Cobalt Sulfide Quantum Dot Embedded N/S-Doped Carbon Nanosheets with Superior Reversibility and Rate Capability for Sodium-Ion Batteries

Abstract

Metal sulfides are promising anode materials for sodium-ion batteries due to their large specific capacities. The practical applications of metal sulfides in sodium-ion batteries, however, are still limited due to their large volume expansion, poor cycling stability, and sluggish electrode kinetics. In this work, a two-dimensional heterostructure of CoS (CoS and CoS) quantum dots embedded N/S-doped carbon nanosheets (CoS@NSC) is prepared by a sol-gel method. The CoS quantum dots are in situ formed within ultrafine carbon nanosheets without further sulfidation, thus resulting in ultrafine CoS particle size and embedded heterostructure. Meanwhile, enriched N and S codoping in the carbon nanosheets greatly enhances the electrical conductivity for the conductive matrix and creates more active sites for sodium storage. As a result, the hybrid CoS@NSC electrode shows excellent rate capability (600 mAh g at 0.2 A g and 500 mAh g at 10 A g) and outstanding cycling stability (87% capacity retention after 200 cycles at 1 A g), making it promising as an anode material for high-performance sodium-ion batteries. A CoS@NSC//NaMnO full cell is demonstrated, and it can deliver a specific capacity of 414 mAh g (based on the mass of CoS@NSC) at a current density of 0.2 A g.

Encapsulation of CoSx Nanocrystals into N/S Co‐Doped Honeycomb‐Like 3D Porous Carbon for High‐Performance Lithium Storage

“…In the next three sweeps, the broad cathodic peak splits into three peaks around 0.63, 1.33, and 1.65 V, corresponding to the multi‐step electrochemical reactions during lithiation. During the anodic process after the first sweep, the three obvious peaks at 1.35, 2.01, and 2.27 V can be ascribed to the reverse reaction to form the CoS x in the electrode 46. Combined with the relevant literature, the total electrochemical reaction could be described as follows:46, 49 ${\mathrm{CoS}}_x\hspace{0.17em}\mathrm{+}\hspace{0.17em}\mathrm{2}x{\mathrm{Li}}^{\mathrm{normal+}}\mathrm{+}\hspace{0.17em}\mathrm{2}x{\mathrm{normale}}^{-}\hspace{0.17em}\leftrightarrow \hspace{0.17em}\mathrm{Co}\hspace{0.17em}\mathrm{+}\hspace{0.17em}x{\mathrm{Li}}_{\mathrm{normal2}}\mathrm{S}$ …”

“…The other two peaks at 163.8 and 165.1 eV could be identified as C‐S 2p 3/2 and 2p 1/2 , indicating the successful sulfur doping of the carbon. In the case of C (Figure 4d), the peaks centered at 284.7, 286.1, and 288.4 eV can be attributed to C—C, C—S/C—N, and C—N bonds, respectively 46, 48, 50. The presence of C—N bond demonstrates that nitrogen is doped into the carbon lattice.…”

“…The high‐resolution spectrum of Co 2p (Figure 4b) displays four main peaks: two peaks centered around binding energies 778.9 and 793.8 eV are attributed to the Co—S bond and two peaks at 781.6 and 797.8 eV belong to the Co—O bond 16, 45. The oxygen element in the CS@PC composite may arise from three parts: the absorbed hydroxide species, precursor residual oxygen after vulcanization, and sulfur species from partial oxidation of material surface 40, 46, 47. Besides, the two satellite peaks at 785.3 and 803.1 eV could be indexed to the shake‐up peak of Co 2+ 16.…”

“…The existence of nitrogen element can be confirmed by N 1s spectra (Figure 4e), including pyridinic‐, pyrrolic‐, and graphitic‐type nitrogen in carbon matrix at binding energies of 398.1, 398.5, and 400.1 eV, respectively, which provide additional evidence of successful doping of nitrogen into carbon 7, 47. The doped nitrogen atoms can not only improve the electronic conductivity of carbon, especially pyrrolic N and pyridinic N, but also provide active sites for the growth of cobalt sulfur nanoparticles because they can influence the electronic properties of the surrounding carbon substrate and act as electron donors 7, 46, 51. In the O 1s spectrum (Figure 4f), the peak at 533.0 eV is corresponding to the Co—O bond, and the intensive peak at 531.6 eV is owing to a high number of defect sites with a low oxygen coordination, indicating that a large number of oxygen vacancies existed in the CS@PC composite.…”

Hierarchical Hollow‐Microsphere Metal–Selenide@Carbon Composites with Rational Surface Engineering for Advanced Sodium Storage

“…These intriguing phenomenon revealed that the reversible SEI films may be formed/ Adv. [73,74] Attracted by the fascinated EIS change, the simplified interfacial models were proposed with the corresponding equivalent circuits, which were used to analyze the variation of the resistance between electrolyte and carbon layer, as well as carbon layer and basic materials. 2019, 9, 1803035 decomposed during cycling, facilitating the improvement of cycling capacity, which have been demonstrated by the previous reports.…”