【作者】 周振华；

【导师】 李澄； 梅天庆；

【作者基本信息】 南京航空航天大学 ， 物理化学， 2010， 硕士

【摘要】 锰酸锂材料由于具有资源丰富、价格低廉、对环境友好、耐过充放电、耐大电流放电和安全性能好等优点,被认为是最有前途的正极材料之一,尤其适合用作未来电动车动力电池的正极材料。在锰氧化物中可用作正极材料的有尖晶石型LiMn₂O₄和层状LiMnO2。但是尖晶石型LiMn₂O₄初始容量较低、循环性能差,而层状LiMn0₂理论容量高达285mAh/g,几乎是LiMn2O4的两倍,循环性能较好,引起来人们极大的兴趣,逐渐成为近年来的研究热点,是一种具有广阔发展前景的正极材料。本文首先以商业级大孔径硅胶为模板,利用硅胶的多孔结构制备了具有纳米尺寸的LiMnO2正极材料,TEM透射电镜显示模板法制备的材料的颗粒尺寸在30—50nm之间,与硅胶孔径尺寸基本吻合。然后采用普通法制备了微米级LiMnO2材料。用循环充放电测试考察了产物的电化学性能,结果显示模板法制备的纳米尺寸LiMnO₂与微米级材料相比显示了更好的充放电性能和循环稳定性,但是两者放电比容量都较低。为了更好提高材料的放电比容量和循环性能,在模板法的基础上分别掺杂不同的稀土元素Ce和La。XRD物相结果表明所制备的掺杂材料结晶度较好,纯度较高。颗粒尺寸也都在硅胶孔径范围内。充放电测试显示掺杂La或者Ce后,无论是材料的放电比容量和循环性能都有了较大幅度的提高。其中2%Ce掺杂的锰酸锂材料初次容量为108.6mAh/g,在30次循环后容量是98.8 mAh/g,容量保持率在90.9%。4%La掺杂的锰酸锂材料初次容量为113.5mAh/g,循环30次后其放电比容量是103mAh/g,容量保持率为90.7%。在模板法单元掺杂的基础上尝试二元掺杂,以期能进一步提高材料的电化学性能。我们分别在2%Ce和4%La掺杂的基础上分别掺杂不同比例的Ni,充放电测试表明掺杂后材料的放电比容量都有一个稳步上升的过程,然后趋于稳定,其中LiMn_0.90Ni_0.08Ce_0.02O₂首次放电比容量是87.8mAh/g,循环30次后其放电比容量为132.4 mAh/g,容量保持率为150.7%。LiMn_0.86Ni_0.10La_0.04O₂首次放电比容量是106.1mAh/g,循环30次后其放电比容量为141.3mAh/g,容量保持率为133.2%。这也同时说明了掺杂元素在抑制结构相变,提高循环稳定性上发挥了关键作用。更多还原

【Abstract】 Lithium manganese oxide material is considered as one of the most promising cathode material because of its abundant resources,low price,friendly environmental,durability to over-discharge and over-charge, discharge at high electric current, and super safety. And it is particularly suitable for future electric vehicle power battery cathode material. In the manganese oxides,spinel LiMn₂O₄ and layered LiMnO₂ can be used as cathode materials. However, the initial capacity of the spinel LiMn₂O₄ is low and the cycle performance is poor, while the layered LiMnO₂ theoretical capacity is up to 285mAh/g,which is almost twice of the LiMn₂O₄, the cycle performance of the LiMnO₂ is also very good ,and which has caused great interests of people. Layered LiMnO₂ has a broad prospects for development in the cathode materials.In this paper, commercial-grade silica with large hole was used as template,we used the porous structure of silica prepare nanosized layered LiMnO₂ cathode material. TEM transmission electron microscopy showed that the particle size of the material prepared by template method is about 30-50nm which is consistent with the pore size of silica gel. Then the micron LiMnO₂ material was prepared by general method. Charge-discharge cycle tests investigated the electrochemical properties of the product.Compared with micron-grade materials,template synthesis of nano-size LiMnO₂ showed better electrochemical performance and cycle stability,but both of them had a poor discharge capacity.In order to improve the discharge capacity and cycle performance of the material, we doped different proportions of rare earth elements Ce and La based on the template method. XRD results showed that the phase of the dopped materials all had a good degree of crystalbility and high purity. Particle size is between silica pore size range. Charge-discharge tests showed that the discharge capacity and cycling performance all have a greatly improved when the materials dopped La and Ce. The initial capacity of 2% Ce-doped LiMnO₂ material is 108.6mAh/g, after 30 cycles the storage capacity is 98.8 mAh/g,the rate of the capacity retention is 90.9%. The initial capacity of 4% La-doped LiMnO₂ materials is 113.5mAh/g, after 30 cycles the discharge capacity is 103mAh / g, the rate of the capacity retention is 90.7%.Based on the mono-doped of the template method,we tried the dual-doped method in order to further improve the electrochemical properties of the material.Based on 2%Ce and 4% La-doped respectively,we doped different proportions of Ni.Charge-discharge tests showed that the discharge capacity of the material had a steady increase in the process,and then stabilized.The initial capacity of LiMn_0.90Ni_0.08Ce_0.02O₂ is 87.8mAh/g,30 cycles later the discharge capacity is 132.4 mAh/g, the rate of the capacity retention is 150.7%. The initial capacity of LiMn_0.86Ni_0.10La_0.04O₂ is 106.1mAh/g, 30 cycles later the discharge capacity is 141.3mAh/g, the rate of the capacity retention is 133.2%. It illustrated that doped elements played a key role in the suppression phase transition and cycle stability.更多还原