【作者】 谢健；

【导师】 赵新兵；

【作者基本信息】 浙江大学 ， 材料学， 2005， 博士

【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。本文旨在开发高容量的新型锑基金属间负极材料,并采用纳米技术和复合技术来改善它们的循环稳定性。 以COCl₂·6H₂O和SbCl₃为原料,以NaBH₄为还原剂,采用两步溶剂热法合成了单相的skutterudite结构的CoSb₃金属间化合物,即,先在190℃下反应24小时,再在240℃下反应48小时。XRD结果表明,在CoSb₃的形成过程中,在190℃下形成的CoSb₂起到了中间体的作用。SEM和TEM结果表明,用溶剂热法制备的CoSb₃的颗粒尺寸为20～40 nm。以相同的原料和还原剂用溶剂热法分别在190℃和220℃合成了单相的CoSb₂和CoSb金属间化合物,这两种化合物的颗粒尺寸均处于纳米级。为了避免使用昂贵的钴,采用Fe-Sb和Ni-Sb化合物来代替对应的Co-Sb化合物。以FeCl-3·6H₂O、NiCl₂·6H₂O和SbCl₃为原料,以NaBH₄为还原剂,采用溶剂热法合成了纳米CoSb₃的对应体纳米Fe₀.5Ni₀.5Sb₃以及纳米CoSb₂的对应体纳米FeSb₂和纳米NiSb₂。 纳米CoSb₃的首次嵌锂和脱锂容量分别为778 mAhg^-1和521 mAh g^-1,经过20个充放电循环后,可逆容量仍保持在391 mAhg^-1。相比之下,用悬浮熔炼/球磨工艺制备的微米CoSb-3经过相同的循环次数后,可逆容量降至107 mA h g^-1。纳米CoSb₂和纳米CoSb的首次可逆容量分别为582 mA h g^-1和362 mA h g^-1,与微米CoSb₂和微米CoSb相比,纳米CoSb₂和纳米CoSb的循环稳定性显著提高。纳米Fe_0.5Ni（0.5）Sb₃显示出与纳米CoSb₃相类似的吸放锂机理,它的首次可逆容量达到559 mAh g^-1,经过20个循环后,可逆容量仍保持在300 mA h g^-1。同样,纳米FeSb₂和纳米NiSb₂显示出与纳米CoSb₂相类似的吸放锂机理。纳米FeSb₂的首次可逆容量达到523 mA h g^-1,经过20个循环,可逆容量仍保持在349 mAh g^-1,而微米FeSb₂经过相同的循环次数后,容量则降至101mAhg^-1。纳米NiSb₂的首次可逆容量为514 mA hg^-1,与微米NiSb₂相比,纳米NiSb₂的循环稳定性有所提高。研究表明,纳米材料由于颗粒尺寸较小且分布较均匀,在充放电过程中绝对体积变化较小,缓解了颗粒的粉化和剥落,因此容量衰减较为缓慢。而微米材料由于在充放电过程中绝对体积变化较大,导致颗粒（尤其是球磨产生的尖角和棱角）的粉化和剥落较为严重,导致了容量的快速衰减。 采用高能球磨工艺制备了CoSb₃/MCMB复合材料。该材料的首次可逆容量达到721mAh g^-1,远高于它的理论容量550 mAh g^-1,并且它的循环稳定性也优于纯CoSb₃。其电化学性能改善的原因在于CoSb₃和MCMB之间存在协同效应。分别采用原位溶剂热和机械研磨法制备了CoSb₃/MWNTs纳米复合材料。研究表明,原位复合材料的循环稳定性远优于机械复合材料,该材料综合了MWNTs和纳米CoSb₃各自的性能优势,即浙江大学博士学位论文某些纳米锑基金属间化合物的合成及电化学吸放理行为MWNTs优异的循环稳定性和纳米Cosb3的高容量特性。原因在于在原位复合材料中,Cosb3是以MWNTs为核心生长的,因此MWNTs对Cosb3颗粒的分散比较均匀,可以有效地吸收Cosb3在吸放铿过程中由于体积变化产生的机械应力,从而一定程度上抑制了Cosb3颗粒的粉化和剥落。 锑基金属间化合物的容量损失主要发生在最初的几个循环内特别是首次嵌铿过程。这是因为在最初的几个循环中（特别是首次嵌铿过程）活性材料的绝对体积变化最大,活性材料的粉化和剥落最严重。电流密度对纳米材料循环稳定性的影响较小,而对微米材料的影响主要发生在最初的几个循环内。在金属间化合物中,惰性基体的含量越高、弹性模量越大、对活性成分的分散越均匀,金属间电极的循环稳定性越好。铿对电极和电解质溶液对锑基金属间电极循环稳定性的影响较小。关键词:铿离子电池、负极材料、纳米材料、锑基金属间化合物、溶剂热、悬浮熔炼、 电化学性能更多还原

