Magnesium is one such alternative that presents itself as cheaper and more abundant than lithium, and environmentally friendly – and one that is currently trending if the following recent research is anything to go by.
Layered cathode materials are a popular choice across many battery systems, and one team at Nanjing University in China has developed nanoflowers of vanadium disulfide (VS2) as a possible layered cathode for use in rechargeable magnesium batteries. The interlayer distance of their final cathode material was almost 10 Ångstroms, nearly double the spacing in the control sample (5.73 Ångstroms). This expansion was achieved by choosing a solvent, 2-ethylhexylamine, that could also act as an intercalation agent during the synthesis process. The resulting expanded lattice allowed the diffusion of magnesium ions at a rate of 10−11–10−12 cm2 s-1, with the full battery system achieving a reversible discharge capacity of 245 mAh g−1 at 100 mA g−1.
After an extensive exploration of the magnesium storage mechanism, checking on recent claims that such materials use MgCl+ rather than Mg2+ ions as the active species, the research team found evidence that, at least for their system, “both MgCl+ and desolvated Mg2+ ions may simultaneously participate [in] the cation insertion/extraction processes of [the] expanded VS2 electrode”.
This work shows how understanding the influence of structure can lead to improvements toward the next generation of battery types. To facilitate such endeavors, scientists at the University of Science and Technology Liaoning and Northeastern University, China, have reviewed what we know about the microstructure of cathodes. Most studies so far, they report, have focused on the internal structure of the cathode in order to improve the intercalation of magnesium ions; more studies of the insertion/extraction mechanisms are called for to support this work.
To identify five key areas for future research: increasing the occupied sites on the cathode surface; forming conductive networks from dispersed particles to improve the electronic properties of the materials; reducing Mg2+ solvation; optimizing synthesis conditions to achieve larger specific surface areas; increasing material conductivity through strategies such as coating or doping.