Design criteria for crystal structures of zero-strain cathode materials for lithium ion batteries

零应变(ZS)电极材料可以利用锂离子对晶体结构进行充放电，而体积变化不大，对于提高锂离子电池的使用寿命非常有吸引力。虽然ZS负极材料钛酸锂尖晶石已经被用于商业电池，尽管其能量密度比石墨低得多，但目前已知的ZS正极材料仍然只有科学价值。然而，目前还不可能从这些化合物的晶体结构中得出任何明显的相似之处，由此可以推断ZS的行为，并有可能有针对性地表示新型ZS正极材料。本项目提案涉及这一问题：是否有针对性地开发ZS正极材料的晶体结构-化学设计标准？在锂离子储存晶体体系中，什么结构、化学和机械性质使得ZS效应的发生成为可能？重点研究了两种已知的ZS材料K0.6FeF3和LiCaFeF6的固溶体形成机理。对于这两种结构类型，阳离子的取代可以提供基本的见解，哪些结构变化有利于ZS效应，哪些结构变化会产生相反的效果。为此，计划在卡尔斯鲁厄的IAM进行协调的实验材料合成和表征，并在弗莱堡的FMF进行理论材料建模和模拟，以阐明潜在的ZS正极材料的化学计量结构和ZS性质关系。该项目旨在从晶体结构化学的角度确定和解释锂离子电极材料的ZS行为的基本前提条件，理想情况下，可以在这种设计标准的基础上以更有针对性的方式生产新的ZS化合物。

Zero-Strain (ZS) electrode materials, in which the charging and discharging of crystal structures with lithium ions can take place without large volume changes, are very attractive for improving the service life of lithium ion batteries. While lithium titanate spinel, a ZS anode material, is already used in commercial battery cells despite its significantly lower energy density compared to graphite, the currently known ZS cathode materials are still exclusively of scientific interest. However, it is not yet possible to derive any obvious parallels in crystal structure from these compounds, from which ZS behaviour could be deduced and a targeted representation of novel ZS cathode materials would be possible. The present project proposal deals with this problem: Are there crystal structure-chemical design criteria for a targeted development of ZS cathode materials? What structural, chemical and mechanical properties make the occurrence of a ZS effect probable in a lithium ion-storing crystal system? The focus is on the mechanism of solid solution formation of the two known ZS materials K0.6FeF3 and LiCaFeF6. For both structure types, substitution of the cations can provide fundamental insights which structural changes favour the ZS effect and which are counterproductive. To this end, coordinated experimental material synthesis and characterisation at the IAM in Karlsruhe and theoretical material modelling and simulation at the FMF in Freiburg are planned, to elucidate stoichiometry structure ZS property relationships of potential ZS cathode materials. This project aims to identify and explain the essential prerequisites for the ZS behaviour of Li+ electrode materials in terms of their crystal structure chemistry, and ideally new ZS compounds can then be produced in a more targeted way on the basis of such design criteria.