二元氧化物诱导MOFs可控生长构筑炭包覆高容量负极材料及其储锂性能研究

The LIBs anodes are facing the problem of large volume expansion, low electrical conductivity and slow Li+ transport dynamics, seriously restricting their electrochemical performance. Exploring the new carbon modification/coating method, constructing the novel anode materials with multiple structural advantages and realizing the precise control of their structures and performances is an important topics in anode study. Focus on high-capacity anode materials, this project is intended to use MOFs-based carbon materials with rich porosity, high graphite degree and nitrogen doping advantage to achieve target and controllable coating, that is, binary oxides Mx(Si/Sn/Mn)yOz template-induced MOFs controllable coating strategy to fabricate high-performance carbon-coated anodes with a core-shell structure. By regulating the release rate of transition metal (M) ions and their complexation with organic ligands, the key physical parameters such as thickness and crystal structure of MOFs coating layer can be well controlled; through the selection of metals with different carbon solubilities and exploration of pyrolysis conditions, the crystal and pore structure, graphite degree of the MOFs-based carbon layer and the structure, composition of metal surface can also be controlled, thus to obtain the controllable coating mechanism of the MOFs-based carbon and electrical conductivity control mechanism of the hybrid, providing theoretical basis and guidance for the design and fabrication of high-performance anode materials.

锂离子电池负极面临体积膨胀大、电导率低和离子迁移动力慢的问题，严重限制了其电化学性能。探索新型的炭修饰/包覆方法，构筑具有多重结构优势的新型负极材料并对其结构和性能实现精确调控是目前负极材料研究的一项重要课题。本项目以高容量负极材料为研究对象，利用具有丰富孔隙结构、高石墨化度和氮掺杂优势的MOFs基炭材料对其进行靶向可控包覆：二元氧化物Mx(Si/Sn/Mn)yOz模板诱导MOFs可控生长策略构筑具有核壳结构的高性能炭包覆负极材料。调控过渡金属（M）离子的释放速率及其与有机配体的络合作用控制MOFs包覆层的厚度和晶型结构等关键物理参数；通过选取具有不同溶碳能力的金属和探索热解条件调控MOFs基炭包覆层晶型、孔结构、石墨化度和金属表面的晶型、成分，从而获得MOFs基炭可控包覆机制和复合材料导电调控机制，为高性能负极材料的设计合成提供理论依据和指引。

针对锂离子电池负极体积膨胀大、电导率低和离子迁移动力慢的问题，本项目以高比容量负极材料为研究对象，利用二元氧化物模板诱导ZIF-8可控生长策略设计合成了一系列形貌结构各异且性能优异的炭修饰高容量负极材料，包括MnOx@C三维纳米骨架结构、SnOx@C量子点导电笼、Zn2SiO4@C纳米束网络和Mn2SiO4@C中空纳米球等。其中SnOx@C量子点导电笼体系展现最高的储锂容量（0.2 A g-1电流密度下循环200圈后可逆比容量为1824 mAh g-1），得益于纳米束网络的结构优势，Zn2SiO4@C体系获得最优的倍率性能（0.2 A g-1电流密度下循环500圈后可逆比容量为1746 mAh g-1，5 A g-1的高电流密度下可逆容量达到0.2 A g-1电流密度下可逆容量的71%，），MnOx@C三维纳米骨架结构展现最优的循环稳定性（0.2 A g-1电流密度下循环300圈后可逆比容量增长至2215 mAh g-1，在2 A g-1电流密度下循环1100圈后容量保持率为108%）。结合原位XRD以及XPS等表征手段进一步对各体系优异性能的原因作了深入的研究并对电化学反应机理进行了推测，获得ZIF-8衍生炭可控包覆方法和复合材料性能调控机制，为高性能负极材料的设计合成提供理论依据和指引。