Three-dimensional graphene-supported nickel disulfide nanoparticles promise stable and fast potassium storage

Nickel sulfide (NiS₂) is generally regarded as an appropriate anode for manufacturing new-type potassium-ion batteries (PIBs), while the development and application of NiS₂ are hampered by poor intrinsic electrical conductivity and huge volumetric change during potassiation/de-potassiation. Herein, we construct self-adaptive NiS₂ nanoparticles confined to a three-dimensional graphene oxide (NiS₂/3DGO) electrode via in situ sulfurization and self-assembly processes. The as-obtained NiS₂/3DGO exhibits high reversible capacity (391 mA h g^-1) and outstanding rate behavior (stable cycling at 1000 mA g^-1) for PIBs. Furthermore, in situ X-ray diffractometry and ex situ Raman test results elucidate partially reversible transformation from the cubic NiS₂ phase to the K_xNiS₂ intermediate, followed by generating a Ni⁰ and K₂S₄ product. This phenomenon is caused by the conversion reaction mechanism of NiS₂ nanocrystals along with an amorphous phase transition during the initial cycle. Such understandings may shed new light on the application of metal sulfides and give directions to design novel electrodes with desirable structural stability and lifespan.