Structural transformation from crystalline to amorphous states to boost sodium storage properties of NaVOPO ₄ cathode

Abstract Polyanionic materials are considered one of the most promising cathode materials for sodium‐ion batteries because of the stable structure framework and high working voltage. However, most polyanionic materials possess limited sodium storage sites and have to undergo complex local structure evolution during charge/discharge. Herein, we conducted a systematic investigation into the impact of structural forms of NaVOPO 4 on the electrochemical properties. Amorphous and crystalline NaVOPO 4 are synthesized through a controlled reflux reduction method, and the amorphous NaVOPO 4 (a‐NVOP) demonstrates much better electrochemical performance compared to the crystalline counterpart. Specifically, the a‐NVOP electrode delivers high reversible capacity (142 mAh g −1 at 14.5 mA g −1 , close to the theoretical capacity of 145 mAh g −1 ), high energy density (497 Wh kg −1 based on cathode material) and remarkable cyclability with capacity retention of 80% after 500 cycles. In situ and ex situ experimental analyses and theoretical calculations reveal that the superior performance is primarily due to the maintaining of the amorphous state during the charge/discharge process to endow high stability and accelerated intercalation/deintercalation of large‐sized Na + without lattice constraints. Furthermore, the amorphous cathode materials show promising electrochemical properties in lithium‐, potassium‐ and zinc‐ion batteries, highlighting their broad adaptability and potential across various battery systems.