Optimizing Electrode Porosity for Enhanced Electrochemical Performance of α-KxMnO2 Composite Positive Electrode,in Rechargeable Magnesium Pouch Cells

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Abstract
Rechargeable Mg batteries (RMBs) are promising energy-storage systems due to the high volumetric capacity of Mg metal (3833 mAh cm-3), its low standard electrode potential among metals usable in air (-2.37 V vs. SHE), its natural abundance, low cost, and operational safety. However, the role of electrode architecture in determining electrochemical performance has not yet been systematically investigated. Herein, α-KxMnO2 composite positive electrodes with an identical active mass loading (0.5 mg cm-2) were roll-pressed to tailor the electrode porosity, and their structural and electrochemical properties were evaluated in rechargeable Mg pouch cells. Moderate roll-pressing (35–60 % thickness reduction) significantly improved the initial discharge capacity (~102 mAh g-1) by enhancing particle packing and reducing pore volume, resulting in more efficient active material utilization than that of the nonpressed electrode. In contrast, excessive roll-pressing (80% thickness reduction) resulted in a lower initial discharge capacity (~89 mAh g-1) and higher overpotential because the electrolyte was expelled and the Mg2+ transport was hindered. Therefore, moderate electrode densification improves particle-to-particle contact without severely hindering Mg2+ transport. This study provides practical design guidelines for optimizing composite positive electrodes by increasing particle-to-particle contact while maintaining sufficient electronic conductivity and ionic transport, thereby improving electrochemical performance.

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