Supercritical CO2 Synthesis of Freestanding Se1-xSx Foamy Cathodes for High-Performance Li-Se1-xSx Battery

Abstract

Selenium-sulfur solid solutions (Se1-xSx) are considered to be a new class of promising cathodic materials for high-performance rechargeable lithium batteries owing to their superior electric conductivity than S and higher theoretical specific capacity than Se. In this work, high-performance Li-Se1-xSx batteries employed freestanding cathodes by encapsulating Se1-xSx in a N-doped carbon framework with three-dimensional (3D) interconnected porous structure (NC@SWCNTs) are proposed. Se1-xSx is uniformly dispersed in 3D porous carbon matrix with the assistance of supercritical CO2 (SC-CO2) technique. Impressively, NC@SWCNTs host not only provides spatial confinement for Se1-xSx and efficient physical/chemical adsorption of intermediates, but also offers a highly conductive framework to facilitate ion/electron transport. More importantly, the Se/S ratio of Se1-xSx plays an important role on the electrochemical performance of Li- Se1-xSx batteries. Benefiting from the rationally designed structure and chemical composition, NC@SWCNTs@Se0.2S0.8 cathode exhibits excellent cyclic stability (632 mA h g−1 at 200 cycle at 0.2 A g−1) and superior rate capability (415 mA h g−1 at 2.0 A g−1) in carbonate-based electrolyte. This novel NC@SWCNTs@Se0.2S0.8 cathode not only introduces a new strategy to design high-performance cathodes, but also provides a new approach to fabricate freestanding cathodes towards practical applications of high-energy-density rechargeable batteries.

Supercritical carbon dioxide technology in synthesis, modification, and recycling of battery materials

“…Recently, Xia et al reported the SC‐CO 2 ‐assisted synthesis of freestanding Se 1− x S x foamy cathodes (noted as NC@SWCNTs@Se 1− x S x ) as demonstrated in Figure 4f. [ 68 ] The X‐Ray diffraction (XRD) and Raman results (Figure 4g) vividly indicate that a small amount of Se occupy S position to form Se 1 −x S x species, which are mainly attributed to the high permeability, rapid diffusivity, and excellent solubility of SC‐CO 2 . In fact, these Se 1 −x S x active species are tightly and uniformly permeated into pores and layer gaps of NC@SWCNTs hosts, guaranteeing the remarkable structural stability, thus greatly enhancing electrochemical performance.…”

“…(f) Schematic of synthesis process of NC@SWCNTs@Se 1−x S x ; (g) X-ray diffrication (XRD) patterns and Raman spectra of various NC@ SWCNTs@Se 1−x S x . Reproduced with permission: Copyright 2021, Frontiers [68].…”

Advances in Selenium Sulfides Cathodes for Lithium/Selenium–Sulfur Batteries

“…Furthermore, Xia et al. introduced a series of novel freestanding Se x S y foamy cathodes (NC@SWCNTs@Se x S y ), fine-tuned with varying Se-to-S ratios and embedded into a nitrogen-doped three-dimensional (3D) porous carbon framework . The creation of these composites was aided by supercritical CO 2 fluid (Figure d).…”

“…(d) Diagrammatic representation of the fabrication procedure for NC@SWCNTs@Se 1– x S x . Reproduced with permission from ref . Copyright 2021 Frontiers Media Sa.…”

Fractal Growth of Quasi Two-Dimensional Copper Dendrites by Template-free Electrodeposition

“…The synthesis of micro-/nanoscale metal materials has aroused tremendous interest due to their important role in photothermal, optoelectronics, catalysts, and sensors. − In particular, the study of micro–nano structures of dendritic metal with multi-level branches has aroused considerable interest in the field of natural science. − The fractal dendrites are extensively reported in the electrochemical deposition process. − Studies show that metals, such as nickel (Ni), copper (Cu), zinc (Zn), and silver (Ag), could form fractal patterns with scale-invariant self-similarity under suitable conditions. , Among the metals, copper dendrites are receiving current attention in fractal theory and functional device aspects due to their excellent properties of high electric and thermal conductivity and a larger specific surface area. − Recently, some studies have reported that the study of two-dimensional (2D) copper dendrites focuses on the 2D adjustment of the static interface. − However, the copper dendritic growth under the action of the directional flow field and electric field is ignored. The regulation of dendrite growth under multi-field coupling is helpful to the new understanding of the electrochemical assembly of new functional materials.…”