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

Abstract

Metal sulfides are the attractive negative materials for sodium-ion capacitors (SICs), primarily thanks to their large and fast Na + storage properties through multi-electron conversion and/or alloying reactions at low average redox potentials. 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 crystallinities encapsulated into carbon nanowires (denoted as Ga2S3/C) through morphology-preserved thermal sulfurization of nanowire-shaped Ga-based metal-organic frameworks. Both structural and theoretical analyses indicate that lower crystallinity endow Ga2S3/C with lower Na⁺ diffusion barrier and higher concentration of active sites, thus leading to superior specific capacity and rate performance. In addition, low-crystallinity Ga2S3/C nanowire has higher structural strength for buffering volume change 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 over 25,000 cycles at 5 A g⁻¹.