Interlayer Engineering of Layered VOPO₄ Through Organic Intercalation for Enhanced Potassium Storage Kinetics

Nonaqueous potassium-ion batteries (KIBs) are emerging as promising next-generation energy storage systems owing to their abundant resources and high energy density. However, their large-scale application is hindered by structural degradation and sluggish kinetics resulting from the large ionic radius of K ions. Engineering electrode materials with open frameworks, such as two-dimensional (2D) layered structures, present an effective strategy to address these challenges by providing rapid ion diffusion pathways and robust host structures. Herein, a rational interlayer engineering strategy is developed by intercalating phenylamine derivatives with varying molecular sizes (P-butylaniline: PTA, P-Methylaniline: PMA, and phenylamine: PA) into layered 2D VOPO₄ nanosheets. The intercalation of PANI derivatives progressively expands the interlayer spacing from 0.76 nm (pristine VOPO₄) to 1.58, 1.85, and 2.09 nm, while maintaining the structural integrity of the layered framework. Notably, the regulated interlayer expansion (from 0.76 to 2.09 nm) not only provides enlarged diffusion pathways for rapid K⁺ ion intercalation/deintercalation kinetics, but also facilitates the formation of oxygen vacancies that may serve as additional active sites for potassium storage. By correlating the electrochemical performance with the modulated interlayer distances, it is established that a preferred spacing of 1.85 nm achieves the best synergy between fast kinetics, high capacity, and structural stability. As expected, the electrode with the optimal interlayer spacing (1.85 nm) exhibits superior potassium-ion storage performance, delivering a high reversible capacity of 333.2 mAh g^-1 at 0.1 A g^-1 over 100 cycles and exceptional rate capability with 205.7 mAh g^-1 retained at 1 A g^-1, as well as maintaining remarkable stability up to 600 cycles even at high rates. This work innovatively proposes phenylamine derivative-enabled interlayer regulation as a promising approach for designing high-performance VOPO₄-based electrode materials.