A Sodium Storage Material Based on Chamber-Confined Conversion of Co₉S₈ Nanorod Encapsulated by N-Doped Carbon Shell

Abstract

Different from the ion intercalation/deintercalation, conversion-based reactions are a promising way to achieve high capacity of storage materials. However, their too much volume change and poor reversibility during discharge/charge are stubborn to overcome. Herein, by combining hydrothermal synthesis and chemical vapor deposition, a Co9S8 nanorod encapsulated by a N-doped carbon shell (r-Co9S8@NC) is built and applied as an anode material for sodium-ion batteries. Benefiting from the advantages of the chamber-confined conversion and sodiophilic interface offered by the N-doped carbon shell, the Co9S8 redox was well restrained in the shell with improved kinetics, which can not only alleviate the Co9S8/electrolyte side reaction and suppress the large volume expansion and aggregation of Co9S8 nanorods but also enhance the sodium storage/diffusion ability. As expected, the r-Co9S8@NC electrodes exhibit a high capacity of 675 mAh g–1 at 50 mA g–1, an excellent rate capability (342 mAh g–1 at 10 A g–1), and a good cycling stability (317 mAh g–1 after 1500 cycles at 5 A g–1 and 483 mAh g–1 after 150 cycles at 500 mA g–1) among which the rate capability is outperforming most of the reported metal-sulfide-based anodes. Further, the sodium storage mechanism and the good reversibility of the r-Co9S8@NC electrode have been revealed and confirmed by the XRD and XPS characterizations. This work provides an effective strategy to design storage materials based on a chamber-confined conversion reaction.

Towards high-performance anodes: Design and construction of cobalt-based sulfide materials for sodium-ion batteries

“…Because of this structure, 7-CoS/C exhibited long-term reversibility; the capacity was 542 mAh g À1 at 1 A g À1 even over 2000 cycles with a high capacity retention of 91.4% and a superior rate capability of 356 mAh g À1 even at 40 A g À1 . In addition, Lin et al [145] successful encapsulated Co 9 S 8 nanorods into an N-doped carbon coating layer by chemical vapor deposition combined with a simple hydrothermal process (denoted as r-Co 9 S 8 @NC). The N-doped carbon shell provided a strong chamber, and thus the electrode delivered an excellent rate capability; the capacity was 342 mAh g À1 at a current of 10 A g À1 and could be maintained at 317 mAh g À1 even over 1500 cycles (Fig.…”

“…(c) Illustration of the synthesis process and (d) SEM and (e) TEM images of 7-CoS/C[144]. (f) Rate capability and (g) cycling performance of the r-Co 9 S 8 @NC anode[145]. (h) Schematic for in situ generation and (i) rate capabilities of Co 9 S 8 @S-CF[146].…”

“…with permission from Elsevier. Reproduced from Ref [145,146]. with permission from the American Chemical Society.…”

Nitrogen and Sulfur Vacancies in Carbon Shell to Tune Charge Distribution of Co6Ni3S8 Core and Boost Sodium Storage

“…[17,18] However, when using N-doped carbon as matrix to anchor Co 9 S 8 for sodium storage, the rate of Na + diffusion is still limited. [19] This is due to that the weak chemisorption between N-doped carbon matrix and the polar hydrophilic Co 9 S 8 will impede the immigration of Na + . For the second point, it has been reported that transition metal (TM) doping can improve the conductivity of TM chalcogenides, [20] the resulting heterogeneous spin states can also lead to expanded interlayer spacings, [21] relaxing the stress and volume expansion upon cycling.…”

A Carbon Foam with Sodiophilic Surface for Highly Reversible, Ultra‐Long Cycle Sodium Metal Anode

“…At present, general anodes for sodium batteries such as hard carbon, [ 3 ] alloy compounds, [ 4 ] metal oxides, [ 5 ] metal sulfides, [ 6 ] phosphorus, [ 7 ] etc., have the capacity limited by the above existing framework, while sodium metal anodes without hosts are based on plating/stripping reactions and thereby could achieve high theoretical capacity. As the anode material of sodium batteries, sodium metal has the advantages of low redox potential (−2.71 V vs SHE) and high theoretical capacity (1165 mAh g −1 ), [ 8 ] Moreover, Na metal anodes are one of the key components of high‐energy‐density Na‐based batteries, such as ZEBRA batteries, [ 9 ] Na–S batteries, [ 10 ] Na–O 2 batteries.…”