A polyelectrolyte multilayer based sulfur cathode.

Mg-ion battery is one of the most promising candidates for a post Li-ion battery due to its high capacity, improved safety and potentially reduced cost. However, since the metallic Mg-anode is prone to passivation by electrolytes, we need to carefully use appropriate electrolytes which have high stability to the Mg metal. For example, common anions such as ClO4 -, BF4 - or TFSI- decompose on the Mg surface resulting in a highly resistive layer that partially or fully blocks Mg-ion transport. Although organo and chloride based reagents were found to be compatible with Mg metal, they still have severe issues such as highly corrosive nature and low Mg-ion transference number.1) We have been pioneering the development of a new class of electrolytes based on a novel design strategy and offering halogen free and non-corrosive boron-hydrogen salts, which can also improve the transport and solubility properties.2) Another serious challenge facing Mg battery technologies is the limited choice of cathode materials due to the difficulty to reversibly intercalate divalent Mg-ion in host structures analogues to those used in Li-ion batteries such as transition metal oxides.3)Therefore, we have been studying alternative cathode chemistries beyond the intercalation types. The inertness and stability of the MMC electrolyte allow us to examine these new cathodes where fast and stable charge/discharge cycles can be performed with a relatively fine coulombic efficiency. In this presentation, we will unveil these new results and also show detailed mechanisms towards understanding the battery performance. [1] J. Wook Choi, D. Aurbach, doi:10.1038/natrevmats.2016.13, Nature Reviews Materials, 2016 [2] a) R. Mohtadi, M. Matsui, T. S. Arthur, S.-J. Hwang, Angew. Chem. Int. Ed. 2012, 51, 9780 –9783; b) T. J. Carter, R. Mohtadi, T. S. Arthur, F. Mizuno, R. Zhang, S. Shirai, J. W. Kampf, Angew. Chem. Int. Ed. 2014, 53, 3173-3177; c) O. Tutusaus, R. Mohtadi, ChemElectroChem. 2015, 1, 51-57 d) O. Tutusaus, R. Mohtadi, T. Arthur. F. Mizuno, Angew. Chem. Int. Ed. 2015, 27, 8011-8015 [3] a) H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, D. Aurbach, Energy Environ. Sci. 2013, 6, 2265-2279; b) R. Mohtadi, F. Mizuno Beilstein J. Nanotechnol. 2014, 5, 1291–1311

The need for abundant, sustainable, and cost-effective energy storage technologies has been generating increased interests in batteries that rely on the use of earth abundant elements such as multivalent batteries. Those that utilize metallic anodes (Mg, Ca, Al) and organic cathodes are attractive as they can offer a path forward toward a competitive gravimetric energy density and in some cases fast charge capabilities. In particular, reports of a variety of Mg metal anode–organic cathodes batteries with good performances compel further research efforts of these systems and understanding of processes that govern their performances. However, studies of organic cathodes in competent, Cl– free Mg electrolytes remain limited, and the mechanisms that govern the cycling of these batteries are unclear. Herein, we assess the Mg battery performance using a typical benzoquinone type organic molecule in a competent Cl– free, single salt electrolyte and investigate the mechanisms at play. Combining the findings from battery and analytical studies reveal reversible structural transformations driven by a new precedence of a unique dissolution/precipitation mechanism. The implications of this mechanism on the performance of the battery are evaluated and discussed. The findings unveiled shed light onto potential challenges and opportunities with these systems and help guide future advancements.