Résumé
The electrochemical behavior of micrometric Bi powder as an active electrode material for Mg batteries is revisited in a half-cell with Mg metal as the counter electrode and organohaloaluminate-based complex electrolyte. A complete biphasic domain is evidenced from Bi to its Mg-alloyed counterpart Mg3Bi2. Operando X-ray diffraction underlines a simple mechanism that does not imply any intermediate phases or amorphization process. The high performances of Bi-based electrodes are confirmed using an optimized electrode formulation, with specific capacity nearing the theoretical value of 385 mA h g−1 at low rates. The capacity fading appears limited when moving to high current densities. In parallel, a micrometric Mg3Bi2 intermetallic compound obtained by high-energy ball-milling exhibits a similar electrochemical behavior. As a proof-of-concept as-prepared Mg3Bi2 is directly associated with a Chevrel-type positive electrode and successfully tested as a complete Mg-ion battery. Despite the high molar mass, the couple Bi/Mg3Bi2 can be considered as a reliable negative electrode candidate and a reference system for testing the next generation of Mg-ion battery electrolytes.