Manipulating the Dispersed Domain of Pinning Dopants in Layered Oxide Cathodes for Sodium-Ion Batteries

Layered oxide cathodes are primary candidates for high-performance sodium-ion batteries, which often suffer from structural degradation during deep Na⁺ (de)intercalation processes. Incorporating electrochemically inactive cations into the transition metal (TM) layers has emerged as a mainstream strategy to enhance structural stability through the so-called pinning effect. However, the microstructural heterogeneity of inactive cations within the TM layers and the spatial extent of their influence remain poorly understood. In this work, we regulate the pinning domain by modulating configurational entropy of inactive ions (S_config-I), thereby promoting their dispersion and maximizing the spatial extent of the pinning effect. Additionally, we establish a correlation between S_config-I and local structural fluctuations using quantitative experimental analyses. Compared with samples lacking sufficient pinning domains, the sample with 21% S_config-I (denoted as S-I-21%) exhibits markedly improved structural homogeneity and optimally dispersed pinning dopants. Accordingly, S-I-21% delivers a high reversible capacity of 145 mAh g^-1 and maintains ∼80% capacity retention after 500 cycles within a wide voltage window (2.0-4.3 V). These findings highlight the effect domain of dopants and their role in regulating structural chemistry, providing design principles for robust layered cathodes.