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

V.E.2 Modeling-Thermo-electrochemistry, Capacity Degradation and
Mechanics with SEI Layer (UM)
Ann Marie Sastry
University of Michigan
2350 Hayward St.
Ann Arbor, MI 48109
Phone: (734) 998-0006; Fax: (734) 998-0028
E-mail: amsastry@umich.edu
Start Date: October 1, 2008
Projected End Date: September 30, 2011
Objectives
· Create a multiscale finite element (FE) model that
considers self-assembled structure in order to evaluate
the effective electrochemical properties of the
aggregated particles
· Perform numerical studies of capacity fade due to the
SEI layer and stress analysis/mechanical stability of
the SEI layer in anode particles
· Characterize the SEI layer and investigate the effect
of different environmental conditions on SEI layer
formation through experimental techniques
Technical Barriers
Inadequate power and life in PHEV systems
Technical Targets
· Available energy: 56 Wh/kg (10 mile) and 96 Wh/kg
(40 mile)
· 10 s discharge power: 750 W/kg (10 mile) and 316
W/kg (40 mile)
· Cycle life: 5,000 cycles
· Calendar life: 15 years
Accomplishments
· Development of a multiscale FE model including
particle aggregation of active and additive materials in
order to determine the effective electrochemical
properties of the electrode material
· Demonstration of capacity fade due to the SEI layer
via a multiphysics model that considers film
resistance and the double-layer charging current
· Demonstration of the stress evolution in both the
active particle and SEI layer by considering a misfit
between the two phases
· Measurement of EIS and XPS for the resistance
variation due to the SEI layer and the concentration
change of elements in the surface of the SEI layer
Introduction
In order for battery performance to improve, the
failure mechanisms of Li-ion batteries, which involve
many mechanisms such as active material dissolution, SEI
layer evolution, mechanical instabilities, and thermal
failure, have to be understood and minimized. As an
extension of multiscale thermo-electrochemistry modeling
in FY2010, this model was refined based on the findings
from simulated performances and experimental
observations. The improved model enabled us to
investigate such key battery performance-determining
parameters as multi-phase particle structure and SEI layer
structure. SEI formation in composite electrode
microstructures and its effect on battery kinetics were
investigated via both experimental and numerical tools.
Improved prediction of lifetime in Li-ion battery cells will
be informed by exploring capacity degradation in
composite multi-phase electrodes in the context of both
multiple scales and multiphysics that considers
electrochemical kinetics
Approach
Aggregation between additive particles and active
particles in the electrode material of batteries strongly
affects their interfacial impedance and power performance.
A three dimensional model that simulates the aggregation
process of carbon black and LiMn 2 O 4 active material
particles within a liquid medium (PVDF polymer dissolved
in NMP solvent) was developed. A Brownian dynamics
was employed in the simulation and the resulting
aggregates are exported to multiphysics finite element
models. This model was then used to evaluate effective
material properties by applying a volume averaging theory.
A mathematical model that includes film resistance and the
double-layer charging current was developed, and this
model was coupled with a frequency responses analysis in
order to characterize capacity fade due to SEI layer
formation. Also calculated were the stress evolutions
Energy Storage R &D 632 FY 2011 Annual Progress Report