Intrinsic differences and realistic perspectives of lithium-sulfur and magnesium-sulfur batteries

Following in the footsteps of lithium-sulfur batteries, magnesium-sulfur batteries offer a high theoretical energy content and are composed of cheap and more environmentally-friendly electrode materials. In comparison to lithium-sulfur, however, current magnesium-sulfur batteries suffer from higher overpotentials at the magnesium anode and the sulfur cathode, lower material utilization and reversibility at the sulfur cathode, and an excessive demand of electrolyte. Here, a side-by-side comparison of the processes at the two metal anodes and at the sulfur cathode in Li+- or Mg2+-based electrolytes highlights how most of the challenges facing magnesium-sulfur batteries are intrinsically rooted in the nature of the magnesium species, requiring different research directions than lithium-sulfur batteries. An evaluation of the energy content and the corresponding costs on a practical cell stack level illustrates the importance of overcoming these challenges. Magnesium-sulfur batteries offer several advantages compared to lithium-sulfur batteries, including a more stable anode and lower material costs. Here, the challenges and prospects for both classes of batteries are discussed, including their outlook for practical energy and cost levels.