NiS2 microsphere/carbon nanotubes hybrids with reinforced concrete structure for potassium ion storage

Transition metal sulfides have attracted attentions because of their high theoretical capacity for potassium-ion batteries (PIBs). However, there are still many challenges in maintaining long-cycle stability and improving specific capacity owing to the low conductivity of active materials and their large volume changes. Herein, NiS 2 /carbon nanotubes (CNTs) hybrids with a reinforced concrete structure are prepared. In this hybrid, one part of CNTs is covered in the interior of the NiS 2 microspheres, while the other part is distributed on the surface of the microspheres. Among them, CNTs with a flexible skeleton embedded in NiS 2 microspheres act as rebar, and NiS 2 with high theoretical capacity acts as concrete. This design effectively buffers the structural strain of NiS 2 and ensures the close interconnection between each nano-building blocks, which not only improves the structural stability, but also facilitates the full utilization of active materials. Meanwhile, the CNTs distributed on the surface of the NiS 2 microspheres are interconnected into a network structure, which provides a highly conductive carbon support for the active material, accelerates the electron transfer on the interface and promotes the effective mass transfer of potassium ions. As anode for PIBs, NiS 2 /CNTs hybrids show attractive rate performance (469.4 mAh g −1 at 50 mA g −1 and 250.8 mAh g −1 at 2000 mA g −1 ) and superior cycling stability with capacity retention of 81.2% (reversible capacity of 353.3 mAh g −1 at 100 mA g −1 after 200 cycles), 7 times higher than that of pristine NiS 2 . The design method of NiS 2 /CNTs hybrids can offer an efficient strategy for resolving the large volume fluctuation of metal sulfides in energy storage applications.