Electrochemical and Thermal Studies of Bismuth Electrodes for Magnesium-Ion Cells

Bismuth (Bi) anodes for Magnesium-ion (Mg-ion) cells were studied for their electrochemical performance and thermal stability. The Bi anodes exhibited reversible capacities over 300 mAh/g with high coulombic efficiencies of > 98%, when cycled between 0.05 and 0.5 V (vs. Mg/Mg2+). Rate capability tests showed that the Bi anodes could be cycled successfully up to a 1C rate. To further understand the magnesiation and demagnesiation processes, the Bi anode was examined using a transmission electron microscope (TEM) at various states. TEM images highlighted impressive morphological changes with the formation of a Bi nanocomposite during cycling, supporting the collected electrochemical data. Additionally, an isotherm micro-calorimetric technique (IMC) was used to record the in-situ heat profile, in an attempt to identify the heat sources contributing at the Bi anode during cycling. The experimental data collected for IMC showed good agreement with the calculated results at a low cycling rate of C/10. Irreversible heat (Qirrev) was found to be the main contributor to the overall in-situ heat generated during magnesiation and demagnesiation of Bi.