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

5 years ago

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 (Li_xO_y with the chemical formulas of Li_xO₂ or Li_xO₄, 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 Li_xO₂ monomers is increased, resulting in the O–O bond lengths being gradually elongated until the bonds break in Li₉O₂ monomer and are converted to Li_xO ones. The calculated electronic and magnetic structures reveal that the Li_xO_y-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