Phase stability of alloy-type lithium storage anode materials

在本项目中，将进行一项系统的研究，以提供关于锂电池储锂阳极的潜在合金系统的一致和广泛的信息。三个项目伙伴结合了CALPHAD方法、纳米材料热力学和相变过程中热力学和动力学的结合方面的理论能力，以及在热力学性质测量、纳米材料生产和纳米结构表征方面的实验能力。将使用CALPHAD方法研究/建立具有各自子系统的Li-Si-SnC-C四元合金系统。由于纳米结构被普遍认为是提高锂电池循环稳定性的一种策略，因此合金系统中晶界和相界对相稳定性的贡献将基于作为结构长度尺度的函数的过剩自由能来模拟。在实验方面，选定的合金将被浇铸成铸锭，并通过粉碎、球磨和随后的SPS系统中的烧结来实现纳米结构。纳米结构将在基本无氧的封闭系统中使用独特的实验设备进行。这种纳米结构材料将得到彻底的表征。重点是确定透射电子显微镜中的晶粒度分布、相分布和取向分布。为此，现有的透射电子显微镜分析方法将进一步发展和扩展到超细晶粒尺寸，利用相图、全面的热力学描述和本项目开发的工具，将有可能对上述合金系统的大范围成分进行循环稳定性估计和储锂容量预测，并将确定有前途的锂电池合金材料。

In the present project, a systematic study will be carried out that provides coherent and extensive information about potential alloy systems for Li storage anodes in Li batteries. Three project partners combine theoretical competences in the Calphad method, the thermodynamics of nanomaterials and the combination of thermodynamics and kinetics during phase transformations, as well as experimental competences in the measurement of thermodynamic properties, production of nanomaterials and characterization of nanoscaled structures.The quaternary alloy system Li-Si-Sn-C with the respective subsystems Li-Si, Li-Sn, Li-Si-C and Li-Sn-C will be investigated/established using the Calphad method. Since nanostructuring is generally accepted as a strategy to achieve an increased cycling stability in Li batteries, the contribution of grain and phase boundaries to the phase stability in the alloy systems will be modeled on the basis of excess free energies as a function of structural length scales.On the experimental side, selected alloys will be cast as ingots and nanostructured by crushing, ball-milling and subsequent sintering in an SPS system. Nanostructuring will be carried out using unique experimental equipment in a closed system with essentially oxygenfree atmosphere. The nanostructured material will be thoroughly characterized. Focus will be to determine grain size distribution, phase distribution and orientation distribution in the Transmission Electron Microscope (TEM). For this, current TEM analysis methods will be further developed and extended to ultra fine grain sizes.With the phase diagrams, the comprehensive thermodynamic description and the tools developed in this project, an estimation of cycling stability and the prediction of Li storage capacity will be possible for a large range of compositions in the above mentioned alloy system, and promising materials for Li battery alloys will be identified.