High-Entropy-Stabilized Polyanionic Cathodes with Multiple Redox Reactions for Sodium-Ion Battery Applications

High-entropy (HE) materials containing multiple elements have created a growing interest in exploring the property limits of electrodes in energy storage and understanding the underlying chemical/physical mechanisms. Here, we show a substantial improvement in performance of HE-based cathodes in sodium-ion batteries (SIBs). Polyanionic structure has a large compositional flexibility and can incorporate many active transition-metal (TM) species, which is an ideal platform to design HE cathode materials. As a proof of concept, we show that HE sodium superionic conductor (HE-NASICON) materials can be synthesized via a facile sol-gel method. By comparing a group of HE-NASICON cathodes containing different contents of TM species, we demonstrate that the multi-Na-ions intercalation/deintercalation process is highly reversible, whereas capacity and cycling stability are improved. The HE-NASICON cathode with equal molarity of five TM species achieves a high capacity of 161 mA h g⁻¹ and capacity retention of 85% when cycling at a high rate of 5 C over 1000 cycles. In-situ XRD and spherical-aberration-corrected transmission electron microscope (ACTEM) also demonstrate a robust trigonal phase with a volume change of merely 4.07% during the multi-Na-ions storage. These results reveal the effectiveness of HE concept in expediting high-performance polyanionic cathodes for real SIBs applications.