Dynamic Variation in Electric Field and K+ Diffusion: A New Insight from Multi‐Heterostructure Evolution for Bi2S3/WS2 Potassium Ion Anode

Abstract Heterostructures are extensively employed in the construction of energy storage materials for their unique electronic structures and the intrinsic heterointerface built‐in electric field. However, the elaborately designed heterostructures inevitably undergo phase evolution during reactions, leading to the formation of heterointerfaces that deviate significantly from the initial configurations. Furthermore, nearly all current research is confined to the original heterojunction interface, resulting in a lack of profound understanding of the impact of heterostructure evolution during ion migration. Herein, a heterogeneous composite, incorporating Bi 2 S 3 with a conversion‐type mechanism and WS 2 with an intercalation‐type mechanism, of carbon coated Bi 2 S 3 /WS 2 , is constructed. The dynamic processes of phase transitions, heterostructure formations, and built‐in electric field evolutions are investigated utilizing in/ex situ experimental techniques coupled with density functional theory calculations, and the influence of these factors on the K + diffusion coefficient is elucidated in detail. Notably, the phase transformation of K 3 Bi 2 ↔ K 3 Bi serves as the pivotal step that governs the overall rate of electrochemical reaction, while the KBi 2 /WS 2 intermediate heterostructure stands out for its exceptional speed in ion/electron transfer. This work sheds light on the dynamic evolution mechanism of heterojunction and built‐in electric field, offering a new perspective for advancing the research on heterogeneous materials.