STTR Phase I: A Roll-to-Roll Process for Manufacturing Nanocellular Polymeric Thin Films

Vesicus Inc., Redmond WA

Investigators

Abstract

This Small Business Technology Transfer Research (STTR) Phase I project aims at developing a roll-to-roll, solid-state, continuous process for manufacturing nanocellular thermoplastic films with open (interconnected) or closed (not interconnected) cells of the order 10-100 nm and as much as 50% porosity. The initial application of this proposed project is an improved Lithium-ion battery separator comprising a nanoporous polyetherimide (PEI) film of 10-25-micron thickness with uniformly distributed interconnected 10-50 nm size cells. The nanoporous PEI separator, which has significantly higher heat resistance than current polyolefin-based separators, addresses a very urgent safety issue, i.e., batteries exploding and causing fire due to thermal instability of the separator. Moreover, compared to the current multi-step process for fabricating battery separators, this continuous process will have higher productivity thereby increasing the nation's global competitiveness in battery manufacturing. The total addressable global market for separators used in both primary (single-use) and secondary (rechargeable) lithium batteries is projected to be $1.65 billion by 2020 growing at 4.7%. This innovative research project will contribute to new knowledge in the areas of gas diffusion and cell nucleation in thermoplastic polymeric films and enable development, characterization and application of a whole new class of solid-state nanocellular polymer films. The intellectual merit of this project resides in the development of a manufacturing process that brings together interdisciplinary knowledge to synthesize and characterize nanostructures under various process conditions. This new knowledge will advance the field of nanomanufacturing and will be used to optimize processes towards commercialization targets. There are two technical challenges: (i) the dynamic seal concept, which has been proven in a 250-micron thick polymer film but not for a film 10-20 times lower in thickness; and (ii) maintaining enough gas concentration during the cell nucleation and growth to create nano-sized cells. The goals of this project are to: (a) establish the feasibility of a roll-to-roll process operating at a minimum speed of 1 meter/minute to produce nanocellular thermoplastic films and (b) develop a 100-mm wide, 10-25 micron thick nanoporous polyetherimide (PEI) film having the desired properties and nanostructure profile for a Li-ion battery separator application. These two goals will be achieved by implementing the dynamic seal technology to process a 100-mm wide film on a continuous basis and immediately heating the film to create nanocells. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.