Quasi-Topological Intercalation Mechanism of Bi0.67NbS2 Enabling 100 C Fast-Charging for Sodium-Ion Batteries

Alloying-type bismuth with high volumetric capacity has emerged as a promising anode for sodium-ion batteries but suffers from large volume expansion and continuous pulverization. Herein, a coordination constraint strategy is proposed, that is, chemically confining atomic Bi in an intercalation host framework via reconstruction-favorable linear coordination bonds, enabling a novel quasi-topological intercalation mechanism. Specifically, micron-sized Bi0.67NbS2 is synthesized, in which the Bi atom is linearly coordinated with two S atoms in the interlayer of NbS2. The robust Nb-S host framework provides fast ion/electron diffusion channels and buffers the volume expansion of Na+ insertion, endowing Bi0.67NbS2 with a lower energy barrier (0.141 vs. 0.504 eV of Bi). In situ and ex situ characterizations reveal that Bi atom alloys with Na+ via a solid-solution process and is constrained by the reconstructed Bi-S bonds after dealloying, realizing complete recovery of crystalline Bi0.67NbS2 phase to avoid the migration and aggregation of atomic Bi. Accordingly, the Bi0.67NbS2 anode delivers a reversible capacity of 325 mAh g(-1) at 1 C and an extraordinary ultrahigh-rate stability of 226 mAh g(-1) at 100 C over 25 000 cycles. The proposed quasi-topological intercalation mechanism induced by coordinated mode modulation is expected to be be conducive to the practical electrode design for fast-charging batteries.