Magnesium sulfide - an alternative to lithium
Batteries should demonstrate a high energy density, they should be inexpensive and should hold many memory cycles. Scientists develop such batteries in the project MASAK. They pursue a new concept: in contrast to the known magnesium - systems not magnesium cation are used for charge transfer, but sulfide anion.
|Project status||Project completed|
|Project duration||September 2012 until August 2015|
The cost-effective storage of electrical energy is an essential premise to realise the energy revolution in Germany. To meet the energy consumption by generating fluctuating regenerative energy like solar and wind power, appropriate storage systems are needed. Electrochemical energy storage offers multible advantages since it is local and independent from geographical conditions, but most available storing systems do not provide enough storage capacity with respect to their price. Therefore the consortium of the Brandenburgische Kondensatorenwerke GmbH, the University of Rostock, Institute for Physical Chemistry and the Fraunhofer-Institute for Manufacturing Technology and Advanced Materials developed a concept for a magnesium and sulfur based energy storage system that will be set up and tested during the three years time span of MASAK.
Many cycles, long life and low price
We aim to develop and manufacture a high power accumulator with high energy density, good efficiency, long term stability and competitive price which is not lithium-based. In the magnesium sulfide accumulator divalent magnesium ions are used as energy storage instead of monovalent lithium ions in lithium ion batteries. Contrary to known magnesium accumulators a sulfide ion is used for charge transfer. Therefore magnesium is oxidized to magnesium sulfide on the cathode side and copper sulfide is reduced to copper on the anode side. One key part in the project is the calculation and simulation as well as the synthesis of a suitable electrolyte e.g. on the basis of ionic liquids. The battery will be a cheap alternative because the whole system does not contain any rare or toxic materials like cobalt or lithium. The theoretical energy density of the electrode material is 1.2 kWh/kg. The battery is expected to give 150Wh/kg.
Cheap, no rare materials and high energy density
The magnesium sulfide accumulator is a very new concept for energy storage, that has not been investigated before. The accumulator will contain only cheap and no rare materials and will have an energy density which is comparable to current Lithium-Ion batteries. But in contrast to known magnesium batteries no magnesium cations but sulfur anions are integrated for charge transport. Because of its exceptional nature all components like the copper/copper sulfide anode, the magnesium/magnesium sulfide cathode and the electrolyte need to be evolved.
All preliminary studies are progressing well, most necessary literature research is done and all investments have been set up. Most of all 14 sub-projects from 7 working packages have started and first results have been obtained. After one year the project had meant to reach the first milestone but the determining phase will be reached when first prototypes of cathode and anode are realised after 18 months and the electrolyte is developed after 20 months. By then we will be able to test the overall potential of the new system. In the last phase of the project all work will go into optimising and constructing a demonstrator of the magnesium sulfide accumulator.
Porous carbon coated on metal foil
The electrode surface is of special interest, because this is where all reactions take place. Hence they are made from powders or by loading of a highly porous carbon matrix, which are coated on metal foil by doctor blade technique. The electrolyte also has to comply serveral conditions. Amongst others there are stability towards magnesium, a large electrochemical voltage window between 1.5V and 3.5V, high sulfide ion conductivity, low toxicity and a reasonable price. One approach is to use ionic liquids on the basis of sulfidic quarternary ammonium salts. Those have the advantage of being easily synthesised and largely available. On a different route the anions in known ionic liquids will be replaced by sulfides.
Cobalt makes lithium-ion batteries expensive
The costs for a lithium-ion accumulator is around 500-700 $/kWh at the moment. A lot of this is caused by the expensive rare materials that are used, e.g. cobalt. If these materials could be replaced by cheaper ones the costs could be reduced significantly. This would give a way to the comprehensive application of electrochemical energy storage.
Independent from all work packages named in the proposal there are three major tasks in this project: 1st the development of suitable anodes and cathodes, 2nd the simulation and synthesis of sulfide ion conducting electrolyte and 3rd the design and assembling of a demonstrator.