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

• Applicant: Dr. Erwin Hüger
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 253211366

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.

• DFG Programme: Research Grants