【作者】 孙涛；

【导师】 方海涛；

【作者基本信息】 哈尔滨工业大学 ， 材料物理与化学， 2007， 硕士

【摘要】 锂离子电池是20世纪90年代发展起来的能源存储器件,具有电压高、体积小、质量轻、比容量高、无记忆效应、无污染、自放电小、寿命长等优点。近年来,随着混合动力汽车的迅速发展,具有高能量高功率密度的锂离子电池日益显得重要。目前所使用的以石墨化碳材料为负极的锂离子电池在大电流充放电时具有不安全隐患以及容量衰减的缺点,必须寻找一种可替代的新型负极材料。而二氧化钛具有嵌锂电位高、循环性能好、大电流下容量高的优点,因而是理想的安全、大功率负极材料。本文采用阳极氧化方法制备了二氧化钛纳米管阵列,并系统研究了纳米管阵列微观形貌与晶体结构对其电化学性能测试的影响。首先研究了甘油体系与乙二醇体系电解液的阳极氧化工艺参数。发现当电解液为甘油与水混合液时,制备的纳米管阵列长度为1.2μm左右;当采用乙二醇为电解液时,制备的纳米管阵列长度可达90μm。同时控制含水量以及氧化电压对形貌的均一性非常关键。结合SEM和TEM结构表征,研究了电解液温度对纳米管阵列管壁厚度的影响,发现随着温度的提高(由0℃升为20℃),管壁逐渐变薄(由80nm变为45nm),管长从18μm增加到90μm左右。其次研究锆掺杂对纳米管阵列形貌、相变及电化学性能的影响。将钛锆固溶合金薄片进行阳极氧化以制备得到锆掺杂的二氧化钛纳米管阵列。研究发现锆元素的掺杂可阻碍锐钛矿相向金红石相的转变,并且有利于增加纳米管阵列长度。甘油电解液体系下制备的纳米管长度增加0.5μm,同时纳米管表面更平滑;循环伏安测试表明锆掺杂的二氧化钛纳米管的脱锂电位较未掺杂二氧化钛纳米管电位低,1mV/s扫速下降低0.05V。最后研究了纳米管阵列对其相变、形貌对电化学性能的影响。研究发现非晶态二氧化钛纳米管在容量倍率性能方面优于晶化的二氧化钛纳米管阵列。在充放电电流密度为1A/g时,非晶态的充放电容量为220mAh/g,而锐钛矿在该电流密度下的充放电容量为150mAh/g。当充放电电流密度为10A/g时,非晶态的充放电容量为175mAh/g,而锐钛矿电容量衰减到60 mAh/g。对比纳米颗粒、管长90μm纳米管与导电碳黑混合压制电极片和管长90μm纳米管阵列电极片发现纳米管导电碳黑混合压制电极电化学性能最好,可达到180mAh/g。循环伏安表明金红石相与锐钛矿相混晶的嵌锂电位低于单纯锐钛矿相;通过两种长度纳米管阵列电极电容量对比发现,容量随着管长增加而减少,这是由于长阵列的导电性不好导致大电流充放时产生过高的电位降。在电流密度为0.1A/g条件下,管长为27μm阵列的容量为110 mAh/g,而管长为90μm阵列的容量为60mAh/g左右。更多还原

【Abstract】 Lithium ion battery （LIB） has become the most important energy storage device since 1990s, because of its several advantages, such as high operation voltage, small pack volume and weight, high specific capacity, little memory-effect, no environmental pollution, and low self-discharge and long cycle life. Recently, due to the fast development of hybrid vehicles, more and more research attention focuses on LIBs with high energy and high power density. At present, most commercial LIBs are based on graphitic carbon anode materials, which are unsafe and suffer from serious capacity fading under high rate operations. Therefore, a new anode material has to be developed. Titania has advantages of high lithium-ion intercalation voltage, good cycle ability, and high capacity at high current density, and thus turns out to be the novel anode material with safety and high power density.This thesis adopted anodic oxidation method to prepared titania nanotubes arrays. The effect of morphology and crystal structure of the nanotubes on their electrochemical performance was investigated.Firstly, we comprehensively investigated the processing of anodic oxidation parameters with glycerol electrolyte and glycol electrolyte, respectively. The experimental results shows that the length of the nanotubes is about 1.2μm using mixed electrolyte of glycerol and water, while the length reaches 90μm in the case of using glycol electrolyte. Based on SEM and TEM observations, the thickness of the nanotubes are found to decrease from 80 nm to 45 nm and the length increase from 18μm to 90μm as the electrolyte temperature increase from 0℃to 20℃.Then we investigated the effect of Zr doping into the titania nanotubes on their morphology characterization, the phase transition and the electrochemical performance. Zr-doped titania nanotubes arrays were fabricated by anodizing of the Zr-Ti thin plates. Zr-doping can retard the phase transition from anatase to rutile, and increase the array length. The length of the nanotubes prepared with glycerol electrolyte increased by 0.5μm, and the surfaces of the nanotubes became smoother. Cyclic voltammetry revealed that the lithium-ion declaration voltage of Zr-doped array is lower than pure titania array by 0.05V at 1mV/s.Finally, we investigated the effect of the phase composition, morphology on the electrochemical performance. We find that the rate capacity performance of amorphous titania nanotubes is superior to anatase and rutile TiO₂ nanotubes. At current density of 1A/g, the capacity of amorphous nanotubes is 220mAh/g and this of anatase is 150mAh/g. While at current density of 10A/g, the capacity is 175mAh/g for amorphous nanotubes and only 60mAh/g for anatase. Cyclic voltammetry shows the lower lithium-ion insertion voltage in mixed phases of anatase and ruitle than that in pure anatase. The highest specific capacity is obtained with 90μm-length TiO₂ nanotubes mixing with carbon black （180mAh/g） compared to nanoparticles （80mAh/g） and the 90μm-length TiO₂ nanotubes array （60mAh/g）. Through comparing the electrochemical performance of different length nanotubes array at a current density of 0.1A/g, we find that the capacity decreases as the array length increases. The reason is ascribed to the higher IR drop due to the worse electric conductivity of long array than short array. The capacity is 110mAh/g for 27μm nanotubes array, and 60mAh/g for 90μm array.更多还原