对苯二甲酸盐有机纳米负极材料的制备及电化学性能研究

Compared with Li4Ti5O12 inorganic anode material, small molecular weight organic materials of terephthalate salts exhibiting many merits such as low redox potential (around 0.8 V vs. Li+/Li), high specific capacity, rich resources on the earth, low cost and environmental friendless, are the qualified competitors as the anode materials for next generation energy storage devices (lithium ion battery, sodium ion battery, magnesium ion battery, etc.). However, the shortcomings including the low electronic conductivity and the solubility in the liquid electrolyte, which are common for most of organic electrode materials, lead to poor rate performance and bad cycle lifetime and low coulombic efficiency in the first cycle. Consequently, these factors have been impeding the rapid development of the organic electrodes seriously. Herein, a spray drying technique is used to fabricate porous microspheres consisting of nanosized particles, which is benefitable for reducing the diffusion distance of Li+ ions and providing large surface areas. Then, a (plasma enhanced) chemical vapor deposition technique is employed to coat N-doped carbon at relatively low temperature so as to enhance the electronic conductivity and modify the surface properties of the electrochemical active material, resulting in the improved rate performance as well as the reduced capacity loss in the first cycle. Following that, the type of the cation is screened so as to optimize the interaction between the cation and the anion, which will impress the solubility and promote the cyclic performance. Simultaneously, the redox potential might be tuned, which might be helpful to elevate the power density. Finally, the relationship between the crystal structure and electrochemical properties is to be analyzed systematically. The key parameters for improving electrochemical performance should be figured out, and the designing criteria for advanced organic electrode material will be worked out. All of these achievements will undoubtly push organic electrode material for the practical application quickly.

与钛酸锂等无机负极材料相比，有机小分子对苯二甲酸盐负极材料具有氧化还原电位低（约0.8V vs. Li+/Li）、比容量高、资源丰富、成本低廉和环境友好等优点，是下一代电化学储能负极材料的有力竞争者。如同其他有机电极材料一样，低电子电导率、在电解液中的可溶性导致其倍率性能差、循环寿命短、首周库伦效率低，是其发展的瓶颈。本项目首先利用喷雾干燥法将材料纳米化，形成由一次纳米粒子组装而成的多孔微球；然后利用（等离子体）化学气相沉积法在较低温度下实现掺氮的碳包覆，增强电子电导率，提高倍率性能，并改善材料表面特性，减少首周容量损失；再改变阳离子种类，优化阳离子与对苯二甲酸阴离子的相互作用，降低活性材料的溶解性，提高循环稳定性，并调控氧化还原电位等性质；最后系统研究盐的晶体结构与电化学性能的构效关系，发现提高储能性质的关键因素，提出新型有机电化学活性材料的设计原则，加速有机电极材料的实用化进程。

商业化锂离子电池的电极一般是无机材料构成，具有重量能量密度低的缺点。而由有机材料构成的有机电池，不仅与柔性电子器件、可穿戴电子器件的兼容性好，而且有机电极材料具有分子种类多及结构的多样性，具有良好的发展前景。本项目首先为了解决有机电极材料（对苯二甲酸盐负极材料）电子电导率差的难题，采用球磨、喷雾干燥等方法制备有机无机复合材料，再进行表面改性的方法，获得较好的效果；特别是发现了将对苯二甲酸银等物质中的重金属离子在首次放电过程中原位电化学还原分散，得到了粒径在数十纳米、且分散性优异的金属颗粒，该复合物大幅度提高了电极材料的倍率性能。其次，系统地研究了阳离子种类对活性材料的晶体结构、形貌及性能的影响，指出了有机电极材料晶体结构与离子输运及倍率性能的关系，发现了对苯二甲酸钙、对苯二甲酸钴两类储锂性能优异的负极材料。再次，开创性地将对苯二甲酸盐作为储钾材料，发现对苯二甲酸钾体现了较佳性能，并将对苯二甲酸盐作为储钠材料进行了研究，发现对苯二甲酸钴、对苯二甲酸银具有较好的性能。在此基础上，进一步调控有机阴离子的种类，增强其共轭性、或者采用杂环等方法以提高其本征电子电导率或者降低其溶解性，均获得了较佳的充放电倍率性能或者循环稳定性，但是可逆容量有所降低。然后选用氰基官能团作为新型反应活性位点，成功地合成了几种电极材料，提升其氧化还原电位在1V以上，但是含氰基小分子盐易于溶解在有机电解液中。最后针对有机小分子材料在有机电解液体系中普遍存在溶解的难题，发展了几种高分子电极材料。特别是，采用含氮活性位点的聚乙烯咔唑（Poly(N-vinylcarbazole)）作为阴离子PF6-的载体，成功地制备了K+/ PF6-双离子电池，在较高倍率下获得了较高的比容量和长循环寿命。