In-situ pre-sodiation of Prussian blue for the construction of high-performance sodium-ion batteries

Prussian blue and its analogs have attracted increasing attention owing to their stable structure and low cost, especially in the field of sodium-ion batteries. However, the insufficient sodium and high contents of water in the structure greatly hinder their practical applications. Herein, an in-situ pre-sodiation strategy is conducted to realize a one-step transformation of sodium-poor Prussian blue (NP-PB) to sodium-rich Prussian blue (NR-PB) without the introduction of other impurities. The introduced sodium ions take the place of coordination water, resulting in richer sodium ion transport channels and higher structural stability. Thanks to the high sodium content and low water content in the structure, the as prepared NR-PB presents a significantly higher initial coulombic efficiency of 95.18% compared to that of NP-PB (41.93%). When coupled with hard carbon (HC), the NP-PB//HC cell exhibits an ultra-high capacity retention of 93.71% after 300 cycles at a current density of 200 mAh/g. Our work provides guidance for the in-situ transformation of sodium-poor Prussian blue into sodium-rich Prussian blue, which is of great importance for the practical applications of sodium ion batteries.