title: Rate-Dependent Morphology of Li2O2 Growth in Li-O2 Batteries.
abstract: Compact solid discharge products enable energy storage devices with high gravimetric and volumetric energy densities, but solid deposits on active surfaces can disturb charge transport and induce mechanical stress. In this Letter, we develop a nanoscale continuum model for the growth of Li2O2 crystals in lithium-oxygen batteries with organic electrolytes, based on a theory of electrochemical nonequilibrium thermodynamics originally applied to Li-ion batteries. As in the case of lithium insertion in phase-separating LiFePO4 nanoparticles, the theory predicts a transition from complex to uniform morphologies of Li2O2 with increasing current. Discrete particle growth at low discharge rates becomes suppressed at high rates, resulting in a film of electronically insulating Li2O2 that limits cell performance. We predict that the transition between these surface growth modes occurs at current densities close to the exchange current density of the cathode reaction, consistent with experimental observations.
authors: †Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.|‡German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany.|§Helmholtz Institute Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany.|∥University of Stuttgart, Pfaffenwaldring 6, 70550 Stuttgart, Germany.
authors: Birger
authors: B
authors: Horstmann
authors: †Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors: Betar
authors: B
authors: Gallant
authors: †Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors: Robert
authors: R
authors: Mitchell
authors: ⊥Offenburg University of Applied Sciences, Badstraße 24, 77652 Offenburg, Germany.
authors: Wolfgang G
authors: WG
authors: Bessler
authors: †Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors: Yang
authors: Y
authors: Shao-Horn
authors: †Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors: Martin Z
authors: MZ
authors: Bazant
keywords: continuum modeling; electrodeposition; lithium−oxygen batteries; surface growth