钛铌氧化物负极材料的制备及其电化学性能研究

发布时间：2018-01-27 14:23

本文关键词： Ti_2Nb_(10)O_(29)新型材料固相合成多孔TiNb_2O_7纳米球溶剂热合成功率密度大长寿命锂离子电池　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：钛铌氧化物具有较高的理论比容量;在锂离子的脱嵌过程中晶格参数和晶胞体积变化很小,可逆性较高;并且其充/放电电位在1.6V左右,循环过程中不易产生SEI膜和锂枝晶;相比同电位的Li4Ti5012表现出更高的比容量,是一种颇具应用前景的新型负极材料。然而,钛铌氧化物存在着离子和电子导电率较低的问题,限制了其电化学性能的提高。我们发展了 Ti2Nb10029新型负极材料;并对Ti2Nb10029进行了碳包覆的改性研究;设计了 TiNb207纳米颗粒构筑的多孔球结构,探讨了其电化学性能与结构的关联性。论文的主要内容概括如下:1.利用固相反应制备了 Ti_2Nb_(10)O_(29)新型负极材料。其钛铌比不同于常见的TiNb207,结构中钛含量减少导致共棱的切变结构减少,更有利于锂离子的扩散,同时锂离子嵌入的活性位点增多,容量增加。作为锂离子电池负极材料,Ti2Nb10O29电极表现出优异的电化学性能:首次库伦效率可达到94.2%(0.1 C);在10 C的电流密度下,经过800次循环以后,放电比容量还稳定在144 mAh/g,而且晶体结构依然保持稳定;另外在快充慢放的不对称倍率性能测试中,电流密度从2C增加到20C时比容量损失很少。另外,将Ti2Nb10029材料作为负极跟正级材料磷酸铁锂组装成全电池,其在1C的电流密度下循环1000次以后,比容量仍然稳定在100 mAh/g,表现出良好的循环稳定性。2.利用乙炔热解碳对已合成的Ti_2Nb_(10)O_(29)进行包覆修饰,制备出Ti2Nb10O29/碳复合材料。碳包覆能够改善材料的电子导电性,进而提高其电化学性能,因此Ti2Nb10029/碳复合材料的循环稳定性和倍率性能相较于未包覆的Ti2Nb10O29材料均有一定提高。Ti2Nb10029/碳复合材料的首次库伦效率达到96%,经过50次循环以后的可逆比容量稳定在245 mAh/g。3.发展了溶剂热反应,制备出由纳米颗粒构筑的TiNb207多孔球。结合微纳化和多孔结构的优势,不仅缩短了锂离子的传输距离,而且增加了电极材料与电解液的接触,进而提高了 TiNb2O7的电化学性能。这种独特的球形多孔纳米材料首次库伦效率达到94%;在5 C的电流密度下,经过10000次循环以后可逆比容量还能稳定在160 mAh/g,相当于每次循环仅有0.0033%的容量损失率,并且形貌结构保持完整;在50 C电流密度(19.8 A/g)下,可逆比容量稳定在167 mAh/g,与钛酸锂材料的理论比容量相差不多;另外,在快充慢放的不对称倍率性能测试中,当电流密度从1 C增加到50 C,可逆比容量仅从277 mAh/g降低到243 mAh/g。
[Abstract]:Titanium niobium oxide has high theoretical specific capacity. During the deintercalation of lithium ion, the lattice parameters and the volume of the unit cell change little, and the reversibility is high. The charge / discharge potential is about 1.6 V, and it is not easy to produce SEI film and lithium dendrite during the cycle. Compared with the same potential Li4Ti5012 has higher specific capacity and is a promising new negative electrode material. However the titanium niobium oxide has the problem of low ionic and electronic conductivity. The improvement of electrochemical performance is limited. We have developed new negative electrode materials for Ti2Nb10029. The modification of Ti2Nb10029 by carbon coating was studied. The structure of porous spheres constructed by TiNb207 nanoparticles was designed. The relationship between electrochemical properties and structure was discussed. The main contents of this paper are summarized as follows: 1. TiSP _ 2NbC _ (10) O _ (T _ (29)) was prepared by solid state reaction. The ratio of titanium to niobium is different from that of TiNb207. The decrease of titanium content in the structure leads to the decrease of the shear structure of the coaxial, which is more favorable to the diffusion of lithium ion. Meanwhile, the number of active sites embedded in the lithium ion increases and the capacity increases. It is used as the anode material for lithium ion battery. The Ti2Nb10O29 electrode shows excellent electrochemical performance: the first Coulomb efficiency can reach 94.2C0. 1 C ~ (-1); At the current density of 10 C, after 800 cycles, the specific discharge capacity is still stable at 144 mg / g, and the crystal structure remains stable. In addition, when the current density is increased from 2C to 20C, the loss of specific capacity is very small. The Ti2Nb10029 material was used as the negative electrode and the positive material, iron lithium phosphate, to form the full battery. The battery was recirculated 1 000 times at the current density of 1 C. The specific capacity is still stable at 100mAh/ g, showing good cyclic stability. 2. Using acetylene pyrolytic carbon to modify the synthesized Ti2NbS10 / OSP _ (29). Ti2Nb10O29 / carbon composites were prepared. Carbon coating can improve the electronic conductivity of the materials and then improve their electrochemical properties. Therefore, the cyclic stability and ratio properties of Ti2Nb10029 / carbon composites are better than those of uncoated Ti2Nb10O29 composites. Ti2Nb10029 / carbon composite is better than that of uncoated composites. The expected first-time Coulomb efficiency reached 96%. After 50 cycles, the reversible specific capacity was stable at 245 mg / g 路3. The solvothermal reaction was developed. TiNb207 porous spheres constructed from nano-particles were prepared. The advantages of micronanocrystalline and porous structure not only shorten the distance of lithium ion transport, but also increase the contact between electrode material and electrolyte. Furthermore, the electrochemical performance of TiNb2O7 was improved. The first Coulomb efficiency of this unique spherical porous nano-material was 94%. At the current density of 5 C, the reversible specific capacity can be stabilized at 160mAh-g after 10000 cycles, which is equivalent to the loss rate of only 0.0033% capacity per cycle. The morphology and structure remained intact. At 50 C current density of 19.8 A / g, the reversible specific capacity is stable at 167 mg / g, which is not much different from the theoretical specific capacity of lithium titanate material. In addition, when the current density is increased from 1 C to 50 C, the reversible specific capacity is only reduced from 277 mAh/g to 243mAh/ g.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912

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