Efficient Sulfur Host Based on Yolk‐Shell Iron Oxide/Sulfide‐Carbon Nanospindles for Lithium‐Sulfur Batteries

Abstract

Numerous nanostructured materials have been reported as efficient sulfur hosts to suppress the problematic “shuttling” of lithium polysulfides (LiPSs) in lithium‐sulfur (Li−S) batteries. However, direct comparison of these materials in their efficiency of suppressing LiPSs shuttling is challenging, owing to the structural and morphological differences between individual materials. This study introduces a simple route to synthesize a series of sulfur host materials with the same yolk‐shell nanospindle morphology but tunable compositions (Fe3O4, FeS, or FeS2), which allows for a systematic investigation into the specific effect of chemical composition on the electrochemical performances of Li−S batteries. Among them, the S/FeS2−C electrode exhibits the best performance and delivers an initial capacity of 877.6 mAh g−1 at 0.5 C with a retention ratio of 86.7 % after 350 cycles. This approach can also be extended to the optimization of materials for other functionalities and applications.

Improvement of Fe0.8Ni0.2S2 Peroxidase-like Activity through the Accelerated Conversion from Fe3+ to Fe2+

“…Two additional peaks are observed at 706.5 and 719.3 eV, which belong to the 2p 3/2 and 2p 1/2 regions of Fe in the pyrite FeS 2 , respectively. The peak at 730.34 eV can be attributed to the Fe 3+ , and its existence is due to the surface oxidation. − In Figure c, Ni 2p was divided into five peaks, among which a pair of peaks at 852.8 and 855.9 eV are attributed to Ni 2+ , the peak at 873.7 eV is attributed to Ni 3+ , and a pair of peaks at 860.6 and 879.4 eV are satellite oscillation peaks. , It is worth noting that the intensity of the Ni 2+ peak is significantly higher than that of Ni 3+ . In Figure d, the peaks for S 2p are attributed to the persulfide S 2 2– with the strongest peak at 161.8 eV.…”

Synergistic Effect between Monodisperse Fe3O4 Nanoparticles and Nitrogen-Doped Carbon Nanosheets to Promote Polysulfide Conversion in Lithium–Sulfur Batteries

“…Their electrochemical properties were first evaluated by cyclic voltammetry (CV), as shown in Figures a and S6, the latter demonstrating stabilization of CV curves after the first activation cycle. During the discharge process, two obvious peaks around 2.26 and 2.01 V were observed, the former representing solid–liquid conversion of sulfur powder to lithium polysulfide (Li 2 S n , 4 ≤ n ≤ 8), and the latter resulting from further reduction of Li 2 S n yielding solid Li 2 S and Li 2 S 2 . , The charge process is also characterized by two peaks around 2.35 and 2.41 V, which are related to the reverse conversion of solid Li 2 S/Li 2 S 2 to soluble Li 2 S n and back to sulfur. ,, Fe 3 O 4 /PNC shows a higher oxidation potential in reverse anodic scanning, indicating slower kinetics of polysulfide conversion. It is therefore evident that nano-Fe 3 O 4 /PNC containing monodisperse Fe 3 O 4 on its surface can accelerate the polysulfide redox conversion process in LSBs.…”

“…48,49 The charge process is also characterized by two peaks around 2.35 and 2.41 V, which are related to the reverse conversion of solid Li 2 S/Li 2 S 2 to soluble Li 2 S n and back to sulfur. 37,38,50 S2 exhibit high-frequency semicircles attributable to charge-transfer resistance (R ct ). 51 Clearly, the R ct value of S@nano-Fe 3 O 4 /PNC is less than that of S@Fe 3 O 4 /PNC and S@PNC, both before or after the cycle.…”

“…It was reported that a yolk–shell Fe 3 O 4 carbon nanobox structure is not only responsible for the physical capture of polysulfides by the carbon shell but also provides strong chemical interactions with the Fe 3 O 4 core, resulting in excellent electrochemical performance of LSBs . Fe 3 O 4 particles anchored on the carbon coating deposited on graphene demonstrated good LSB cycling stability and rate performance . However, iron-based oxide particles accumulated on carbon matrices usually have irregular shapes and are prone to agglomeration during synthesis, resulting in lower specific surface areas and limited exposed active sites, which is not conducive to the adsorption and catalytic conversion of sulfur .…”

“…37 Fe 3 O 4 particles anchored on the carbon coating deposited on graphene demonstrated good LSB cycling stability and rate performance. 38 However, iron-based oxide particles accumulated on carbon matrices usually have irregular shapes and are prone to agglomeration during synthesis, resulting in lower specific surface areas and limited exposed active sites, which is not conducive to the adsorption and catalytic conversion of sulfur. 39 Compared to large irregular particles, well-dispersed spherical nanostructures can provide greater specific surface areas with more exposed active sites for the adsorption and catalytic conversion of polysulfides.…”