Regulating Built-in Polar States via Atomic Self-Hybridization for Fast Ion Diffusion Kinetics in Potassium Ion Batteries

Abstract

Potassium ion batteries (PIBs) are of great interest owing to the low cost and abundance of potassium resources, while the sluggish diffusion kinetics of K ⁺ in the electrode materials severely impede their practical applications. Here, self-hybridized BiOCl _0.5Br _0.5 with a floral structure is assembled and used as anode for PIBs. Based on the systematic theoretical calculation and experimental analysis, the unbalance of charge distribution between Cl and Br atoms leads to an enhanced built-in electric field and a larger interlayer spacing, which can enhance the K ⁺ diffusion. Furthermore, the K ⁺ insertion causes the energetic evolution of polar states in the BiOCl _0.5Br _0.5 crystal framework, where the dynamic correlation between the K ⁺ and the halogen atoms leads to the formation of hole-like polarons, which significantly improves the K ⁺ diffusion and reaction kinetics during the charging/discharging process, giving important implications to design the electrode materials with high electrochemical performance by engineering the interaction between electronic structure and interface. Therefore, the BiOCl _0.5Br _0.5 anode obtains an excellent performance of 171 mAh·g ^–1 at 1 A·g ^–1 over 2000 cycles in PIBs.

Keywords

Bismuth oxyhalide / Self-hybridized structure / Potassium-ion battery / Polar states / Density functional theory

RIGHTS & PERMISSIONS

2024 SIOC, CAS, Shanghai, & WILEY-VCH GmbH