Magnesium sulfur battery

In 2011 Toyota Motor announced a research project in this area,[2] and in the same year they reported a new electrolyte that is chemically compatible with sulfur.[3] The electrolyte was prepared as a Lewis acid-base complex from the Hauser base (HMDS)MgCl, where HMDS = hexamethyldisilazide,[4] introduced by C. Liebenow et al. in 2000[5] and AlCl₃, conceptionally similar to Aurbach's binuclear electrolyte complex from 2001.[6] Although the complex had to be refined by recrystallization and only THF could be used as solvent, a discharge voltage of 1 V was obtained over two cycles, demonstrating the principle feasibility.

Currently, efforts on rechargeable magnesium battery research are known to be underway at Apple, Toyota, and Pellion Technologies,[7] as well as in several universities.

In 2013 researchers announced a new electrolyte and accompanying magnesium-based batteries.[8] 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 were mixed in a solvent, the product can then be used directly as an electrolyte.[9][10]

In 2015 a Mg rechargeable battery was presented built with 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 were 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.[11]

Recently, a new class of sulfur-compatible and Cl-free electrolytes was introduced.[12] It is based on a weakly coordinated Mg salt with big anions (fluorinated alkoxyborate) which can be prepared by a simple reaction and used in-situ.

In 2015, 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.[13] The obtainable energy density of the cell at material level is 874 Wh/kg, about half of its theoretical value.

In 2017, the same team successfully increases the cycling stability of a Mg/S cell to 110 cycles, by suppressing the dissolution of polysulfide with a concentrated electrolyte, a major reason for the loss of active material and capacity fading in Mg/S batteries. They also demonstrate that the MgTFSI₂-MgCl₂-DME electrolyte is compatible with sulfur cathode. Unlike the complex electrolytes made through Lewis acid-base reaction or the electrolytes using Mg salts with big anions, this electrolyte can be simply made by blending dried MgTFSI2, MgCl₂ with DME. This facile synthesis procedure enables this electrolyte to be a convenient platform for the community to further study the Mg/S chemistry.[14]