【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 Sb-based intermetallic anode materials with high capacity are developed and their cycling stability is improved by applying nano-technology and composite-technology.Single phase skutterudite-structured CoSb3 intermetallic compound is prepared by two-step solvothermal method using CoCl2·6H2O, SbCl3 as the starting materials and NaBH4 as the reducing agent, namely, the solvothermal reactions are carried out at 190℃ for 24 h and are continued at 240℃ for another 48 h. CoSb2 formed at 190°C acts as the intermediate during the formation of CoSb3 as proved by XRD results. SEM and TEM observations show that the particle size of CoSb3 prepared by solvothermal method is 20 ~ 40 nm. Single phase CoSb2 and CoSb intermetallic compounds are prepared by solvothermal method at 190℃ and 220°C, respectively, using the same starting materials and reducing agent as that used in the synthesis of CoSb3. The particle size of both the compounds is in nanoscale. To avoid the use of expensive cobalt, Co-Sb compounds are replaced by their corresponding Fe-Sb and Ni-Sb compounds. Nano-Fe0.5Ni0.5Sb3, the counterpart of nano-CoSb3, and nano-FeSb2 and nano-NiSb2, the counterparts of nano-CoSb2, are prepared by solvothermal method using FeCl3·6H2O, NiCl2·6H2O, SbCl3 as the starting materials and NaBH4 as the reducing agent.The first Li-absorption/extraction capacities of nano-CoSb3 are 778 mA h g-1 and 521 mA h g-1, respectively. A reversible capacity of 391 mA h g-1 is still maintained after 20 charge and discharge cycles for this material. In contrast, the reversible capacity of micro-CoSb3, prepared by levitation-melting/ball-milling route, drops to 107 mA h g-1 after same cycle number. The first reversible capacities of nano-CoSb2 and nano-CoSb are 582 and 362 mA h g-1, respectively. Compared with the micro-CoSb2 and micro-CoSb, nano-CoSb2 and nano-CoSb exhibit significantly improved cycling stability. Nano-Feo.5Ni0.5Sb3 exhibits similar Li-absorption/extraction mechanism to nano-CoSb3. The first reversible capacity of this material reaches 559 mAh g-1 and a reversible capacity of 300 mA h g-1 is still maintained after 20 cycles. Similarly, nano-FeSb2 and nano-NiSb2 show similar Li-absorption/extraction mechanism to nano-CoSb2. The first reversible capacity of nano-FeSb2 reaches 523 mAh g-1 and a reversible capacity of 349 mA h g-1 is still maintained after 20 cycles, while the reversible capacity of micro-FeSb2 drops to 101 mAh g-1 after same cycle number. The first reversible capacity of nano-NiSb2 is 514 mA h g-1, and its cycling stability is somewhat improved compared to micro-NiSb2. It is found that small absolute volume changes occur for nanomaterials due to their small particle size and uniform particle distribution, which mitigate the pulverization and exfoliation of the particles, leading to slow capacity fade. In contrast, severe pulverization and exfoliation of the particles (especially for the sharp-angles and edges generated by ball-milling) occur for micromaterials due to the large absolute volume changes, causing rapid capacity fade.CoSb3/MCMB composite is prepared by high-energy ball milling. The first reversible capacity of this material reaches 721 mA h g-1, which is higher than its theoretical capacity, 550 mA h g-1. In addition, the composite shows improved cycling behavior compared to bare CoSb3. The improvement of its electrochemical performance can be attributed to the synergetic effect between CoSb3 and MCMB. CoSb3/MWNTs nanocomposites are prepared by in-situ solvothermal and mechanical milling methods, respectively. It is found that the composite prepared by in-situ solvothermal method shows rather better cycling stability compared to the one prepared by mechanical milling. This material combines the respective virtue of MWNTs and nano-CoSb3, namely, good cycling stability of MWNTs and l更多还原