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

V.B.12 Developing Materials for Lithium-Sulfur Batteries (ORNL)
Chengdu Liang
Oak Ridge National Laboratory
Center for Nanophase Materials Sciences
Building 8610 MS 6493
Oak Ridge, TN 37831-6493
Phone: (865) 574-8408; Fax: (865) 574-1753
E-mail: liangcn@ornl.gov
Collaborators:
Nancy J. Dudney and Jane Howe (ORNL)
Start Date: June 2010
Projected End Date: September 2014
Objectives
· Expand the scientific understanding of lithium-sulfur
chemistry and nanoporous cathode architecture to
direct continued improvement in cycle life and
capacity utilization to meet goals for PHEV and EV
application.
· Optimize the nanostructure of the S/C composites to
retain sulfur and suppress the migration of the
polysulfide species.
· Improve the reversibility of Li 2 S formation through
optimization of the electrolyte composition.
· Establish a chemical mechanism to suppress the
lithium dendrite formation or heal the damaged
lithium anode.
Technical Barriers
Deployment of the Lithium-Sulfur (Li-S) chemistry in
EV batteries has the potential to improve the energy
density by a factor of 2 to 5 but suffers from poor cell
performance and short cycle-life. The key challenge for Li-
S batteries is the dissolution of sulfur and lithium
polysulfides in liquid electrolytes. The soluble sulfur
species create the polysulfide shuttle phenomenon inside
the electrochemical cell, which carries sulfur from the
cathode to the anode. The migrated sulfur species
chemically react with the lithium anode and cause a
“chemical short” of the battery. The “chemical short” leads
to the loss of active materials, corrosion of the Li anode,
and low coulombic efficiency. The mobile sulfur species
cause the redistribution of sulfur in the battery and impose
a poor cycle-life. New materials are crucial to enable Li-S
battery chemistry in PHEV and EV applications.
Technical Targets
· Verify the previous ORNL discovery on the additives
that prolong the cycle life of Li-S batteries
· Optimize the structure of carbon/sulfur composite
electrode for the improvement of cycling
performance.
· Invent new electrolyte compositions that are
compatible with battery components
· Achieve long cyclability of lithium metal anode in Li-
S batteries.
Accomplishments
· Demonstrated the additive effect of LiBr on Li-S
batteries. A cycle-life of 1000 cycles was repeated
using a Swagelok cell.
· Verified the battery chemistry of Li-S cell with LiBr
as the additive by bench-top wet chemistry approach.
· Discovered new electrolyte additives that are less
corrosive than LiBr.
· Explored approaches for lithium metal anode
protection.
· Developed a sample transfer stage that can handle airsensitive
materials for the diagnosis of Li-S batteries.
Introduction
The DOE Vehicle Technologies Program is pursuing
technologies to reduce U.S. petroleum consumption
through vehicle electrification. Advances in lithium-ion
battery development have enabled commercialization of
both PHEVs and EVs. However, achieving significant
market penetration and maximum petroleum reduction
from advanced electric drivetrains will require lower costs
and increased electric range. Li-S batteries provide a
potential solution to both of these development challenges.
Li-S batteries have significantly lower raw material costs
and much higher energy density than lithium-ion batteries.
However, Li-S batteries currently suffer from short cyclelife
and poor efficiency. The goal of this project is to
identify new materials and architectures that improve the
cycle-life and performance of Li-S batteries.
Three key phenomena cause the short cycle-life of the
Li-S batteries: (1) the irreversible deposition of Li 2 S on the
lithium anode through the intrinsic polysulfide shuttle, (2)
the irreversible deposition of Li 2 S and sulfur on the
Energy Storage R&D 524 FY 2011 Annual Progress Report