硫化钨基纳米材料锂化/退锂化及电化学性能影响因素研究

Graphite, the current commercial anode material of lithium-ion batteries (LIBs), has a stable structure, a good conductivity etc., but it’s specific capacity can’t meet the needs of large-scale power equipments. Tungsten disulfide (WS2), which has a graphite-like layered structure, possesses a larger interlayer spacing and a higher specific capacity. However, fast capacity degradations and poor cycling performance have appeared in LIBs with WS2 as anodes, which severely limits the practical application of WS2. The electrochemical performance of LIBs with WS2 nanomaterials as anodes is closely related to WS2 nanomaterials’ structural change and the consequent stress during lithiation/delithiation, but so far no systematic research has been reported. Through combining in-situ study in transmission electron microscope/scanning electron microscope with the conventional method of analyzing charging/discharging products’ structure and composition in LIBs, this project intends to study the lithiation/delithiation process of WS2 nanomaterials, to determine the electrochemical reaction mechanism and to explore the influencing factors of electrochemical performance degradations. The experiment results show that WS2/carbon composites have an improved electrochemical performance by the synergistic effect between different constituents. On this basis, this project will carry out systematic in-situ study on the structure, composition and mechanical property in WS2 nanotubes/carbon composites during lithiation/delithiation. The results of this subject will provide an important reference on how to improve electrochemical performance of WS2-based nanomaterials.

商用化锂电池负极材料石墨具有结构稳定、导电性好等优点，但其比容量不能满足大型功耗设备的需要。WS2具有与石墨类似的层状结构，且具有层间距大、比容量高的优势，但目前存在的容量退化快、循环性能差等问题严重限制了其实际应用。以WS2纳米材料为负极的锂电池电化学性能与其锂化/退锂化过程中WS2的结构演变以及由此产生的应力息息相关，然而当前未见系统的相关研究报道。本课题拟通过将分析锂电池充放电产物结构和成分的常规方法与透射电子显微镜/扫描电子显微镜中的原位手段相结合，研究WS2纳米材料的锂化/退锂化过程，判定其电化学反应机理并探讨电化学性能变差的影响因素。同时，基于WS2/碳复合材料中两种组分发生协同作用从而提高电化学性能这一实验事实，针对锂化/退锂化时WS2纳米管和碳组成复合材料的结构、成分、力学性能变化展开系统的原位研究。本课题的研究结果将为改善WS2基纳米材料的电化学性能提供重要依据。

目前商用化锂电池的比容量不能满足大型功耗设备的需要，WS2具有与商业化石墨负极类似的层状结构，且具有层间距大、比容量高的优势，但目前存在的容量退化快、循环性能差等问题严重限制了其实际应用。本课题通过透射电子显微镜中的原位手段确认WS2纳米管锂化后的产物是Li2S和W，单质W呈现出颗粒状并分布在Li2S中，确定以WS2纳米材料为负极的锂电池在放电过程发生的反应，WS2纳米管在锂化过程中层间距变化达到20%，直径变化率达到38%，长度变化率达到12.6%，锂化速率为180 nm/s。WS2纳米管完全锂化后层状结构消失，而且在退锂化过程中不能恢复，另外， WS2纳米管在锂化后变脆并且很容易折断，这可能是WS2纳米材料容量退化快、循环性能差的部分原因。基于WS2和碳形成的复合材料中WS2和碳之间会发生协同作用从而提升锂电池的电化学性能这一结论，在本研究中设计出具有三维多孔结构的WS2-碳复合材料NGQDs-WS2/3DCF来提升其电化学性能。本课题的研究结果将为改善WS2基纳米材料的电化学性能提供重要依据。