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

V.E.3 Intercalation Kinetics and Ion Mobility in Electrode Materials (ORNL)
Claus Daniel
Oak Ridge National Laboratory
One Bethel Valley Road
P.O. Box 2008, MS-6472
Oak Ridge, TN 37831-6472
Phone: (865) 241-9521; Fax: (865) 241-5531
E-mail: danielc@ornl.gov
Collaborators: Sergei Kalinin, Nina Balke, Nancy
Dudney, Hongbin Bei, ORNL
Ann Marie Sastry, University of Michigan
Start Date: September 2009
Projected End Date: September 2011
Objectives
· Develop fundamental understanding of deformation
processes and stress generation during lithium (Li)
intercalation (and deintercalation).
· Understand the role of crystal orientation and
deformation damage in Li ion kinetics in intercalation
compounds.
Technical Targets
· Apply Electrochemical Strain Microscopy (ESM) to
focused ion beam (FIB) micromachined samples of
lithium intercalation electrode materials.
· Develop and validate a coupled kinetic, thermal, and
mechanical model based on the experimental results.
· Investigate Li ion kinetics as a function of state of
charge.
Accomplishments
· Validated coupled kinetic, thermal, and mechanical
model based on the experimental results from AFM
and ESM
· Correlated crystal orientation and deformation
damage in Li ion kinetics in intercalation compounds
with ion mobility.
Introduction
It is commonly accepted that Li-ion battery life is
limited due to the process of degradation of electrode
materials with repeated charging/discharging. One of the
degradation mechanisms is related to development of
internal stresses in electrode particles due to repeated
lithium insertion and removal, which ultimately leads to
cracking and fracture of particles. This project targeted the
fundamental understanding, description through
mathematical modeling, and controlled experimental
validation of internal stress generation and morphology
change of electrode particles in a Li-ion battery. While the
intercalation/deintercalation process induces displacements
changing the overall dimension of the specimen, the Li
diffusion should be investigated on the single grain level.
The second integral part of the project looks into the local
lithium ion mobility, which is the underlying process for
diffusion-strain coupling.
This project was heavily leveraged by our
collaborators, the Kalinin group at the Center for
Nanophase Materials Science funded by the Office of
Science, Basic Energy Sciences Program and Nina Balke’s
Presidential Early Career Award for Scientists and
Engineers.
Approach
Thin films, produced by radio frequency (RF)
magnetron sputtering, as well as single grains of cathode
material embedded in the current collector were
investigated for Li ion mobility using the Electrochemical
Strain Microscopy (ESM) technique at ORNL. This
technique, based on strain-bias coupling, was recently
developed at CNMS and allows for studying Li ion
kinetics at the nanometer scale. A high frequency low
voltage pulse was applied via the AFM tip, which redistributed
lithium in the tip vicinity causing local
displacements in the grains. A dense population of
microcracks and slip lines can be introduced by nanoindentation
of the thin film cathode, in which case the
severity of damage is controllable via indenter penetration
depth.
Investigation of diffusion-stress coupling on the
micro-scale was performed on samples of pre-defined
simple geometry. The goal was to quantify the
intercalation induced strains in the representative microsample
of cathode material, analogously to the mechanical
behavior studies on the macroscopic samples. Samples of
cylindrical shape with micrometer dimensions were
fabricated from the thin films of cathode material. The
Energy Storage R&D 636 FY 2011 Annual Progress Report