Enhanced Internal Magnetic Field for Long‐Cycle NCM‐Li All‐Solid‐State Batteries via Dual‐Inhibition of Anode Dendrite and Cathode Cation Disorder

ABSTRACT Solid‐state batteries, which incorporate a Li metal anode and a high‐voltage Ni‐rich layered oxide (LiNi x Co y Mn 1–x–y O 2 , x ≥ 0.8) (NCM) cathode, offer the promise of high energy density for next‐generation batteries. Although solid‐state electrolytes are anticipated to enhance safety and performance over conventional liquid‐state electrolytes, they still fail to prevent non‐uniform lithium deposition on the anode surface. Moreover, while solid‐state electrolytes can partially suppress parasitic reactions at the cathode‐electrolyte interface, mitigating structural degradation caused by Li/Ni antisite disorder remains challenging. Herein, we demonstrate a two‐orders‐of‐magnitude enhancement in the internal magnetic field during battery cycling by incorporating Fe 3 O 4 nanorods within the solid electrolyte. The strengthened magnetic field alters the deposition behavior of lithium ions on the anode via the magnetohydrodynamic effect and, concurrently, suppresses the structural degradation of the cathode by regulating the spin state of Ni 3 + . The enhanced internal magnetic field applies throughout the entire life of the NCM||Li all‐solid‐state battery, improving its cycling stability. Unlike external magnetic fields, this internal approach requires no complex equipment and avoids integration challenges.