An In Situ TEM Liquid Cell for Imaging Electrode/Electrolyte Interactions

The transmission electron microscope (TEM) has provided valuable insights about electrochemical processes in solid battery electrode nanostructures [1], and recent advances in microfabrication have enabled the encapsulation of volatile liquids in miniature, high-vacuum electrochemical cells [2]. Imaging the electrode/electrolyte interfaces in a standard liquid electrolyte environment will enable the study of electrolyte decomposition processes such as the formation and evolution of solid-electrolyte interphases (SEI) on Li-ion battery anodes. We have developed a custom TEM liquid cell platform that is well suited to quantitative electrochemical control on Li-ion battery materials and electrolytes. The liquid cell design incorporates a thin, electron-transparent liquid cavity (0.1-1 micron thick) between two silicon nitride membranes, multiple current-collector electrodes with minimal exposed area optimized for facile nanomaterial assembly, and sealable fluid fill ports which allows the cell to be electrochemically cycled either on or off the TEM holder.

            To test the cell operation, we imaged Li electrodeposition on a nanopatterned Ti working electrode. The liquid electrolyte consisted of 1:1 ethylene carbonate:diethyl carbonate with 1M LiPF₆, and a galvanostatic two-electrode charging experiment was performed to deposit Li from the electrolyte onto the working electrode. The TEM was operated in scanning mode (STEM) with a low electron dose to minimize beam effects on the liquid electrolyte. Upon application of a few pA of current, we acquired a characteristic chronopotentiometric curve and saw clear deposition of Li particles in the STEM images and movies (see Figure 1). Following Li deposition, a thick growth of SEI was evident near the Li nanoparticles, consistent with electrolyte decomposition in the presence of reactive Li. We also imaged electrodeposition/stripping of Cu nanoparticles in the same liquid environment and will explore battery-relevant materials such as LiFePO₄ and Si nanostructures. Our TEM liquid cell provides a unique, high-resolution view of the electrode/electrolyte interfacial phenomena, and both the challenges in fabrication as well as the successes in imaging electrochemical processes will be presented.

1.         Sullivan, J. P. et al. “Real-time Studies of Battery Electrochemical Reactions Inside a Transmission Electron Microscope.” Sandia Technical Report SAND2012-0103 (2012). doi:10.2172/1038174

2.         de Jonge, N. & Ross, F. M. “Electron microscopy of specimens in liquid.” Nat Comms 6, 695–704 (2011).