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

V.E.5 Analysis and Simulation of Electrochemical Energy Systems (LBNL)
Newman – LBNL
V.E.5 Analysis and Simulation of Electrochemical Energy Systems (LBNL)
John Newman
Lawrence Berkeley National Laboratory
306 Gilman Hall
University of California, Berkeley
Berkeley, CA 94720
Phone: (510) 642-4063; Fax: (510) 642-4778
E-mail: newman@newman.cchem.berkeley.edu
Start Date: October 1, 2010
Projected End Date: September 30, 2011
Objectives
· Develop experimental methods for measuring
transport, thermodynamic, and kinetic properties.
· Model electrochemical systems to optimize
performance, identify limiting factors, and mitigate
failure mechanisms.
Technical Barriers
This project addresses the following technical barriers
from the USABC:
(A) Capacity and power fade
(B) Safety and overcharge protection
Technical Targets
This project contributes to the USABC Requirements
of End of Life Energy Storage Systems for PHEVs and
EVs:
· 300,000 shallow discharge cycles
· 15 year calendar life
Accomplishments
· Developed both steady-state and transient methods to
characterize the SEI using through-film reduction
kinetics of ferrocene
· Expanded ferrocene characterization method from
model surface (glassy carbon) to highly-oriented
pyrolytic graphite, a more realistic battery material
(collaboration with Takeshi Abe, Kyoto University)
Introduction
Our main project in FY10 was the experimental study
of SEI formation reactions and the interaction of the SEI
with redox shuttles. Our novel method of SEI
characterization contributes to understanding of
passivation in nonaqueous electrolytes, which is in turn
critical to battery performance and lifetime. While FY09
was spent primarily on the development of reproducible
experimental methods, FY10 saw both experimental
refinement and the development of theoretical tools for
data analysis. Additionally, we began to expand our
studies from glassy carbon, a model surface, to highlyoriented
pyrolytic graphite (HOPG), which more
accurately resembles the carbon found in a lithium-ion
battery.
Approach
· Utilize classical electrochemistry experiments to
understand the fundamental growth kinetics of the
SEI, as well as how it interacts with a redox shuttle.
· Measure shuttle reduction kinetics in the presence and
absence of passivating films to determine the relative
transport and kinetic inhibitions to reaction.
· Use a rotating-disk electrode (RDE) to measure the
steady-state through-film reduction current, and
electrochemical impedance spectroscopy (EIS) to
measure the frequency response of the ferrocene
reaction in the presence and absence of the SEI.
Results
1. Steady-state characterization. Steady-state
measurements and model fits are shown in Figure V - 201.
The markers show the current measured at 900 rpm after
films were built on the electrode for 30 seconds, 6, 30, and
60 minute holds at 0.6 V. Dashed lines are model fits to
the passivated current, and the dotted line is the reversible
current, which is seen on the clean electrode. Current
decreases with passivation time because the electrode has
had longer to grow a “thicker” film. The model includes
only three adjustable parameters: a transfer coefficient α,
an exchange current density i 0 , and a through-film
ferrocene limiting current i lim , given below.
i lim
FD
εC bulk
O, f O
L
bulk c bulk a
i 0
k (C O
) (C R
)
Energy Storage R &D 644 FY 2011 Annual Progress Report