Effects of Polymeric Layers on Li Depletion and Electrochemical Performance of Li-O2 Rechargeable Batteries

Abstract

Li‒O2 batteries have received enormous attention as alternatives to current state-of-the-art rechargeable Li-ion batteries because of their high theoretical specific energy density. However, there are still substantial technical obstacles to developing a practical battery. One of the most significant challenges arise from reactivity of Li metal anode resulting in Li depletion such as solid electrolyte interphase (SEI) and Li dendrite formation. Most approaches to reduce Li depletion focus on adjusting electrolyte components, additives and mechanical barrier. On the other hand, extremely high capacity from a cathode in Li-O2 batteries needs much higher Li utilization of an anode. High Li utilization accelerates Li depletion seriously and consequently results in poor electrochemical performance including cycle stability. Therefore, it is recommended to study on Li depletion and its prevention in more detail for rechargeable Li-O2 batteries. In this study, effects of polymer coating layers on the cycle stability were investigated. Li metal adopting poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) highly and effectively increased the cycle stability of a Li-O2 battery. The introduction of this polymeric layer, which exhibited sufficient mechanical strength, suppressed the needle-like dendrite formation. This indicates that the coating may prevent shape changes of the metal during discharge and charge cycles. It was found that improved reversibility of Li redox was achieved by coating with PVdF-HFP polymer.