溶胶—凝胶法制备纳米NiO及电化学性能研究

发布时间：2018-04-23 00:08

  本文选题：高分子络合 + 纳米NiO　； 参考：《河南科技大学》2011年硕士论文

【摘要】：NiO是典型的过渡金属氧化物,在电致变色、催化剂、热/气敏传感等方面的研究已相对成熟,但关于纳米NiO作为锂离子电池新型高性能负极材料的报道较少。溶胶-凝胶法具有化学计量容易控制、设备简单、成本低等优点,受到广泛关注。本文以镍盐为镍源,高分子聚合物为螯合剂,去离子水为溶剂在一定温度下合成溶胶,采用旋转涂布法在基体上沉积薄膜,结合热处理工艺制备NiO薄膜。考察溶胶粘度、干燥条件、升温速率和烧结温度对NiO薄膜表面形貌的影响。研究了烧结过程中前驱体的热分解行为,并考察了烧结温度对薄膜结构和电化学性能的影响。通过电化学阻抗技术初步探讨了NiO与Li的反应机理。此外,进一步采用溶胶凝胶法获得了纳米NiO粉体,考察了烧结温度对NiO粉体形貌、结构和电化学性能的影响。主要得到以下结论: 1.以聚丙烯酸(PAA)为螯合剂,醋酸镍为镍源,加入去离子水通过高分子络合过程在一定温度下合成了均匀稳定的溶胶。干凝胶前驱体在450℃时有机物基本分解完全并逐步形成NiO晶体结构。随着烧结温度升高,晶粒尺寸逐渐增大且晶体结构趋于完整。 2.随着溶胶粘度降低、干燥温度升高和升温速率降低,溶胶中的水分和有机物挥发更加充分,薄膜表面形貌更加致密、光滑。以粘度为5.45cst的溶胶沉积的溶胶薄膜,经200℃干燥后以0.5℃/min的升温速率至烧结温度获得了表面光滑致密,无气孔和裂纹NiO薄膜。 3.随着烧结温度升高,薄膜表面颗粒逐渐长大,晶体结构趋于完善。500℃烧结2h得到的NiO晶体结构完整,薄膜表面粒径分布均匀,光滑致密。该薄膜在0.01mA/cm~2的电流密度下,首次放电比容量达1174mAh/g,且在循环过程中容量损失率低于0.1%,经100次循环后比容量仍有500mAh/g,表现出良好的循环稳定性。当充放电电流密度增大时,NiO薄膜比容量和循环性能逐渐略有降低,表现出良好的大电流充放电承受能力。 4.通过电化学阻抗分析,提出了等效电路R_S(Q_(dl)(R_(Ct)Z_W))(Q_(SEI)R_(SEI)),拟合误差小于10%,合理解释了Li与NiO电极的电化学反应机理。首次放电过程中,固体电解质薄膜(SEI膜)随着极化电位的降低逐渐生长,在0.6V时基本形成。Li~+穿过SEI膜与NiO反应,形成Ni和Li_2O。充电过程中,SEI膜部分分解且Ni与Li_2O可逆的形成NiO和Li。 5.利用上述溶胶,通过溶胶凝胶法,获得了纳米NiO粉体。随着烧结温度升高,NiO粉体晶体粒径逐渐长大并趋于完善。烧结温度700℃时获得的NiO颗粒尺寸约34nm,随着烧结时间的延长,颗粒尺寸变大,团聚现象加剧。经600℃烧结8h制备的纳米NiO首次比容量能达800mAh/g左右,在0.01mA/cm~2的电流密度下进行恒电流充放电循环20次后比容量保持率高,约为500mAh/g,在0.2mA/cm~2电流密度下仍具有良好的循环性能,表现出良好的大电流承受能力。
[Abstract]:NiO is a typical transition metal oxide. The research on electrochromism, catalyst, thermal / gas sensing and so on has been relatively mature. However, there are few reports on nanometer NiO as a new type of high performance anode material for lithium ion batteries. The sol-gel method has many advantages, such as easy control of stoichiometry, simple equipment and low cost. In this paper, the sol was synthesized by nickel salt as nickel source, polymer as chelating agent, deionized water as solvent at a certain temperature. The thin films were deposited on the substrate by rotating coating method, and NiO thin films were prepared by heat treatment. The effects of sol viscosity, drying conditions, heating rate and sintering temperature on the surface morphology of NiO films were investigated. The thermal decomposition behavior of the precursor during sintering was studied, and the effect of sintering temperature on the structure and electrochemical properties of the film was investigated. The reaction mechanism between NiO and Li was studied by electrochemical impedance technique. In addition, nanocrystalline NiO powders were obtained by sol-gel method. The effects of sintering temperature on the morphology, structure and electrochemical properties of NiO powders were investigated. The main conclusions are as follows: 1. Using polyacrylic acid PAA) as chelating agent and nickel acetate as source, the homogeneous and stable sol was synthesized by adding deionized water through high molecular complexation process at a certain temperature. At 450 鈩，

本文编号：1789549