Cu-substituted Prussian white with low crystal defects as high-energy cathode materials for sodium-ion batteries

Prussian white (PW) has emerged as a promising cathode material for high-energy sodium-ion batteries owing to its high working voltage, high specific capacity, and cost-effectiveness. Nonetheless, its practical utilization is impeded by challenges related to insufficient cycling stability, primarily stemming from poor structural stability due to large defects in the lattice structures and irreversible phase transitions. In this study, we propose a novel strategy to overcome these challenges by substituting the manganese sites of PW with 10 mol% copper. During the synthesis process, substitution with Cu enabled the formation of fewer defects and interstitial water. Cu has no electrochemical redox reactions during the charge-discharge process; so, it showed an initial lower capacity(120 mAh g-1 at 0.1C). However, Cu substitution resulted in a significant improvement in the long-term cycling stability(67.6% at 10C after 500 cycles) by relieving structural stress due to the reversible rhombohedral-to-cubic phase transition. Moreover, the pouch cell (PW-Cu10/hard carbon) exhibits a discharge capacity of 85.4 mAh g−1 and stable cycling retention of 80% at 1.0C after 250 cycles. This work demonstrates a feasible strategy for designing practical Prussian white cathode materials for sodium-ion batteries.