Thermodynamic corrections of high salinity system for selective lithium extraction from brines with LiMn2O4/λ-MnO2

Abstract

LiMn2O4/λ-MnO2 redox couple, possessing the advantage of high selectivity and intercalation capacity, is the most promising candidate for efficient electrochemically switched ion exchange (ESIX) from salt-lake brines. Currently Eh-pH diagrams are the main means for studying the dissolution mechanism of LiMn2O4/λ-MnO2 redox couple, however, the dissolution behavior obtained from experiments deviates significantly from the thermodynamic calculations. By introducing ionic strength correction into the thermodynamic calculation matrix of high salinity system, precise species distributions of Mn3+/Mn2+ are successfully predicted, which are in good accordance with the experimental results. Based on the novel thermodynamic calculations, the strong dependence between pH and the dominant species of Mn3+/Mn2+ is clarified, which in return determines the manganese dissolution (MD) behavior and intercalation capacity of the redox couple. The MD behavior differentiation between LiMn2O4 and λ-MnO2 electrodes is induced by the electrode potential and pH. At pH > 5, high capacity (>30 mg/g) and low MD ratio (<0.1 %) can be achieved. This research sheds light on the existence status of Mn3+ on the MD behavior and suggests the reasonable application range of ESIX with LiMn2O4/λ-MnO2 redox couple.