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

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.