The Electrochemical Mechanism of Preparing Mn from LiMn2O4 in Waste Batteries in Molten Salt

Abstract

The electrochemical reduction mechanism of Mn in LiMn2O4 in molten salt was studied. The results show that in the NaCl-CaCl2 molten salt, the process of reducing from Mn (IV) to manganese is: Mn (IV)→Mn (III)→Mn (II)→Mn. LiMn2O4 reacts with molten salt to form CaMn2O4 after being placed in molten salt for 1 h. The reaction of reducing CaMn2O4 to Mn is divided into two steps: Mn (III)→Mn (II)→Mn. The results of constant voltage deoxidation experiments under different conditions show that the intermediate products of LiMn2O4 reduction to Mn are CaMn2O4, MnO, and (MnO)x(CaO)(1−x). As the reaction progresses, x gradually decreases, and finally the Mn element is completely reduced under the conditions of 3 V for 9 h. The CaO in the product can be removed by washing the sample with deionized water at 0 °C.

Spinel LiMn2O4 Cathode Materials in Wide Voltage Window: Single-Crystalline versus Polycrystalline

“…Compared to currently prevailing Co-and Ni-based layered-oxide cathode materials (such as LiCoO 2 and Ni-rich LiNi 1−x−y Co x Mn y O 2 ), the Mn-based spinel LiMn 2 O 4 cathode possesses unique characteristics of low toxicity, abundant source, superior safety, and environmental friendliness [4,5]. The 4 V electrochemistry of the LiMn 2 O 4 cathode has been popularly explored in LIBs [4][5][6][7][8][9][10][11][12]. Unfortunately, practical specific capacities of spinel LiMn 2 O 4 cathodes in the 4 V region are limited to ~80-120 mA•h•g −1 , which are lower than layered-oxide cathode materials.…”

“…Both Jahn-Teller distortion and Mn(III) disproportionation reactions would lead to the severe capacity fading of spinel LiMn 2 O 4 cathodes. Thus, most previous efforts in spinel LiMn 2 O 4 cathodes were mainly focused on electrochemical studies in the 4 V region [4][5][6][7][8][9][10][11][12].…”