A Combined High Temperature Tape-Casting and 2D Freeze-Casting Method for Polymer Membranes with Vertically Oriented Pores

Author: Gokuli, Mahi

Year: 2021

Degree: Senior thesis (Major)

Advisor: Faber, Katherine T.

Committee Member: None, None

Option: Materials Science

DOI: 10.7907/ywpf-cx09

Abstract

Alternatives to lithium-ion batteries often require novel electrolytes, such as solvent-in-salt electrolytes and ionic liquids, for which commercial battery separators are unsuited. The Faber Lab at Caltech is researching processing methods for separators made of polymer/ceramic composite materials to ensure high wettability in novel liquid electrolytes. To this end, a flexible polymer separator is needed which provides a short working-ion transportation path for high ionic conductance. Here, a method was developed for the fabrication of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membranes with vertically aligned, nontortuous pores with pore diameters of a few microns by directional crystallization of dimethyl sulfone (DMSO₂). The method combines high-temperature tape casting and bidirectional freeze casting into a single step. Important considerations for the improvement of the method (particularly, avenues for reducing the pore size to below 1 μm) are discussed. In addition, the role of PVDF-HFP crystallization in bidirectional freeze-casting, a solvent crystallization method, is discussed.

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