Dopant-Engineered NASICON-Type LiZr ₂ (PO ₄ ) ₃ Solid-State Electrolyte: Unraveling the Mechanisms of Fe-Induced Li ⁺ Transport Enhancement

Heterovalent ion doping is a promising strategy for boosting the electrochemical performance of NASICON-type LiZr2(PO4)3 (LZP) solid-state electrolytes, yet the atomistic origins of this enhancement remain elusive. Here, we integrate experimental and computational approaches to elucidate the structural, electronic, and transport evolution from pristine LZP to Fe-doped LZP (LFZP). Electrochemical impedance spectroscopy demonstrates that Fe doping elevates room-temperature Li+ conductivity from 4.6 × 10–5 to 1.1 × 10–4 S/cm, accompanied by a reduction in activation energy from 0.42 to 0.36 eV. Ab initio molecular dynamics simulations reveal that the Fe doping redistributes Li+ site occupancies, accelerates hopping frequencies, and promotes cooperative migration. Climbing-image nudged elastic band calculations further identify a substantial reduction in migration barrier along dominant Li+ diffusion pathway from 0.76 eV in LZP to 0.46 eV in LFZP. The synergy of reduced barriers, correlated multi-ion dynamics, and optimized three-dimensional conduction channels fully accounts for the conductivity enhancement. These findings establish Fe substitution as an effective paradigm for engineering high-conductivity NASICON frameworks and provide a mechanistic blueprint for dopant-driven solid-state electrolyte design.