Influence of Na2CO3 on structure and electrochemical properties of nanometre Co substituted nickel hydroxide

Abstract

Co substituted nanonickel hydroxide, which used NiCl2 and Na2CO3 as nickel source and buffer respectively, was synthesised by ultrasonic method. XRD, TEM, PSD and EDS were used to characterise the physical and electrochemical performance of the prepared samples respectively. The electrochemical performance affected by Co substituted ratio and buffer content were determined by cyclic voltammogram and discharge–charge test. The results demonstrated that the Co substituted nanonickel hydroxide was the mixed phase of α- and β-Ni(OH)2 and the increasing Co content led to the larger proportion of α-nickel hydroxide. An increase in Na2CO3 content was beneficial to form α-nickel hydroxide. The morphology of all samples was the needle-like and the length/diameter ratio decreased with increasing Na2CO3 content. Composite electrodes were made by mixing 8 wt-% nickel hydroxide with commercial β-nickel hydroxide. The discharge capacities of electrodes first increased and then decreased with the change of Na2CO3 content. When Ni2+ was 0·4 mol L−1 and Na2CO3 was 0·5 g, the electrode had the maximum discharge capacity, which reached 306·9 mAh g−1 at 0·5 C discharge/charge rate.