Synergy Effects of Dual‐Gel‐Assisted Structural Engineering and Bimetallic Doping Regulation Realize Ultrastable High‐Rate Performance of NASICON Cathodes for Sodium‐Ion Batteries

ABSTRACT

Na‐superionic‐conductor‐type (NASICON) Na ₄ MnV(PO ₄ ) ₃ (NMVP) is an appealing cathode for sodium‐ion batteries (SIBs), but its application is hindered by Jahn–Teller distortions, sluggish Na ⁺ kinetics and poor conductivity, leading to rapid capacity fade. Herein, an integrated strategy through dual‐gel assisted structural engineering with Al ³⁺ /Zr ⁴⁺ bimetallic doping to synergistically enhance NMVP. The dual‐gel (ethylene glycol/citric acid) process leverages a dynamic contraction‐competition mechanism to enrich ∼10 nm mesopores, boosting pore volume by 38% to 0.18 cm ³  g ⁻¹ for rapid Na ⁺ diffusion. Concurrently, Al ³⁺ /Zr ⁴⁺ co‐doping at Mn sites implements triple atomic‐scale modulation: Zr ⁴⁺ (0.72 Å) expands the [MnO ₆ ] octahedral framework (increasing c ‐axis by 0.08 Å), whereas Al ³⁺ (0.535 Å) forms shorter Al–O bonds (2.00 vs. 2.12 Å for Mn–O). This establishes a beneficial bond‐length gradient (Al–O: 2.00 Å → Mn–O: 2.12 Å → Zr–O: 2.15 Å) that effectively suppresses Jahn–Teller distortion. This dual‐modification synergistically lowers Na ⁺ migration barriers by 28% (to 0.088 eV) and narrows the bandgap to 0.326 eV, thus elevating electrical conductivity to 1.14 × 10 ⁻²  S cm ⁻¹ . Consequently, the optimized cathode delivers exceptional rate capacity (78.8 mAh g ⁻¹ at 30C), long cycle life (88.1% retention after 4000 cycles at 10C), and high full‐cell energy density (312 Wh kg ⁻¹ with 74.4% retention after 400 cycles at 5C). This study demonstrates the effectiveness of “pore engineering‐doping synergy” towards advanced SIB cathodes.