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Magnesium – a promising candidate for rechargeable batteries

Crystalized magnesium. (Reference image by CSIRO, Wikimedia Commons).

A research team at the Tokyo University of Science has achieved some success in its search for new cathode materials for magnesium batteries.

In particular, the researchers are focusing on ways to improve the performance of cathode materials based on the magnesium-vanadium system.

In a paper published in the Journal of Electroanalytical Chemistry, the group explains that they worked with the Mg1.33V1.67O4 system but substituted some amount of vanadium with manganese, obtaining materials with the formula Mg1.33V1.67−xMnxO4, where x goes from 0.1 to 0.4. While this system offered high theoretical capacity, more details about its structure, cyclability, and cathode performance needed to be analyzed to understand its practical utility.

Accordingly, the researchers studied the composition, crystal structure, electron distribution, and particle morphologies of Mg1.33V1.67−xMnxO4 compounds using X-ray diffraction and absorption, as well as transmission electron microscopy. The analyses showed that Mg1.33V1.67−xMnxO4 has a spinel structure with a remarkably uniform composition.

Next, they conducted a series of electrochemical measurements to evaluate the battery performance of Mg1.33V1.67−xMnxO4, using different electrolytes and testing the resulting charge/discharge properties at various temperatures.

The team observed a high discharge capacity for these cathode materials—especially Mg1.33V1.57Mn0.1O4—but it also varied significantly depending on the cycle number. To understand why this happened, they analyzed the local structure near the vanadium atoms in the material.

“It appears that the particularly stable crystal structure along with a large amount of charge compensation by vanadium leads to the superior charge/discharge properties we observed for Mg1.33V1.57Mn0.1O4,” lead researcher Yasushi Idemoto said in a media statement. “Taken together, our results indicate that Mg1.33V1.57Mn0.1O4 could be a good candidate cathode material for magnesium rechargeable batteries.”

Idemoto said that through future research and development, magnesium batteries could surpass lithium-ion batteries thanks to the former’s higher energy density.

The scientist pointed out that, in addition to the potential to realize higher battery capacities, magnesium is considered a promising candidate for rechargeable batteries because the metal is safer for battery chemistries than lithium and is more abundant.

Thus, his research aims to address the low voltage window that Mg ions provide, as well as the unreliable cycling performance observed in Mg battery materials.