Superparamagnetic Fe Conversion Induces MoS₂ Fast Ion Transport in Wide‐Temperature‐Range Sodium‐Ion Batteries

Abstract MoS₂ is widely reported as anode material for sodium‐ion batteries (SIBs). However, its ability to operate effectively across a wide temperature range and at high rates continues to pose fundamental challenges, limiting its further development. Herein, a monolayer Fe‐doped MoS₂/N,O‐codoped C overlapping structure is designed and employed as an anode for wide‐temperature‐range SIBs. Fe doping imparts MoS₂ electrode with zero bandgap characteristics, an increased interlayer spacing, and low sodium‐ion diffusion energy barriers across wide operation temperatures. Impressively, Fe atoms doped into the MoS₂ lattice can be reduced to superparamagnetic Fe⁰ nanocrystals of ≈2 nm during conversion reactions. In situ magnetometry reveals that these Fe⁰ nanocrystals can be used as electron acceptor in the formation of space charge zones with Na⁺, thereby triggering strong spin‐polarized surface capacitance that facilitates fast sodium‐ion storage over a wide temperature range. Consequently, the designed MoS₂ electrode demonstrates exceptional fast‐charging capability in half/full cells operating at −40–60 °C. This study provides novel perspectives on the utilization of heteroatom doping strategies in conversion‐type electrode material design and proves the effectiveness of spin‐polarized surface capacitance effect on enhancing sodium‐ion storage over a wide temperature range.