Recent progress in two-dimensional van der Waals heterojunctions for flexible energy storage applications

Two-dimensional van der Waals heterojunctions (2D vdWHs) have emerged as promising materials for next-generation flexible energy storage devices. Their unique physicochemical properties and interface engineering capabilities drive this potential. This comprehensive review systematically analyzes the recent developments in 2D vdWHs, focusing on their fundamental principles, fabrication methodologies, and applications in flexible energy storage systems. We first introduce the background of vdWHs and discuss four main synthesis strategies: direct stacking, chemical vapor deposition (CVD), in situ growth, and solution processing techniques. The review then extensively examines their applications in various flexible energy storage devices, including supercapacitors, lithium-ion batteries, zinc-ion batteries, and emerging storage systems such as potassium-ion, sodium-ion, and metal-air batteries. The review emphasizes the crucial role of heterojunction interfaces. These interfaces enhance electrochemical performance by improving charge transfer kinetics and maintaining structural stability. The superior performance of these materials is attributed to their large interfacial contact areas, synergistic effects between components, and optimized electron/ion transfer pathways. Despite significant progress, challenges remain in interface stability, scalable production, and performance optimization. We conclude by discussing future research directions, including novel materials development, advanced fabrication technologies, and emerging applications beyond energy storage. This review provides valuable insights for researchers working on next-generation flexible energy storage devices and highlights the transformative potential of 2D vdWHs in practical applications.