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

V.D.4 Bi-functional Electrolytes for Lithium-ion Batteries (CWRU)
Daniel Scherson and John Protasiewicz
Case Western Reserve University
Department of Chemistry
Cleveland, OH 44106
Phone: (216) 368-5186
E-mail: dxs16@po.cwru.edu
Start Date: October 1, 2009
Projected End Date: September 30, 2013
Objectives
· Design, synthesize, and characterize the physical
and electrochemical properties of functionalized Li
salt anions containing phosphorous and boron
moieties, Such chemical functionalities are known
to impart materials with flame retardant properties
(Flame Retardant Ions or FRIons) and as such are
expected to improve device safety.
· Gain insight into the overall chemical and
electrochemical behavior of these novel
bifunctional electrolytes toward charged Li and Liion
anodes using a combination of electrochemical
and in situ spectroscopic techniques.
· Develop structure-function relationships that will
guide further search of optimized FRIons and other
species that contribute to enhanced abuse tolerance.
Technical Barriers
This project addresses the abuse tolerance barriers
from the BATT program.
Technical Targets
· Demonstrate superior abuse characteristics
compared to a baseline cell: Conoco Philips CPG-8
Graphite/1 M LiPF 6 +EC:DEC (1:2)/Toda Highenergy
layered (NMC)
Accomplishments
· Two new classes of FRIons were developed and
certain aspects of their flammability characteristics
examined with state of the art combustion methods.
· The second generation of FRIons revealed a
substantial increase in the cycling performance of
2032 coin cells when incorporated as additives to
conventional solvent formulations.
· The cell initially designed to perform in situ ATR­
FTIR measurements was successfully modified to
allow spectra to be recorded in the external
reflection mode (IRAS).
Introduction
The main objectives of this project are to develop
rational guidelines for the design and synthesis of new
classes of Li-based salts endowed with flame retardant
properties. In addition, such bifunctional electrolytes
should be weakly coordinating and of low molecular
weight, exhibit low toxicity, promote formation of low
impedance solid electrolyte interfaces (SEI) and from an
economic viewpoint be relatively inexpensive.
Approach
The tactic being implemented in our research group
seeks to impart lithium ion batteries with enhanced
safety features by incorporating flame retardant and
overcharge protection chemical groups to anionic
species that display good transport properties and
optimum SEI properties. These new materials are
expected to either substitute for currently used
electrolyte salts or be introduced as additives in
conventional formulations. Systematic studies of
compounds of this type will provide guidelines for the
search of materials displaying optimized characteristics.
Also to be thoroughly investigated is the structure of the
SEIs formed in these new media via a combination of
electrochemical and in situ ATR-FTIR and in situ
external reflection FTIR (IRAS). To this end a cell was
optimally designed to avoid problems associated with
impurities was constructed with an interchangeable
window, either diamond for ATR or CaF 2 for IRAS.
Results
Synthesis. In the previous annual report we
introduced two new FRIons, LiBOBPHO-Ph and
LiBOBPHO-Ar. These compounds were synthesized by
the dehydration of boric acid in the presence of oxalic
acid, lithium hydroxide and the corresponding disubstituted
phosphinic acid (Figure V - 144).
Unfortunately, we experienced severe problems with
isolation of these materials, forcing us to shift attention
momentarily toward the synthesis of two completely
new classes of FRions.
FY 2011 Annual Progress Report 605 Energy Storage R&D