【作者】 秦海英；

【导师】 赵新兵；

【作者基本信息】 浙江大学 ， 材料学， 2006， 硕士

【摘要】 开发高容量、高循环稳定性的负极材料以取代传统的碳材料成为近年来锂离子电池研究的热点之一。本文旨在探索高容量的新型金属间化合物负极材料,并采用纳米技术和复合技术来改善它们的循环稳定性。 以SnCl₂·2H₂O和NiCl₂·6H₂O为原料,以NaBH₄为还原剂,采用溶剂热法合成纳米Ni₃Sn₂。XRD结果表明,在Ni₃Sn₂的形成过程中,在150（?）下形成的产物中所含有的单质Sn起到了中间体的作用,在240（?）反应24h合成了单相的Ni₃Sn₂。SEM结果表明,合成的单相Ni₃Sn₂晶粒大小为30-50nm。纳米Ni₃Sn₂的首次充放电容量为386/136 mAhg^-1,且20次循环后,容量衰减较快。采用非原位XRD测试探讨了其低容量及容量快速衰减的原因。研究结果表明,在嵌锂过程中,单相Ni₃Sn₂会分解为单质Ni和Sn,其中Sn可以与锂离子反应形成Li-Sn合金,但是单质Ni会包覆在颗粒的表面形成一层钝化膜,阻止了Sn与锂离子进一步反应。在脱锂过程中,单质Ni和和脱锂后的单质Sn化合重新生成原始相Ni₃Sn₂。探讨了退火处理对于纳米Ni₃Sn₂的电化学性能的影响,研究表明,退火后纳米Ni₃Sn₂的晶化程度更高,并且表现出更好的循环稳定性。 以FeCl₃-6H₂O和SbCl₃为原料,以NaBH₄为还原剂,采用溶剂热法合成了FeSb₂纳米棒。XRD结果表明,在250（?）反应72h合成了单相的FeSb₂。TEM和HRTEM结果表明,合成的FeSb₂是直径为20-40nm,长度为0.2-1μm的纳米棒。FeSb₂纳米棒的首次充放电容量为543/854mAhg^-1,经过10次循环后,可逆容量保持在353mAhg^-1,是首次可逆容量的65%。虽然首次库仑效率仅64%,但经过10次循环后基本稳定在90%,表现出较高的容量和良好的循环稳定性。非原位TEM结果表示,循环后的FeSb₂纳米棒大部分逐渐粉化断裂。 以BiCl₃和Te为原料,以NaBH₄为还原剂,采用溶剂热法合成Bi₂Te₃纳米颗粒以及Bi₂Te₃纳米颗粒与多壁纳米碳管的复合材料。XRD结果表明,在150（?）反应24h合成了单相的Bi₂Te₃以及Bi₂Te₃/MWNTs复合材料。SEM结果表明合成的Bi₂Te₃为细小晶粒堆砌的片状结构。此外,Bi₂Te₃/MWNTs复合材料中Bi₂Te₃与MWNTs形成微观缠绕结构。Bi₂Te₃纳米颗粒的容量较低,通过改变充电的截止电压来可以抑制相应的电化学反应,从而有效提高电极的循环稳定性。Bi₂Te₃/MWNTs复合材料与Bi₂Te₃纳米颗粒相比表现出更好的循环稳定性。 以SNCl₂·2H₂P、SbCl₃和BiCl₃为原料,以NaBH₄为还原剂,采用低温湿化学法分别合成了单质Sn、Sb和Bi以及复合材料Sn/MWNTs、Sb/MWNTs和Bi/MWNTs。XRD结果表明,在65（?）反应12h合成了各种目标产物。SEM结果表明,合成的复合材料中更多还原

