Testing the reversible insertion of magnesium in a cation-deficient manganese oxy-spinel through a concentration cell

Abstract

A new electrochemical procedure to explore the intercalation of magnesium using a concentration cell with two cubic spinels Mg1−xMn2O4.

Magnesium Deintercalation From the Spinel‐Type MgMn2‐yFeyO4 (0.4≤y≤2.0) by Acid‐Treatment and Electrochemistry

“…Recent studies found a phase intermediate between MgMn 2 O 4 and λ‐MnO 2 , [7f] although it could be affected by kinetics effects. We found that for partially demagnesiated Mg x Mn 2 O 4 , the Mn‐vacancies can decrease the cell polarization [7g] . Other authors studied the relevant role of water content in the electrochemistry of MgMn 2 O 4 [11] …”

“…The partial demagnesiation of MgMn 2‐y Fe y O 4 nanoparticles was performed by using acid‐treatment [6a,7g,14] . The raw sample was added to a solution of nitric acid at pH=2 with continue stirring for two hours.…”

“…Unit cell parameters and atomic coordinated were relaxed. The different structures Mg x Mn 2‐y Fe y O 4 were defined as follow: for y=0 the classical tetragonal spinel structure was used as starting point; for y=0.5 and y=1.5 a cation distribution of Fe and Mn similar to that found in LiNi 0.5 Mn 1.5 O 4 was assumed; [19] for y=1 the cation distribution was the same used for MgNiMnO 4 ; [20] and for deficient Mg samples, as already described for MgMn 2 O 4 [7g] …”

“…The acid treatment of LiMn 2 O 4 results in conversion to cubic λ‐MnO 2 , although some Li atoms remain in the oxide. The chemical and acid treatments of MgMn 2 O 4 have been recently studied by several groups [6a,c,7g] . The cationic diffusion would be slower in MgMn 2 O 4 compared to LiMn 2 O 4 .…”

“…Potentially, the manganese spinel could operate in the region of Mn 3+ /Mn 4+ redox pair and in the region of Mn 2+ /Mn 3+ redox pair. Thus, one can find in the literature that some authors reported the electrochemical cycling experiments starting by discharge[ 7g , 7h ] and others starting by charge. [ 7d , 7e ] On the other hand, the stability of the spinel framework and the stability of the electrolyte solution in contact with the electrode material are very different depending on the voltage window.…”