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

V.D.8 Sulfones with Additives as Electrolytes (ASU)
Austen Angell (Project Manager)
Arizona State University
Department of Chemistry and Biochemistry
PO Box 871604
Tempe, AZ 85287-1604
Phone: (480) 965-7217; Fax: (480) 965-2747
E-mail: caa@asu.edu
Subcontractor: None
Start Date: March 2009
Projected End Date: December 2012
Objectives
· Primary:To evaluate the possibility of enhancing the
ionic conductivity of sulfone solvents that are known
for their high resistance to oxidating and reducing
conditions, by fluorination, or mixed solvent methods.
· Secondary: (a) to develop a novel type of nanoporous
framework support for high voltage stable electrolyte
systems, (b) to explore possible alternative glassy and
composite solid ionic conductor systems that avail
themselves of structure-uncoupled conductivity
mechanisms that permit conductivities comparable to
those of liquid electrolytes but with fewer
complications from side reactions.
Technical Barriers
1. Electrolyte solvents
(a) Synthetic obstacles to fluorination of organic sulfones
(b) Lack of knowledge of mixing rules for sulfones with
low viscosity cosolvents
(c) unknown ability to form SEIs at lithium or graphite
surfaces
(d) Unknown stability at high voltage cathode surface
2. Nanoporous nets as electrolyte supports
(a) mechanism of formation of nets
(b) manner of forming continuous films as opposed to
insoluble amorphous powders
(c.) manner of incorporating ionically conducting solutions
or other ionic phases within nets
(d) lack of knowledge about mobility of ions in the
nanoporous environments
3. Decoupled conducting carrier solid state glassy
or microcrystalline Li conductors as liquid electrolyte
substitutes
(a) lack of knowledge about decoupling mechanisms
(b) lack of knowledge about conditions for amorphization
of highly decoupled conducting systems
Technical Targets
· Develop synthetic methods for new fluorinated
materials.
· Develop alternative solvents-cosolvent systems and
examine performance
· See remaining barriers
Accomplishments
· Demonstrated high conductivity in solvent with 5.5
volt stability windows.
· Developed graphical representations of measured
quantities that differentiate mobility from ionic
concentration and clarify efficacy of different solvents
systems (Walden plot approach).
· Demonstrated reversible Li intercalation at Gr
anodes.
· Developed procedures forming nanoporous
framework membranes of variable pore dimensions.
Introduction
The end of the first full year of support of this project
comes with a mixture of success and uncertainty. We have
succeeded in synthesizing a group of fluorinated sulfone
solvents, and their electrochemical windows have been
found, in some cases, to be as wide as those of their
unfluorinated progenitors. However there has been
disappointment in the conductivities of the solutions they
have formed with LiPF 6 as preferred salt. On the other
hand, concern about the conductivity performance should
be weighed against the findings from recent studies
(reported at a Japanese battery workshop this past August)
that the sulfones prove to be much safer electrolyte
solvents than the carbonate solvents of common usage
because of the thermal balance factors that determine
whether or not thermal runaway occurs on failure. The
well-known cyclic sulfone, tetramethylene sulfone
(commonly known as sulfolane) was the solvent used in
the Japanese study, because of its low melting point.
Indeed sulfolane has been a component in many of the
solutions of the present study, serving as a known starting
point and reference case as will be seen below. A number
FY 2011 Annual Progress Report 621 Energy Storage R&D