Li Transport in Nano-sized Silicon Electrode Materials for Li-Ion Batteries

本建议的目的是建立一种新的方法来测量锂传输通过只有纳米尺寸的薄非晶硅层，这是一个有前途的负电极材料在锂离子电池，也有兴趣作为选择性膜。锂在电极中的扩散是锂离子电池性能的关键参数，对充电和放电速率、功率密度、自放电和实际容量很重要。为了克服结构退化，纳米级电极是有利的。薄硅膜对锂的选择性过滤对于锂空气电池、锂离子选择性电极和传感器尤其重要。将建立一种方法，允许测量锂运输通过纳米薄非晶硅层从相邻的固态锂水库。用中子反射计和二次离子质谱法研究了[6LiNbO 3/Si/natLiNbO 3/Si]多层膜在低温（室温~ 400°C）等温退火过程中6Li/7 Li同位素相对分数的变化。实验将允许确定整个传输过程的速率决定步骤（扩散控制或界面控制），并首次在纳米尺寸的电极材料中量化Li扩散率和渗透率。特征活化能将从温度依赖性测量中提取。为了解决锂离子电池研究领域中其他重要的未决问题，实验将在第三年的资助期间扩展到示例性地研究含Li的Li 2Si层和Si层中的Li输运，所提出的方法的基本概念结合其灵活性将其应用于各种材料系统，使其适用于广泛的感兴趣领域。

Aim of the present proposal is to establish a new methodology for measuring Li transport through only nanometer sized thin amorphous silicon layers, which are used as a promising negative electrode material in Li-ion batteries and also interesting as selective membranes. Lithium diffusion in electrodes is a key parameter for the performance of Li-ion batteries, important for charging and discharging rates, power density, self-discharge and practical capacity. In order to overcome structural degradation, nanoscaled electrodes are advantageous. The selective filtering of Li by thin silicon membranes is especially important for lithium-air batteries, Li-ion selective electrodes, and sensors. A methodology will be established that allows measuring Li transport through nanometer thin amorphous silicon layers from adjacent solid-state Li reservoirs. The modification of the relative 6Li/7Li isotope fraction in [6LiNbO3/Si/natLiNbO3/Si] multilayers during isothermal annealing at low temperatures (room-temperature - 400°C) will be detected by neutron reflectometry and secondary ion mass spectrometry. The experiments will allow to determine the rate determining step (diffusion controlled or interface controlled) of the overall transport process and to quantify Li diffusivity and permeability for the first time in nanometer sized electrode materials. Characteristic activation energies will be extracted from temperature dependent measurements. In order to also address additional important open questions in the field of Li-ion battery research, the experiments will be extended to study exemplarily Li transport in Li containing Li2Si layers and in Si layers under mechanical stress during the third year of funding,The fundamental concept of the proposed method in combination with its flexibility to adopt it to various materials systems makes it applicable for a broad field of interest.