A New Pyrrolidinium-Based Electrolyte for Secondary Magnesium Batteries

Abstract

A critical roadblock toward practical Mg-based energy storage technologies is the lack of efficient electrolytes that are safe and electrochemically stable.[1] Despite their excellent electrochemical performance existing electrolytes based on ethereal solvents and organomagnesium compounds[2][3] are inadequate for meeting the needs of functional devices in portable electronics and transportation applications. It was recently shown[4][5][6] that haloaluminate ionic liquids (ILs) can provide a viable alternative to conventional electrolytes due to their low volatility, negligible flammability and good electrochemical performance. Despite of this, IL-based electrolytes usually show a narrow electrochemical stability window, which limits their use with high voltage cathode materials.[7] Furthermore, in the case of IL-based electrolytes in order to improve their performance, several issues[4][8] should be addressed such as: a) a fundamental understanding of the relation between Mg-ion speciation and the long-range charge transfer mechanism; b) SEI structure and formation; and c) long-term performance. Following this, here we are proposing a new high-performing electrolyte based on 1-Butyl-1-Methylpyrrolidinium chloride (BMPyCl) doped with AlCl3 and highly amorphous δ-MgCl2. The chemical composition of the samples is determined by ICP-AES and microanalysis. The structure and interactions are investigated with vibrational spectroscopies while the thermal stability and transitions are studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) respectively. In addition, the applicability of the [BMePyCl/(AlCl3)m]/(δ-MgCl2)n electrolytes in prototype cells is evaluated by studying the conductivity as well as the electrochemical performance of the materials.