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Electroactive
Polymer Separator to Protect from Overcharging in Lithium Ion Batteries—Physical
Sciences Inc., 20 New England Business Center, Andover, MA
10810-1077; 978-689-0003
Dr.
Aron Newman, Principal Investigator, newman@psicorp.com
Dr.
B. David Green, Business Official, green@psicorp.com
DOE
Grant No. DE-FG02-05ER84249
Amount:
$749,882
Battery
packs for hybrid electric vehicles need to be low cost and have a 15-year
lifetime. However, the cycle life of
lithium-ions cells, which are configured in series, is reduced by the
overcharging of individual cells. The
current method of overcharge control, which uses external control circuitry, has
a gravimetric and cost burden, and is ineffective at eliminating all of the cell
damage during overcharge. This
project addresses the overcharging issue by developing an alternative separator
that becomes temporarily conductive when a cell reaches an over-voltage
condition, shunting electrons between the electrodes.
This separator/shunt will keep the cell voltage below the value at which
deleterious reactions occur. When
the charging current is no longer applied to the cell at higher voltages, the
separator will switch to an insulator and allows normal battery operation.
The process will be fully reversible and will not limit the number of
charging cycles that can be applied to the cell. In
Phase I, the fabricated separator demonstrated the technical feasibility for
controlling overcharge. At
over-voltage conditions (> 3.9V), the electroactive polymer separator
functioned as a current shunt at current densities up to 10 mA/cm2. At
cell operating voltages, the separator performed as an ion shuttle as the cell
charged and discharged, maintaining cell capacity at typical C-rates. In
Phase II, the polymer blend components that make up the separator will be
modified to enable 10 mA/cm2 current on overcharge and to allow
performance as a typical separator with a fully charged open circuit voltage of
4.2 volts. The selected polymer
blend will be scaled-up via film production on continuous process, solvent
casting equipment. Experimental and
control separators will be tested in 240 mAh pouch cells for overcharge and
cycle life.
Commercial
Applications and other Benefits as described by the awardee:
The new
separator technology should be appropriate for lithium ion battery stacks that
require greater cycle life than what is available currently.
The electroactive separator is a cost-effective and
gravimetrically-effective means of protecting the electrodes locally for
improved cycle life. In addition to
the HEV and electric vehicle markets for this separator, other potential
consumer applications include laptop computer batteries.