Polycrystalline Prussian White Aggregates as a High-Rate and Long-Life Cathode for High-Temperature Sodium-Ion Batteries

Cost and resource consideration requires the use of sodium-ion batteries (SIBs) instead of lithium-ion batteries for grid-scale stationary energy storage, which requires a battery to provide high energy density, high power density, and stable cycling over a wide temperature range. Prussian white (PW) is emerging as a potential cathode for SIBs, and the electrochemical properties of PW at room temperature and below have been intensively studied; however, the rapid capacity decay at elevated temperatures still remains a big challenge. In this work, we demonstrate a polycrystalline Prussian white aggregate cathode with fast and stable Na+ ion storage performance at high temperatures up to 70 degrees C. Thanks to the small surface-to-volume ratio and uneven surfaces, the thermodynamic stability of the surface and electric contact with conductive agents are evidently improved. In addition, the stability of the low-spin Fe redox pair at elevated temperatures is significantly improved, resulting in impressive cycling stability and high rate capability. The capacity retentions of Poly-PW cathodes cycled at 50 and 70 degrees C are, respectively, 82.8 and 77.8% over 300 cycles. At a high rate of 30C, Poly-PW shows a capacity of 99 mAh g(-1), corresponding to 73% of that at 0.3C. In addition, we investigated the crystal nucleation and growth mechanism of the polycrystalline aggregated structure. These findings offer a direction to facilitate the practical viability of PW for hot climates.