1D Insertion Chains Induced Small-Polaron Collapse in MoS₂ 2D Layers Toward Fast-Charging Sodium-Ion Batteries

Molybdenum disulfide (MoS₂ ) with high theoretical capacity is viewed as a promising anode for sodium-ion batteries but suffers from inferior rate capability owing to the polaron-induced slow charge transfer. Herein, a polaron collapse strategy induced by electron-rich insertions is proposed to effectively solve the above issue. Specifically, 1D [MoS] chains are inserted into MoS₂ to break the symmetry states of 2D layers and induce small-polaron collapse to gain fast charge transfer so that the as-obtained thermodynamically stable Mo₂ S₃ shows metallic behavior with 10⁷ times larger electrical conductivity than that of MoS₂ . Theoretical calculations demonstrate that Mo₂ S₃ owns highly delocalized anions, which substantially reduce the interactions of Na-S to efficiently accelerate Na⁺ diffusion, endowing Mo₂ S₃ lower energy barrier (0.38 vs 0.65 eV of MoS₂ ). The novel Mo₂ S₃ anode exhibits a high capacity of 510 mAh g^-1 at 0.5 C and a superior high-rate stability of 217 mAh g^-1 at 40 C over 15 000 cycles. Further in situ and ex situ characterizations reveal the in-depth reversible redox chemistry in Mo₂ S₃ . The proposed polaron collapse strategy for intrinsically facilitating charge transfer can be conducive to electrode design for fast-charging batteries.