Beyond lithium: A promising cathode material for magnesium rechargeable batteries

Among the various elements being tested as efficient energy carriers for rechargeable batteries, magnesium (Mg) is a promising candidate. Apart from its safety and abundance, Mg has the potential to realize higher battery capacities. However, some problems need to be solved first. These include the low voltage window that Mg ions provide, as well as the unreliable cycling performance observed in Mg battery materials.

To tackle these issues, a research team led by Vice President and Professor Yasushi Idemoto from Tokyo University of Science, Japan has been on the lookout for new cathode materials for Mg batteries. In particular, they have been searching for ways to improve the performance of cathode materials based on the MgV (V: vanadium) system. Fortunately, as reported in a recent study made available online on 8 December 2022 and published in Volume 928 of the Journal of Electroanalytical Chemistry on 1 January 2023, they have now found the right track to success.

The researchers focused on the Mg_1.33V_1.67O₄ system but substituted some amount of vanadium with manganese (Mn), 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 characterized the synthesized cathode materials using a wide variety of standard techniques.

First, they 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, the researchers 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 Mg_1.33V_1.57Mn_0.1O₄ -- but it also varied significantly depending on the cycle number. To understand why, 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 Mg_1.33V_1.57Mn_0.1O₄," remarks Prof. Idemoto. "Taken together, our results indicate that Mg_1.33V_1.57Mn_0.1O₄ could be a good candidate cathode material for magnesium rechargeable batteries."

Satisfied with the present findings and hopeful about what is to come, Prof. Idemoto concludes: "Through future research and development, magnesium batteries could surpass lithium-ion batteries thanks to the former's higher energy density."

Indeed, substituted MgV systems could eventually lead to the much awaited next-generation batteries. Let us hope the highly anticipated alternative to lithium for our rechargeable battery needs will be realized soon!