title: Limitations in Rechargeability of Li-O2 Batteries and Possible Origins.
abstract: Quantitative differential electrochemical mass spectrometry (DEMS) is used to measure the Coulombic efficiency of discharge and charge [(e(-)/O2)dis and (e(-)/O2)chg] and chemical rechargeability (characterized by the O2 recovery efficiency, OER/ORR) for Li-O2 electrochemistry in a variety of nonaqueous electrolytes. We find that none of the electrolytes studied are truly rechargeable, with OER/ORR <90% for all. Our findings emphasize that neither the overpotential for recharge nor capacity fade during cycling are adequate to assess rechargeability. Coulometry has to be coupled to quantitative measurements of the chemistry to measure the rechargeability truly. We show that rechargeability in the various electrolytes is limited both by chemical reaction of Li2O2 with the solvent and by electrochemical oxidation reactions during charging at potentials below the onset of electrolyte oxidation on an inert electrode. Possible mechanisms are suggested for electrolyte decomposition, which taken together, impose stringent conditions on the liquid electrolyte in Li-O2 batteries.
authors: †Almaden Research Center, IBM Research, 650 Harry Road, San Jose, California 95120, United States.
authors: B D
authors: BD
authors: McCloskey
authors: †Almaden Research Center, IBM Research, 650 Harry Road, San Jose, California 95120, United States.
authors: D S
authors: DS
authors: Bethune
authors: †Almaden Research Center, IBM Research, 650 Harry Road, San Jose, California 95120, United States.
authors: R M
authors: RM
authors: Shelby
authors: ‡Central Glass International, Inc., 2033 Gateway Place, Suite 569, San Jose, California 95110, United States.
authors: T
authors: T
authors: Mori
authors: §Volkswagen Group, Inc., Belmont, California 94002, United States.
authors: R
authors: R
authors: Scheffler
authors: §Volkswagen Group, Inc., Belmont, California 94002, United States.
authors: A
authors: A
authors: Speidel
authors: †Almaden Research Center, IBM Research, 650 Harry Road, San Jose, California 95120, United States.
authors: M
authors: M
authors: Sherwood
authors: †Almaden Research Center, IBM Research, 650 Harry Road, San Jose, California 95120, United States.|∥SUNCAT, SLAC National Accelerator Laboratory, Menlo Park, California 94025-7015, United States.
authors: A C
authors: AC
authors: Luntz
keywords: Li air battery; electrolyte stability; oxygen evolution; oxygen reduction; parasitic electrochemistry; salt stability