A New Type of Li-Rich Rock-Salt Oxide Li₂ Ni_1/3 Ru_2/3 O₃ with Reversible Anionic Redox Chemistry.

Abstract

Li-rich oxide cathodes are of prime importance for the development of high-energy lithium-ion batteries (LIBs). Li-rich layered oxides, however, always undergo irreversible structural evolution, leading to inevitable capacity and voltage decay during cycling. Meanwhile, Li-rich cation-disordered rock-salt oxides usually exhibit sluggish kinetics and inferior cycling stability, despite their firm structure and stable voltage output. Herein, a new Li-rich rock-salt oxide Li₂ Ni_1/3 Ru_2/3 O₃ with Fd-3m space group, where partial cation-ordering arrangement exists in cationic sites, is reported. Results demonstrate that a cathode fabricated from Li₂ Ni_1/3 Ru_2/3 O₃ delivers a large capacity, outstanding rate capability as well as good cycling performance with negligible voltage decay, in contrast to the common cations disordered oxides with space group Fm-3m. First principle calculations also indicate that rock-salt oxide with space group Fd-3m possesses oxygen activity potential at the state of delithiation, and good kinetics with more 0-TM (TM = transition metals) percolation networks. In situ Raman results confirm the reversible anionic redox chemistry, confirming O^2- /O^- evolution during cycles in Li-rich rock-salt cathode for the first time. These findings open up the opportunity to design high-performance oxide cathodes and promote the development of high-energy LIBs.