Reversible LiOH chemistry in Li-O2 batteries with free-standing Ag/δ-MnO2 nanoflower cathode

Abstract

The low energy efficiency and poor cycle stability arising from the high aggressivity of discharge products toward organic electrolytes limit the practical applications of Li-O2 batteries (LOBs). Compared with the typical discharge product Li2O2, LiOH shows better chemical and electrochemical stability. In this study, a free-standing cathode composed of hydrangea-like δ-MnO2 with Ag nanoparticles (NPs) embedded in carbon paper (CP) (Ag/δ-MnO2@CP) is fabricated and used as the catalyst for the reversible formation and decomposition of LiOH. The possible discharge mechanism is investigated by in situ Raman measurement and density functional theory calculation. Results confirm that δ-MnO2 dominantly catalyzes the conversion reaction of discharge intermediate LiO2* to LiOH and that Ag particles promote its catalytic ability. In the presence of Ag/δ-MnO2@CP cathode, the LOB exhibits enhanced specific capacity and a high discharge voltage plateau under humid O2 atmosphere. At a current density of 200 mA g−1, the LOB with the Ag/δ-MnO2@CP cathode presents an overpotential of 0.5 V and an ultra-long cycle life of 867 cycles with a limited specific capacity of 500 mA h g−1. This work provides a fresh view on the role of solid catalysts in LOBs and promotes the development of LOBs based on LiOH discharge product for practical applications.