positive material respectively. This kind of battery was brought to the market soon after that declaration. Lithium ion batteries have many advantages, such as high voltage, high specific energy, long cycle life, reliable performance and wide range of working temperature. Among the various kinds of cathode material, spinel lithium manganese oxide LiMn2O4 was believed to be the most promising one because of its abundant resources, low cost, little pollution and simple synthesis process.In this thesis, the spinel LiMn2O4 was synthesized in serial production by solid-state reaction and the electrochemical properties was tested in rectangular lithium ion battery with microcarbon Microbead(MCMB) as anode material and 1 M LiPF6 desolved in the mixture of ethylene carbonate(EC) , dimethyl carbonate(DMC) and ethylene methyl carbonate(EMC) as the electrolyte. To optimize the synthetic process, we investigated the effect of four factors: different row material, the ratio of lithium and manganese, calcination temperature and calcinations time on the properties of the production. The production which was fabricated from LiOH or LiNO3, instead of Li2CO3, displays significant advantages. Optimum results were a reaction time about 75h and a calcinations temperature about 800.On the other hand, we studied the influence of doped-cations, such as Ni2+, Mg2+ and Co3+. The structure of the doped spinel LiMn2O4 was proved to be pure spinel through X-ray diffraction measurements. The cycle life was improved by doped-cations. The properties of LiCoo.ogMn1.92O4 were studied especially which initial capacity is about 78mAh/g and 85percent is remained after 1000 cycles. The attractive advantage is that LiCoo.o8Mn1.92O4 can work at high discharge rates. The discharge capacity at 4C is about 85percent of the capacity at 0.1C . The specific energy and power at 4C is about 60Wh/kg and 520W/kg. The self-discharge rate isis below 6 percent per month. So LiCoo.o8Mn1.92O4 is a promising cathode material which can be put into use.