High Entropy Activated and Stabilized Nickel-based Prussian Blue Analogue for High-performance Aqueous Sodium-ion Batteries

Aqueous sodium-ion batteries (SIBs) represent a cost-effective, safe, and reliable candidate for grid-scale energy storage towards a low-carbon society. The development of cathode materials for aqueous SIBs that have both high capacity and good cycling stability still remains a big challenge. This study proposes a high entropy strategy to boost both specific capacity and capacity retention by introducing equimolar Fe, Co, Mn, and Cu at the Ni sites in the Prussian blue analogue (PBA) frameworks. Attributing to the hybridization of 3d energy levels and improved valence electron concentration deriving from the exotic equimolar four transition metals, significantly increase the number of electrochemically active sites and raised the configuration entropy of PBA frameworks, contributing intensive valence electron transport to faster Faraday reaction and more stable hosts for Na+ ion (de)intercalation. Therefore, the high-entropy PBA (HE-PBA) cathode delivers an enhanced capacity of 118.6 mAh g−1 at the current density of 100 mA g−1, which is nearly 1.6 times higher than that of Ni-PBA, resulting in a high energy density of 74.8 Wh kg−1. Moreover, the HE-PBA demonstrates stable operation over 1800 cycles at a high rate of 5 C. This high entropy strategy provides a feasible strategy for the practical application of aqueous SIBs.