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

V.D.2 Interfacial Behavior of Electrolytes (LBNL)
John B. Kerr (Principal Investigator Name)
Lawrence Berkeley National Laboratory,
MS 62R0203, 1 Cvclotron Road,
Berkeley, CA 94720
Phone: (510) 486-6279; Fax: (510) 486-4995
E-mail: jbkerr@lbl.gov
PI has participated in BATT program since 1998.
1994-1999 USABC/3M/HQ project on Li/Polymer
batteries.
FY10-12 Project started October 1, 2009
70% completed
Objectives
FY10
· Demonstrate whether single-ion conductor
polyelectrolytes (gel and dry polymer) prevent
concentration polarization in composite cathodes and
facilitate thicker electrodes.
· Determine whether single-ion conductor polyelectrolytes
(gels and dry polymers) are beneficial for large volumeexpansion
anodes.
FY11
· Determine whether available single-ion conductor
polyelectrolytes function with the high voltage NiMn
spinel cathodes.
· Determine the stability of base-line and single-ion
electrolyte to NiMn spinel cathodes including
chemical analysis of electrolyte degradation products.
Technical Barriers
This project addresses the following technical barriers
· Poor cycle and calendar life.
· Low power and energy densities.
· High manufacturing cost.
· Safety
Technical Targets
· Determine the contribution to the interfacial
impedance of the salt structure in terms of reactivity
versus intrinsic electrode kinetics.
· Determine the contribution to the interfacial
impedance of the solvent or polymer structure in
terms of reactivity versus intrinsic electrode kinetics.
· Determine the contribution to the interfacial
impedance of the physical properties of the electrolyte
– liquid vs. gel. vs. solid polymer electrolyte.
· Develop analytical methods for determination of side
reaction products and chemical characterization of the
SEI layer.
Accomplishments
· Prepared and tested new single ion conductor
materials based on fluoroalkylsulfonylimide anions
which appear stable to 5 Volts or higher.
· The new salts appear to have interesting and
potentially beneficial effects in conventional lithium
ion cells when used as additives.
Introduction
The choice of electrolyte used in lithium ion batteries
presents significant challenges. The impedances presented
by the electrolyte are the bulk ohmic resistance
(conductivity), concentration polarization (transport
properties) and interfacial impedance (intrinsic
electrochemical kinetics of charge transfer at the
electrodes). Most of the attention of electrolyte researchers
over the years has focused upon the ohmic resistance
(conductivity) of the bulk electrolyte yet this impedance is
usually smaller than that due to concentration polarization
(especially in composite electrodes) and much smaller than
that of the interface. Interfacial impedance is a critical
barrier to the deployment of lithium ion batteries in
traction vehicles.
Single-ion polyelectrolyte lithium conductors possess
the solution for many of the problems with present
electrolytes. They can be used with no liquid electrolyte
thereby reducing the safety problem. They can be prepared
and deployed in ways that avoid many of the reactivity
issues both in the bulk of the electrolytes and at the
interfaces and hence offer a solution to the lifetime
problem. Because they possess a unity transference
number, there is no concentration polarization through the
composite electrodes. Thus, provided the conductivity is in
excess of 10 -4 S/cm, the single ion conductors (SIC) can
facilitate the use of thicker composite electrodes thereby
leading to higher energy and power densities. They further
appear to have application to the operation of large volume
expansion electrodes where concentration gradients have a
considerable negative effect.
FY 2011 Annual Progress Report 597 Energy Storage R&D