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Poly(vinylidene fluoride) (PVDF) Binder Degradation in Li-O2Batteries: A Consideration for the Characterization of Lithium Superoxide

  • Author(s): Papp, JK
  • Forster, JD
  • Burke, CM
  • Kim, HW
  • Luntz, AC
  • Shelby, RM
  • Urban, JJ
  • McCloskey, BD
  • et al.
Abstract

© 2017 American Chemical Society. We show that a common Li-O2battery cathode binder, poly(vinylidene fluoride) (PVDF), degrades in the presence of reduced oxygen species during Li-O2discharge when adventitious impurities are present. This degradation process forms products that exhibit Raman shifts (∼1133 and 1525 cm-1) nearly identical to those reported to belong to lithium superoxide (LiO2), complicating the identification of LiO2in Li-O2batteries. We show that these peaks are not observed when characterizing extracted discharged cathodes that employ poly(tetrafluoroethylene) (PTFE) as a binder, even when used to bind iridium-decorated reduced graphene oxide (Ir-rGO)-based cathodes similar to those that reportedly stabilize bulk LiO2formation. We confirm that for all extracted discharged cathodes on which the 1133 and 1525 cm-1Raman shifts are observed, only a 2.0 e-/O2process is identified during the discharge, and lithium peroxide (Li2O2) is predominantly formed (along with typical parasitic side product formation). Our results strongly suggest that bulk, stable LiO2formation via the 1 e-/O2process is not an active discharge reaction in Li-O2batteries.

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