Balanced coordination enables low-defect Prussian blue for superfast and ultrastable sodium energy storage

As a promising cathode material of sodium-ion batteries, the crystallinity of Prussian blue and its analogues (PB/PBA) is extremely pivotal for the electrochemical reaction kinetics and longevity. However, the controllable modulation of the PB/PBA crystallinity still remains an intractable challenge. Herein, we propose a balanced coordination principle to prepare low-defect Prussian blue (LD-PB) materials for outstanding sodium energy storage. Sodium carboxymethylcellulose is demonstrated as a moderate chelating agent to regulate the precipitation of LD-PB with negligible trace of vacancies and crystal water molecules. The high-crystalline open framework permits superfast and highly reversible sodium insertion/extraction. Impressively, an unprecedented specific capacity of 101 mAh g⁻¹ is achieved at an ultrahigh rate of 100 C in combination with remarkable capacity retention of 97.4% over a 3000-cycling test. The present study will shed a fundamental insight into the balanced coordination strategy for advancing the PB/PBA cathode materials toward superfast and durable alkali-metal energy storage.