V,Mo氧化物纳米阵列的制备及锂电性能研究

发布时间：2018-01-06 13:44

本文关键词：V,Mo氧化物纳米阵列的制备及锂电性能研究　出处：《北京化工大学》2014年博士论文　论文类型：学位论文

【摘要】：过渡金属氧化物材料由于特有的锂离子脱嵌机理和转化机理,理论容量是传统碳材料理论容量的2-3倍,成为锂离子电池研究的热点。然而,由于氧化物自身导电性差、体积膨胀系数大、实际容量偏低的缺陷,限制了商品化的进程。大量的文献研究表明,电极材料的纳米化在很大程度上解决了以上存在的问题：纳米材料的体积膨胀系数小,Li+的嵌入/脱出不会损坏电极材料的结构,使得电池保持了较高的循环寿命；纳米材料具有小尺寸效应,能够缩短有效距离,有利于电子的传输和锂离子的扩散；纳米材料的比表面积大,增加了电极与电解液的接触面积,在高倍率下依然保持较高电容量。众多类型的纳米材料结构中,纳米阵列以其独特结构(微/纳结构相结合)在锂离子电池应用中脱颖而出。作为有序排列的低维纳米阵列,其阵列之间的空隙,能够允许电解液充分地渗透到阵列的底部,很大程度上减小材料内部的电化学反应产生的界面电阻；每一个结构单元都与电解液直接接触,都可参与电化学反应,使得电容量较大；电子可沿着纳米结构直接到达极板,加速了电子传输,在高倍率电池应用中展现出特有的优势。过渡金属氧化物的纳米阵列应用于锂电电极,有望为开发薄膜锂电池提供材料基础。本论文主要的研究内容如下： (1)通过水热法在导电基底Ti片上原位生长VO2前驱体,经煅烧后得到V205纳米带阵列。纳米带自组装形成泡沫结构,孔径约2-3μm。讨论了反应温度和反应酸度对V2O5纳米带阵列的影响。改变调节反应酸度的酸种类(盐酸、磷酸、冰醋酸和草酸),得到了不同形貌的V205纳米阵列(纳米棒、纳米片和纳米带)。通过XRD、SEM、TEM、XPS、 Raman等仪器对不同形貌的产物进行表征,推测出造成V205纳米阵列形貌的差异主要是由酸的电解能力和氧化还原性质决定的。将三种不同形貌的V205纳米阵列作为锂电池正极材料,测试其电化学性能。实验结果表明,盐酸条件下制备的V205纳米棒阵列的初始容量高达305mAh·g-1,但随后衰减严重；磷酸条件下制备的V205纳米片阵列则倍率特性好；V205纳米带阵列的循环稳定性好,具有高电容值(255mAh·g-1)。讨论了V205纳米阵列的结构与其锂电性能之间的关系,发现电性能与材料的比表面积和结晶度有关。大比表面积、高结晶度的材料对应高的比容量、好的倍率特性。 (2)选用低价态的V02做为牺牲模板,在pH=1的情况下,水热反应在导电基底Ti片上制备出直径10nm,长约100nm的多级结构Mo03纳米棒阵列。其中,纳米棒是垂直于微米级孔的泡沫结构的“墙壁”两侧生长。借助SEM, XRD、Raman、EDS等表征手段,从热力学角度探讨新型的多级结构Mo03纳米棒阵列的生长机理。结果发现,随着V02的溶解,M0042-逐渐质子化,同时在V02表面水解形成Mo03沉淀。我们将多级结构MoO3纳米棒阵列做为锂电池负极材料,进行电化学性能测试,结果发现该材料的首次放电容量在633mAh·g-1,但随后衰减很严重。推测是由于阵列上的纳米棒排列不规则造成的,使得本身导电性不好的Mo03更是内阻增大。 (3)利用碳还原法制备了多级结构MoO2纳米颗粒。MoO2保留了多级结构Mo03的泡沫构造,其基本单元是由直径在50nm左右的颗粒构成。测试了多级结构MoO2纳米颗粒的锂电性能。发现放电容量随循环圈数的增加发生递增。分析该现象后推测在充放电过程中,对于无序结构的材料存在一个活化的过程。在电流密度为100mA·g-1进行循环测试,80圈后还保留了611mAh·g-1,体现了电化学稳定性。 (4)利用水热法制备长200nm左右,厚5nm的MoS2纳米片阵列。在此基础上,利用转化法氧化MoS2,制备出直径为50nm、宽度约20nm的纳米颗粒组成的厚500nm的M003薄膜。相比于纳米棒阵列的电性能,M003薄膜在循环了120圈后,依然保持在650mAh·g-1,并且库仑效率在99.9%以上,有着较高的比容量和稳定的循环性能。
[Abstract]:The nano - array has the advantages of small volume expansion coefficient , large volume expansion coefficient and low actual capacity . The main contents of this thesis are as follows : ( 1 ) VO _ 2 precursor was grown in situ on Ti sheet of conductive base by hydrothermal method . After calcination , V205 nano - band array was obtained . The effect of reaction temperature and acidity on V2O5 nano - band array was discussed . The acid type ( hydrochloric acid , phosphoric acid , glacial acetic acid and oxalic acid ) was used to change the acidity of reaction . XRD , SEM , TEM , XPS and Raman spectroscopy were used to characterize the morphology of V205 nano - array , which was determined by the electrolysis capacity and redox nature of acid . The experimental results show that the initial capacity of V205 nanometer rod array prepared under hydrochloric acid condition is as high as 305mAh 路 g - 1 , but then attenuation is severe . The V205 nano - strip array prepared under phosphoric acid condition has good multiplying power and high capacitance value ( 255mAh 路 g - 1 ) . ( 2 ) Low - valence V02 was used as the sacrificial template . In the case of pH = 1 , hydrothermal reaction was carried out on the conductive base Ti sheet to prepare the multi - stage structure Mo03 nanorods array with the diameter of 10nm and the length of about 100 nm . The growth mechanism of the novel multi - stage structure Mo03 nanorods array was discussed from the thermodynamic angle by means of SEM , XRD , Raman and EDS . The results show that the first discharge capacity of the material is 633mAh 路 g - 1 , but the decay is very serious . It is speculated that Mo03 with bad conductivity is more internal resistance due to the irregular arrangement of nanorods on the array . MoO2 nanoparticles were prepared by carboreduction method . MoO2 retained the foam structure of multi - stage structure Mo03 . The basic unit was composed of particles with diameter of about 50 nm . It was found that the discharge capacity increased with the increase of the number of cycles . It was found that the discharge capacity increased with the increase of the number of cycles . After analyzing the phenomenon , it was speculated that there was an activation process in the material of disordered structure . After cycling test at the current density of 100mA 路 g - 1 , 611mAh 路 g - 1 was also retained after 80 turns , which showed electrochemical stability . The M003 thin film with a diameter of 50 nm and a width of about 20 nm was prepared by using a hydrothermal method . The M003 thin film with a diameter of 50 nm and a width of about 20 nm was prepared by the conversion method .

【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TB383.1;TM912

【共引文献】