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

V.B.13 Studies on the Local State of Charge (SOC) and Underlying
Structures in Lithium Battery Electrodes (ORNL)
Jagjit Nanda (PI)
Materials Science and Technology Division
Oak Ridge National Laboratory
Oak Ridge, TN 37934
Phone: (865) 241-8361; Fax: (865) 574-4066
E-mail: nandaj@ornl.gov
Postdoctoral Worker: Dr. Surendra Martha
Industrial Collaborator: Dawn Bernardi and Andy Drews,
Ford Motor Co.
Start Date: October 2010
Projected End Date: December 2013
Objectives
· Combined micro-Raman-AFM study of Li-ion
electrodes subjected to various SOC’s and stress
cycles
· Understand cycle life and voltage depression issues in
Li-rich NMC compositions and correlate the
electrochemical performance with microstcructral
phase changes
Technical Barriers
· Poor cycle life, structural stability, rate limitation and
loss of energy due to voltage suppression during
cycling. The Li-rich compostions also have very high
1st cycle irreversible capacity loss upon high voltage
cycling.
Accomplishments
· Monitored SOC variation on the surface of
commercial NCA electrodes as a function of SOC.
· Doubled the rate performance for Li-rich MNC from
Toda.
· Conducted electrochemical benchmarking of Li-rich
composition voltage suppression.
Introduction
State of charge (SOC) of a battery is a macroscopic
indicator of the amount of stored energy and is often used
as a diagnostic tool for observing battery performance. The
microscopic origin of the SOC in connection to Li-ion
electrodes is related to the local lithium content in
individual electrodes particles. However, electrodes for Liion
are composite materials comprised of active electrode
material, polymeric binders and carbon diluents. At an
electrode level, the local SOC could be non-uniform. Such
variations could then become more noticeable as the cell
degrades resulting in power fade and/or capacity fade.
Understanding the spatial variation of SOC on the
electrode surafce therefore could provide a microscopic
picture of the degradation occurring at a local scale. The
other aspect of our study relates to understanding the
electrochemical performance of the high voltage Li-rich
MNC composition and correlating it to microstructural
changes during cycling.
Approach
We have undertaken ex situ Raman mapping of
electrodes which have been electrochemically cycled under
different conditions. Utilizing a particle level SOC, we
obtained a SOC Raman map showing their distribution at a
micron length scale. The ex situ SOC map is expected to
change as we cycle the electrodes at different rates and
under extreme duty cycle conditions. This provides a
statistical means for studying the micron scale SOC
variation of commercially fabricated electrodes. The
studies will provide key failure modes at the electrode (or
materials) level that has impact on the cycle life of the Liion
cell. Apart from these we also measure and benchmark
electrochemcial performance of various capacity and high
voltage cathode compostion and correlate those with
microstrcutral analysis and degradation.
Results
SOC maps using confocal Micro-raman
measurement of cycled electrodes. We first report the ex
situ SOC analysis undertaken on production-ready
commercial LiCoNiAlO 2 (NCA) electrodes obtained from
SDI, Korea through our industrial collaborator Ford Motor
Co. Part of the work was done at their Research and
Innovation Laboraty and SOC analysis was carried out at
ORNL. The NCA electrodes were left in a charaged state
using a CCCV protocol and the difference of the surface
SOC Raman maps were compared in Figure V - 68. The SOC
distributions across the electrode were analyzed using a
histogram analysis.
FY 2011 Annual Progress Report 529 Energy Storage R&D