Defect-Engineered Ce-Substituted High-Entropy Perovskites for Enhanced Bifunctional Oxygen Electrocatalysis in Li–O ₂ Batteries

Defect engineering in high-entropy perovskites through aliovalent doping provides a controlled strategy to modulate defect chemistry and accelerate oxygen redox kinetics in rechargeable Li–O 2 batteries. Herein, a high-entropy perovskite oxide, La 0.9 Ce 0.1 (NiCuFeCoMn) 0.2 O 3 (Ce-HEPO), is synthesized through A-site incorporation of Ce. Aliovalent substitution of Ce 4+ introduces the Ce 4+ /Ce 3+ redox couple and enhances oxygen vacancies, enabling efficient electron mediation and oxygen-intermediate transport. Concurrently, the multimetallic B-site elements, such as Ni, Cu, Fe, Co, and Mn, stabilize the variable oxidation states and modulate the energy level, providing feasible charge transport to enhance the catalytic performance. The structural framework further stabilizes the mixed-valence B-site cation network (e.g., Fe 3+ –O–Fe 4+, Ni 2+ –O–Ni 3+, Mn 3+ –O–Mn 4+ ) through charge-neutralization mechanisms, supports double-exchange-type electron hopping, accelerating Li 2 O 2 reaction kinetics, and lowers the polarization. Owing to the synergistic A-site and B-site effects, Ce-HEPO delivers a high bifunctional activity with a low ΔE of 0.88 V (vs RHE). In comparison to the undoped perovskite and carbon-based cathodes, Ce-HEPO establishes a higher reversible capacity (11,231 mAh g –1 at 200 mA g –1 ), a narrower charge–discharge gap of 1.28 V, and extended cycling stability up to 241 cycles. Furthermore, the reversible formation and decomposition of Li 2 O 2, together with structural endurance during cycling, are confirmed through ex situ analyses. The present study demonstrates A-site engineering in perovskites of multivalent cations to generate redox centers and tune the electronic structure in perovskites as an effective design strategy for high-performance Li–O 2 battery cathodes.