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    Mechanically and thermally robust microporous copolymer separators for lithium ion batteries

    Year: 2022

    Journal: Electrochim. Acta, Volume 425, SEP 1

    Authors: Manly, Alexander J.; Tenhaeff, Wyatt E.

    Organizations: National Science Foundation [1845805]; University of Rochester Materials Science Program; DOE Vehicle Technologies Office (VTO); Div Of Chem, Bioeng, Env, & Transp Sys; Directorate For Engineering [1845805] Funding Source: National Science Foundation

    Keywords: Separators; Polymerization induced phase separation; Co-polymer; Batteries

    Next generation, multifunctional separators can enhance energy storage, power, and safety performance of lithium ion batteries but must be simple to fabricate and incorporate with existing roll-to-roll manufacturing. This study presents a strategy to facilely prepare these separators using UV-initiated polymerization-induced phase separation (PIPS), wherein microporous polymer separators are fabricated directly from constituent monomers and ethylene carbonate (EC) porogen. This enables a wide compositional design space as comonomers with specific chemical functionality can be readily incorporated into the PIPS precursor mixture. Herein, 1,4-butanediol diacrylate (BDDA) was copolymerized with poly(ethylene glycol) diacrylate (PEGDA) to increase the acrylate conversion in the photopolymerization and improve mechanical properties. By tuning the ratio of PEGDA and EC, separators with high porosity (41.3%) and effective ionic conductivity (2.09 mS cm-1) were prepared. Inclusion of PEGDA was essential to increasing the elastic modulus to > 345 MPa, which is required for cell assembly by roll-to-roll manufacturing. All separators prepared were shown to enable reversible cycling of lithium metal/LiNi0.5Mn0.3Co0.2O2 half-cells for 100 cycles. Unlike conventional polyolefin separators, which were shown to melt at 160 degrees C and shrink by up to 29.8% at elevated temperatures, the PIPS separators possess exceptional, safety-enhancing thermomechanical properties, undergoing no phase transitions or thermal shrinkage.
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