Selenium-Doped Amorphous Black Phosphorus@TiO2/C Heterostructures for High-Performance Li/Na/K Ion Batteries

Heterostructures have been confirmed to demonstrate better electrochemical performance than their individual building blocks, which is not only attributed to the complementary advantages of diverse materials but also to various synergistic effects, such as increased active sites at the heterointerfaces, enhanced kinetics from a built-in electric field, stable structure due to physical or chemical bonding, etc. However, constructing a desired heterostructure remains greatly challenging owing to the mismatch of crystal structures, atomic spacings, and reaction mechanisms between different electrode materials. In this study, an amorphous heterostructure composed of Se-doped black phosphorus and metal-organic framework (MOF)-derived TiO2/C (Se-BP@TiO2/C) was successfully fabricated using a simple Se-assisted ball-milling method. In addition to the inherent advantages of heterostructures, the novel material also had considerable free volume in the amorphous domains, which not only buffered the volume change of active materials during cycles but also provided space and interconnected channels for ion diffusion. When used as anode materials for Li/Na/K ion batteries, the Se-BP@TiO2/C achieved high specific capacities, good cyclability, and fast rate capability. This work opens up a new route to design amorphous heterostructure electrodes for high-performance battery systems.