464913 Charged Polysulfone Based Polymer Electrolytes for Lithium Ion Batteries

Monday, November 14, 2016
Grand Ballroom B (Hilton San Francisco Union Square)
Kyle M. Diederichsen and Bryan D. McCloskey, Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, CA

Polymer electrolytes have long been proposed as a means to solve many of the challenges inherent in Li-ion batteries. Numerous studies have highlighted promising polymer electrolytes that improve battery safety through mechanical suppression of dendrite growth, reduced flammability compared to typical liquid organic electrolytes, and high electrochemical stability. Within any binary salt system, including most traditional polymer electrolytes with dissolved salt, concentration gradients arise during battery operation due to a substantial fraction of current being carried by the anion, ultimately limiting the rate at which batteries can be cycled. These concentration gradients further limit the possible thickness of the porous electrode and thereby the possible cell-level energy density. To address this issue, covalently binding anions to the polymer backbone has been employed as a strategy to substantially suppress their mobility relative to Li+. These so-called high transference number polymer electrolytes significantly reduce the effects of concentration gradients, potentially enabling higher discharge rates desirable for applications in automobiles, and increasing the possible amount of active electrode material relative to the amount of electrolyte and other passive cell components. This presentation will introduce a new class of high transference number polymer electrolytes based on the simple polysulfone condensation reaction between 4’,4’-dichlorodiphenyl sulfone (DCDPS) and 4’,4’-biphenol (BP). Polysulfone has long been known as one of the most thermally, electrochemically, and mechanically strong polymers, having an inherent Tg near 200 °C. A sulfonated, commercially available DCDPS monomer can readily be introduced to the polymer backbone and ion-exchanged to its Li+-neutralized form. Short chain (Mn=1,000 Da), -OH terminated poly(ethylene glycol) can also be directly added to the initial condensation reaction and incorporated into the polymer backbone. The final copolymer is completely miscible, resulting in a single Tg that can be lowered well below ambient, and exhibits no crystallization, thereby providing a several order of magnitude increase in the ionic conductivity over the pure sulfonated polysulfone. A systematic study on ionic conductivity will be presented as a function of PEG content and degree of sulfonation, demonstrating a promising new system for high transference number polymer electrolytes.

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