Pilot Line Characterization and Process Optimization for Magnesium-Based Battery Prototypes

Magnesium metal batteries hold great promise for achieving higher energy densities in stationary energy storage, potentially at a lower cost than lithium-ion batteries. This potential arises from magnesium's (Mg) natural abundance, affordability, environmental sustainability, and favourable electrochemical characteristics. The magnesium battery chemistry with the most stable electrochemical performance employs a Chevrel phase (Mo6S8) cathode, an all-phenyl complex (APC) electrolyte, and Mg foil as the anode. However, most studies for this chemistry were conducted on a laboratory-scale coin cell. To advance this system to a higher Technology Readiness Level (TRL), it must be evaluated in a pilot-scale pouch cell configuration. In this context, the Mg/APC/Mo6S8 system was examined first in a laboratory-scale coin cell configuration. Based on the insights gained from laboratory data, the electrode fabrication was successfully scaled to a pilot line pouch cell format. Electrochemical evaluations of the Mg pouch cell displayed good electrochemical performance, with a stable specific capacity of approximately 70 mAh/g at a rate of C/5 and around 65 mAh/g at 1C. Remarkably, the cell exhibited high coulombic efficiency, nearly 100% over 300 cycles at 1C. Additionally, postmortem characterisation of cycled Mg cells was performed to investigate the surface morphology of electrodes, the chemical composition and morphology of solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) related to the degradation of the electrolyte at the electrode/electrolyte interphase. Preliminary results from surface characterisation showed the formation of a porous film on the Mg foil during the stripping and plating process, with negligible SEI formation. In contrast, the Mo6S8 cathode displayed a thick CEI formation. The initial operando GC-MS (gas-chromatography mass-spectroscopy) results of the Mg battery in coin cell format reveal that the decomposition of the APC electrolyte causes gas formation, and this decomposition continues throughout the cycling process.