(606g) High Li-Ion Transference Number Poly(ethylene oxide) Electrolytes for Li-Ion Batteries

In response to the needs of major car manufacturers, the US Department of Energy has set aggressive cell-level performance goals for electric vehicle batteries, particularly with respect to specific energy. To meet these goals, most Li-ion materials research has focused on either cathode material engineering to increase battery operating voltage or capacity, or developing new anode materials with a large Li storage capacity. However, the development of electrolytes in which the ionic current is carried either predominantly or entirely by Li⁺ (instead of a combination of Li⁺ and its necessary counteranion) could dramatically enhance cell-level energy densities by reducing transport limitations within porous electrodes. High Li⁺ transference number, t_Li, polymers are designed to have the Li⁺ counteranion covalently bound to the polymer matrix (an ionomer), therefore disallowing significant anion mobility. High t_Li electrolytes could significantly reduce, or perhaps eliminate, concentration polarization at high discharge rates desirable for electric vehicles, enabling thicker electrodes to be used, which would increase the ratio of electrochemically active battery components to passive cell components (such as the electrolytes), thereby increasing the energy density of the cell. However, single ion conducting polymers have been hampered by poor conductivity and high interfacial ionic resistance, particularly at low temperature (<60 ^oC).  It is imperative to understand the physical and chemical characteristics that an ionomer should possess in order to mitigate these limitations.  This presentation will outline the synthesis and characterization of a model sulfonated poly(ethylene oxide-co-allyl glycidyl ether)-based single ion conducting system where ion concentration can be easily controlled. We will present a systematic study linking polymer physical properties and phase behavior to ionic conductivity and interfacial Li metal impedance.