Electrochemical Performance of LiMn2O4 Cathodes in Zn-Containing Aqueous Electrolytes

Electrochemical properties of LiMn2O4 cathode were investigated in three types of Zn-containing electrolytes: lithium-zinc sulfate electrolyte (1M ZnSO4/2M Li2SO4), zinc sulfate electrolyte (2MZnSO4) and lithium-zinc-manganese sulfate electrolyte (1MZnSO4/2MLi2SO4/0.1MMnSO4). Cyclic voltammetry measurements demonstrated that LiMn2O4 is electrochemically inactive in pure ZnSO4 electrolyte after initial oxidation. The effect of manganese (II) additive in the zinc-manganese sulfate electrolyte on the electrochemical performance was analyzed. The initial capacity of LiMn2O4 is higher in presence of MnSO4 (140 mAh g−1 in 1 M ZnSO4/2 M Li2SO4/0.1 M MnSO4 and 120 mAh g−1 in 1 M ZnSO4/2MLi2SO4). The capacity increase can be explained by the electrodeposition of MnOx layer on the electrode surface. Structural characterization of postmortem electrodes with use of XRD and EDX analysis confirmed that partially formed in pure ZnSO4 electrolyte Zn-containing phase leads to fast capacity fading which is probably related to blocked electroactive sites.