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

Magnesium-ion batteries could be competitive with lithium-ion batteries, but the reversible intercalation of magnesium in the framework of the host material needs to be verified. A concentration cell was built by using electrodes with different concentrations of magnesium ions in the cubic spinel MgxMn2O4. For this purpose, firstly cations were partially extracted from MgMn2O4 by acid-treatment. This concentration cell was used to test the reversible intercalation of magnesium and the effect of the cationic vacancies. The theoretical results of the percolation energy can explain the lower polarization experimentally observed in the voltage curve of the acid-treated sample. The reversible capacity (ca. 115 mA h g−1) is preserved after charge–discharge cycling.