Rational construction of Prussian blue analogue with inverted pyramid morphology as ultrastable cathode material for lithium-ion battery

Prussian blue analogue material is regarded as an ideal cathode candidate for Li-ion batteries due to its open 3D frame structure and various transition metals with different valence states. However, poor electronic conduc-tivity and structural collapse severely limit its application in the electrochemical field. In this work, Na1.13Fe[Fe (CN)]6.3.22H2O electrode materials with stepwise hollow inverted pyramid morphology are prepared by simple hydrothermal method. The inverted pyramid Na1.13Fe[Fe(CN)]6.3.22H2O maintains the stability of the crystal structure and slows down the volume expansion during the Li + insertion-extraction process. Benefiting from the unique structure and composition, the discharge specific capacities of the optimal Na1.13Fe[Fe(CN)]6.3.22H2O electrode (FeHCF-2) are 153.7, 126.28, 119.4 and 113.4, 107.61, 102.52 and 92.46 mAh.g ? 1 at 0.1, 0.3, 0.5, 1, 2, 5 and 10 C, respectively. The first discharge capacity of FeHCF-2 electrode at 1 C is 111.88 mAh.g ? 1, and the discharge capacity of FeHCF-2 electrode is 115.04 mAh.g ? 1 after 1000 cycles, indicating that FeHCF-2 electrode has ultrastable cycle stability. Therefore, designing the hollow inverted pyramid morphology can be regarded as an available way to enhance the electrochemical activity of Na1.13Fe[Fe(CN)]6.3.22H2O for advanced lithium-ion batteries, and effective design strategies can be used for the modification of other cathode materials for Li-ion batteries.