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

零应变（ZS）电极材料可以在不发生大的体积变化的情况下进行晶体结构与锂离子的充电和放电，对于提高锂离子电池的使用寿命非常有吸引力。虽然钛酸锂尖晶石（ZS阳极材料）已经用于商业电池单元中，尽管与石墨相比其能量密度显著较低，但目前已知的ZS阴极材料仍然仅具有科学意义。然而，还不可能从这些化合物中推导出晶体结构中的任何明显的相似之处，从中可以推导出ZS行为，并且有针对性地表示新型ZS阴极材料将是可能的。目前的项目提案涉及这个问题：是否有晶体结构的化学设计标准，有针对性的发展ZS阴极材料？在锂离子存储晶体系统中，什么样的结构、化学和机械特性使ZS效应可能发生？重点是两个已知的ZS材料K0.6FeF3和LiCaFeF6的固溶体形成的机制。对于这两种结构类型，阳离子的取代可以提供基本的见解，结构变化有利于ZS效应，这是适得其反。为此，协调实验材料合成和表征在IAM在卡尔斯鲁厄和理论材料建模和模拟在FMF在弗赖堡计划，以阐明化学计量结构ZS性能关系的潜在ZS阴极材料。该项目旨在确定和解释Li+电极材料在晶体结构化学方面的ZS行为的基本先决条件，理想情况下，新的ZS化合物可以在这种设计标准的基础上以更有针对性的方式生产。

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.