AVS 56th International Symposium & Exhibition
    In Situ Microscopy and Spectroscopy: Interfacial and Nanoscale Science Topical Conference Thursday Sessions
       Session IS+AS-ThA

Paper IS+AS-ThA8
Direct Observation of Interfacial Layer Formation in Li-Ion Battery using In-Situ TEM and EELS

Thursday, November 12, 2009, 4:20 pm, Room C4

Session: In-Situ Microscopy and Spectroscopy: Surface Reactions
Presenter: C.M. Wang, Pacific Northwest National Laboratory
Authors: C.M. Wang, Pacific Northwest National Laboratory
W. Xu, Pacific Northwest National Laboratory
L. Saraf, Pacific Northwest National Laboratory
B. Arey, Pacific Northwest National Laboratory
J. Liu, Pacific Northwest National Laboratory
Z. Yang, Pacific Northwest National Laboratory
J.G. Zhang, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
D.R. Baer, Pacific Northwest National Laboratory
Correspondent: Click to Email
One of the fundamental challenges facing the Li-ion battery development is the understanding of the fading mechanism of the active electrode materials during the repeated charging and discharging. In-situ methods based on x-rays have provided some information regarding the structural evolution of the electrode materials during the operation of a battery. However, in-situ work using x-ray only gives the average results, yielding no spatial resolution. Furthermore, it has been generally realized that the microstructural evolutions both at the interface between the electrolyte and the electrode and within the electrode (active materials) due to Li migration play a vital role on the performance as well as the overall life-cycle of the battery. In-situ transmission electron microscopy (TEM) and spectroscopy will be ideal tools for probing the structural evolution of the electrode materials during battery operation. However, related to the high vacuum operation of a TEM as well as the requirement of electron transmission through the sample, a prototype battery must be sealed with thin membrane that enables the electron transmission at the interested region. It is known that electrolytes based on ionic liquid have a low vapor pressure. Therefore, it is generally expected that using ionic liquid as electrolyte, the prototype battery may be operated in vacuum without sealing the whole system using a thin membrane. In this work, we report our exploratory work on developing in-situ TEM devices that will eventually enable direct and high spatial resolution observation of the structural evolution of the interface between the electrolyte and the electrode materials. In a model experiment, a prototype Li-ion battery was developed in the system of using SnO2 nanowire as anode, an air stable salt LiTFSI in a hydrophobic ionic liquid as electrolyte, and LiCoO2 as cathode. Focused ion beam (FIB) manipulation of a single nanowire enables the assembling of a prototype battery. Furthermore, due to the low vapor pressure of the ionic liquid, the whole system can be directly loaded into a TEM without sealing. The interface across the solid-ionic liquid was studied during charging and discharging using TEM imaging and electron energy loss-spectroscopy (EELS). By comparing these results with those obtained from batteries based on coin cell design, several challenges were identified. These results will be discussed along with the future research directions.