MnO2 cathode in an aqueous Li2SO4 solution for battery applications
A manganese dioxide (MnO2) cathode with zinc (Zn) as the anode has been investigated using lithium sulphate (Li2SO4) as an electrolyte. Previously we demonstrated that cells comprising MnO2 and lithium hydroxide (LiOH) as an electrolyte can be made rechargeable to over one-electron capacity with a discharge capacity of 150 mAh g-1. Here we have extended our work to assess Li2SO4 as an electrolyte and have found that the battery is not rechargeable. Based on the electrochemical (discharge/charge) performance and the products formed following discharge and charge, the mechanism proposed for the sulphate-based media is one of proton insertion into the MnO2 cathode, rather than the lithium ion insertion observed for the LiOH electrolyte. The addition of bismuth species to the Li2SO4- based cell results in a transition to rechargeable behaviour. This is believed to be due to the influence of Bi ions on the formation of soluble Mn3+ soluble intermediates. However, the coulombic efficiency of the cell diminishes rapidly with repeated charge/discharge cycles. This confirms that the nature of the Li-containing electrolyte has a marked influence on the electrochemistry of the cell.