【作者】 杨树斌；

【导师】 宋怀河；

【作者基本信息】 北京化工大学 ， 材料学， 2008， 博士

【摘要】 锂离子电池由于具有高的能量密度、高的输出电位和无污染等优点,在广泛用于手机、相机、笔记本电脑等小型电器的同时,在电动车等大型电动设备上也有着广阔的应用前景。要把锂离子电池真正用于大型电动设备上,良好的高倍率充放电性能和高的可逆容量是其必须具备的关键性能。但目前锂离子电池这两方面的性能均有待于进一步提高,这已成为锂离子电池在大型电动设备上应用的“瓶颈”。负极材料是影响锂离子电池性能的关键之一,针对目前锂离子电池炭负极材料在高倍率充放电时具有较大容量衰减和较低可逆容量的问题,本论文首先设计制备具有不同孔隙率和长径比的炭材料,采用SEM、TEM、HREM、XRD、BET和一系列电化学手段系统考察它们的形貌、结构和作为锂离子电池负极材料时的电化学性能,包括可逆容量、库仑效率、循环性能、储锂机理及动力学性能等;并在此基础上,分析炭材料的形貌、结构与其电化学性能的相关性,得出孔隙率和长径比对炭材料高倍率性能的影响原因。这将为具有良好高倍率性能的锂离子电池炭负极材料的设计奠定基础。然后以既具有较高导电性又具有适当孔隙率的炭材料作为锡和锡氧化物的缓冲材料制备新型锡和锡氧化物/炭复合材料,利用FE-SEM、XRD、EDX、XPS等技术对其形貌和微观结构进行分析,采用恒电流充放电、循环伏安（CV）和交流阻抗（ElS）等技术对其电化学性能进行测试和分析,考察制备条件、形貌结构与电化学性能的关系,优化条件制备出具有较高可逆容量、较好循环性能的新型复合负极材料。这对拓宽新型炭材料的研究领域和促进高容量锂离子电池负极材料的发展有重要的理论和现实意义。研究结果表明,孔隙率对膨胀中间相沥青炭微球（Expandedmesocarbon microbeads,EMCMB）高倍率性能的影响是通过改变电解液在电极材料中的浸润量,从而改变反应固/液界面状态,进而影响锂离子在固/液界面的电化学活性实现的。而长径比对碳纳米管（Carbonnanotubes,CNTs）高倍率性能的影响则主要是通过改变锂离子在材料中的扩散路径和速率实现的。在优化的条件下,EMCMB和长径比小的CNTs在较大电流密度下(0.8 mA·cm^-2)充放电时,可逆容量分别可达到260和170 mAh·g^-1,且具有良好的循环性能。以既具有较高导电性又具有适当孔隙率的炭材料（EMCMB、膨胀石墨（Expanded graphite,EG）、笼状碳纳米管球）作为锡和锡氧化物的缓冲材料来制备新型锡和锡氧化物/炭复合材料时,缓冲材料的种类、制备方法、制备条件和锡含量对复合材料的形貌、结构及电化学性能均产生很大影响。其中在优化的条件下,锡和锡氧化物/EMCMB复合材料具有401 mAh·g^-1的可逆容量和30次循环后94%的容量保持能力,在较大电流密度下充放电时仍具有较高的可逆容量和循环性能;氧化亚锡/EG复合材料也具有350 mAh·g^-1,在30次循环过程中无容量衰减的良好电化学性能;原位法制备出的二氧化锡/笼状碳纳米管球复合材料的可逆容量高达669 mAn·g^-1,而浸渍炭化法制备的二氧化锡/笼状碳纳米管球复合材料在30次循环后容量保持率为98%。以上复合材料的电化学结果均表明EMCMB、EG和笼状CNTs球是锡基负极的良好缓冲材料,因为它们既能保证复合材料的导电性,又能对其内部的锡和锡氧化物在充放电过程中起到有效的缓冲作用。更多还原

