V. Focused Fundamental Research - EERE - U.S. Department of ...

Unocic – ORNL
V.E.9 In situ Electron Spectroscopy of Electrical Energy Storage Materials (ORNL)
Figure V - 213: SEM micrograph of a MEMS-based silicon microchip used
to enclose the liquid electrolyte
Biasing contacts are deposited onto the lower
chip/window of the cell, which doubly serves as a platform
for attaching battery electrodes and for interfacing with an
external potentiostat for electrochemical testing. A 500nm
spacer material patterned on the upper chip controls the
thickness of the liquid electrolyte layer in the cell.
The cell incorporates a liquid delivery system
(microfluidic syringe pump and microfluidic tubing) to
flow liquid electrolyte between the SiN x membranes
comprising the cell. This holder was built specifically for
the Hitachi HF3300 S/TEM operating at 300kV, which is
equipped with TEM and STEM imaging detectors and a
Gatan Quantum GIF for EELS and EFTEM. The
experimental setup of the in situ electrochemical cell TEM
holder, microfluidic syringe pump, and potentiostat is
shown in Figure V - 214.
Figure V - 214: Experimental setup of the in situ electrochemical cell TEM
holder, microfluidic syringe pump to deliver liquid electrolyte to the cell and
potentiostat for electrochemical testing.
Results
This device has been used to dynamically monitor the
formation of the SEI on a graphite anode in situ within an
electrolyte consisting of 1M LiClO 4 in EC:DEC. Figure V -
215 shows the biasing chip platform (Figure V - 215a) with a
highly oriented pyrolytic graphite (HOPG) anode and
LiCoO 2 cathode attached using a focus ion beam (FIB)
instrument, experimental charging curve Figure V - 215b), and
TEM micrographs of the HOPG anode through the silicon
nitride viewing window before (Figure V - 215c) and during
(Figure V - 215d) an in situ electrochemistry experiment.
Figure V - 215d clearly shows the formation of the SEI on the
graphite anode.
Figure V - 215: a) SEM micrograph of battery electrodes (HOPG anode and LiCoO2 cathode) attached to biasing microchips and across the SiNx membrane b)
charging curve, c) bright-field TEM image of HOPG anode before experiment and d) snapshot acquired during in situ electrochemistry experiment depicting the
formation of the SEI on the surface of the graphite anode.
FY 2011 Annual Progress Report 659 Energy Storage R&D