Effect of cobalt alloying on the electrochemical performance of manganese oxide nanoparticles nucleated on multiwalled carbon nanotubes

MnO is an electrically insulating material which limits its usefulness in lithium ion batteries. We demonstrate that the electrochemical performance of MnO can be greatly improved by using oxygen-functional groups created on the outer walls of multiwalled carbon nanotubes (MWCNTs) as nucleation sites for metal oxide nanoparticles. Based on the mass of the active material used in the preparation of electrodes, the composite conversion-reaction anode material Mn1-xCoxO/MWCNT with x = 0.2 exhibited the highest reversible specific capacity, 790 and 553 mAhg-1 at current densities of 40 and 1600 mAg-1, respectively. This is 3.1 times higher than that of MnO/MWCNT at a charge rate of 1600 mAg-1. Phase segregation in the nanoparticles was not observed for x ≤ 0.15. Capacity retention in x = 0, 0.2, and 1 electrodes showed that the corresponding specific capacities were stabilized at 478, 709 and 602 mAhg-1 respectively, after 55 cycles at a current density of 400 mAg-1. As both MnO and CoO exhibit similar theoretical capacities and MnO/MWCNT and CoO/MWCNT anodes both exhibit lower performance than Mn0.8Co0.2O/MWCNT, the improved performance of the alloy likely arises from beneficial synergistic interactions in the bimetallic system.