Synergetic compositional and morphological effects for improved Na+ storage properties of Ni3Co6S8-reduced graphene oxide composite powders

Abstract

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 2^nd and 100^th 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 2^nd and 100^th 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.