锂硒电池用高硒负载复合纳米结构的设计制备与储锂机理研究

Selenium is one of the potential candidates for high-performance cathode materials of lithium ion batteries (cathode material of lithium-selenium batteries). Targeting at problems such as low selenium mass loading, loss of active materials due to dissolution and shuttle effect of polyselenides, volume changes of cathode material during cycling, we propose a novel structure of nitrogen-doped metal/metal-based composites@porous-hollow carbon/selenium nanostructures. This kind of structure simultaneously addresses the following issues which are of critical importance when capacity and cycling stability of lithium-selenium (Li-Se) batteries are concerned: 1) Porous shell/hollow interior structure (hierarchal pore structures) maximizes the selenium mass loading and buffers the volume changes during cycling; 2) Polar-material-shell shields the polyselenides from dissolution physically and forms bonding with polyselenides chemically as well. In this project, the compositions of metal coordination polymers and their wrapping metal would be tuned in order to investigate the binding abilities of different polar nanoparticles on polyselenides, as well as their impact on lithium storage capabilities. Meanwhile the electrochemical mechanism of this proposed composite would be thoroughly studied with the help of all kinds of characterization and in/ex-situ techniques. In addition, the correlation between the composition/structure and electrochemical performance would be revealed to obtain the optimized synthetic conditions of maximized selenium accommodation, uniform wrapping/distribution of selenium nanoparticles and enhanced lithium storage properties. The successful implementation of this project ensures the maximized bosting of the rate capabilities and long-term stable cycle life of the cathode materials of Li-Se batteries. Therefore, the present project is expected to lay a solid foundation for the synthetic and electrochemical studies of novel cathode materials of Li-Se batteries.

硒单质是锂离子电池高容量正极的优选材料。针对硒负载量过低、多硒化物溶解和穿梭效应造成活性物质和能量的损失、体积膨胀对电极结构的破坏等不利因素，本项目拟设计构筑新型氮掺杂的金属/金属化合物@多孔空心碳/硒纳米球结构，从而同时实现“多孔壳层/空腔的多级孔径结构-最大化硒负载量/体积变化缓冲”和“极性壳层物理限制和化学吸附多硒化物”三项提高电池容量和循环稳定性的重要特性。本项目将通过对不同金属配位聚合物及其包覆金属的调控，探索各种极性纳米颗粒对多硒化物的化学作用和电池性能的影响。同时，结合各种电化学手段和原位表征技术，研究该复合材料的储锂机理，揭示各项结构和动力学性能的内在联系和规律。以期获得最佳制备条件和工艺，达到Se的完全包袱、均匀分布和最大载量，从而最大限度的提升该材料的高倍率性能和长寿命循环稳定性。这对推动新型Li-Se电池正极复合材料的可控制备及性能调控具有重要的研究意义和指导作用。

硒单质具有价格低廉、储量丰富、体积能量密度高等优势，锂硒电池因此被认为是未来动力电池系统的优选体系之一，近年来受到了科研工作人员的广泛关注。而开发高性能硒碳复合正极材料是锂硒电池实用化的关键。针对硒负载量过低、反应动力学缓慢、体积膨胀和活性物质脱落对电极结构的破坏等亟待解决的问题，本项目提出了设计构筑“氮掺杂的极性物质@多孔空心碳/硒纳米结构”来同时解决上述问题的新思路。本项目的主要成果包括：1.提出相比于结晶形态的硒，无定形硒具有更高的电化学活性，硒与氮掺杂碳载体材料的强结合力是稳定无定形硒和增加硒载量的关键；2.通过研究碳载体材料的比表面积及孔径分布发现硒有效载量和性能的提升与载体的比表面积关联不大，而构筑适合孔道尺寸的载体材料来筛选活性更高的小分子硒物种对优化材料性能起了决定作用。3.多种极性物种，包括非金属、金属、金属化合物等，都能有效促进硒碳正极材料的转化反应、减小极化、加速材料反应动力学和加强对生成物硒化锂的吸附，从而获得多种高比容量高倍率长寿命的硒碳复合正极材料。4.我们还对比了此“氮掺杂的极性物质@多孔空心碳”结构对和硒同主族的硫单质的负载及电化学性能提升的作用机理。本项目的实施，为高性能锂硒/硫电池正极材料的发展奠定了理论和材料基础。在本项目的资助下，共发表了高水平论文14篇，申请中国发明专利1项，培养硕士研究生2人。