Electrochemical Performance of LiMn2O4 Cathodes in Zn-Containing Aqueous Electrolytes

Abstract

Electrochemical properties of LiMn 2 O 4 cathode were investigated in three types of Zn-containing electrolytes: lithium-zinc sulfate electrolyte (1 M ZnSO 4 / 2 M Li 2 SO 4 ), zinc sulfate electrolyte (2 M ZnSO 4 ) and lithium-zinc-manganese sulfate electrolyte (1 M ZnSO 4 / 2 M Li 2 SO 4 / 0.1 M MnSO 4 ). Cyclic voltammetry measurements demonstrated that LiMn 2 O 4 is electrochemically inactive in pure ZnSO 4 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 LiMn 2 O 4 is higher in presence of MnSO 4 (140 mAh g -1 in 1 M ZnSO 4 / 2 M Li 2 SO 4 / 0.1 M MnSO 4 and 120 mAh g -1 in 1 M ZnSO 4 / 2 M Li 2 SO 4 ). The capacity increase can be explained by the electrodeposition of MnO x layer on the electrode surface. Structural characterization of postmortem electrodes with use of XRD and EDX analysis confirmed that partially formed in pure ZnSO 4 electrolyte Zn-containing phase leads to fast capacity fading which is probably related to blocked electroactive sites.