5 years ago

Spatially Confined Li–Oxygen Interaction in the Tunnel of α-MnO2 Catalyst for Li–Air Battery: A First-Principles Study

Spatially Confined Li–Oxygen Interaction in the Tunnel of α-MnO2 Catalyst for Li–Air Battery: A First-Principles Study
Yong Pei, Hengfeng Li, Zhongyun Ma, Hongling Liu, Guang Zhou
α-MnO2 has great potential as an electrochemical catalyst for promoting the round-trip efficiency of Li–air battery. Herein, by employing first-principles calculations, we investigated the geometric, electronic, and magnetic structures of α-MnO2 crystals accommodating lithium, O2 molecule, and monomeric Li–oxygen species (LixOy with the chemical formulas of LixO2 or LixO4, 1 ≤ x ≤ 12) in the (2 × 2) tunnel with loose-packed density. The studies in thermodynamics show that Li+ ions can readily be intercalated into the tunnel space and are coordinated strongly with the crystalline framework structure of α-MnO2, while both the components interact weakly with the inserted O2 molecules. A pathway for O2 dissociation in the tunnel is dominated by the spatially confined interactions between Li+ ions and O2 moiety, which are enhanced as the intercalated excess Li in LixO2 monomers is increased, resulting in the O–O bond lengths being gradually elongated until the bonds break in Li9O2 monomer and are converted to LixO ones. The calculated electronic and magnetic structures reveal that the LixOy-inserted α-MnO2 structures become half-metallic or metallic or semiconductors with small band gaps and ferrimagnetic spin configuration. These results offer new insights into the important roles of the α-MnO2 tunnel structure in assuring the reversible cycles and shed light on the rational design of highly effective catalysts with new tunnel structures in Li–air battery.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b01855

DOI: 10.1021/acs.jpcc.7b01855

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