【Abstract】 One of the hotspots in the research of lithium-ion batteries is the development for the high-capacity and high-cycling-behavior anode materials to replace the conventional carbon-based materials. In the present work, some novel intermetallic anode materials with high capacity are explored and their cycling stability is improved by using nano-technology and composite-technology.In the present work, single-phase nano-Ni₃Sn₂ intermetallic compound has been prepared by a solvothermal method using SnCl₂·2H2_O, NiCl₂-6H₂O as the starting materials and NaBH₄ as the reducing agent. The solvothermal reactions were carried out at 150℃ for 24 h with Sn as the intermediate product during the formation of Ni₃Sn₂ as detected by XRD characterization. Single-phase nano-Ni₃Sn₂ can be successfully prepared by the solvothermal method at 240℃ for 24 h. SEM observation shows that the particle size of Ni₃Sn₂ prepared by the solvothermal method is 30-50 nm. The first lithiated and delithiated capacities for nano-Ni₃Sn₂ are 386 and 136 mA h g^-1 respectively, and rapid capacity fade occurs during the following cycles. The reasons for its low reversible capacity and poor cyclic performance have been explored by ex-situ XRD experiments. It was found that nano-Ni₃Sn₂ decomposes into Ni and Sn atoms during the lithiated process, then Sn atoms react with Li to formation Li_xSn. However, Ni atoms may form an impenetrable "skin" on the surface of particles or grains, and this skin may block the complete reactions of the intermetallic compound with Li. During the delithiated process, the Li_xSn decomposes into Li and Sn atoms, then Sn atoms react with Ni to form the original phase Ni₃Sn₂. The effect of annealing on the electrochemical performance of nano-Ni₃Sn₂ has been discussed. It was found that the nano-Ni₃Sn₂ after annealing shows improved crystallization and better cycling stability than the unannealed annealed one.Single-phase FeSb₂ nanorods have been prepared by the solvothermal method using FeCl3·6H₂O, SbCl₃ as the starting materials and NaBH₄ as the reducing agent. It can be successfully prepared by the solvothermal method at 250℃ for 72 h as detected by XRD characterization. TEM observation shows that the FeSb₂ nanorods are 20 40 nm in diameter and 0.2 ¹ μm in length. The first charge and discharge capacities for FeSb₂ nanorods are 543 and 854 mA h g^-1, respectively. A reversible capacity of 353 mA h g^-1 is still maintained after 10 cycles with a retention rate of 65%. Although the first coulomb efficiency of this materialis only 64%, it reaches 90% after 10 cylces. However, the ex-situ TEM results show that the FeSb2 nanorods may undergo pulverization and cracking during cycling.Single-phase nano-Bi2Te3 and Bi2Te3/MWNTs composite materials have been prepared by the solvothermal method using B1CI3, Te as the starting materials and NaBFLj as the reducing agent. It was found that nano-Bi2Te3 and Bi2Te3/MWNTs can be successfully synthesized by the solvothermal method at 150eC for 24 h. SEM observation shows that nano-Bi2Te3 particles are sheet-like composed of fine particles, and Bi2Te3 and MWNTs wrap together in Bi2Te3/MWNTs composite material. The capacity for nano-Bi2Te3 is relatively low, but the cycling stability can be improved by changing the range of the cut-off voltage to control correlative electrochemical reactions. The Bi2Te3/MWNTs nano-composite exhibits superior cycling stability than nano-Bi2Te3.Furthermore, a simple low temperature aqueous chemical route using SnCl2-2H2O, SbCb and BiCb as the starting materials and NaBRj as the reducing agent has synthesized Sn, Sb, Bi-based composite materials such as Sn/MWNTs, Sb/MWNTs and Bi/MWNTs. XRD results show that the products have been successfully synthesized at 65QC for 12 h. SEM observation shows that the metal and MWNTs wrap together in composite materials. The sharp difference between the Sb and Sb/MWNTs shows that composite-technology can increase the capacity obviously and improve cycling stability effectively. Ex-situ TEM experiments also show that the capacity fade for the intermetallic compounds occurs in the initial cycles especially in the first lithiated process. This is due to the fact that the largest volume changes occur in the initial cycles causing the severe pulverization and exfoliation of active material.更多还原