Oxyhalide‐Derived Nb‐O‐Cl Interfacial Frameworks for Mitigating Oxygen‐Related Degradation and Facilitating Li + Transport in High‐Voltage Ni‐Rich Cathodes

High‐voltage Ni‐rich cathodes coupled with sulfide solid electrolytes suffer from coupled instability of highly oxidized Ni‐O configurations and Li + transport discontinuity under deep delithiation. Conventional oxide coatings mainly act as passive barrier layers that separate reactive contacts but remain structurally isolated from layered cathodes without simultaneously regulating interfacial chemistry and Li + transport. Here, we report an oxyhalide‐enabled interfacial chemistry strategy based on a reconstructive Nb‐O‐Cl framework on LiNi 0.83 Co 0.07 Mn 0.10 O 2 cathodes (denoted as C‐NCM). Derived from a mixed‐anion LiNbOCl 4 (LNOC) precursor, the Nb‐O‐Cl framework undergoes mechanochemically assisted interfacial reconstruction, forming an amorphous oxyhalide interphase coupled with a Nb‐containing near‐surface region. Unlike passive oxide barriers, this chemically integrated architecture simultaneously reshapes the local Ni‐O electronic environment and mediates interface‐crossing Li + transport. Nb‐O/Nb‐O‐Cl coordination redistributes local charge and is associated with improved retention of highly oxidized Ni‐O configurations and mitigated oxygen‐related irreversible evolution, while the Cl‐containing oxyhalide framework provides an ionically conductive transition region that facilitates Li + migration across the cathode/electrolyte interface. Accordingly, C‐NCM exhibits reduced sulfide‐derived interphase formation and slower resistance growth, together with 88.17% capacity retention after 500 cycles at 4.5 V under high cathode loading. This work shifts cathode/sulfide‐electrolyte interface design from passive oxide‐barrier protection toward reconstructive mixed‐anion interfacial chemistry.