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

V.D.7 Development of Electrolytes for Lithium-ion Batteries (URI)
Brett L. Lucht (Project Manager)
University of Rhode Island
Department of Chemistry
51 Lower College Rd., Pastore
Phone: (401) 874-5071; Fax: (401) 874-5072
E-mail: blucht@chm.uri.edu
Start Date: April 1, 2009
Projected End Date: March 31, 2014
Objectives
· Investigate cathode film forming additives for high
voltage (> 4.5 V) cathode materials.
· Investigate properties of LiPF 4 C 2 O 4 /carbonate
electrolytes at low temperature after accelerated
aging.
· Investigate incorporation of electrolyte solid
electrolyte interphase (SEI) forming additives for Sibased
anodes.
· Investigate the surface of cathodes and anodes cycled
with novel electrolytes, with or without additives, to
develop a mechanistic understanding of interface
formation and degradation.
Technical Barriers
This project addresses the following technical barriers
from the Batteries for Advanced Transportation
Technologies Research, Development Plan regarding
electrolytes.
· Improve cell performance, life and cost
· Improve calendar Life
· Expand survival temperature range
Technical Targets
· Cell performance, life, cost: Calendar life: 40°C, 15
yrs
· Survival Temp Range: -46 to +66°C
· Unassisted Operating & Charging Temperature
Range, -30 to + 52°C.
Accomplishments
· Development of cathode film forming additives that
improve the performance of high voltage cathodes.
· Development of a thorough understanding of the
source of poor first cycle efficiency for LiPF 4 (C 2 O 4 )
electrolytes on graphite anodes.
· Investigation of the low temperature performance of
LiPF 4 (C 2 O 4 )/PC electrolytes after accelerated aging.
· Investigation of novel electrolytes additives to
improve performance of Si-based anodes.
Introduction
While commercial lithium-ion batteries (LIBs)
perform well for most home electronic applications,
currently available LIB technology does not satisfy some
of the performance goals for Plug-in Hybrid Electric
Vehicles (PHEV). In particular, currently available LIB
technology does not meet the 15 year calendar life
requirement set by the United States Advanced Battery
Consortium (USABC).
The most extensively used LIB electrolytes are
composed of LiPF 6 dissolved in organic carbonates.
However, LiPF 6 based electrolytes have poor thermal
stability and performance when cycled to high voltage (>
4.5 V vs Li). Significant energy fading occurs after several
years at room temperature and over only a few months at
the moderately elevated survival temperature of 66°C
required by the USABC. While there are several different
factors that limit the thermal stability, calendar life and
voltage window of LIBs, the reactions of the electrolyte
with the surface of the electrode materials are frequently
reported to be the most important.
Approach
Test cells were constructed with novel electrolyte
formulations and ex situ analysis of the surfaces of
cathodes and anodes was conducted to develop a
mechanistic understanding of interface formation and
degradation. Cathode film forming additives for high
voltage (> 4.5 V) cathode materials were studied to
improve cycling performance at high potential. An
investigation of the properties of the thermally stable
highly conductive salt, LiPF 4 C 2 O 4 , in carbonate solvents
was conducted to better understand the novel salt. The
electrode surface films for cells cycled with LiPF 4 (C 2 O 4 )
electrolyte were investigated to determine source of
performance differences compared to LiPF 6 . Incorporation
of electrolyte SEI forming additives was studied to
improve the performance of Si-based Alloy anodes.
Energy Storage R&D 616 FY 2011 Annual Progress Report