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

V.E.9 In Situ Electron Spectroscopy of Electrical Energy Storage Materials
(ORNL)
Raymond R. Unocic
Oak Ridge National Laboratory
Materials Science and Technology Division
One Bethel Valley Rd
PO Box 2008 MS-6064
Oak Ridge, TN 37831-6030
Phone: (865) 574-0096; Fax: (865) 576-5413
E-mail: unocicrr@ornl.gov
Start Date: January 2010
Projected End Date: December 2014
Objectives
· The primary aim of this research is to develop and
perform quantitative in situ electron microscopy
experiments of electrical energy storage materials
using an electrochemical cell holder built specifically
for in situ transmission electron microscopy (TEM)
characterization.
· The key benefits include the ability to wholly contain
and image through volatile organic electrolytes while
performing nanoscale electrochemistry experiments
within the high vacuum environment of the TEM
column at high spatial and temporal resolution.
· This technique will enable evaluations of critical nmscaled
microstructural and micro-chemical changes as
a function of battery test conditions, electrode
materials, electrolyte, and electrolyte additives.
Technical Barriers
The technical barrier is the present lack of highresolution
electrochemical characterization techniques,
which allow for the direct observations of dynamically
evolving electrochemical reactions during
charge/discharge cycling.
Technical Targets
· Develop in situ characterization technique and
methodology to investigate dynamically evolving
electrochemical reaction mechanisms.
Accomplishments
· Developed a prototype in situ electrochemical cell
capable of performing in situ mircroscopy
experiments
· Studied the formation and growth of the solid
electrolyte interphase (SEI) on graphite electrodes in
real time and at high spatial resolution.
Introduction
The accelerated development of materials for
utilization in electrical energy storage systems will hinge
critically upon our understanding of how interfaces
(particularly electrode-electrolyte solid-liquid interfaces)
control the physical and electrochemical energy
conversion processes. A prime example is found in Li +
ion-based battery systems, where a passive multiphase
layer grows at the electrode/electrolyte interface due to the
decomposition of the liquid electrolyte. Once formed, this
SEI protects the active electrode materials from
degradation and also regulates the transport and
intercalation of Li + ions during battery charge/discharge
cycling. Due to the dynamically evolving nature of this nm
scaled interface, it has proven difficult to design
experiments that will not only elucidate the fundamental
mechanisms controlling SEI nucleation and growth, but
will also track microstructural and chemical evolution of
the SEI as a function of charge/discharge cycling to be
monitored in real time.
Approach
In this program, we have developed an
electrochemical fluid cell for in situ TEM studies of
electrochemical reactions of energy storage materials. The
core challenge of preventing the evaporation of high vapor
pressure and volatile organic liquid electrolytes has
recently been overcome through sealing of the fluid
between thin electron transparent viewing membranes.
Typically this is accomplished through the use of silicon
microchip devices containing a central thin electron
transparent silicon nitride (SiN x ) viewing membrane as
shown in Figure V - 213. To create the electrochemical cell,
two silicon microchips are stacked upon one another and
placed within the tip of a precision machined TEM holder.
Energy Storage R&D 658 FY 2011 Annual Progress Report