【作者】 伍凌；

【导师】 李新海； 王志兴；

【作者基本信息】 中南大学 ， 冶金物理化学， 2011， 博士

【摘要】 随着全球能源和资源的日益短缺,开发新能源和综合利用矿物资源成为当今世界的两大热点。本文将冶金、能源、材料等领域联系起来,提出了综合利用钛铁矿（或废料）制备新能源材料—磷酸铁锂和钛酸锂的新思想,并对钛铁矿冶金和材料制备的物理、化学过程及原理进行了详细的研究。采用机械活化—盐酸常压浸出法对钛铁矿进行了选择性浸出。结果表明,机械活化可以细化钛铁矿的粒径,增加颗粒表面的粗糙度,从而增大其比表面积；机械活化可以破坏钛铁矿晶粒的完整性,并产生大量晶格缺陷,使晶格膨胀。上述行为均能强化钛铁矿浸出。最优条件下Ti的浸出率仅为1.07%,Si几乎不被浸出,而Mg、Al、Mn和Ca的浸出率均在95.5%以上,最终Ti和Si富集在渣中,其它元素进入浸出液。将上述富钛渣直接煅烧得到了品位高于90wt.%的人造金红石。首次以H₂O2为配位剂将Ti从富钛渣中浸出,最优条件下Ti的浸出率达98.9%。将配位浸出液直接加热制备了颗粒粗大（2～5μm）且含少量Si的过氧钛化合物。同样以配位浸出液为反应物,在加热前添加适量的NaOH模板剂,不仅防止了颗粒团聚,得到纳米级针球状的过氧钛化合物,而且还成功地将Si除去；将该过氧钛化合物在400～800℃下煅烧制备了线状（长100～200nm）和棒状（长200-500nm,宽约20～40nm）的TiO2,其纯度高达99.3%。将模板剂改为LiOH,制备了纳米级片状（长宽约100～200nm）的过氧钛化合物,同时也成功地将Si除去。首次以过氧钛化合物为前驱体制备了锂离子电池负极材料Li₄Ti₅O₁₂。结果表明,以针球状和片状的过氧钛化合物为前驱体制备的Li₄Ti₅O₁₂均为单一的尖晶石结构,其电化学性能优良,二者在0.1C倍率下的首次充电比容量分别达到158.5和161.6 mAh·g-1，且均具有优异的倍率性能和循环性能。用溶度积原理计算了钛铁矿浸出液中各元素在磷酸盐体系下的初始沉淀pH值。结果表明,当Fe的总浓度为0.25 mol·L-1时,Fe、A1和Ti产生沉淀的初始pH值分别为0.318、0.728和0.784,而Mg、Mn和Ca形成沉淀的初始pH值均在3.4以上。在pH=2.0和P/Fe=1.1的条件下,首次从钛铁矿浸出液制备了FePO₄-2H₂O。结果表明仅有少量的Ti和Al进入沉淀,而其它元素均保留在溶液中。以上述FePO₄·2H₂O为前驱体制备了单一橄榄石结构的Ti-Al共掺杂LiFePO₄,其粒径为50～500 nm,该样品在1C、2C和5C倍率下的首次放电比容量分别为151.3、140.1和122.9 mAh·g-1,循环100次后的容量保持率为99.2%、99.8%和95.9%。首次研究了Ti-Al共掺杂对LiFePO₄结构及性能的影响,对Ti、Al及Ti-Al掺杂的机理作了较深入的研究。XRD及Rietveld精修结果表明,适量的Ti、Al及Ti-Al掺杂不会破坏LiFePO₄的晶体结构,当掺杂量较低时,Ti优先占据Li位,Al优先占据Fe位；当掺杂量较高时,Ti、Al均同时占据Li位和Fe位,且可能产生杂相。SEM表明少量的Ti、Al掺杂能有效抑制LiFePO₄颗粒团聚,而Al掺杂量过高反而促使LiFePO₄颗粒团聚；对于双掺杂样品,在总掺杂量一定（2mol%）时,LiFePO₄的形貌受Al/Ti比的影响不大。HRTEM表明Ti、Al和Ti-Al掺杂LiFePO₄的晶粒表面都均匀地包覆着一层几纳米厚的无定形碳膜,且晶粒之间有纳米碳网相连。各样品的晶格清晰,但晶格中均存在缺陷,这些缺陷是由于离子掺杂引起。通过研究电极动力学,发现Tu Al单掺杂时,LiFePO₄的Li+扩散系数和交换电流密度均随着掺杂量的升高而先增大后减小；但对于双掺杂样品,当总掺杂量一定而Ti/Al比变化时,其动力学参数并无明显差异。电化学测试结果表明,适量的Ti、Al及Ti-Al掺杂均能极大地改善LiFePO₄的电化学性能。对于双掺杂样品,在总掺杂量一定（2mol%）时,LiFePO₄的电化学性能受Al/Ti比的影响较小。首次以钛白副产物硫酸亚铁为原料,用选择性沉淀的方法制备了含少量Tu Al和Ca的FePO₄-2H₂O,并以它为前驱体制备了多元金属（Ti、Al、Ca）掺杂的LiFePO₄。XRD及Rietveld精修结果表明LiFePO₄为单一的橄榄石相,多元金属掺杂导致其晶格中产生Li空位。该样品在0.1C、1C和5C倍率下的放电比容量分别为161、145和112 rnAh·g-1,其循环性能优异。本方法为硫酸法钛白企业产生的大量硫酸亚铁废渣提供了一条新的处理途径。更多还原

