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Lower Cost, Nanoporous Block Copolymer Battery Separator

IB-3024

APPLICATIONS OF TECHNOLOGY:

ADVANTAGES:

ABSTRACT:

Although the polyolefin polymer material often used for lithium battery separators costs approximately $1.30/kg, the difficult process used to make it porous, to allow the flow of ions and electrons, raises its cost by two-orders of magnitude, to $120–$240/kg. A Berkeley Lab team led by Nitash Balsara has developed an inexpensive and easily controlled process yielding a nanoporous polymer separator that performs just as well as those made by conventional means.

The Berkeley Lab team used a wet process with polystyrene-block-polyethylene-block-polystyrene (SES) copolymer mixed with an amorphous polystyrene polymer (PS). The highly ordered structure of SES lines up the amorphous PS chains naturally, and when PS material is dissolved in the subsequent step, well-defined holes are left in the SES membrane. Strict controls of the process are not necessary, as they are in the current, standard process, because the block copolymer architecture dictates uniformity of the pore structure.

Different blends of SES and amorphous polymers will produce predictable performance traits. Electrical conductivity measurements on electrolyte-filled SES separators yielded values similar to those of commercial separators, and refinements of the process could produce separators that outperform their commercial counterparts.

Advancements in lithium ion battery technology require improvements to the
non-energy-producing support components, which make up about 50 percent of the weight of a lithium battery. Among the most costly of these is the separator, typically an extremely thin polymer layer laced with tiny pores that allow ions flowing in an electrolyte to pass through in one direction while electrons travel the other way. The high cost is primarily due to the current fabrication process requiring strict controls to assure pores a are distributed uniformly. A faulty separator can produce short circuits and catastrophic battery failure.

DEVELOPMENT STAGE: Bench-scale prototype. 

STATUS: Patent pending.  Available for licensing or collaborative research.

FOR MORE INFORMATION:

D. T. Wong, S. A. Mullin, V. S. Battaglia, N.P. Balsara. "Relationship between morphology and conductivity of block-coplolymer based battery separators," Journal of Membrane Science 394-395 (2012) 175-183.

SEE THESE OTHER BERKELEY LAB TECHNOLOGIES IN THIS FIELD:

Block Copolymer Cathode Binder to Simultaneously Transport Electronic Charge and Ions, IB-3025

Non-Cross-Linked Gel Polymer Electrolytes for Lithium Ion Batteries, JIB-2731

Precise Control of Nanoparticle Self-Assembly over Multiple Length Scales, JIB-2662

REFERENCE NUMBER: IB-3024

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