Synergetic compositional and morphological effects for improved Na+ storage properties of Ni3Co6S8-reduced graphene oxide composite powders†
The electrochemical properties of binary transition metal sulfide-reduced graphene oxide (RGO) composite powders, relevant for their performance as anode materials in sodium ion batteries, were firstly studied. (Ni,Co)O–RGO composite powders prepared by spray pyrolysis are transformed into Ni3Co6S8–RGO composite powders by a simple sulfidation process. Plate-shape nanocrystals of nickel-cobalt sulfide (Ni3Co6S8) are uniformly distributed over the crumpled RGO structure. The discharge capacities of the Ni3Co6S8–RGO composite powders for 2nd and 100th cycles at a current density of 0.5 A g−1 are 504 and 498 mA h g−1, respectively. However, the discharge capacities of the bare Ni3Co6S8 powders for 2nd and 100th cycles are 522 and 125 mA h g−1, respectively. The NiO–Co3O4 and (Ni,Co)O–RGO composite powders prepared by spray pyrolysis also show low discharge capacities of 122 and 119 mA h g−1, respectively, after 100 cycles. The high structural stability of the Ni3Co6S8–RGO composite powders during repeated sodium ion intercalation/deintercalation processes results in excellent cycling and rate performances for Na+ storage.