【Abstract】 With the growing shortage of global energy and resources, the development of new energy and comprehensive utilization of mineral resources have become the focus of worldwide attention. In this paper, we propose a new idea to synthesize lithium-ion battery cathode material LiFePO₄ and anode material Li₄Ti₅O₁₂ from natural ilmenite （or waste）. Meanwhile, the physical and chemical processes and theories of the ilmenite metallurgy and materials preparation are studied in detail.The elements of ilmenite are selectively leached by mechanical activation and hydrochloric acid leaching at atmospheric pressure. The results show that mechanical activation can refine the grain size and increase the surface roughness of ilmenite particles, which result in the increase of the specific surface area. The mechanical activation can also disrupt the integrity of ilmenite crystal grains, and induce the formation of a large number of lattice defects, which lead to the lattice expansion. All the above actions could strengthen the leaching of ilmenite. Under the optimal conditions, the leaching ratio of Ti is only 1.07%, and Si is almost not leached, while the leaching ratios of Fe, Mg, Al, Mn and Ca are all more than 95.5%. As a result, Ti and Si are still in the slag, and the other elements are enriched in the lixivium. In addition, the synthetic rutile with the grade of over 90 wt.% is obtained by calcinating the above titanium-slag directly.For the first time, titanium is leached from the titanium-slag by using H₂O2 as coordination agent. Under the optimal conditions, the leaching ratio of Ti reaches 98.9%. A peroxo-titania compound is prepared by heating the coordination lixivium, but the compound contains a small amount of Si and its particle size is as large as 2～5μm. However, by adding the template agent NaOH before heating, the particle agglomeration is prevented and a nano-sized needlelike-spherical peroxo-titania compound is obtained, which does not contain Si. Subsequently, the linear （100～200 nm long） and rod-shaped （200～500 nm long,20～40 nm wide） TiO2 are obtained by calcinating the compound at 400～800℃, and the purity of TiO2 reaches 99.3%. Furthermore, when the template agent NaOH is substitued by LiOH, a nano-sized platelike peroxo-titania compound is obtained, and the Si is also removed. For the first time, peroxo-titanic compound is used as the precursor of Li₄Ti₅O₁₂ anode material. The results reveal that the Li₄Ti₅O₁₂ samples prepared from the needlelike-spherical and platelike peroxo-titania compounds exhibit excellent performance with the initial charge capacities of 158.5 and 161.6 mAh·g-1 at 0.1 C rate, and excellent rate performance and cycling performance.The initial precipitation pH values of the elements in ilmenite lixivium are separately calculated according to the solubility product principle. It is found that the initial precipitation pH values of Fe, Al and Ti are 0.318,0.728 and 0.784, while those of Mg, Mn and Ca are all greater than 3.4. It is the first time that FePO₄·2H₂O is prepared from the ilmenite lixivium. The results indicate that only small amounts of Al and Ti precipitate into FePO₄·2H₂O particles under the conditions of pH=2.0 and P/Fe=1.1, while the other elements, Mg, Mn and Ca still remain in the solution. Then, Ti-Al doped LiFePO₄ is prepared from the FePO₄·2H₂O precursor. The LiFePO₄ sample shows a well crystallized, single olivine-type phase, and its particle size is 50～500 nm. Electrochemical test results show that the sample exhibits the first discharge capacity of 151.3,140.1 and 122.9 mAh·g-1 at 1 C,2 C and 5 C rate, respectively, and a capacity retention of 99.2%,99.8%and 95.9% after 100 cycles.For the first time, the influences of Ti-Al co-doping on the structure and properties of LiFePO₄ are investigated, and the mechanism of Ti, Al and Ti-Al doping are specifically studied. XRD and Rietveld-refine results indicate that appropriate amounts of Ti, Al and Ti-Al doping do not obviously change the structure of LiFePO₄. When the doping level is low, Ti atoms tend to occupy Li sites and Al atoms prefer to occupy Fe sites, but at higher doping levels, Ti and Al atoms will occupy both Li and Fe sites, and impurity phases might be appear. SEM shows that small amounts of Ti or Al doping could limit the agglomeration of LiFePO₄ particles, but the excessive increase in the doping amount of Al will promote the particles aggregation. The Al/Ti ratio has little influence on the morphology of Ti-Al doped LiFePO₄ when the total doping content is constant （2 mol%）. HRTEM shows that all the LiFePO₄ samples are wrapped with amorphous nano-carbon films, and the particles are connected with nano-carbon nets. All the LiFePO₄ crystal lattices are clear but contain lattice defects which are caused by the cation doping. For the Al, Ti single doped LiFePO₄, electrode kinetics tests show that the lithium-ion diffusion coefficient and exchange current density first increase as the doping quantity rises, and then decrease. However, the kinetic parameters of Ti-Al doped LiFePO₄ samples vary little as the Al/Ti ratio changes when the total doping content is constant. Electrochemical tests indicate that appropriate amounts of Ti, Al and Ti-Al doping can significantly improve the electrochemical performance of LiFePO₄. For the Ti-Al dual doped samples, the electrochemical properties show little change with the variation of Al/Ti ratio （2 mol% total doping content）.For the first time, the FePO₄·2H₂O which contains small amounts of Ti, Al and Ca is prepared from the byproduct of titanium dioxide （FeSO₄·7H₂O waste slag）. Then the multi-metal doped LiFePO₄ is prepared with the as-obtained FePO₄-2H₂O as raw material. XRD and Rietveld-refine results indicate that the LiFePO₄ sample is well crystallized, single olivine-type phase, and multi-metal doping results in the formation of Li vacancies in crystal lattices. The sample exhibits a first discharge capacity of 161,145 and 112 mAh·g-1 at 0.1 C,1 C and 5 C rate, respectively, and shows excellent cycling performance. This method provides a new approach for hydrate-sulfuric titanium dioxide enterprises, which can deal with the large amount of FeSO₄-7H₂O residue.更多还原