Role of aluminum doping in enhancing high-temperature stability of lithium-rich cathodes

Li-rich layered oxides have emerged as promising high-energy-density cathode materials; however, their performance at elevated temperatures (>50 °C) is severely limited by irreversible anion redox reactions including oxygen release and structural degradation associated with transition metal migration. While aluminum-doping has been theoretically proposed to enhance the structural and electrochemical stability of Li-rich cathodes, its experimental validation under high-temperature conditions (e.g., 60 °C) has remained elusive. Here, we present the comprehensive experimental validation of Al-doping effects on high-temperature stability in 4d-metal-based Li-rich cathodes, specifically Li₁.₂₂Ru₀.₆₁Ni₀.₁₀Al₀.₀₅O₂ (LRNAO). Notably, Al-doped LRNAO retains 97.7 % of its initial specific capacity (~222 mAh g⁻¹) after 50 cycles at 60 °C, representing unprecedented thermal stability for Li-rich cathodes. Mechanistic studies reveal that Al-doping provides thermal stability through a dual-function mechanism: (1) oxygen stabilization via strong Al[sbnd]O bonds that suppress O[sbnd]O dimerization and (2) facilitation of reversible Ni migration during cycling through creation of thermally stable local environments. Al-doping prevents spinel-like phase formation during prolonged cycling, maintaining the layered structure integrity even after 100 cycles at elevated temperature. It enables a remarkable combination of high-temperature stability and high capacity, setting a new benchmark for Li-rich layered cathodes. This work provides fundamental insights into temperature-dependent degradation mechanisms and offers practical design strategies for the development of high-energy-density lithium-ion batteries operable under demanding thermal conditions.