Unlocking Polyanion-Type Materials through High-Entropy Effect for Aqueous Potassium-Ion Batteries
Bingqiu Liu, Qi Zhang, Xiaoyu Yu, Yutong Feng, Zhuo Yang, Wanhai Zhou, Dan Xie, Chengyu Li, Yongjin Chen, Lu Li, Chungang Wang, Dongliang Chao
Abstract
Exploration of electrode materials for aqueous batteries has predominantly followed the established principles and design strategies derived from organic electrolyte-based systems. However, this conventional approach faces inherent limitations. Although V-based polyanion materials (e.g., Na 3 V 2 (PO 4 ) 3 ) are compelling for organic electrolyte-based alkali metal ion batteries, their applications in aqueous K-ion batteries remain untapped, probably due to the limited cation electroactivity and uncontrollable dissolution. Herein, we unlock reversible and stable aqueous K + storage in V-based polyanion materials via a high-entropy strategy. Unlike the phase-transition mechanism in traditional polyanionic electrodes, in situ spectroscopic characterizations reveal a solid-solution process in the entropy-tuned polyanionic electrode, facilitated by reduced steric hindrance during K + uptake. Time-of-flight secondary ion mass spectrometry and density functional theory simulations further confirm the suppressed Na + /K + -migration barrier and solubility of the entropy-tuned polyanionic cathodes. As a result, the high-entropy V-based polyanion cathodes are demonstrated promising for aqueous K-ion batteries, even in dilute aqueous electrolytes, achieving an ultrahigh initial Coulombic efficiency of 98.7%, rate capability at 36C, and impressive cycling durability up to 3500 cycles. This work uncovers the charge storage gap between organic and aqueous electrolyte-based systems and provides insights into activating the electroactivity of other materials in an aqueous environment.