基于阳极氧化钛纳米管阵列的高比容全固态电容器的研究

This research project will focus on the fabrication of metal/insulator/metal dielectric capacitors, mainly through simple anodization processes, on the basis of anodic titania nanotube arrays. Firstly, titania nanotube arrays are converted into TiN nanotube arrays via a nitridation route in an ammonia atmosphere. Then, a layer of conformal titania films is formed on the surface of TiN nanotube arrays after an anodization process. Subsequently, another layer of conducting polymer films served as counter electrode is uniformly deposited onto the surface of the dielectric titania films. Finally, all-solid-state TiN/TiO2/conducting polymer capacitor arrays with nanotubular geometry are obtained. For the electrical energy storage devices, it is highly desirable to possess high energy density and high power density as well as long cycle life simultaneously. Unlike the popular strategy, in this project, an alternate way is proposed to approach this goal by increasing energy density of dielectric capacitors while maintaining their inherent high-power nature. That is, the surface areas of dielectric materials can be enlarged by using nanoengineering techniques, thereby enhancing their specific capacitance and achieving supercapacitor-level energy density. In this project, the conversion of ordered titania nanotube arrays into TiN nanotube arrays will be investigated. The anodization behaviors of TiN and the growth kinetics of its barrier oxide film will be studied. The physical model for describing the relationships between the specific capacitance of the nanotubular capacitor and the morphological parameters of ordered nanotube arrays will be established. The performances of the nanotubular capacitor such as energy density, power density, charge-discharge cycle life and frequency characteristics will be examined. These efforts will hold the promise of achieving high energy density combined with long cycle life and high power density.

本项目主要依赖简单的阳极氧化技术，以有序氧化钛纳米管阵列为基础，构建导体/电介质/导体型纳米管电介质电容器。首先通过氮化将氧化钛纳米管阵列膜转变为氮化钛纳米管阵列膜，然后在氮化钛纳米管阵列表面保形性地制备氧化钛电介质膜，再均匀沉积一层导电高分子膜作为对电极，最终形成氮化钛/氧化钛/导电高分子体系的全固态纳米管电容器阵列。与流行的研究思路不同，本项目从电介质电容器固有的高功率密度特点出发，通过纳米结构工程提高其比容和能量密度，以制备具有超级电容器能量密度量级的电介质电容器。本项目主要研究有序氧化钛纳米管阵列膜到氮化钛纳米管阵列膜的无损转换；研究氮化钛的阳极氧化行为及其致密型氧化膜生长动力学；建立纳米管电容器阵列物理模型，探索其比容与纳米管微结构参数之间的关系；研究纳米管电容器的能量密度、功率特性、循环寿命、频率特性等性能。为获得兼具高能量密度和高功率密度的电储能器件提供新方法和新思路。

本项目从电介质电容器固有的特点（功率密度高、损耗角正切值小等）出发，基于阳极氧化钛纳米管比表面积大，氧化钛介电常数高的特点，期望构建氮化钛/氧化钛/导电高分子的纳米结构的新型电介质电容器。本项目通过金属阳极氧化的方法，首先制备出长度和结构可控的阳极氧化钛纳米管，通过高温氮化处理转化成氮化钛纳米管阵列，再经过二次阳极氧化得到氮化钛/氧化钛的纳米管阵列，最后制备出氮化钛/氧化钛/导电高分子结构的电容器。主要的研究内容包括：通过研究钛的阳极氧化过程，深入探讨TiO2纳米管的生长动力学，为实现氧化钛纳米管的可控制备提供理论指导。研究TiO2纳米管的氮化工艺，实现TiO2纳米管向TiN纳米管的转换。再经过二次阳极氧化构建TiN/TiO2纳米管结构。通过电化学聚合的方法在TiN/TiO2纳米管内部形成聚苯胺，构建TiN/TiO2/导电高分子的全固态电容器，并研究其电性能。经过四年的持续研究，本项目取得的重要成果如下：首先，在阳极TiO2纳米管的形成机理上取得很大突破，证明了氧气气泡模具效应导致了纳米管胚胎的形成，并证明了纳米管底部的氧化物是在两个界面同时生长的。证明了纳米管生长的主要动力还是离子电流和电子电流，这就否定了传统的场致溶解理论。成功构建了TiN/TiO2纳米管结构的电容器，该电容器在电解液体系中的比电容是78 μF cm-2，漏电流密度为0.26 mA cm-2。为提高电介质膜的介电常数，通过碱性水热反应，TiO2电介质膜可完全转化为BaTiO3膜。与TiN/TiO2结构相比，TiN/BaTiO3/电解液体系的电容器性能有很大改善，其比电容为97 μF cm-2，漏电流密度为0.04 mA cm-2。最后，成功构建了TiN/TiO2/导电高分子的全固态电容器，电化学沉积聚苯胺后，TiN/TiO2/聚苯胺体系的比电容达到98.5 mF cm-2。以上成果为构建新型的全固态电容器提供了一条全新思路。