A Configuration Entropy Enabled High‐Performance Polyanionic Cathode for Sodium‐Ion Batteries

Abstract

AbstractPolyanionic sodium ion cathodes have attracted lots of concern because of their excellent structural stability. However, the low specific capacity is still a pressing issue hampering their practical application. In this work, a medium‐entropy NASICON‐structure cathode Na3.5V0.5Mn0.5Fe0.5Ti0.5(PO4)3 (Me‐NVMP) is proposed. The Me‐NVMP achieves a highly reversible specific capacity of 165.8 mAh g−1 (1.8–4.4 V vs Na+/Na) at 0.1 C via the stepwise redox reactions of Ti3+/Ti4+‐Fe2+/Fe3+, V3+/V4+‐Mn2+/Mn3+, and V4+/V5+‐Mn3+/Mn4+. More impressively, the Me‐NVMP yields super rate capability and cycling stability via the regulation of configuration entropy in NASICON. Specifically, the Me‐NVMP cathode can preserve a capacity retention of 83.5% after 10,000 cycles at 100 C (17 A g−1). Furthermore, excellent cycling performance even at the temperature of 0 °C (capacity retention of 93.45% at 20 C after 1000 cycles) is also demonstrated. In situ X‐ray diffraction analysis reveals that the enhanced performance can be mainly attributed to the solid–solution‐type Na+ storage behavior in Me‐NVMP. Moreover, issues such as Jahn‐Teller distortion of Mn3+ and irreversible structural change at high voltage (>4.0 V vs Na+/Na) are effectively mitigated. This work inspires a new strategy to design high‐performance polyanionic electrode materials.