A Porous Electrode Model for the Magnesiation and Demagnesiation of a Bismuth Electrode in Rechargeable Magnesium-Ion Cells

Abstract

The transport and electrochemical properties of magnesium ions (Mg2+) in a magnesium organohaloaluminate electrolyte were estimated experimentally. The key properties of a Bismuth (Bi) electrode; such as solid-state Mg2+ diffusion, electronic conductivity, particle size, and electrode porosity were also estimated, both experimentally and theoretically. The magnesium organohaloaluminate electrolyte was utilized in an electrochemical cell to study the Mg2+ insertion/extraction reactions in a Bi electrode. The existing porous electrode pseudo two-dimensional model was extended in the proposed study to describe the behavior of the α-Mg3Bi2/Mg cell system during charge-discharge reactions. The model was also modified to include experimentally evaluated parameters such as internal resistance, electrode kinetics, thermodynamics, and the diffusion of Mg2+ in the active particles. This electrochemical model, modified with estimated parameters for the electrolyte, Mg, and α-Mg3Bi2 electrodes, was formulated with both, direct 2-electron transfer and multi-electron transfer from each magnesium atom of the magnesium dimer present in the electrolyte. Details of the electrochemical performance from both mechanisms are compared with the experimental data, and factors governing the performance of the α-Mg3Bi2/Mg cell are discussed in the present study.