【作者】 石璐；

【导师】 胡社军；

【作者基本信息】 广东工业大学 ， 微电子学与固体电子学， 2008， 硕士

【摘要】 当今世界上主要使用的能源是以煤炭、石油、天然气为主的化石能源,但化石能源存在的污染大、破坏生态环境等问题,使得开发绿色无污染的新型高能化学电源成为研究热点。由于目前锂离子电池的商用负极材料已不能满足实际需求,对高比容量、高稳定性、高安全性、长寿命、低成本的新型锂离子电池负极材料的开发已显得迫不容缓。本文在综合评述了锂离子电池及其负极材料研究进展的基础上,选取锡（Sn）基负极材料作为研究对象,创新性的采用真空溅射技术在铜箔基片上制备了不同工艺参数的Sn、Sn/Ti和Ti/Sn复合膜。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、电感耦合等离子体发射光谱（ICP）等设备和技术,以及循环伏安（CV）、恒电流充放电等电化学测试方法,研究了制备方法、工艺参数对Sn、Sn/Ti和Ti/Sn复合膜的形貌、成份、相结构及电化学性能等的影响,为利用真空溅射技术开发新型的锡基薄膜负极材料提供了理论依据和关键制备技术。研究了溅射功率对直流溅射Sn薄膜沉积速率、微结构及电化学性能的影响。结果表明,功率与沉积速率存在近似线性关系。随着溅射功率的增加,薄膜的晶化加剧,晶粒粗化;当功率达24W时,锡铜相互扩散生成CuSn合金相。16W功率下制备的Sn薄膜电极具有最优的电化学性能:首次循环效率达82.2%,30次循环后比容量维持在300mAh/g。研究了溅射时间对Sn薄膜微结构的影响,随着时间的增加,Sn薄膜晶化程度逐渐加剧,颗粒不断增大。当沉积时间达20分钟时,Sn颗粒的棱角收缩,使表面颗粒存在球形化趋势,从而使Sn薄膜电极具有最优的循环性能。研究了复合金属钛对Sn薄膜表面形貌和电化学性能的影响。制备了Sn/Ti和Ti/Sn复合膜,研究了复合薄膜的表面形貌、成份及锂离子嵌脱行为,分析了Sn/Ti和Ti/Sn复合膜电极的容量衰减机理以及加入Ti后的作用机制。研究发现,金属Sn和Ti的溅射顺序对性能有极大影响,先溅射Sn的Sn/Ti复合膜具有较佳的电化学性能。从整体上说,金属Ti的引入大大地改善了Sn/Ti复合膜的锂离子嵌脱行为。Sn/Ti复合膜电极的首次放电容量为896.1mAh/g,第2次循环时放电容量为827.9mAh/g,容量损失仅为7.58%,远远小于Ti/Sn复合膜电极的容量损失。电极第3次循环的放电容量为788.5mAh/g,到第12次循环时其放电容量达到最低值749.1mAh/g,随后其放电容量开始缓慢增加,到第50次循环时达到777.8mAh/g。从第3次到第50次循环,Sn/Ti复合膜电极组装的电池几乎没有容量损失,Sn/Ti复合膜电极组装电池的电化学性能远优于Ti/Sn复合膜和纯Sn电极。Sn/Ti复合膜电极的首次充放电容量为875.8mAh/g,从第2次到第20次循环仅有27%的容量损失,远远小于Ti/Sn复合膜电极的容量损失。对比Sn薄膜20次循环后300mAh/g左右的充放电容量,有了29%的性能提升。最后,本文简要介绍了密度泛函理论的基本原理,并采用基于密度泛函理论的第一性原理,用Material Studio 4.0软件中的CASTEP模块,研究了Li_xSn合金不同嵌锂中间相的物理性质和电化学性能,对Li-Sn合金的嵌锂机理进行了解释。计算了Sn-Ti合金嵌锂中间相Li-Ti₂Sn/Ti₃Sn的电子结构,并对其嵌锂性能进行预测,为实验结果提供了理论解释。更多还原

【Abstract】 The fossil energy,which includes coal,oil and natural gas is the world’s main energy provider.Due to the huge damage the fossil energy done to the environment, the new pollution-free and high-energy chemical energy has become the hot spots around the world.As the current business anode materials can’t meet the actual demand,there is an interest in developing new cathode materials with higher capacity, higher stability,higher safety and lower cost for lithium ion batteries.On the basis of reviewing the development of lithium ion battery and cathodes materials,this thesis selected tin-based materials as cathodes for lithium ion batteries.Different types of Sn, Sn/Ti and Ti/Sn composite films were prepared by vacuum sputtering on Cu foil.The composition,phase structure,electrochemical performance of films with different technology parameters were investigated by X-Ray Diffractionthesis（XRD）,Scanning Electron Microscopy（SEM）,Inductively Coupled Plasma Spectroscopy（ICP）and electrochemical methods like cyclic voltammetry（CV）and constant current charge/ discharge（CC）.This work results provide the mechanism and preparation technology for tin-based films cathode materials by vacuum sputtering.The influence of sputtering power on the deposition rate,microstructures and electrochemical properties of Sn films was investigated.The result showed that the sputtering power and the deposition rate have a approximate linear relationship.The crystallization of the film increased with the sputtering power.When the sputtering power is 24W,tin and copper diffused to each other and created a alloy phase of CuSn. When the sputtering power is 16W,Sn films got the optimum electrochemical performance:the 1^stcycle efficiency reached 82.2%,the reversible capacity retained 300mAh/g after 30 cycles.The influence of sputtering time on the microstructures of Sn thin films was investigated.With the sputtering time increased,the crystallization intensified as well. When the sputtering time reach 20 min,the grain of Sn shrinked and turned the surface of the grain to round form.As a result,the Sn film got the optimum electrochemical performance.The influence of adding Ti to Sn films on the microstructures,composition and electrochemical performance was investigated.The Sn/Ti and Ti/Sn composite films were perpared,the film’s microstructures,electrochemical performance,composition and the inset and emersion behavior of Li⁺ were researched.The mechanism of the composite film’s capacity decrease and the function of the Ti were analyzed.It was founded that the sputtering sequence of the Sn and Ti metal would greatly change the performance of the film.The Sn/Ti composite film which sputtered Sn first got a better electrochemical performance.Mainly,the addition of Ti greatly improved the inset and emersion behaving of Li⁺.The 1^stcycle capacity of the Sn/Ti composite films reached 896.1mAh/g.The 2^nd cycle capacity is 827.gmAh/g with only 7.58%capacity decrease which is far less than the Ti/Sn composite films.The 3^rdcycle capacity is 788.5mAh/g,and the 12^th cycle capacity reached the lowest 749.1mAh/g,then the cycle capacity kept growing slowly to the 777.8 mAh/g of 50^thcycle.From the 3^rdto the 50^th,the cycle capacity almost didn’t have a decrease,which make the Sn/Ti composite films got a far better electrochemical performance then Ti/Sn composite films and pure Sn films.At the end of the thesis,the basic principles of density functional theory were introduced.With the CASTEP modules from the Material Studio 4.0 software which base on the density functional theory and the first principles,the physical and electrochemical performance of Li-Sn alloys were studied.The electronic structures of the Li-Ti₂Sn/Ti₃Sn alloy were calculated,the properties of lithium intercalation were forecasted,and the theoretical explanation for the experiments were provided.更多还原