Mitigating reaction heterogeneity in Li-rich layered cathodes through surface-phase regulation enabled by tailored concentration gradients engineering

Lithium-rich layered oxides are promising cathodes for high-energy lithium-ion batteries, yet their applications are hindered by voltage decay, structural instability, and heterogeneous reaction dynamics. These degradations stem from the coexistence of Li 2 MnO 3 and LiMO 2 domains, which exhibit distinct redox kinetics and trigger phase mismatch during cycling. To address this challenge, we propose a tailored concentration gradient design that regulates the spatial distribution of transition metals. Nickel is intentionally enriched near the surface while manganese dominates the interior, creating a coordinated balance between interfacial stability and bulk capacity retention. Regulating Ni content deliberately induces a moderate Li/Ni cation-mixed phase, and the tailored gradient builds a surface composite structure that stabilizes the layered framework and suppresses interfacial degradation. This architecture homogenizes redox activation, alleviates surface–bulk reaction mismatch, and retards the formation of spinel or rock-salt phases. Structural characterizations with in situ and ex situ methods confirm coherent variations in composition and valence states. Electrochemical analyses demonstrate suppressed voltage hysteresis, smaller polarization, and enhanced cycling stability. Simulations further verify homogeneous ion transport with stabilized phase evolution, collectively validating that surface-phase regulation enabled by tailored concentration gradients effectively mitigates reaction heterogeneity in Li-rich layered cathodes. The findings highlight surface-phase regulation enabled by tailored concentration gradients as a scalable strategy that mitigates reaction heterogeneity in lithium-rich layered cathodes and extends applicability to other cathode systems for large-scale energy storage. This study demonstrates that a tailored transition metal concentration gradient, with a Ni-rich surface and Mn-rich bulk, effectively regulates the surface phase and suppresses reaction heterogeneity, leading to significantly enhanced structural stability and electrochemical performance in Li-rich layered cathodes. • Modulated the transition metal distribution in Li-rich cathodes suppresses surface oxygen loss, boosting initial Coulombic efficiency to 80.12%. • Spatially balanced redox activity (Ni-rich surface/Mn-rich core) homogenizes reactions, reducing lattice strain and phase transition during cycling. • Optimized gradient cathode (CG-2) achieves 87.46% capacity retention after 100 cycles and superior rate capability (136.1 mAh g -1 at 10 C). • Gradient engineering mitigates reaction heterogeneity , stabilizes structure against spinel/rock-salt transformation, and minimizes voltage decay.