Enabling High-Capacity Electrochemical Magnesium Intercalation in Prussian Blue Cathode Via Synthesis Route Optimization

Magnesium-ion batteries (MIBs) have emerged as a promising candidate for post-lithium-ion batteries. However, their widespread adoption is hindered by the limited number of host materials that can intercalate magnesium ions reversibly in a nonaqueous electrolyte with a high operating voltage, such as Prussian Blue analogues. Unfortunately, the capacity of Prussian Blue is by far limited (<100 mAh g−1), resulting in low energy density, despite their high operating voltage. In this study, we present a systematic synthesis route optimization that allows for high-capacity magnesium ion insertion into Prussian Blue. Our defect-free and water-free Prussian Blue demonstrates reversible magnesium intercalation with a first discharge capacity of 127 mAh g−1 at 25 °C and 156 mAh g−1 at 60 °C, with an average discharge voltage of ~2.1 V (vs. Mg/Mg2+) in a nonaqueous, chloride-free electrolyte. The high-capacity magnesium ion insertion into our optimized Prussian Blue offers insights into the importance of material preparation for high-energy cathode materials in MIBs.