新型晶态氧化锡纳米材料的制备、表征及在锂离子电池中的应用/Synthesis and Characterization Novel Crystalline Ti

2018-10-01 13:05:41

crystal TiN oxide monoxide 氧化亚



氧化锡纳米材料由于其独特的结构特性,在气敏材料、高效锂离子二次电池负极材料、太阳能储存材料和选择性开环氧化催化剂中具有非常广泛的应用前景,吸引着众多研究者投身到这个领域中来。随着纳米材料的发展,目前的研究方向主要集中在新型结构的合成、功能化以及应用探索方面。在本论文中,我们开展了两部分的工作。一方面,可控合成了具有特殊几何形貌和晶体结构的新型晶态锡基氧化物纳米材料;另一方面,对所合成的材料性能进行了考察,研究了材料在锂离子电池方面的应用。
我们以CTAB、柠檬酸三钠等不同的添加剂为结构导向剂发展了水相体系超声辅助化学沉淀法,制备了规整有序的晶态氧化亚锡纳米材料;实验表明不同的添加剂以不同的方式降低反应化学势,从而达到控制晶体生长历程并最终诱导其结构的作用。其中CTAB显示了优良的结构诱导作用,能够有效地抑制氧化亚锡晶体沿[001]方向生长,从而得到具有超大{001}晶面的两维纳米单晶薄片结构;并且随着CTAB加入量的增加{001}晶面相应增大,晶胞也随之膨胀。
为了提高氧化亚锡晶体的结构稳定性,尝试了各种金属掺杂。大量实验发现,使用超声辅助化学沉淀法可以非常简单有效地将不同种类、浓度的杂原子引入氧化亚锡晶体晶格中。结果表明,沉淀过程中氧化亚锡晶体的首先出现是决定产物晶体保持两维纳米薄片的首要条件;并且随着杂原子的进入,氧化亚锡晶体结构缺陷增加,引起了结构重排,在晶格中形成了两倍于正常周期的超晶格结构;其1/2衍射斑点相应出现,并随孪生缺陷增加而裂分。
采用氧化亚锡和掺杂型氧化亚锡纳米薄片为原料,使用通空气焙烧的方法成功地制备了晶态二氧化锡纳米薄片材料。产物具有两维薄片形貌及超大{101}晶面结构,但由于焙烧过程中液态单质锡出现,造成了表面粗糙。对于掺杂型氧化亚锡,在焙烧过程中杂原子仍然保留在二氧化锡晶格中,没有相应的氧化物出现。并且,为了降低体系能量,掺杂型二氧化锡更倾向于形成长周期结构。如镍掺杂后形成有序长周期结构,而铜掺杂则形成密堆长周期结构。
作为锂离子电池负极材料,发现纳米薄片结构氧化亚锡的两维结构及晶格膨胀有利于锂离子的扩散和嵌入,使得氧化亚锡负极材料具有了接近理论值的超大首次可逆充放电容量。并且随着杂原子的进入,可以有效地提高其循环性能。相比于一般的锡基氧化物纳米材料,两维薄片结构的晶态锡基氧化物作为锂离子电池负极显示出了更高的可逆容量和良好的循环性能。



Synthesis of nanomaterials with controlled morphology, size, chemical composition, crystal structure, and in large quantity has received considerable attention because of their putative applications in nanotechnology. Being a promising semiconducting material, tin-based oxide materials have attracted much attention due to its important applications in high energy density rechargeable lithium batteries, storage of solar energy, gas sensors and organic synthesis. Great endeavors have been devoted to the synthesis of tin oxide materials with different dimensions and morphologies. And the research in tin-based oxide materials now is mainly focused on the syntheses of novel structures and functionalization. This thesis concentrated on the controllable synthesis of tin-based oxide materials with special morphology, and the application of tin monoxide materials as anode material for lithium secondary batteries.
The thesis developed a facile solution-based chemical route to tin monoxide materials with controllable morphology by using different salts, organic compounds and surfactants as structure-directing agents. Different additive reduces the chemical potential in the formation of tin monoxide via different route, and consequently influences the morphology and crystal structure of the products. The results show that CTAB has superior structure-directing function, which can effectively restrain the crystal growth along the [001] direction. As a result, single crystalline tin monoxide with nanosheet-like morphology is obtained. Moreover, it is found that the crystal lattices expand proportionally with the addition of CTAB. However, most inorganic additives such as tri-sodium citrate direct the growth via a different mechanism. They prefer to coordinate with the intermediate product, stannous hydroxide species, to reduce the growth rate. Thus the plane with lowest surface energy appears easily, leading to tin monoxide covered by {110} crystal planes.
To improve the physical and chemical performances of the tin monoxide materials, metal heteroatoms are successfully doped into the crystal lattices with the facile solution-based chemical route. Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, La, Ce, Al, Sn (IV) and Pb doped tin monoxide crystals are all successfully fabricated, which further confirms the generality of the synthesis route. Structural analysis shows that the crystal lattice parameters change regularly with the electron configuration, ionic radius and coordination number of the doped elements. The crystal defect increases remarkably with the doped heteroatoms, and the defects arrange orderly and exhibit a long periodic structure. The (1/2){110} reflections which is not available for tin monoxide thus appear.
Based on the tin monoxide nanosheets, tin oxide is produced by thermal calcination. The resulted tin oxide also has 2D nanosheet morphology and is dominated by the {101} crystal plane. However, the liquid tin metal appears during the formation of tin oxide, which roughens the surface of the nanosheets. Tin oxide doped with Cu and Ni can also be synthesized in this method. Structural analysis reveals that the crystal defects increase and prefer to arrange in long periodic structure. SAED patterns show the Ni-doped tin oxide nanosheets have the (1/2){101} reflections. It is also found that the crystal surface becomes smooth with the doping of the heteroatoms.
The application of the tin monoxide nanosheets in lithium ion battery anode material is investigated. The tin monoxide nanosheets fabricated by using CTAB as the structure-directing agent display a high reversible capacity, and the capacity can be improved to 830 mA h/g by increasing the CTAB addition, which is much higher than that of the fully lithiated graphite (372 mA h/g). It is suggested that the loosely packed {001} surfaces and expanded lattice of the as-prepared tin monoxide nanosheets render a high reversible capacity. However, the crystal structure is destroyed completely by the lithium-ion insertion and extraction, therefore deteriorate the capacity. It is found that the heteroatom doping may be promising in improve the cycling performance. When using tin monoxide doped with Cu, 50.5% reversible capacity is left after ten cycles. It is proposed that the doped Cu can prevent the aggregation of the tin species and increase the conductivity, thus offering advantages in the cycling performance.