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

Abstract

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, NiS2/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 NiS2 microspheres, while the other part is distributed on the surface of the microspheres. Among them, CNTs with a flexible skeleton embedded in NiS2 microspheres act as rebar, and NiS2 with high theoretical capacity acts as concrete. This design effectively buffers the structural strain of NiS2 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 NiS2 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, NiS2/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 NiS2. The design method of NiS2/CNTs hybrids can offer an efficient strategy for resolving the large volume fluctuation of metal sulfides in energy storage applications.