Novel Ordered Rocksalt-Type Lithium-Rich Li2Ru1–xNixO3−δ (0.3 ≤ x ≤ 0.5) Cathode Material with Tunable Anionic Redox Potential

In this work, a series of ordered rocksalt (OR) type Li-rich Li2Ru1–xNixO3−δ (LRNxO, 0.3 ≤ x ≤ 0.5) are successfully synthesized and investigated for the first time. X-ray diffraction and neutron powder diffraction patterns exhibit an obvious phase transition from layered to an OR structure as the Ni content gradually increases from x = 0 to x = 0.5, which leads to different electrochemical behaviors. In the case of OR-LRN0.4O, an ∼350 mV decrease of the oxygen oxidation potential compared with Li2RuO3 (LRO) is observed from around 4.2 to 3.85 V, which is confirmed by both X-ray photelectron O 1s spectra and dQ/dV results. The role of Ni substitution on the oxygen redox reaction is studied by first-principles calculations, and it is concluded that the formation of the OR structure caused by Ni substitution is the main reason for lowering the oxygen oxidation potential. In addition, the average discharge voltage of OR-LRN0.4O is also enhanced compared with LRO. This work provides a novel innovative strategy to modulate and control the oxygen anion redox reaction for high-energy-density Li-rich materials, which shed light on the fundamental understanding and optimizing of the anion redox process in Li-rich materials.