Fatigue Phase Suppression in Aged High Nickel Layered Cathodes by Aluminum Substitution during Co-precipitation

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a promising cathode material for lithium-ion batteries (LIBs) in electric vehicle applications but faces severe capacity and voltage decay issues, especially when cycled at high voltages (>4.2 V) which is essential to fully exploit its energy density. A portion of aged NMC811 becomes fatigued above 4.2 V, making further delithiation difficult and limiting the charge window to <74% lithium, which contributes to capacity loss and significant overpotential growth at high voltage. This fatigue structural degradation is universal in pure NMC cathodes with various morphologies and cannot be alleviated by tuning the kinetic limitation via slow charging. However, substituting aluminum uniformly into the NMC811 material effectively suppresses this fatigue phase. Consequently, the mid-point voltage decay was reduced by nearly 84%, enhancing the energy density from 529 to 645 Wh/kg after 150 cycles. This work provides insights into the stabilization mechanism of high-Ni layered oxides and realizes high-energy-density cathodes for LIBs.