Unveiling the effect of crystallinity on rapid sodium storage of digallium trisulfide/carbon nanowires

Abstract

Metal sulfides are attractive negative materials for sodium-ion capacitors (SICs). Although the degree of crystallinity of metal sulfides affects Na⁺ storage properties significantly, the corresponding relationship is not well established and even in debate. Here, we report a series of digallium trisulfide nanocrystals with adjustable crystallinity encapsulated into carbon nanowires (denoted as Ga₂S₃/C) through morphology-preserved thermal sulfurization of nanowire-shaped Ga-based metal–organic frameworks. Structural analyses indicate that lower crystallinity endows Ga₂S₃/C with a higher concentration of active sites, thus leading to superior specific capacity and rate performance. In addition, in situ TEM analysis revealed that the low-crystallinity Ga₂S₃/C nanowire has higher structural strength for buffering volume changes and faster Na⁺ diffusion kinetics along the long-axial direction than high-crystallinity Ga₂S₃/C, thus achieving longer cycling life. A SIC using low-crystallinity Ga₂S₃/C as the negative electrode yields an impressive energy/power output of 108 Wh kg⁻¹/48 kW kg⁻¹ and a cycling life of over 25 000 cycles at 5 A g⁻¹. Thanks to these characteristics, which combine both compositional and structural advantages, the LC-Ga₂S₃/C composite exhibits outstanding performance, thereby offering new research insights for the design of high-performance sodium-ion anodes.