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Lower Cost, Nanoporous Block Copolymer Battery Separator

Lawrence Berkeley National Laboratory

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Technology Marketing Summary

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.

  • Substantially lower cost
  • Simple manufacturing process
  • Potentially higher performance
Applications and Industries
  • Lithium battery manufacturing
  • Electronic vehicle makers
  • Consumer electronics
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
IB-3024Prototype - Bench scale.Available01/20/201201/20/2012

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