Multi‐Step Data‐Driven High‐Voltage MgMn ₂ O ₄ with Inorganic‐Rich Cathode‐Electrolyte Interphase for Stable Mg ²⁺ Storage

ABSTRACT Rechargeable magnesium batteries (RMBs) are a promising post‐lithium battery, but suffer from insufficient energy density and shortened cycle life due to a lack of suitable cathode materials. Herein, a high‐voltage spinel MgMn 2 O 4 cathode with a stable and dense cathode‐electrolyte interphase (CEI) was obtained via a multi‐step data‐driven strategy combined with an ingenious experimental design for high‐performance RMBs. In detail, computational evaluation of energy above the convex hull and electrochemical voltage windows first identified spinel MgMn 2 O 4 as a suitable Mg 2+ ‐intercalation host, and then ionic‐radius matching and electronic‐configuration considerations motivated Ni substitution at Mn sites of MgMn 2 O 4 . Finally, to demonstrate the theoretical predictions, Ni‐doped MgMn 2 O 4 nanoparticles were designed with a low‐level Ni substitution, in which the Ni incorporation stabilizes the spinel lattice while altering the surface chemical affinity of MgMn 2 O 4 , thereby shifting interfacial reactions from solvent‐dominated decomposition toward anion/additive‐driven inorganic chemistry. Consequently, the CEI evolves from a loose and organic‐rich layer into a compact and inorganic‐rich one, and this transition lowers the energetic barrier for Mg 2+ interfacial desolvation, suppresses continuous parasitic reactions, and stabilizes the cathode surface during cycling. Therefore, the designed high‐voltage cathode exhibits reversible Mg 2+ storage with outstanding cycling stability, retaining ∼150 mAh g −1 after 200 cycles at 200 mA g −1 .