A Li-O2 battery works based on the reversible formation and decomposition of Li2O2, which is insulating and highly reactive. Designing a catalytic cathode capable of controlling Li2O2 growth recently became a challenge to overcome this barrier. In this work, we present a new design of catalytic cathode by growing porous Au/δ-MnO2 electrocatalyst directly on a conductive substrate. We found that Au/δ-MnO2 can catalyze the directed growth of Li2O2 into a thin/small form, only inside porous δ-MnO2, and along the surface of δ-MnO2 sheets. We proposed the catalytic mechanism of Au/δ-MnO2, where Au plays a critical role in catalyzing the nucleation, crystallization and conformal growth of Li2O2 on δ-MnO2 sheets. Li-O2 batteries with an Au/δ-MnO2 catalytic cathode showed excellent electrochemical performance due to this favorable Li2O2 growth habit. The battery yielded a high capacity of 10,600 mA h g(-1) with a low polarization of 0.91 V at 100 mA g(-1). Superior cycling stability could be achieved in both capacity-limited (500 mA h g(-1), 165 times at 400 mA g(-1)) and unlimited (ca. 3000 mA h g(-1), 50 cycles at 800 mA g(-1)) modes.
The working of nonaqueous Li–O2 batteries relies on the reversible formation/decomposition of Li2O2 which is electrically insulating and reactive with carbon and electrolyte. Realizing controlled growth of Li2O2 is a prerequisite for high performance of Li–O2 batteries. In this work, a sandwich‐structured catalytic cathode is designed: graphene/Au‐nanoparticles/Au‐nanosheets (G/Au‐NP/Au‐NS) that enables controlled growth of Li2O2 spatially and structurally. It is found that thin‐layer Li2O2 (below 10 nm) can grow conformally on the surface of Au NPs confined in between graphene and Au NSs. This unique crystalline behavior of Li2O2 effectively relieves or defers the electrode deactivation with Li2O2 accumulation and largely reduces the contact of Li2O2 with graphene and electrolyte. As a result, Li–O2 batteries with the G/Au‐NP/Au‐NS cathode exhibit superior electrochemical performance. A stable cycling of battery can last 300 times at 400 mA g−1 when the capacity is limited at 500 mAh g−1. This work provides a practical design of catalytic cathodes capable of controlling Li2O2 growth.
Owing to their extremely high energy density, Li‐O2 batteries have attained increasing attention in recent studies. However, deposition of the discharge product, insulating Li2O2, is known to seriously limit the electrochemical performance of Li‐O2 batteries. While extensive studies have focused on relieving electrode deactivation by controlling Li2O2 growth, no permanent or effective mechanism is delivered. Here, a unique design comprising a catalytic cathode constructed by cracked carbon submicron tube (CST) arrays decorated with Au nanoparticles on inner walls is proposed. The introduction of Au nanoparticles not only improves electrode conductivity but also provides catalytic sites, guiding conformal growth of thin‐layered Li2O2 inside the cracked CST. Density functional theory calculations support that Au decoration on CST favors the conformal growth of Li2O2 on inner tubular walls. This growth behavior of Li2O2 renders easy decomposition of Li2O2, prevents carbon tube electrode from full, rapid deactivation, and preserves the free space for reactants transport. Li‐O2 cells with Au@CST exhibit good rate capability (1208 mAh g–1 at a high current density of 1000 mA g–1) and long cycle life (112 cycles at a current density of 400 mA g–1 with a limited capacity of 500 mAh g–1).
Li-O 2 (or Li-air) battery currently represents a hot topic in the field of energy storage and conversion. The electrochemical performance of Li-O 2 battery depends largely on the material and architecture of the catalytic cathode. In this work, we propose a unique design of binder-free catalytic cathode for Li-O 2 batteries. The electrode consists of novel mushroom-like Au/NiCo 2 O 4 nanohybrid on three-dimensional graphene (3D-G) grown directly on the skeleton of Ni foam. The Au/NiCo 2 O 4 /3D-G catalyst exhibits good catalytic effect for Li-O 2 batteries, where Au directs the growth of Li 2 O 2 mainly on the top of mushroom-like Au/NiCo 2 O 4 , and induces the crystallization of Li 2 O 2 into thin-flake or thin-film form that is found to decompose relatively easily compared with large-particle form upon charge. Mushroom-like NiCo 2 O 4 provides additional catalytic sites and acts as the support for both Au and Li 2 O 2 . Li-O 2 battery with Au/NiCo 2 O 4 /3D-G catalyst can deliver a capacity of around 1275 mAh g -1 at 42.5 mA g -1 . When the capacity is limited at 510 mAh g -1 , the Li-O 2 battery can sustain a stable cycling for 40 times.
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