尖晶石锂锰氧化物的湿化学合成及其性能检测

【作者】 王晨生；

【导师】 李运姣；

【作者基本信息】 中南大学 ， 有色金属冶金， 2002， 硕士

【摘要】 湿化学法是一种较有发展前景的合成尖晶石锂锰氧化物的方法。本论文采用湿化学法合成了锂离子电池正极材料尖晶石锂锰氧化物和掺杂尖晶石锂锰氧化物。在进行理论分析和实验研究的基础上，通过X射线衍射、热重／差热分析、扫描电镜等手段，系统地考察了不同实验条件对产物的化学组成及粒度、形貌、物相结构等粉末特征的影响规律；并将合成的产物组装成模拟电池进行了电化学性能测试。 在湿化学法合成锂锰氧化物前驱体过程中，研究了不同盐系对合成产物结构、粒度、形貌及比表面积等性能的影响。结果表明，不同盐系合成的产物性能基本相近，但硝酸盐水溶液体系更有利于Li⁺嵌入到锰的氧化物中。 系统考察了不同热处理温度及热处理时间对产物结构及粒度等性能的影响。研究发现湿化学合成的前驱体，经适当的热处理可得到晶型结构完整的尖晶石锂锰氧化物；热处理温度对产物的晶型结构及粒度影响较大，随热处理温度的升高，衍射峰的强度明显增大，晶型结构更趋于完善，且晶粒明显变粗，在700℃时烧制4h即可获得晶型结构完整、粒度均匀的产物；而热处理时间对锂锰氧化物的晶型结构影响不大。 湿化学合成过程通过加入钴或铬化合物可获得掺杂锂锰氧化物，它们具有与LiMn₂O₄相同的尖晶石结构，且粒度及形貌较不掺杂锂锰氧化物更细更均匀。 将合成的富锂尖石样品Li_1.04Mn_1.96O₄和Li_1.05Mn_1.59O₄制成正极片，组装成模拟电池，研究了它们在1MLiClO₄／EC+DEC（1：1wt）和1MLiPF₆／EC+DEC（1：1wt）两种电解液体系中的电化学性能。实验结果表明：采用不同的电解液时样品的充放电容量不同，在1M LiClO₄／EC+DEC（1：1wt）中的容量更高，循环稳定性好，Li_1.05Mn1.95O4在LiClO4电解液中，首次充电容量为118.0mAh／g，循环5次后充电容量为112.9mAh／g ，容量衰减较低。而相同测试条件下，Li1.05Mn1.95O4在LiPF6电解液体系中的首次放电容量仅104.9mAh／g，第二次放电容量为80.2 mAh／g。表明该富锂尖晶石样品与1MLiClO4／EC+DEC（1：1wt）电解液的相容性较好。 探讨了掺钴和掺铬对锂锰氧化物电化学性能的影响。在1M LiPF6／EC+DEC（1：1wt）电解液中，掺铬富锂尖晶石Li1.04Cro.03Mn1.93O4首次放电容量为115.4mAh／g，第二次放电容量为113.0mAh／g；相对于富锂尖晶石，在相同的测试条件下，掺杂的富锂尖晶石循环性能更好。</sub>更多还原

【Abstract】 The spinel LiMn₂O₄ and cobalt-doped or chrome-doped lithium manganese oxides of the cathode for rechargeable lithium-ion batteries was synthesized by wet chemical process which is considered as a most promising method for the synthesis of spinel lithium manganese oxides. Based on the theoretical analysis and experimental study, the influence of technological conditions on the chemical composition and the powder characteristics, such as particle size, morphology, structure and so on, was systematically investigated by modern Analytical methods of XRD, SEM, BET, TGA/DTA and so onThe changes of the structure, particle size ,morphology and specific surface area of the products prepared in different systems of salts were discussed. The results suggest that the precursors from different systems of salts have similar characteristic and the system of nitrate be in favor of embedded Li+ inserting manganese oxides.The characteristic of different products at different calcinating temperatures and time was investigated. The results show that perfect spinel LiMn₂O₄ crystals can be obtained from the precursor of LiMn2O4 after being calcinated. It is founded that calcinating temperature has great influence on the crystal structure of LiMn2O4. With the elevating of the temperature, the crystal structure becomes more perfect and the particle size gets larger. A spinel LiMn2O4 with regular crystal structure and well-distributed particle size can be obtained after being calcinated for 4 h at 700 "C. However, it is also observed that the calcinating time has less effect on the perfection of the LiMn2O4 structure and the samples maintain the same XRD patterns when the calcinating time is prolonged at the same temperature.Cobalt-doped or chrome-doped lithium manganese oxides were prepared by the wet chemical process and the circling performance of the products were studied. The results shown that the Cobalt-doped or chrome-doped spinel has the same structure as spinel LiMn2O4 and is more slender and uniformity.A test cell was tested, presented by using the sample Lii.o4Mn1.96O4or Li1.05Mn1.95O4 as cathode active material. Electrical properties of samples were depicted by charging and discharging curves respectively. Emphasis was placed on the two kind of electrolytes, 1M UC1O4/EC+DEC （1:1wt） 1MLiPF6/EC+DEC（1:1wt）.The electrochemical properties of the sample Lii.o4Mni.96O4or Lii.osMni.95O4 used asa cathode active mater of a test cell were examined in both IM LiQO4/EC+DEC （l:lwt）和1M LiPF6/EC+DEC（l:lwt） electrolytes. The battery with LiClO4 electrolyte has higher capacity and more stable performance than that with LiPFe electrolyte. When the sample Lii.o5Mni.95O4 is in the electrolyte of IM LiCKVEC+DEC （1:1 wt）, the first discharge capacity is 118.0mAh/g, and the sixth discharge capacity isl!2.9 mAh/g. At the same condition, the capacity of the sample Lii.osMni.9sO4 respectively is 104.9 mAh/g and 80.2 mAh/g in the first circle and the second circle.The results of constant-current cyclic test show that the cycling stability of the cobalt-doped or chrome-doped lithium manganese oxides is more stable than the spinel LiMnaCU- For example, the first discharge capacity of the sample Lii.wCr0.03Mn1.93O4 in the IM LiPF6/EC+DEC（l:lwt） is 115.4mAh/g, and the second discharge capacity is 113.0 mAh/g. Compared with Li-rich spinel Li1.04Cr0.03Mn1.93O4 and Lii.osMni.95O4, the cobalt-doped or chrome-doped spinel has higher capacity and more stable circling performance.更多还原