Tuning cyanide coordination electronic structure enables stable Prussian blue analogues for sodium-ion batteries

Prussian blue analogues exhibit significant potential as positive electrode materials for sodium-ion batteries, particularly due to their three-dimensional cyanide-bridged frameworks which facilitate fast charging capabilities. However, the labile chemical bonds coordinated by transition metal ions and cyanide ligands often lead to structural instability, causing serious electrochemical degradations during cycling. Fundamentally understanding and controlling the local electronic structure to mitigate this instability remains challenging. Herein, we approach this problem by modulating the local electronic structure surrounding nitrogen-coordinated transition metal ions to create a uniform electron distribution within the Prussian blue analogues frameworks. The resulting uniform electronic structure enhances the reactivity of both nitrogen-coordinated and carbon-coordinated transition metals. More importantly, the reduction of electronic displacement through regulated coordination significantly improves the crystal structural stability, yielding a capacity retention of over 91% at 5 C after 1000 cycles. These findings provide insights into the local structural chemistry of Prussian blue analogues and offer guidance for the development of positive materials for sodium-ion batteries.