Layered-to-Tunnel Structure Transformation and Oxygen Redox Chemistry in LiRhO2 upon Li Extraction and Insertion

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• 作者：Daria Mikhailova ; Olesia M. Karakulina ; Dmitry Batuk ; Joke Hadermann ; Artem M. Abakumov ; Markus Herklotz ; Alexander A. Tsirlin ; Steffen Oswald ; Lars Giebeler ; Marcus Schmidt ; Jürgen Eckert ; Michael Knapp ; Helmut Ehrenberg
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：July 18, 2016
• 年：2016
• 卷：55
• 期：14
• 页码：7079-7089
• 全文大小：826K
• 年卷期：0
• ISSN：1520-510X

文摘

Layered Li(M,Li)O₂ (where M is a transition metal) ordered rock-salt-type structures are used in advanced metal-ion batteries as one of the best hosts for the reversible intercalation of Li ions. Besides the conventional redox reaction involving oxidation/reduction of the M cation upon Li extraction/insertion, creating oxygen-located holes because of the partial oxygen oxidation increases capacity while maintaining the oxidized oxygen species in the lattice through high covalency of the M–O bonding. Typical degradation mechanism of the Li(M,Li)O₂ electrodes involves partially irreversible M cation migration toward the Li positions, resulting in gradual capacity/voltage fade. Here, using LiRhO₂ as a model system (isostructural and isoelectronic to LiCoO₂), for the first time, we demonstrate an intimate coupling between the oxygen redox and M cation migration. A formation of the oxidized oxygen species upon electrochemical Li extraction coincides with transformation of the layered Li_1–xRhO₂ structure into the γ-MnO₂-type rutile–ramsdellite intergrowth Li_yRh₃O₆ structure with rutile-like [1 × 1] channels along with bigger ramsdellite-like [2 × 1] tunnels through massive and concerted Rh migration toward the empty positions in the Li layers. The oxidized oxygen dimers with the O–O distances as short as 2.26 Å are stabilized in this structure via the local Rh–O configuration reminiscent to that in the μ-peroxo-μ-hydroxo Rh complexes. The Li_yRh₃O₆ structure is remarkably stable upon electrochemical cycling illustrating that proper structural implementation of the oxidized oxygen species can open a pathway toward deliberate employment of the anion redox chemistry in high-capacity/high-voltage positive electrodes for metal-ion batteries.