NiTi合金复合锂离子电池负极材料嵌锂、脱锂行为的原位透射电子显微学研究

For the unique super-elasticity property of NiTi alloy, it induced a superior performance in alleviating the huge volume expansion of anode materials (Sn or Si based) during lithiation and improving the cycling performance of lithium battery, which has drawn considerable research focus in lithium ion battery and relevant field. However, up to now, our knowledge on the structure evolution of NiTi alloy during the charge-discharge process is very limited, and the relationship between NiTi alloy structure and the lithium ion battery performance is still unclear, although which is of significant importance in designing new anode materials. The aim of this project is uncovering the lithiation and delithiation process of NiTi alloy composited Sn-based, Si-based anode materials by in situ transmission electron microscopy. Specifically, the microscopic mechanism of the phase transformation of NiTi alloy during charge and discharge process, and the battery performance, including specific capacity, cycling performance and charge-discharge rate as a function of the microstructure of NiTi alloys will be studied in details. Meanwhile, combined with electrochemical experiments, the structure evolution of NiTi alloy in longtime charge-discharge process and the effect of this structure change on the battery performance will also be evaluated. The completion of this project will give in-depth insight into the lithiation and delithiation behaviors of the NiTi alloy composited Sn-based, Si-based anode materials, providing theoretical support for the designing of new high-performance anode material, as well as finding new applications for NiTi shape memory alloy.

NiTi合金因其独特的超弹特性，可有效缓解锂离子电池负极材料在嵌锂时的巨大体积膨胀和提高电池循环性能，因而倍受关注，并有望在高性能Sn基、Si基负极材料中得到广泛应用。但NiTi合金缓解负极材料体积膨胀的微观变化过程和影响电池性能的机制尚不清楚。本项目拟借助原位透射电子显微技术，构建纳米锂离子电池，原位研究NiTi合金复合Sn基、Si基负极材料的嵌锂、脱锂行为，实时、直观地记录NiTi合金缓解负极材料体积膨胀的微观变化过程，揭示其微观机理及影响因素。在此基础上，结合电化学测试技术，原位研究此复合材料微结构变化与电池比容量、循环性能和充放电速率等的关系，揭示NiTi合金独特机械行为影响锂离子电池性能的微观机制与规律。项目的实施，将进一步加深对NiTi合金复合锂离子电池负极材料嵌锂、脱锂行为的认识，还有望在设计新型高性能NiTi复合负极材料方面获得突破，为其实际应用提供科学依据，拓宽应用领域。

近些年来，随着世界能源和环境危机的日益加剧，人们越来越需要开发新的能源材料来替换已被广泛使用的石油、煤和天然气等传统能源材料。锂离子电池具有工作电压高、体积小、质量轻、充放电速度快、零污染、自放电小、能量密度大、无记忆效应、安全性能高和循环寿命长等优点，已得到了世界广泛的认可。目前锂离子电池所用的负极材料大多采用石墨，而石墨的理论质量比容量只有372mAh／g，比容量十分有限，限制了其在未来发展中的应用。寻找一种致密的、高比容量的负极材料来代替传统的碳材料成为当前研究的热点。如今，锡基和硅基电极材料因其分别具有781Ah g-1和4200mAh g-1的超高理论容量密度而成为将来最具潜力的锂离子电池阳极材料。然而与碳质阳极（如石墨）不同，锡基或硅基合金阳极在充放电过程中体积变化十分显著。这些变化通常会引入高密度位错，宏观缺陷等，从而降低了锂离子电池的使用效果并缩短了电池的寿命。最近，研究人员尝试了许多方法，例如碳包覆等，用于缓冲锡基或硅基阳极材料在使用过程中的巨大的体积变化。对比这些常规方法，本项研究使用电弧熔炼法制备一种新型的Ti3Sn/NiTi多层夹心复合结构阳极。通过透射电镜对Ti3Sn阳极在充放电过程中的微观变化和相转变进行原位记录与观察。通过项目实施，我们揭示了： NiTi形状记忆合金克服阳极材料体积膨胀效应影响机制；在充放电过程中，NiTi形状记忆合金与阳极材料的界面耦合机制。此外，我们还发明了一种全新的原位电镜样品焊接方法，为探索材料拉伸力学性能提供了新的思路。研究发现，NiTi合金复合确实可以有效地调节Sn基Si基阳极材料在锂化和脱锂过程中的体积变化。这项研究为应用NiTi合金可以有效缓解阳极循环过程中的体积变化提供直接的证据表明，为提高锂离子电池的循环性能开辟了新的途径。