Mitigating Voltage Decay via Chemo‐Mechanical Decoupling Enabled by a Rigid‐Soft Gradient Interphase in Li‐Rich Layered Oxides

ABSTRACT Li‐rich layered oxides (LLOs) deliver high capacities through anionic redox, yet their practical application is hindered by severe voltage decay. The decay originates from surface reconstruction, which drives chemo‐mechanical amplification of oxygen loss, cation migration, and particle cracking. Here, we construct a rigid‐soft gradient interphase within LLO secondary particles by exploiting the distinct coprecipitation behaviors of Mg, Zn, and Cu cations regulated by their complexation and solubility characteristics. This architecture chemically strengthens the outer region to suppress surface reconstruction and interphase growth, while maintaining a compliant interior that accommodates cyclic strain and alleviates strain localization. Multiscale X‐ray and electron probes combined with 3D chemical state imaging reveal reduced reconstructed layer thickening, restrained interphase penetration, mitigated cracking, and improved structural homogeneity after extended cycling. The cathode retains 90.01% capacity over 300 cycles at 1.0 C with a low voltage decay rate of 0.86 mV/cycle, and the stability is maintained in Ah‐level graphite full cells. This work establishes rigid‐soft gradient interphase engineering as a scalable principle for achieving long‐term voltage stability in high‐energy‐density anionic‐redox cathodes.