Catenated pyrrolidinium-magnesium-organochlorostannate ionic liquid electrolytes for multivalent metal batteries

Abstract

The quest for the development of high performing secondary batteries is prompting the research activities in this field towards the exploitation of new cell concepts. In this concern, next-generation secondary batteries based on multivalent metals such as magnesium and tin are an important promise. In this report, a new family of multivalent metal-based ionic liquid (IL) electrolytes is developed. The proposed ILs are obtained by reacting 1-butyl-1-methylpyrrolidinium chloride (Pyr14Cl), dimethyl-tin dichloride and the highly electroactive δ-MgCl2 material. Thermal and vibrational spectroscopy studies reveal that the proposed electrolytes consist of domains of complex catenated 3D magnesium-organochlorostannate coordination networks neutralized by aggregates of Pyr14+ stacks. The anionic domains are composed by a network of catenated [Me2xSnxCl2x+y]y− repeat units bonded by MgClx bridges. Cyclic voltammetry studies reveal that the metal deposition and stripping processes occur with a low overpotential in the order of few tens of mV. Finally, broadband electrical spectroscopy studies show that these new IL electrolytes: (i) are characterized by a room temperature ionic conductivity in the order of 10−3 S cm−1; and (ii) exhibit host matrix relaxations which are very effective in facilitating the long-range charge migration processes responsible for the overall conductivity of materials.