In Situ Characterization of Lithium Deposition and Microstructure Evolution of Silicon Anodes By Synchrotron X-Ray Imaging

Abstract

Advanced lithium batteries are crucial for next-generation energy storage systems such as portable electronics and electric vehicles. Due to a low specific capacity (372 mAh/g) batteries using traditional graphite-based anode materials can hardly meet the increasing demands of light weight and high energy density. With theoretical specific capacities that are approximately 10 times higher than that of conventional graphite anodes metallic lithium (3860 mAh/g) and silicon (4200 mAh/g) anodes are regarded as two excellent candidates. Specifically, the energy density of batteries could be dramatically increased approximately from 250 Wh/kg to 440 Wh/kg by replacing graphite with lithium anodes.[1] However these two promising anodes suffer from the dramatic volume change due to microstructure degradation and low coulombic efficiency derived from unstable solid electrolyte interphase (SEI) during cycling. In addition, the dendritic and/or fiber-like deposition on lithium anode could initiate an internal short circuit and thus leads to a fast battery failure. Despite great progress recently achieved on improving electrochemical performance, a clear picture of the microstructure degradation of electrode and battery failure mechanisms is still elusive, largely due to a lack of feasible in situ characterization techniques. Synchrotron X-ray imaging has evolved into a tool of choice allowing in situ or operando analysis of the internal morphology/structure evolution non-invasively.[2, 3] With this technique the internal microstructure of a silicon electrode in a lithium ion battery was visualized during battery operation.[4] The silicon particles were found to change their sizes upon lithiation/delithiation and the changes could be quantified. An expansion prolongation phenomenon of Si particle was discovered involving that some particles continue expanding even after switching the battery current direction and shrinkage would be expected. In addition, Li deposition at the Li/separator interface as well as within a porous carbon matrix was visualized and quantified three dimensionally. The study provides new basic insights into expansion/shrinkage processes inside Si particles and uncovers the Li deposition behavior that can hardly be probed by surface imaging techniques. Finally investigations on Li anode degradation mechanisms are presented.[5] References [1] D. Lin, Y. Liu, Y. Cui, Reviving the lithium metal anode for high-energy batteries. Nature Nanotechnology, 2017, 12, 194. [2] M. Ebner, F. Marone, M. Stampanoni, V. Wood, Visualization and quantification of electrochemical and mechanical degradation in Li ion batteries. Science, 2013, 342, 716-720. [3] K. J. Harry, D. T. Hallinan, D. Y. Parkinson, A. A. MacDowell, N. P. Balsara, Detection of subsurface structures underneath dendrites formed on cycled lithium metal electrodes. Nat Mater, 2014, 13, 69-73. [4] K. Dong, H. Markötter, F. Sun et al., In situ and Operando Tracking of Microstructure and Volume Evolution of Silicon Electrodes by using Synchrotron X-ray Imaging. ChemSusChem, doi:10.1002/cssc.201801969. [5] Fu Sun, Xin He, Xiaoyu Jiang, et al., Advancing Knowledge of Electrochemically Generated Lithium Microstructure and Performance Decay of Lithium Ion Battery by Synchrotron X-ray Tomography, Materials Today, accepted.