【Abstract】 Recently,Lithium-ion batteries have been widely used in portable electronic devices such as cellular phones,camcorders,notebook computers due to their high energy density,high voltage and non-pollution. Meanwhile,they have great potential for using in electric vehicles. However,at present high rate ability and high reversible capacity of Lithium ion batteries are urgently needed to improve because they are the large obstacles for the application of Lithium ion batteries in electric vehicles.For the problems of larger capacity loss and lower reversible capacity of carbon materials using in lithium ion batteries during charge and discharge at high rate,this research firstly focused on the design and preparation of the carbon materials with different porosity and length/diameter aspect ratio,involving expended mesocarbon microbeads （EMCMB）and carbon nanotubes（CNTs）.The morphology,structure and electrochemical properties regarding reversible capacity,coulombic efficiency,cycle performance,lithium storage mechanism and kinetics of the materials as negative electrode materials for lithium-ion batteries were systematically investigated by SEM,TEM,HREM,XRD,BET and a variety of electrochemical test techniques.On the basis of above investigation,the relationship between the morphology,structure and electrochemical properties at high rate was analyzed,and the effecting reasons of porosity and length/diameter ratio on the high-rate performance of carbon materials were elucidated,which lays a foundation for the design of negative materials with favorable high-rate performance for lithium ion batteries in the future.And then the novel tin and tin oxides/carbon composites were prepared using the carbon materials with both high electronic conductivity and high porosity as the matrix of tin and tin oxides.The morphological and structural characteristics of the tin and tin oxides/carbon composites were studied by FE-SEM,XRD,EDX,XPS measurements and the electrochemical properties of the composites were investigated via galvanostatic charge and discharge,cyclic voltammetry and electrochemical impedance spectroscopy tests.The relationship between the synthesis condition,morphology,structure of composites and their electrochemical properties was analyzed.Finally,the novel composites with higher reversible capacity and better cycle performance were successfully prepared through optimizing the synthesis condition.It had great academic and practical significances for the broadening of new carbon materials and the promotion of the development of negative materials with high capacity for lithium ion batteries.The results showed that the effect of porosity on the high rate performance of EMCMB was carried out through the variation of soakage amount of electrolyte in electrode materials,which changed the amount of the solid/liquid interface and significantly influenced the electrochemical activity of lithium ion at electrode materials/electrolyte interface;while the effect of length/diameter aspect ratio on the high rate performance of CNTs was achieved by changing the diffusion path and velocity of lithium ions in the materials.At optimized condition,EMCMB and CNTs with lower length/diameter ratio could deliver the reversible capacities of 260 and 170 mAh·g^-1,respectively,and both showed excellent cycle performance at the higher current density of 0.8 mA·cm^-2.When the novel tin and tin oxides/carbon composites were prepared using the carbon materials（EMCMB,EG and CNTs spheres）with both high electronic conductivity and high porosity as the matrix of tin and tin oxides,the type of matrix,synthesis method,synthesis condition and the content of tin in composites had significant influence on the morphology, structure and electrochemical properties of composites.At optimized condition,the tin and tin oxides/EMCMB composite had the reversible capacity of 401 mAh·g^-1and capacity retention of 94%over 30 cycles,and also showed higher reversible capacity and stable cycle performance at higher current density.Similarly,the tin oxide/EG composite delivered the reversible capacity of 350 mAh·g^-1and almost didn’t show capacity loss over the same cycles.The tin dioxide/CNTs sphere composite prepared by in-situ method showed the reversible capacity as high as 669 mAh·g^-1. Whereas the tin dioxide/CNTs sphere composite prepared by impregnation and carbonization treatment had the capacity retention of 98%over 30 cycles.All above results indicated that EMCMB,EG and CNTs spheres are the suitable matrix of tin and tin oxides because they not only could ensure the high electronic conductivity of composites,but also could efficiently buffer the specific volume change of tin during charge and discharge process.更多还原