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-O 2 batteries (LOBs). Compared with the typical discharge product Li 2 O 2 , LiOH shows better chemical and electrochemical stability. In this study, a free-standing cathode composed of hydrangea-like δ-MnO 2 with Ag nanoparticles (NPs) embedded in carbon paper (CP) (Ag/δ-MnO 2 @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-MnO 2 dominantly catalyzes the conversion reaction of discharge intermediate LiO 2* to LiOH and that Ag particles promote its catalytic ability. In the presence of Ag/δ-MnO 2 @ CP cathode, the LOB exhibits enhanced specific capacity and a high discharge voltage plateau under humid O 2 atmosphere. At a current density of 200 mA g −1 , the LOB with the Ag/δ-MnO 2 @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.

Advances in Lithium–Oxygen Batteries Based on Lithium Hydroxide Formation and Decomposition

“…Mu et al (2019) reported that an activated graphene electrode can adsorb enough water (4.56%) for the formation of LiOH. A similar observation was also reported in the Ag/δ-MnO 2 electrode (Dai et al, 2022).…”

Water‐Trapping Single‐Atom Co‐N4/Graphene Triggering Direct 4e− LiOH Chemistry for Rechargeable Aprotic Li–O2 Batteries

“…[49] From the thermogravimetric analysis (TGA) curves (Figure 2g), the amount of water trapped in Co-SA-rGO was weighted to ≈12 wt%. [26,50] In contrast, pure graphene adsorbed only a small amount of water, suggesting that the H 2 O adsorbed in Co-SA-rGO catalyst was mainly from the MOF derived carbon matrix (Figure S7, Supporting Information).…”

Freestanding MOF-Derived Honeycomb-Shape Porous MnOC@CC as an Electrocatalyst for Reversible LiOH Chemistry in Li-O2 Batteries

“…Among the transition metal catalysts, Mn-based catalysts are regarded as a kind of promising electrocatalyst for Li-O 2 batteries due to their abundant resources, low cost, and good intrinsic catalytic activity. − Earlier, Bruce’s group found that electrolytic manganese dioxide can facilitate the occurrence of electrode reactions for the formation of Li 2 O 2 , and in addition, manganese oxides were proven to reduce the charging potential and contribute to the charging process. Subsequently, many reports confirmed that Mn-based catalysts for Li-O 2 batteries can effectively accelerate the reaction kinetics of ORR and OER. − Mn-based catalysts can also be used as effective catalysts to catalyze the reversible formation and decomposition of LiOH. ,, For example, Zhou and his coworkers reported that Li 2 O 2 is converted to LiOH at the Ru/MnO 2 /SP cathode and the DMSO-based electrolyte containing a trace amount of water, in which MnO 2 plays an important role. This battery exhibits a small discharge/charge potential gap (0.32 V) and superior cycling stability (200 cycles, 800 h), resulting in alleviating the carbon-related side reactions.…”

“…30−41 Mn-based catalysts can also be used as effective catalysts to catalyze the reversible formation and decomposition of LiOH. 15,42,43 Herein, a three-dimensional (3D) freestanding cathode composed of honeycomb-shape porous MnOC composite units anchored on carbon cloth (MnOC@CC) was fabricated for Li-O 2 batteries. In this battery, the MnOC@CC cathode can effectively induce the generation of flower-like low-activity LiOH as a discharge product rather than high-activity Li 2 O 2 in a humid environment.…”