Cobalt sulfide nanoflakes grown on graphite foam for Na-ion batteries with ultrahigh initial coulombic efficiency

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2020-08, Vol.8 (3), p.149-1497
• Main Authors: Wang, Haisheng, Liu, Jilei, Wang, Huanhuan, Cai, Xiaoyi, Ye, Xinli, Zhang, Lili, Chen, Zhen, Shen, Ze Xiang
• Format: Article
• Language: English
• Subjects: Anodes; Batteries; Cobalt; Cobalt sulfide; Electrode materials; Electrolytes; Electron transfer; Graphite; Lithium; Lithium-ion batteries; Rechargeable batteries; Side reactions; Sodium; Sodium-ion batteries; Substrates; Sulfide; Sulfides
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta04312e

Sodium-ion batteries (SIBs) are regarded as promising low-cost alternatives to the prevailing lithium-ion batteries. However, most anode materials for SIBs suffer from low initial coulombic efficiency (ICE), limiting their commercial applications. Herein, we demonstrate a Na-ion anode with an extremely high ICE of 99.4%, based on cobalt sulfide (Co 9 S 8 /CoS) nanoflakes grown on graphite foam (GF) in a diglyme-based electrolyte. The achievement of such a high ICE can be ascribed to the following three aspects: (i) negligible side reactions between a diglyme-based electrolyte and Co 9 S 8 /CoS, owing to a much higher Fermi level of diglyme reduction than anode potential μ A of Co 9 S 8 /CoS, which can block electron transfer from the anode to the electrolyte, (ii) highly reversible conversion reaction of Co 9 S 8 /CoS, and (iii) much lower initial capacity loss of substrate GF, compared with other sorts of carbon. The underlying rules revealed in this study serve as general guidelines in the development of sodium-ion anodes to achieve superb ICE. Three underlying root causes for ultrahigh initial coulombic efficiency (99.4%) of Na-storage cobalt sulfide nanoarrays.