Characterization of battery anode materials by X-ray and electron-based imaging techniques

To tackle the problem of increasing carbon dioxide emissions, Li batteries have been proposed as a promising storage medium of electricity harvested from renewable clean energy sources. In addition, Li batteries are the predominant power sources in cell phones, laptops and electric vehicles. However, state-of-art Li-ion batteries with an energy density below 300 Wh kg-1 cannot meet the ever-increasing demands for lighter and safer batteries with longer life time and lower costs. Li batteries based on anode materials with higher specific capacity (e.g. silicon and lithium) could potentially boost the energy density of Li batteries. In this dissertation, X-ray and electron-based imaging techniques were used to investigate the currently existing challenges that prevent the massive commercial deployment of silicon and lithium anodes. Firstly, in-situ and operando synchrotron X-ray radiography was employed to visualize the internal microstructure change of a silicon electrode during cell operation. The volume expansion and shrinkage of individual Si particles during lithiation and delithiation were dynamically displayed. An expansion prolongation phenomenon was discovered and quantified whereby some particles continue expanding even after the reversal of the external battery current direction when shrinkage would be expected. Secondly, lithium deposition at the Li/separator and at the Li/carbon matrix interregion was discovered by synchrotron X-ray tomography. A higher concentration of widely distributed deposition sites was found under an increased deposition density. The morphology and distribution of Li deposition within the commercial Celgard® 2325 separator are, for the first time, presented in three dimensions. In addition, the spatial distribution of Li deposition inside a carbon deposition host was visualized and quantified. Thirdly, the Li deposition mechanism was further investigated using focused ion beam scanning electron microscopy. Li nucleation was found to preferably stem from surface irregularities (cracks and impurities, etc.) of the Li substrate. Surface heterogeneity of the Li substrate is concluded as one critical fundamental cause for the initial inhomogeneous nucleation, rather than the SEI properties and/or an uneven Li-ion flux. Computational modeling of the electrode/electrolyte interface further confirms the favorable nucleation sites and helps to explain the nucleation and growth behavior of dendrites. Lastly, a Li10SnP2S12 (LSPS) solid-state electrolyte was employed in a Li-S cell to mitigate the side reactions of liquid electrolyte and suppress the dendritic growth. In-situ and operando synchrotron tomography and energy dispersive diffraction were simultaneously conducted to visualize the morphological and compositional evolution. Cavities/voids observed at the InLi/LSPS interface demonstrated the interfacial mechanic degradation during battery operation, which was also reflected by the energy dispersive diffraction results and the electrochemical performance.

Author dc:creator

• Dong, Kang

Advisor dc:contributor.advisor

• Banhart, John

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Identifier URI

http://dx.doi.org/10.14279/depositonce-9072

OAI identifier oai:identifier

oai:depositonce.tu-berlin.de:11303/10081