基于高压扭转工艺的脱Al功能材料结构演变机理研究

For the metal nanomaterials of lithium-ion battery anode, there is an urgent need for a more high-efficiency, less-contaminated efficient preparation method. Al and non-Al metal are alternately stacked into multilayer foils and processed by high-pressure torsion and alkali etching to obtain a kind of two-stage nanostructured material including nanopores and nanolayers. The research contents include: (1) establishing a mathematical model between the strain and the diffusion distance of the heterogeneous metal atoms at the interface during initial HPT stage and clarifying the mechanism that the pure shear deformation provided by HPT promotes the interface bonding of the heterogeneous metal overlapping foils; (2) determining the quantitative correlation between the large number of crystal defects and the internal free energy of the binary immiscible metals system during deeply deformation and describing the mechanism that severe plastic strain provided by HPT influences the expansion of solid solubility; (3) fitting the relationship between the super-high accumulated deformation and the grain boundary orientation difference , the dislocation density and discussing the mechanism that the high-angle grain boundary and high-density dislocations during HPT influence the two-stage nanostructure generating during the alkali etching process. This project provides theoretical support and technical methods for the “green” preparation of functional materials with new nanostructures of for nanomaterials.

面向锂离子电池金属负极纳米材料需要更高效、环保制备方法的迫切需求，本项目通过对Al和非Al金属交替堆叠的多层箔片进行高压扭转和碱蚀处理，以获得“纳米孔-纳米层片”双级纳米构型材料，并对其结构演变机理展开研究。研究内容包括：（1）在高压扭转变形初期，构建应变量和异质金属原子界面处扩散距离之间的数学模型，阐明高压扭转提供的纯剪切变形对促进异质金属交叠箔片界面焊合固结的影响机理；（2）在深度变形阶段，确定晶体缺陷和二元不互溶金属体系内部自由能之间的定量关系，揭示高压扭转提供的剧烈塑性应变对固溶度扩展的作用机理；（3）建立超高累积变形量与晶界取向差、位错密度之间的函数关系，明确由高压扭转引入的大角度晶界、高密度位错对碱蚀脱Al后的双级纳米结构成型的作用机制。本项目为“绿色”制备具有新型纳米构型的功能材料提供了必要的理论支持和技术手段。

通过高压扭转工艺对A1/Zn异种金属进行合金化处理以及后续退火处理，结合表征手段和分子动力学模拟研究了Al/Zn金属体系在变形后的微观结构演变机理，标定了A1/Zn混合物的相组成，揭示了其中非晶相成因与特定晶面处原子扩散和高位错密度（2.17×1017 m-2）之间的关系。对高压扭转技术制备的纳米晶粒/石墨烯复合结构进行了研究，试制了高性能的无枝晶电极，并表征分析了掺杂石墨烯-Li复合材料经过高压扭转处理之后的室温强度和延伸率，验证了快速锂离子传输通道和极高机械强度的这种合理组合使得复合阳极具有显着增强的电化学性能，且能够用于高能Li电池中。将高压扭转技术应用到Fe3O4和层片状石墨（GNS）的复合物制备过程中，并通过相应的电化学实验印证了该方法原位生成的Fe3O4/GNS复合材料具有良好的储锂性能并在多次较大电流循环下（5C）仍能保持较好的容量（608.2 mAh·g-1），同时也间接印证了剧烈塑性变形技术在锂电池负极材料制备尤其是在金属基纳米功能材料制备中的较大潜力。结合高压扭转法和高能球磨的双重机械合金化技术生成次级结构，以锗铜共晶合金为对象，获得了高堆积密度块状纳米次级结构，并对样品的颗粒间导电性和电池循环性能也有大幅促进，在经过2800个循环后，其容量保持率依然能达到96%。基于以上研究，为未来更高效、环保地制备具有纳米结构的金属电极材料提供了一定的实验和理论基础。