Boosting the sodium storage performance of Prussian blue analogs by single-crystal and high-entropy approach

Prussian blue analogs (PBAs) are widely considered to be one of the most promising types of cathode materials for sodium ion batteries. However, unsatisfactory structural stability upon excessive sodium storage and long-term cycling is still a bottleneck in industrial applications. Herein, a two-pronged approach of single-crystal and high-entropy PBA (SC-HEPBA), is first reported to solve this challenge simultaneously from the bulk phase and interface. The nature of high entropy enables the unrestricted Na+ diffusion and the suppressed metal dissolution, while the micrometer-sized single crystals help to improve the tap density with less structural degradation upon cycling. As a result, the Na-rich SC-HEPBA with an intact monoclinic crystal structure delivers a high capacity of 115 mAh g-1 at 100 mA g-1, outstanding rate performance (i.e. 74.4 mAh g-1 at 3000 mA g-1) and good capacity retention (79.6%) over 1000 cycles with a stable operating voltage of 3.25 V. The SC-HEPBA/NaTi2(PO4)3 full cell achieves 109.4 mAh g-1 and a stable cyclability over 2000 cycles with 77.8 % capacity maintained. The proposed two-pronged approach not only paved the way for the practical application of PBAs in SIBs but also provided guidance on inhibiting the structure evolution of battery materials during cycling.