Ion-Exchange Route Induced Heterostructured CoS₂/FeS Nanoparticles Confined in Hollow N-Doped Carbon Frameworks for Enhanced Sodium Storage Performance

Abstract

As a result of the high theoretical capacities, transition metal sulfides have attracted increasing attention as potential anodes for sodium-ion batteries (SIBs), but severely suffer from large volumetric variations, sluggish kinetics, and polysulfide shuttling. Herein, utilizing metal–organic frameworks (MOFs) as functional templates, heterostructured CoS2/FeS nanoparticles confined in a hollow N-doped carbon framework are successfully fabricated via a controlled ion-exchange reaction combined with subsequent carbonization and sulfurization processes. The construction of CoS2/FeS heterointerfaces promotes electron transfer and provides more active sites, while the derived N-doped carbon framework with a unique hollow interior effectively improves the electrical conductivity, alleviates the volumetric variations, and facilitates the sodium storage process with shortened Na+ diffusion paths. As anodes for SIBs, the optimal CoS2/FeS hybrid composite exhibits a high initial Coulombic efficiency (ICE) of 89.3%, a prolonged cycle life with a capacity of 494 mAh g–1 over 500 cycles under a current density of 1.0 A g–1, and an excellent rate capability of 428 mAh g–1 at 5.0 A g–1, showing the great promise for SIBs. This research offers an efficient and feasible approach for exploring and fabricating bimetallic sulfide heterostructures with a unique hollow structure for high-performance metal-ion batteries.

Prussian Blue Analogues Derived Heterostructured CoS2/FeS2 Particles Anchored on Carbon Nanosheets as Anodes for Boosted Sodium Storage Properties

“…During the initial cathodic process, a reduction shoulder peak at 1.13 V is assigned to the insertion of Na + into CoS 2 and FeS 2 to form Na x CoS 2 and Na y FeS 2 , [45,46] while a strong reduction peak centered at 1.04 V is attributed to the formation of irreversible solid electrolyte interface (SEI) film, [47] which disappears in the following scans. Besides, several reduction peaks appearing in the range of 0.72–0.14 V are correlated to the continuous conversion reactions of Na x CoS 2 and Na y FeS 2 to form metallic Co and Fe, and byproduct Na 2 S [34,48] . In the corresponding anodic process, the oxidation peaks at 1.33 and 1.74 V originate from the reverse conversion reaction between metallic Co, Fe and Na 2 S to generate Na x CoS 2 and Na y FeS 2 , [14,49] while the other peaks at 1.95 and 2.08 V might belong to the further desodiation of Na x CoS 2 and Na y FeS 2 [50] .…”

“…Figure 3A shows the corresponding XPS survey spectrum, clearly illustrating the existence of Co, Fe, S, C, N and O elements in the composite. In the high‐resolution spectrum of Co 2p as shown in Figure 3B, the peaks located 781.0 and 795.9 eV can be attributed to the Co 2+ state of Co 2p 3/2 and Co 2p 1/2 , while the peaks centered at 779.2 and 794.2 eV are assigned to the Co 3+ state of Co 2p 3/2 and Co 2p 1/2 , along with their two shake‐up satellites at 784.3 and 802.6 eV, indicating the presence of mixed valence states of Co 3+ and Co 2+ [34] . In the high‐resolution spectrum of Fe 2p as presented in Figure 3C, the two distinct peaks at 708.0 and 720.6 eV are related to the Fe 2+ state of Fe 2p 3/2 and Fe 2p 1/2 , while the peaks at 711.3 and 723.9 eV are related to the Fe 3+ state of Fe 2p 3/2 and Fe 2p 1/2 , in conjunction with the satellite peak at 714.4 eV, [35,36] suggesting the coexistence of both Fe 2+ and Fe 3+ species in the hybrid composite induced by partial oxidation of Fe 2+ .…”

“…The surface chemical composition and valence states of the CoS 2 /FeS 2 /C hybrid composite were investigated by XPS analysis. Figure 3A shows the corresponding XPS survey spec- [34] In the high-resolution spectrum of Fe 2p as presented in Figure 3C, the two distinct peaks at 708.0 and 720.6 eV are related to the Fe 2 + state of Fe 2p 3/2 and Fe 2p 1/2 , while the peaks at 711.3 and 723.9 eV are related to the Fe 3 + state of Fe 2p 3/2 and Fe 2p 1/2 , in conjunction with the satellite peak at 714.4 eV, [35,36] suggesting the coexistence of both Fe 2 + and Fe 3 + species in the hybrid composite induced by partial oxidation of Fe 2 + . As depicted in Figure 3D, the S 2p spectrum can be deconvoluted into three components.…”

Prussian Blue Analogue Derived CoS2/FeS2 Confined in N, S Dual-Doped Carbon Nanofibers for Sodium Storage

“…Figure A shows the full spectrum of the H-CoS 2 /FeS 2 @CNFs-2 hybrid composite, indicating the presence of Co, Fe, S, C, N, and O elements in the composite, consistent with the result of the EDS spectrum. A distinct oxygen signal can be clearly observed, which is most likely due to the partial oxidation of surface metal sulfides. , The high-resolution spectrum of Co 2p, as shown in Figure B, reveals that two spin–orbit doublet peaks at 793.5/778.8 and 797.1/782.0 eV are associated with Co 3+ 2p 1/2 /Co 3+ 2p 3/2 and Co 2+ 2p 1/2 /Co 2+ 2p 3/2 , respectively. , Additionally, two shakeup satellites at 786.1 and 802.9 eV are also identified. From the high-resolution Fe 2p spectrum as shown in Figure C, two pairs of characteristic peaks located at 720.2/707.4 and 723.9/710.9 eV are assigned to Fe 2+ 2p 1/2 /Fe 2+ 2p 3/2 and Fe 3+ 2p 1/2 /Fe 3+ 2p 3/2 , respectively .…”

“…During the second scan, a new reduction peak was observed at around 1.97 V, arising from multistep extraction of Na + from Na y FeS 2 . The reduction peaks at 1.12 and 0.84 V shift positively to 1.3 and 0.89 V caused by electrode activation and structural changes, while the oxidation peaks are almost unchanged . In subsequent scans, one can see that the reduction peaks stabilize at 1.97, 1.5, 0.89, and 0.45 V, while the oxidation peaks stabilize at 1.3, 1.54, 1.8, and 2.1 V, reflecting the good reversibility of the H-CoS 2 /FeS 2 @CNFs-2 electrode during the electrochemical process.…”