In the past few years, significant research effort has been conducted for “Li-excess” oxides, which utilize anionic redox reaction, for high-capacity positive electrode materials.&lt;span style="margin:0px"&gt; &lt;/span&gt;Nevertheless, in many Li-excess oxides with different transition metal ions, oxidation of oxide ions results in irreversible oxygen loss. Reversibility of the anionic redox process depends on the difference in chemical stability of oxidized cationic species. For instance, Fe4+ is not chemically stable, and is therefore reduced by oxygen after charge, leading to oxygen loss. In this article, we report the importance of coordination numbers of transition metal ions to oxide ions, which significantly influences stabilization/destabilization in redox reaction of oxide ions.&lt;span style="margin:0px"&gt; &lt;/span&gt;Our systematic studies on Li3NbO4-NiO binary system reveal that ligand holes are reversibly created in “stoichiometric” LiMeO2 (Me = Ni2+ and Nb5+), surprisingly with small polarization (less than 0.3 V) for charge/discharge processes. In contrast, for the “Li-excess” composition, Li1.33Me0.67O2, oxygen loss is dominative as an irreversible process.These results indicate that ligand holes are energetically stabilized for the stoichiometric composition, and Li-enrichment in the structure destabilizes the redox reaction of oxide ions.

Li-excess cation-disordered rocksalt oxides with cationic/anionic redox for non-aqueous batteries

2019 Spring National Meeting

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