电极纳米材料合成过程中微波对其形貌的调控作用及机理研究

The morphologies, including size and hierarchical structure, of electrode materials play a key role on the electrochemical performance of energy storage devices. In conventional methods, hard templates are used to assist the synthesis of electrode materials with desired morphologies, which are expensive, environmental-unfriendly, and usually could only fabricate simply-structured products. In our preliminary work, microwave was found to be capable of tuning the morphologies of electrode materials during synthesis due to its effect on hydrogen bonding and molecular cluster structures those exist in the chemical reaction. Therefore, in this work, we propose to explore the application of microwave on constructing electrode materials with tunable morphologies for high performance energy storage devices for the first time. Firstly, a microwave chemical reactor that could heat the reacting materials homogeneously, enables temperature control and stirring, as well as could work under different microwave power and frequency input, will be designed. Secondly, effect of microwave parameters including power, frequency, irradiation time point and length on the size, hierarchical nanostructure, and energy storage performance of the as-synthesized electrode materials will be studied to direct the synthesis of electrode materials with complex nanostructure and enhanced performance. Thirdly, effect of microwave on the inter-molecular hydrogen bonding and molecular cluster structures in the system will be investigated using molecular simulation methods to help study the tuning mechanism of microwave on the morphologies of electrode nanomaterials. This work aims to provide fundamental understanding in exploring green and efficient methods for synthesis of high performance electrode materials.

电极材料的形貌，包括颗粒尺寸及多级结构，对其性能至关重要。实现电极材料形貌的可调控合成是储能装置发展的关键。然而，传统化学法依赖于模板的使用，价格昂贵、容易造成环境污染且合成形貌单一。基于微波对分子间氢键、团簇结构的影响，申请人在前期工作中发现微波能够在电极纳米材料合成过程中调控其形貌。因此，本项目创新性地提出采用微波调控合成具有复杂形貌的高性能电极纳米材料，并探索其调控机理。主要包括：（1）设计一套频率和功率可调、温度可控、加热均匀、可搅拌的微波化学反应器；（2）研究微波功率、频率、作用的反应阶段及时长，对产物尺寸、多级结构的影响，建立微波参数与电极纳米材料形貌的关系，实现高性能电极纳米材料复杂形貌的可调控制备；（3）利用分子模拟的方法，分析微波对体系中分子间氢键及团簇结构等的影响，探索微波调控纳米材料形貌的分子机理。本项目拟为高性能电极纳米材料绿色、高效的合成技术的发展做出有益的探索。

电极材料的形貌对其性能影响重大。本项目基于微波的特殊加热机制，围绕电极材料纳米结构的可调控合成，开展了以下工作：（1）利用自主研发的微波恒功率、恒温反应器，研究了微波功率对乙二醇/水体系中合成镍钴双金属氢氧化物形貌的调控及机理：调节微波功率获得了具有独特纳米片上花结构的镍钴双金属氢氧化物，作为超级电容器电极材料比微米球结构的油浴法产物表现出更高的储能容量；表征反应液的介电，结合多物理场仿真计算，提出微波的去溶剂化效应是可能的调控机制。（2）研究了微波对丙三醇/水体系中合成（氟化）磷酸钒钠/碳复合物超细纳米结构的调控及机理：调节微波作用时长、微波功率和丙三醇的体积分数，获得了磷酸钒钠/碳的3D超薄纳米片花结构和1D超细核壳纳米棒结构，分别表现出优异的高温及低温储钠性能；调节反应离子，获得了均匀分散于多孔碳纳米球中的氟化磷酸钒钠纳米颗粒，表现出优异的常温储钠性能；这些超细的纳米结构均无法通过普通法获得，证实了微波对产物形貌的调控作用；利用分子动力学模拟计算的方法，发现实验温度和压力条件下微波场对丙三醇分子间氢键的影响导致丙三醇分子团簇结构变大，从微波场效应的角度很好地解释了实验现象。（3）提出了金属-含氮有机配体复合物（MOC）超薄纳米片的微波宏量制备新策略：基于微波快速加热、及催化尿素快速缩聚的作用，在反应的最后10s引入微波膨化尿素缩聚后与金属离子形成的复合物，获得Co-MOC, CoFe-MOC, CoNi-MOC等多种金属离子与含氮有机配体的复合物的纳米片，约5nm厚。.本项目的实施揭示了微波作用于纳米材料合成反应过程中存在场效应的微观机制，并为高效电极纳米材料的绿色合成提供了新思路，相关研究成果总结为SCI论文9篇，授权中国发明专利2件。