Advanced Materials for Magnesium-Ion Rechargeable Batteries (ADMIRE)

Concerns over environment and future energy security drive researchers and policy makers to harvest energy from renewable energy sources such as sun, wind etc. Batteries, with its ability to store and transport energy produced from the renewable sources are considered to be an integral part of this ecosystem. Batteries composed of positive and negative electrode and electrolyte. Ions are transported from the negative to the positive electrode through the electrolyte during discharging while the electrons pass in an outer circuit and vice-versa during charging. For this to occur smoothly, the positive electrode material is able to take up (or intercalate) quickly as many of the cations as possible (discharge) and vice-versa during charging. Furthermore, the electrolyte has to conduct the ions as rapidly as possible. In order to optimize and maximize the battery performance, knowledge of all the components is thus imperative. In addition, all the materials used in these batteries have to be stable over a large period of time during operation at various conditions (temperature, load cycle etc.). In ADMIRE we aimed at using the electrochemistry of magnesium instead of lithium as magnesium is abundant in nature, has high stability and are safe to use. In this project, we were successful in developing potentially new electrolytes based on ionic liquids which are inherently safe. These newer ionic liquids are found to transport magnesium ions between the electrodes during discharge and charge for many cycles. However, many diferent cathode materials based on V2O5 like V2O5-P2O5, V2O5-B2O3 V2O5-TeO2, etc that are investigated failed to work. Other methods such as incorporation of graphene or other systems like VOPO4 are also failed. It is found that Mo6S8 is still the only fairly stable material that performs for multiple charge-discharge cycles. some of the findings regarding electrolytes are already published and the newer findings are being written as scientific articles and will be published in the coming months.

The project aimed at developing electrolyte and cathode materials for rechargeable magnesium ion batteries. We have achieved the following on the cathode:1. Developed different V2O5-glass amorphous materials (V2O5-SiO2, V2O5-P2O5, etc) 2. Investigations found that these materials are not suitable for Mg intercalation 3. Found that the already known Mo6S8 is still the only working cathode material investigated in this project We have achieved the following on the electrolyte:1. Ionic liquid systems based on EMIM with different Mg salts such as MgCl2, Mg(BH4)2, Mg(HMDS)2, Mg(TFSI)2 showed reversible Mg deposition and stripping 2. IL system with EMIM-magnesium bis(isopropyl) amide is found to be the best one with the battery showing more than 300 cycles 3. Ration between THF and DME is found to affect the cell performance when using APC-type electrolyte Breakthroughs in cathode materials should happen to realize a practical rechargeable Mg battery in the future.

The primary objective of ADMIRE is to develop advanced rechargeable magnesium-ion batteries with high energy density, better durability and safe operation for future stationary, transport and grid storage applications. Magnesium metal as anode electrode for batteries is very attractive as it is the fifth most abundant material in earth (low cost), it can pack more energy per unit volume than lithium and it is very safe during operation. Nevertheless, due to the ability of magnesium to form a insulation layer when it comes to contact with oxygen and aqueous solvents, it is difficult to recharge these batteries repeatedly using the current electrolyte systems. Also, to make magnesium-ion batteries commercially viable it is necessary to make these batteries less heavy by developing advanced materials for cathode with high operating voltages. In ADMIRE, we propose to develop a new category of cathode materials that can facilitate insertion and extraction of magnesium at high potentials by developing novel amorphous vanadium oxides. In addition, we also propose to develop new electrolyte systems based on ionic liquids which is compatible with anode to have more charge/discharge cycles and cathode to accommodate high performance cathodes with wider voltage limit. The advantage of having amorphous materials is that they increase the kinetics of heavy magnesium in the cathode at high voltages resulting in high charge/discharge capacity at high current rates. On the other hand, ionic liquids with their structured tuned as explained in the application and inherent safety will be developed to improve the magnesium plating/stripping at the anode and to provide a platform for high voltage cathodes by being stable and electrochemically active. If successful, this project will motivate industries (both battery and materials) to look at this technology for future energy market.