Heterostructured Ni3S4/Co9S8 Encapsulated in Nitrogen-Doped Carbon Nanocubes for Advanced Potassium Storage

Potassium-ion batteries (PIBs), act as an emerging renewable secondary battery technology, have drawn substantial attention because of the easily available potassium resources and excellent electrochemical properties. At present, exploiting desirable anode materials is still a challenge. Transition metal sulfides (TMSs) are considered as the advanced anode materials for PIBs due to the high theoretical specific capacity and abundant resources. But they experience large deformation during the potassiation/depotassiation process resulting in the unsatisfying long-term cyclability, which impedes their widespread applications in PIBs. Hence, we report a bimetallic sulfide heterostructure confined in nitrogen-doped carbon nanocubes (NCS@NC) as the host for PIBs, which delivers an inspiring capacity (637.5 mAh g(-1) at 0.1 A g(-1)) and the remarkable lifespan (417.7 mAh g(-1) at 2 A g(-1) after 1000 cycles). We show that the nano-heterojunction can not only accelerate the K+ diffusion, but also promote charge transfer at heterointerfaces. Moreover, scanning electron microscopy after cycling reveals that the carbon shell can tolerate the volume expansion during cycling, resulting in the robust structural stability. NCS@NC anode experiences a four-stage K+-storage mechanism of combined intercalation and conversion reactions, as demonstrated by in-situ X-ray diffraction and ex-situ transmission electron microscopy techniques. This strategy of combining morphology engineering with heterostructure construction may enlighten the design of desirable anode materials towards the development of advanced PIBs.