Rate-Dependent Morphology of Li[subscript 2]O[subscript 2] Growth in Li–O[subscript 2] 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 Li[subscript 2]O[subscript 2] 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 LiFePO[subscript 4] nanoparticles, the theory predicts a transition from complex to uniform morphologies of Li[subscript 2]O[subscript 2] with increasing current. Discrete particle growth at low discharge rates becomes suppressed at high rates, resulting in a film of electronically insulating Li[subscript 2]O[subscript 2] 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.