【作者】 胡猛；

【导师】 雷立旭；

【作者基本信息】 东南大学 ， 材料物理化学， 2006， 硕士

【摘要】 层状氢氧化物(layered double hydroxides,缩写LDHs)具有结合紧密的氢氧化物层和处于层间的可自由交换的阴离子。它是一类近年来引起人们关注的新型材料,在离子交换、水处理、复合材料、催化材料、阻燃材料等方面得到广泛的研究和应用。在电化学方面,研究集中在Ni/MH电极材料、阴离子粘土修饰电极、传感器及电化学电容器等领域。本文研究了理想组成为[Ni4Al(OH)10]X (X = OH-, NO3-)的层状氢氧化物的电化学性质,特别是大电流充放电情况下的电化学可逆性和充放电容量等性质。本文采用共沉淀-水热处理-离子交换的实验路线,制备出结晶性比较好的的层状氢氧化物[Ni4Al(OH)10]OH。使用ICP、CV、XRD、XPS对其组成、电化学行为、充放电循环过程中晶体结构和Ni离子价态的变化进行了研究。结果表明,该化合物的层间距为7.9 ?,化学组成为Ni3.94Al(OH)9.88OH?5.37H2O;充放电过程中层状结构稳定,Ni离子价态发生变化。它在40 mA恒流充电(电流密度800 mA?g-1)、20 mA恒流放电(电流密度400 mA·g-1)情况下,首次放电容量为248 mAh·g-1,在第25次循环时放电容量达到最大值330 mAh·g-1,60次循环后容量仍有315 mAh·g-1。对晶粒大小不同的层状氢氧化物[Ni4Al(OH)10]NO3的电化学性能研究表明,晶粒的尺寸对大电流密度充放电行为有一定的影响:在较低的电流密度下充放电时,较大粒径样品具有较大的放电容量;但随着电流密度增大时,容量下降得较快;较小粒径样品,尽管电流密度较小时容量可能略低,但大电流密度放电(≥4000 mA?g-1)时,容量得到较好的保持。本论文还比较了[Ni4Al(OH)10]OH与[Ni4Al(OH)10]NO3的电化学性能。实验结果显示[Ni4Al(OH)10]OH的大电流放电性能明显较好,具有较大的放电容量和平均单个镍原子交换电子数。例如,电流密度为50 mA?g-1时,前者的恒流放电容量达到348.8 mAh?g-1,而后者为332.9 mAh?g-1,相应的交换电子数分别为1.78和1.66个;电流密度为2500 mA?g-1时,二者的恒流放电容量分别为195.5 mAh?g-1和144.6 mAh ? g-1,交换电子数分别为0.99和0.72个。实验还表明,不论层间阴离子是OH-或NO3-,充电电流密度分别为80 mA (1600 mA?g-1)、40 mA (800 mA?g-1)和20 mA (400 mA?g-1),且过充电条件下,样品在40 mA (800 mA?g-1)下的放电容量是基本相同的。更多还原

【Abstract】 Layered double hydroxides (short as LDHs) are composed of rigid hydroxide layers, interlamellar anions and co-crystallized water. They outstand there because of their marvelous reversible anion-exchange capabilities and have been found uses in anion exchange, preparations of various materials, chemical separations of organic geometric isomers, controls of chemical reactions, storage and control release of biomolecules, preparation of flame retarding materials/addictives, catalysts and catalysts supports and topochemical syntheses in the recent years. They can also be employed as electrode materials. In this paper, electrochemical performances, especially the electrochemical reversibilities and charge-discharge capacities at high currents, of layered double hydroxides with a ideal composition of [Ni4Al(OH)10]X?mH2O (X = OH-, NO3-)are investigated.In the second chapter of this paper, cyclic voltammetry, X-ray diffraction, X-ray photoelectron spectrum, inductively coupled plasma are employed to investigate electrochemical behaviours of a layered double hydroxide, [Ni4Al(OH)10]OH, as well as any changes of its crystal structure and valance transformation of nickel ions during charge-discharge cycles. The results show that the layered structure of [Ni4Al(OH)10]OH is stable to charge-discharge cycles; and the valence transformation of nickel ions in the hydroxide layer is confirmed by XPS. The discharge capacities of the electrode are found to be 248 mAh?g-1 at the first cycle, a maximum of 330 mAh?g-1 are found at the 25th cycle, and 315 mAh?g-1 at the 60th cycle.The electrochemical performances of a layered double hydroxide, [Ni4Al(OH)10]NO3 of different particle sizes are reported. The results show that the particle size of the sample has evident effect on its discharge capacity at high current densities: sample of bigger particle size may have a larger capacity when they are discharged at lower current density; but their capacity decreases quickly when the current density is increased; however, the capacity of samples of smaller particle size remains high even at very high current density, i.e. 4000 mA?g-1.Electrochemical comparisons of [Ni4Al(OH)10]OH and [Ni4Al(OH)10]NO3 were done in the last chapter of this paper, which show that the former has better performance, especially when the discharge is carried out at very high current densities. For example, the discharge capacity of the former, which is 348.8 mAh?g-1 (corresponding to 1.78 electrons exchanged per nickel atom), is higher than that of the latter, which is 332.9 mAh?g-1 (1.66 electrons exchanged per nickel atom) at a current density of 50 mA?g-1; the former also has a capacity of 195 mAh?g-1 at a current density as high as 2500 mA?g-1, which is also larger than that of [Ni4Al(OH)10]NO3, 144.6 mAh?g-1. In addition, studies on the effect of charge current densities on the discharge capacities of the two samples show that each sample has very similar discharge capacity no matter it is charged at 1666 mA?g-1, 833.3 mA?g-1 or 416.7 mA?g-1 when the sample is overcharged and discharged at a current density of 833.3 mA?g-1.更多还原