Nanostructured (Mg,M)2SiO4 As Cathode Material in Mg Ion Batteries

Rechargeable Li-ion batteries are already widely used, and the dominating solution for automotive as well as portable, high-power applications due to the superior power density. However, several challenges of Li-ion battery technology are yet to be overcome, e.g. with respect to cost, resource availability, safety issues related to risk of thermal runaway of batteries and the limited temperature window of Li-ion batteries due to electrolyte deterioration at low temperatures. Although expected to dominate the portable battery market in the foreseeable future, the above mentioned drawbacks of Li-based batteries mean they have limited suitability in several markets, including stationary energy storage systems and auxiliary power applications where low cost and high reliability under a wide temperature range are more important than low weight and high power density. There is therefore a need for development of new battery types, specifically aimed at low cost markets.

Batteries based on magnesium and other divalent metal ions, with the option of transferring two electrons, compared to the one electron transferred in Li-ion batteries, were introduced around 2000 by Aurbach et al.^[1] and represent a promising solution for future low cost, high energy density batteries. Rechargeable Mg-batteries are not yet commercially available, but have a theoretical energy density in the range of 100 Wh/kg^[2] for Chevrel-phase cathodes and up to 500 Wh/kg for MgMnSiO₄ cathodes^[3]. Still, fundamental research is needed in order to produce high-performance batteries which are also stable and recyclable. In this aspect, an interdisciplinary approach covering modeling, innovative material synthesis routes and advanced experimental characterization techniques is a powerful combination which is herein proposed for the development of low cost novel Mg-ion batteries. Such developments will be beneficial for a wide range of applications, mainly stationary, that require use of batteries, such as for storage of renewable energy from intermittent energy sources (solar, wind and wave), stand-alone power systems, telecommunication base stations, auxiliary power, etc.

In this work, selected (Mg,M)₂SiO₄ (M=Mn or Co) materials are synthesized through an advanced sol-gel route as well as flame spray pyrolysis, aiming to obtain enhanced electrical conductivity. The developed cathode materials are characterized electrochemically by using Mg alloys as the anode and a state-of-the art electrolyte. In-situ X-ray diffraction (XRD) is used to characterize phase evolution in the materials during cycling. The effect of different synthesis methods on morphology, phase purity, crystal structure and electrochemical properties will be presented.

[1] D. Aurbach, Lu, Z., Schechter, A., Gofer, Y., Gizbar, H., Turgeman, R., Cohen, Y., Moshkovich, M., Levi, E., Nature2000, 407, 724-727.

[2] D. Aurbach, Y. Gofer, Z. Lu, A. Schechter, O. Chusid, H. Gizbar, Y. Cohen, V. Ashkenazi, M. Moshkovich, R. Turgeman, E. Levi, Journal of Power Sources 2001, 97-98, 28-32.

[3] Z. Z. Feng, J. Yang, Y. Nuli, J. L. Wang, X. J. Wang, Z. X. Wang, Electrochemistry Communications 2008, 10, 1291-1294.

Acknowledgements

 Financial support is gratefully acknowledged from the Research Council of Norway, grant number 221785/F20.