Lithium-ion batteries have remained unrivaled in terms of overall performance for multiple applications, as evidenced by their widespread use in everything from portable electronics to cellular base stations. However, they suffer from some important disadvantages that are difficult to ignore. For one thing, lithium is pretty expensive, and the fact that it’s being mined at an extreme rate doesn’t help. In addition, the energy density of lithium-ion batteries is not sufficient to provide autonomy for electric vehicles and heavy machinery. These concerns, coupled with the fact that the batteries are very unsafe when punctured or at high temperatures, have prompted scientists to look for alternative technologies.
Among the various elements being tested as efficient energy carriers for rechargeable batteries, magnesium (Mg) is a promising candidate. Aside from its safety and abundance, Mg has the potential to realize higher battery capacities. However, some problems must first be solved. These include the low voltage window offered by Mg ions as well as the unreliable cycling performance observed with Mg battery materials.
To address these issues, a research team led by Vice President and Professor Yasushi Idemoto of Tokyo University of Science, Japan, has been searching for new cathode materials for Mg batteries. In particular, they have been looking for ways to improve the performance of cathode materials based on the MgV (V: vanadium) system. Fortunately, according to a recent study made available online on December 8, 2022 and published in Volume 928 of the Journal of Electroanalytical Chemistry on January 1st, 2023 they have now found the right path to success.
The researchers focused on the Mg1.33v1.67O4 system, but replaced some vanadium with manganese (Mn), yielding materials with the formula Mg1.33V1.67−xMnxO4, where X goes from 0.1 to 0.4. Although this system offered a high theoretical capacity, more details about its structure, cyclability and cathode performance had to be analyzed to understand its practical utility. Accordingly, researchers characterized the synthesized cathode materials using a 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 analyzes revealed that Mg1.33V1.67−xMnxO4 has a spinel structure with a remarkably uniform composition. Next, researchers performed a series of electrochemical measurements to evaluate the battery performance of Mg1.33V1.67−xMnxO4 using different electrolytes and testing the resulting charge/discharge characteristics at different temperatures.
The team observed high discharge capacity for these cathode materials – particularly Mg1.33v1.57Mn0.1O4 — but also varied greatly depending on the number of cycles. To understand why, they analyzed the local structure near the vanadium atoms in the material. “It seems that the particularly stable crystal structure together with a large charge compensation by vanadium leads to the superior charge-discharge properties that we have observed for Mg1.33v1.57Mn0.1O4“, notes Prof. Idemoto. “Taken together, our results show that Mg1.33v1.57Mn0.1O4 could be a good candidate for cathode material for rechargeable magnesium batteries.”
Pleased with the current results and hopeful for what is to come, Prof. Idemoto concludes: “Through future research and development, magnesium batteries could outperform lithium-ion batteries thanks to the former’s higher energy density.”
Indeed, substituted MgV systems could eventually lead to the long-awaited next-generation batteries. Let’s hope that the much-anticipated alternative to lithium for our rechargeable battery needs will be realized soon!