Sn-NiTi复合锂离子电池负极的超弹性与其电极性能

In this project, the capacity fading issues induced by the large volume expansion during lithation of Sn anode are researched, wherein the superelasticity of NiTi alloys has been applied to improve the cycle performance of Sn-base anodes. Firstly, this study concerns on the preparation of Sn-NiTi composite anode materials, which contain pure Sn and B2-NiTi matrix phases, by the plasma-assisted ball milling and magnetron sputtering and so on. Secondly, the study focuses on the quantitative and qualitative analysis for microstructure of the Sn-NiTi composites. The electrochemical performances, such as lithiation/delithiation capacities and cycleability, especially the stress-strain effects during phase (Sn, NiTi) transformation and thermodynamics and dynamics properties of the composite anodes will be investigated. On this basis, the mechanism of interaction between stress-strain of Sn and martensitic transformation of NiTi will be studied. And finally, the influences of synergistic action of stress, induced by the phase transformations of Sn and NiTi, on the electrochemical performance of Sn-based anodes will be revealed. The research results will not only demonstrate a new concept which provides a simple way to improve the cycle performance of metal-based Li insertion electrodes, but also are very important to provide the guidance for overcoming the capacity fading of alloy (Sn, Al, Si, Sb, etc.) -based anode materials by the stress-induced martensitic transformation of NiTi and other shape memory alloys.

针对Sn负极的体积膨胀效应大而导致其容量衰减的问题，本项目拟利用NiTi合金的超弹性效应来改善Sn基负极的循环性能。首先采用等离子体辅助球磨、磁控溅射等方法制备出单质Sn相均匀分散于B2-NiTi基体中的两相复合负极材料；然后对复合结构电极的相结构、相尺度、分布等微观特征进行定性和定量表征；着重研究Sn和NiTi在充放电过程中分别发生的应力诱发马氏体相变与嵌锂-脱锂反应这两个过程的应力/应变效应、电极的嵌锂-脱锂容量、循环稳定性等电化学特性；进而揭示应力诱发马氏体相变的超弹性应变与Sn嵌锂-脱锂反应过程的应力应变的相互作用机理，复合电极中应力协同作用对Sn负极电化学性能的影响规律。开展本项研究的主要意义在于提供了一种全新的改善金属基负极材料循环性能的方法，对于用形状记忆合金的超弹性解决Sn、Al、Si、Sb等各种金属基负极材料的容量衰减问题具有重要的理论和实际指导意义。

在项目研究中，针对高容量Sn、SnO2，Si基等金属负极的体积膨胀效应大而导致其容量衰减、嵌锂/脱锂可逆性差的问题开展研究；主要通过多相多尺度微纳结构调控的方法，利用NiTi的合金的超弹性效应和碳（C，graphene）基体材料的形变缓冲作用来改善金属基负极材料的循环性能。在研究中，注重材料结构调控方法的创新，主要采用磁控溅射等方法制备出Sn、SnO2相均匀分散于B2-NiTi基体中的两相复合或三明治结构薄膜负极材料；采用等离子体辅助球磨、简易溶液化学法、电化学沉积等方法制备结构出不同微观结构的Si-C，Ge-C，SnO2-C等复合负极材料。该类负极材料均显示出优良的储锂特性。主要取得重要成果为：1）针对Sn基氧化物负极转化反应可逆性差的问题，提出多尺度界面抑制纳米Sn相粗化可提高Sn/Li2O界面反应活性的机制，通过纳米结构调控在SnO2负极中实现高达86.2-95.5%的首次库仑效率，为目前所有报道中的最高值。实现嵌锂电极材料中Li2O的Li+脱出的高度可逆将有助于推动一系列新型高容量金属基电极材料的应用2）首次将NiTi形状记忆合金作为活性Sn负极的基体材料，揭示出NiTi合金的应力诱发马氏体相变和超弹性效应可有效克服Sn电极的性能衰减，提供一种全新的改善金属基负极循环性能的思路和方法。在本项目执行期间，共在Energy Environ. Sci, Nano Energy, J. Mater. Chem.，Nanoscale等知名期刊上发表学术论文14篇,其中影响因子大于5.0的9篇。 撰写英文专著1章; 申请发明专利7项，已获授权发明专利4项。获广东省优秀博士学位论文奖、广东省科学技术奖一等奖等奖励。