Vacancy-Ordered Superstructure-Induced Delocalized States Enable Superior Sodium Ion Storage

Transition metal sulfides (TMSs) are perceived as competitive candidate anodes for sodium-ion batteries (SIBs) on account of their high capacity and admirable reversibility. However, a majority of TMSs suffer from huge volume expansion and poor kinetics so they cannot achieve durable and fast Na+ storage. Herein, a cation vacancy-ordered Cr2/3S is fabricated by extracting quantitative Cr atoms from nickel arsenide type CrS via sulfur "atomic pump," that is, sulfur and particular sit Cr atoms are bonded to extend a new structure. The ordered vacancies not only construct a loosely-packed crystal structure but also induce delocalized electron states of Cr atoms, hence effectively accelerating Na+ diffusion and releasing volume strain to enable high-rate and longevous SIBs. The new Cr2/3S anode presents a high reversible capacity of 544 mAh g(-1) after 100 cycles at 1 A g(-1) and excellent high-rate performance of & AP;100% capacity retention after 7000 cycles at 20 A g(-1). Subsequent in situ and ex situ characterizations reveal the Na+ storage mechanism of Cr2/3S. The proposed cation exaction strategy through an innovative sulfur "atomic pump" can be an efficient way to achieve loosely-packed structure material for large-capacity and fast-kinetics anodes.