Magnesium Deintercalation From the Spinel‐Type MgMn_2‐yFe_yO₄ (0.4≤y≤2.0) by Acid‐Treatment and Electrochemistry

Abstract

Rechargeable magnesium batteries attract lots of attention because of their high safety and low cost compared to lithium batteries, and it is needed to develop more efficient electrode materials. Although MgMn 2 O 4 is a promising material for the positive electrode in Mg rechargeable batteries, it usually exhibits poor cyclability. To improve the electrochemical behavior, we have prepared nanoparticles of MgMn 2-y Fe y O 4 . The XRD results have confirmed that when Mn 3 + (Jahn-Teller ion) ions are replaced by Fe 3 + (non-Jahn-Teller ion), the resulting MgMn 2-y Fe y O 4 is a cubic phase. The structure and theoretical voltage are theoretically calculated by using the DFT method. The obtained samples have been chemically treated in acid solution for partial demagnesiation, and it is observed that the presence of iron inhibits the deinsertion of Mg through disproportionation and favors the exchange reaction. The electrochemical behavior in nonaqueous magnesium cells has been explored.

Facile Surface Modification of MgMn2O4 Positive-Electrode Material for Improving Cycle Performance of Magnesium Rechargeable Batteries

“…According to previous theoretical studies, 44 , 46 Mg deinsertion and insertion with redox of Mn 3+ /Mn 4+ can occur around 2.8 V vs Mg/Mg 2+ in the case of MgMn 2 O 4 . As for the acid-treated MgMn 2 O 4 (demagnesiated Mg x Mn 2 O 4 ), 20 it was also suggested that a pseudoplateau due to the oxidation up to Mn 4+ was observed at ca. 2.5 V vs Mg/Mg 2+ .…”

“…As can be seen in Figure 3 , the averaged structure could be refined under these hypotheses, and thus it is demonstrated that Mg and Mn exist basically at the tetrahedral and octahedral sites, respectively, as reported previously. 20 , 44 Distortions of the tetrahedra ( M O 4 ) and octahedra ( M O 6 ) were calculated from the refined structural parameters. Table 3 summarizes the polyhedral volumes, quadratic elongations (λ), and bond-angle variances (σ 2 ), which are indices of the polyhedral distortions.…”

Advancing towards a Practical Magnesium Ion Battery

“…A way to overcome this could be the partial replacement of Mn by other elements. Thus, the partial substitution of Mn by iron has been explored to increase the stability of MgMn 2-y Fe y O 4 during the electrochemical cycling [ 38 , 39 ]. The Jahn–Teller distortion of the structure can be suppressed by incorporating iron to the spinel and the structure becomes cubic (s.g. Fd m).…”

“…The maximum reversible capacity usually observed for these materials is about 130 mAh g −1 [ 39 ], although the maximum theoretical capacity is 616 mAh g −1 (referred to MnO 2 , and Mg content up to Mg 2 Mn 2 O 4 ). Kobayashi et al raised the experimental capacity of MgMn 2 O 4 up to 230 mAh g −1 by using cubic particles with ca.…”

“…The results in red color were taken from reference [ 34 ]. For MgMMnO 4 with M = Mn and Fe the data were taken from [ 39 ]. The results for M = Ti, V, Cr, Ni and Al have been calculated in this work (previously unpublished) using the same method described in [ 39 ], with U eff = 3.25 eV (for V), 3.7 eV (for Cr) and 6.45 eV (for Ni) [ 34 ].…”