Three dimensional characterization of failure evolution of tin and silicon in lithium ion battery electrodes

Silicon;Tin;X-ray tomography;Li ion batteries;3D characterization

Gonzalez, Joseph Fernando

关键词: Silicon;    Tin;    X-ray tomography;    Li ion batteries;    3D characterization;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/88957/GONZALEZ-DISSERTATION-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

High capacity lithium ion (Li+) host materials, such as silicon (Si) and tin (Sn), serve as potential replacements to graphite in composite battery electrodes because of their higher gravimetric capacity when reacted with lithium, thus providing higher energy and power. Sn has a theoretical capacity of 994 mAh/g, which is three times that of graphite, while Si possesses over eleven times that of graphite with a capacity of 4200 mAh/g. However, unlike graphite, full lithiation to the composition of Li3.75Sn or Li3.75Si, at room temperature, is accompanied by significant volume expansion, resulting in particle fracture and subsequent loss of functionality. In this work, the utilization of Sn and Si as high capacity alternate host materials in the form of particles within composite electrodes or wire was investigated in Li-ion batteries. Galvanostatic cycling with potential limitation was used in conjunction with the three-dimensional (3D) imaging technique of X-ray micro-computed tomography (microCT) to gather detailed accounts of Sn/Si microstructural evolution, allowing the analysis and characterization of these host materials during the critical early cycles of lithiation/delithiation (i.e., the insertion and extraction of Li+, respectively). Combining in-house algorithms with commercial software, 3D visualizations and measurements were made of particle/wire expansion and cracking. To portray the Li intercalation phase within the host material, a phase characterization method for both global and local imaging was suggested and showed promising results in relation to observed 2D extracted slice data and SEM imaging. Different failure mechanisms were resolved for Si and Sn, in addition to inhomogeneous Li diffusion into host particles/wire. Particles were also characterized into three different categories based on their evolution: inactive, partially active, and fully active. “Effective” volume expansions (i.e., without accounting for individual crack boundaries) were computed between 200% and 450% during lithiation, and effective volume reductions of 50% were measured during delithiation. Relationships between the gray scale intensity change, volumetric expansion, and particle size were established. A correlation between gray scale intensity and volumetric expansion was also recognized allowing the determination of particles as inactive, partially active, or fully active. Finally, the relaxation effects of Sn following lithiation were also investigated showing varying reaction mechanisms between damaged and undamaged material.