锂电池用过渡金属基和石墨烯的片片相隔复合结构的设计合成和储锂机理研究

Graphene and transition metal oxides have been both suggested as promising andoe materials due to their high Li-ion storage capacities. This proposal designs new composies, namely the dispersion of transition metal oxides on graphene nanosheets (sheet-on-sheet composites), which aims to solve the current crucial problem with two component anodes. These problems are the heavy agglomeration of graphene materials, losing their intriguing properties; poor electrical conductivity of transition metal oxides; and partial pulverization and electrode cracking caused by the volume change of the metal oxide anodes during the repetitive cycling process with lithium ions, leading to a loss of electrical activity. In the proposed sheet-on-sheet composite, two components work together and exhibite complimentary synergistic effect. This is ascirbed to the following points: two dimensional transition metal oxides have large contact area with two dimensional graphene materials, leading to an effective separation of graphene nanosheets against further agglomeration. In addition, graphene materials are tightly stacked with transitional metal oxide nanosheets, therefore their volume changes or electrical conductivity can be accommodated or improved in the presence of graphene nanosheets.Compared to common nanoparticle, nanosheet structure is more stable and hard to aggregate during cycling.This project will focus on the improvement of electrochemical properties by optimal adjusting the weight ratio of two components, morphology and size, dispersion uniformity of two components in the sheet-on-sheet nanostructure, etc. Moreover, this project will summarize and analyze the mechanism of lithium ion diffusion, insertion, extraction and storage in the suggested sheet-on-sheet nanostructure.

石墨烯和过渡金属基氧化物锂电池材料，由于具有较高的储锂容量，都被认为具有潜力替代商业碳负极。本项目设计了过渡金属氧化物纳米片分散在石墨烯纳米片上的片片相隔复合结构，针对性地解决两者仍存在的一些关键问题即：石墨烯极易团聚或堆积成为常规石墨片，失去其优异性能；金属氧化物的电导性较差，储锂时存在一定体积变化，导致储锂活性受到一定抑制。在设计的片片相隔复合结构中，两组分通过相似的纳米片结构的复合，能够最大程度地发挥协同功效,这是因为：二维的金属氧化物纳米片同石墨烯具有较大的接触或隔离面积，能够有效分隔石墨烯，防止其团聚；同时石墨烯也能通过片片紧密接触，有效缓解金属氧化物储锂时的体积变化和提高其电导性能。纳米片相对常见纳米粒子结构也更加稳定，不容易团聚。本项目将结合复合结构两种组分比例，形貌尺寸，复合匹配均匀程度等，达到储锂性能的优化，同时着重总结分析锂离子在该片片复合结构中插入、析出和储存的机理。

本项目重点研究了石墨烯负载高容量纳米片电极材料的片片复合结构，包括石墨烯负载金属氧化物纳米片（氧化铁、氧化铜、氧化钼）、石墨烯负载金属硫化物纳米片（硫化锡、硫化钴和硫化铜）、,以及石墨烯负载硫纳米片、锡钴合金和硫化钴纳米粒子等其它形貌复合材料。通过这些研究，一定程度上解决了目前存在的一些关键问题即：石墨烯极易团聚或堆积成为常规石墨片，失去其优异性能；金属氧化物和硫化物的电导性较差，储锂时存在一定体积变化，导致储锂活性受到一定抑制。本工作通过石墨烯片片复合结构组分比例，形貌尺寸，复合匹配均匀程度等的调控，一定程度上实现了储锂性能的优化，通过讨论也分析锂离子在石墨烯片片复合结构中储存的机理。