钒酸铵@碳复合结构的构建、电化学性能及协同作用机制研究

NH4V3O8 as cathode material for lithium ion battery presents more stable layered structure, better cycling stability and higher discharge capacity than LiV3O8. While the steric hindrance block effect from NH4+ and the low conductivity will result in poor rate performance of the NH4V3O8. Therefore, improving the rate performance of the NH4V3O8 is a problem that should be solved urgently. This project proposes a in-situ topology transformation technology to control the size and morphology of nano-layered NH4V3O8 and constructing NH4V3O8@C composite to optimize the structure and improve the rate performance. At first, we prepare the controllable V2O5 nanosheet on the surface of carbon by a induction heating hydrothermal technology. Then we try to make a topology transformation of the V2O5@C to NH4V3O8@C. The controllable size, morphology and exposed crystal plane of the nanosheet will be researched; and the regulation and controlling mechanism the NH4V3O8@C composite interface structure also will be investigated. The purpose is that constructing the relationship model of NH4V3O8@C, lithiation mechanism and electrochemical performance by optimizing the preparation process, structure and property. The electrode kinetics of the NH4V3O8 and the co-electrochemical mechanism of the NH4V3O8@C will be illuminated to provide the foundation for improving the rate performance and broaden the application field of NH4V3O8 materials.

NH4V3O8比LiV3O8具有更稳定的层状结构、更优的循环稳定性和容量，是一类理想的新型锂离子电池正极材料。但由于其层间NH4+的位阻滞后效应和材料的低导电性致其倍率性能较差，是亟待解决的难题。针对该问题，本项目提出了采用NH4V3O8纳米片尺寸控制拓扑原位转变技术及与碳材料键合复合的思路来实现结构优化，提高倍率性能。拟先采用感应加热水热法实现特定暴露晶面V2O5纳米片的可控合成，并完成与碳材料的键合复合；再通过拓扑转变技术实现纳米片-V2O5@C向纳米片-NH4V3O8@C的拓扑原位转变；通过优化工艺、结构和电化学性能，探索纳米片尺寸、形貌与暴露晶面控制、复合结构界面调控等机制，构建NH4V3O8@C复合结构-嵌锂与脱嵌机制-电化学性能的关系模型，阐明其电极动力学过程，揭示NH4V3O8@C复合结构协同电化学反应机制，为进一步提升NH4V3O8倍率性能和拓宽其应用领域奠定理论基础。

钒酸铵具有原材料丰富、制备简单、容量高、安全性能好等特点，同时也具有光催化、电传导、储锂、储钠性能。与钒酸锂材料相比，由于NH4+的引入，扩大了材料的层间距，同时由于氢离子的存在，形成分子内氢键，有效提高了材料结构的稳定性，是一种具有良好发展前景的正极材料。但是由于NH4V3O8低的电导率和离子迁移率，使得在大电流密度充放电时，容量衰减快，能量密度小，作为锂离子电池的正极材料，其在大电流密度下的充放电性能有待进一步的提高。本项目主要通过溶剂热方法制备不同形貌、不同晶粒尺寸的NH4V3O8微纳米颗粒。通过溶剂热方法，成功制备出形貌可控的三维花球状的NH4V3O8材料，对溶液pH值的调整，反应溶液的pH值为4时，在15mA g-1的电流密度下，放电比容量能够保持在365mAh g-1，并且经过50次的充放电循环，放电比容量的保持率为83.8 %，表现出较好的循环性和倍率性能。同时选择合适的碳材料，通过探索实验工艺，实现NH4V3O8和碳材料的键合复合。成功的制备出NH4V3O8和Super P的复合材和rGO/NH4V3O8复合材料。在电流密度为15mA g-1时，样品rGO/NH4V3O8的最大的放电比容量达到253mAh g-1，经过一系列大电流下的循环之后，容量的保持率依然稳定在为88%。成功的制备了具有氮原子掺杂碳层包覆的V2O5材料和具有钴离子掺杂的V2O5材料，其作为锂离子电池的正极材料，均表现出较好的储锂性能。掺杂的氮原子不仅能够提高电子电导率而且提升了材料的放电比容量，经过不同电流密度的循环，容量保持率为90%，提高了材料的储锂性能。通过钴离子含量的调控，对V2O5纳米片的尺寸控制和纳米带的生长起到一定的作用，当钴离子含量为10%时，储锂的能力最佳，钴离子掺杂之后，样品的晶格参数扩大，有利于Li+的扩散和转移。