Stable cycling of ultra-high nickel cathode at 4.5 V achieved by modulation of Ni and O synergistic redox

Ultra-high nickel layered oxides (UHN, LiNi x Co y Mn 1−x−y O 2 , x ≥ 0.9) represent the most promising cathode materials for next-generation lithium-ion batteries due to their high energy density and low cobalt content. However, irreversible oxygen evolution at high voltages (> 4.3 V) triggers dramatical structural degradation and electrolyte decomposition, limiting their practical implementation. The underlying atomistic mechanisms governing oxygen redox activity and subsequent release remain poorly understood, hindering rational design strategies. Here, we propose a synergistic competitive redox reaction mechanism between Ni and O, as well as a carbon nanotube-assisted annealing process that can induce controlled Li/Ni mixing and surface restructuring. This process is associated with a lower O 2p band center, more reversible oxygen redox behavior, a thinner cathode electrolyte interphase (CEI), and improved high-voltage cycling stability. Benefiting from this strategy, a “dynamic CEI evolution” was achieved in modified LiNi 0.94 Co 0.055 Mn 0.005 O 2 (Ni94). The corresponding pouch cell exhibited a capacity retention of 80.4% after 500 cycles at 4.5 V. A series of in situ electrochemical techniques and DFT (density functional theory) calculations confirm the mechanisms underlying the synergistic competitive oxidation reaction and suppressed irreversible oxygen evolution. This work establishes quantitative structure–property relationships between atomic modulation, electronic structure, and oxygen stability, providing a universal design principle for UHN cathode materials.