A magnesium sulfur battery is a rechargeable battery that uses magnesium ion as its charge carrier, magnesium metal as anode and sulfur as cathode. To increase the electronic conductivity of cathode, sulfur is usually mixed with carbon to form a cathode composite. Magnesium sulfur battery is a emerging energy storage technology and now is still in the stage of research. It is of great interest since in theory the Mg/S chemistry can provide 1722 Wh/kg energy density with an voltage at ~1.7 V.
Magnesium is abundant, non-toxic and doesn't degrade in air. Most importantly, magnesium does not form dendrites during deposition/stripping process, which is attributed to be the main cause for the safety issue in lithium ion battery and rechargeable lithium battery.
In 2011 Toyota Motor announced a research project in this area, and in the same year they reported a new electrolyte that is chemically compatible with sulfur. Currently, efforts on rechargeable magnesium battery research are known to be underway at Apple, Toyota, and Pellion Technologies, as well as in several universities.
In 2014 researchers announced a new electrolyte and accompanying magnesium-based batteries. The electrolyte is more stable and works well with various solvents and at high concentrations. It supports sulfur cathodes. Two commercial chemicals, a magnesium amide and aluminum chloride. Adding them to a solvent can then be used directly as an electrolyte.
In 2015 a Mg rechargeable battery used a graphene–sulfur nanocomposite cathode, a Mg–carbon composite anode and a non-nucleophilic Mg-based complex in tetraglyme solvent as the electrolyte. The graphene–sulfur nanocomposites are prepared with a combination of thermal and chemical precipitation. The Mg/S cell delivers 448 mA h g−1 and 236 mA h g−1 after 50 cycles. The graphene–sulfur composite cathode, with a high surface area, porous morphology and oxygen functional groups, along with a non-nucleophilic Mg electrolyte, gives improved performance.
In the same year, a team at University of Maryland discovered that Li ion additive can enhance the reversibility of the electrochemical reaction in a Mg/S battery. The Mg/S cell delivers ~1000 mAh/g capacity for 30 cycles with two discharge plateau at 1.75V and 1.0V. The obtainable energy density of the cell at material level is 874 Wh/kg, about half of its theoretical value.