Anionic MOF‐Derived Ni/Ni _1‐x O Heterojunctions with Electrochemically Induced Vacancy Reconstruction: Enabling High‐Rate and Stable Room‐Temperature Na–S Batteries

Abstract Room‐temperature sodium‐sulfur (RT Na‐S) batteries are attractive next‐generation energy storage systems owing to their high theoretical energy density and low cost. However, their practical application is hindered by both sluggish polysulfide redox kinetics and severe shuttle effects. While transition metal‐based heterostructured catalysts are promising, their precise engineering and electrochemical reconstruction remain poorly understood. Herein, an anionic metalorganic framework (Bio‐MOF‐1) templating strategy is developed to fabricate atomically dispersed Ni/NiO heterojunctions embedded in hierarchical carbon nanofibers (CNF). This work integrates strong ion exchange for atomic‐level Ni ²⁺ dispersion with confined pyrolysis to enable controlled phase transformation, forming intimate heterointerfaces that generate a built‐in electric field (BIEF). The BIEF accelerates charge transfer and weakens Ni‐O bonds, promoting electrochemically driven vacancy reconstruction. Ex situ characterizations reveal that electrochemical activation induces Ni ²⁺ vacancies, increasing Ni ³⁺ content and further strengthening the BIEF. The resulting S/Ni/Ni _1‐x O‐Bio‐MOF‐1@CNF exhibits enhanced polysulfide chemisorption and conversion, delivering an exceptional reversible capacity (1590.1 mAh g ⁻¹ at 0.1 A g ⁻¹ ), outstanding cycling stability (795.8 mAh g ⁻¹ after 1000 cycles at 1 A g ⁻¹ ), and superior rate performance (541.4 mAh g ⁻¹ at 5 A g ⁻¹ ). This work provides a new strategy to construct a precision heterostructure for advanced metal‐sulfur batteries.