Metal chalcogenide hollow polar bipyramid prisms as efficient sulfur hosts for Na-S batteries

Abstract

Sodium sulfur batteries require efficient sulfur hosts that can capture soluble polysulfides and enable fast reduction kinetics. Herein, we design hollow, polar and catalytic bipyramid prisms of cobalt sulfide as efficient sulfur host for sodium sulfur batteries. Cobalt sulfide has interwoven surfaces with wide internal spaces that can accommodate sodium polysulfides and withstand volumetric expansion. Furthermore, results from in/ex-situ characterization techniques and density functional theory calculations support the significance of the polar and catalytic properties of cobalt sulfide as hosts for soluble sodium polysulfides that reduce the shuttle effect and display excellent electrochemical performance. The polar catalytic bipyramid prisms sulfur@cobalt sulfide composite exhibits a high capacity of 755 mAh g−1 in the second discharge and 675 mAh g−1 after 800 charge/discharge cycles, with an ultralow capacity decay rate of 0.0126 % at a high current density of 0.5 C. Additionally, at a high mass loading of 9.1 mg cm−2, sulfur@cobalt sulfide shows high capacity of 545 mAh g−1 at a current density of 0.5 C. This study demonstrates a hollow, polar, and catalytic sulfur host with a unique structure that can capture sodium polysulfides and speed up the reduction reaction of long chain sodium polysulfides to solid small chain polysulfides, which results in excellent electrochemical performance for sodium-sulfur batteries.

High‐Capacity and Stable Sodium‐Sulfur Battery Enabled by Confined Electrocatalytic Polysulfides Full Conversion

“…[ 16a ] However, the peak intensity was maintained at about 0.39 after interaction between CFC and Na 2 S 6 , indicating the limited polysulfide trapping ability (62% sulfur lost) just based on physical confinement. [ 18 ] Aligning with our expectations, a stable Na‐S cell can be obtained if certain sulfur host was designed. Intensity reduction and position shift of the retrieved sample in XPS spectra confirms the existence of chemical interaction (Figure 2b).…”

“…As illustrated in Figure 3c, when the CFC/S@FC‐PPy||Na cell is discharged from 1.7 to 1.0 V, the long‐chain and short‐chain polysulfides Raman vibrational peaks were diminished and just one peak at ≈428 nm, indexed to the Na 2 S characteristic peak, was generated at the fully discharged state. [ 4a,6a,18a ] This means that FC‐PPy can catalyze Na 2 S 4 complete conversion. While some irreversible Na 2 S 2 was reflected in the XRD patterns in CFC/S@PPy electrode (see Figure 3d), indicating that the confined intermediates are more fully reduced to the final discharged product in CFC/S@FC‐PPy than in CFC/S@PPy and CFC/S, agreeing well with CV and GCD results above.…”

“…The CFC/S@FC‐PPy also shows the smallest average polarization of 248 mV among the three cells during 200 cycles, indicating the high energy efficiency and fast redox kinetics. [ 18b ] After 200 cycles at 200 mA g −1 , the CFC/S@FC‐PPy cell still maintains a reversible capacity of 700 mAh g −1 , corresponding to the capacity retention of 72.8% at nearly 100% stable Coulombic efficiency (Figure 4c). In contrast, the CFC/S@PPy cathode exhibited a stable capacity of 340 mAh g −1 with capacity retention of 51.4% after 100 cycles.…”

Recent Advances in Emerging Non‐Lithium Metal–Sulfur Batteries: A Review

“…In contrast, metal and metal compounds show high chemical adsorption capabilities with intermediate polysulfides. [88][89][90] Therefore, a more reasonable approach is to design hybrid hosts that combine highly conductive carbonaceous materials with highly polar compounds such as metals, [91][92][93][94][95] metal oxides, [96,97] metal sulfides, [98][99][100][101][102] metal carbides, [103,104] metal phosphides, [105] and metal oxyhydroxides. [106] Taking molybdenum disulfide (MoS 2 ) as a typical example; Xu et al prepared a sulfur carrier of hollow carbon spheres decorated with MoS 2 nanosheets (Figure 7a).…”

“…[75,79,81,[90][91][92][93]95,98,99,101,102,153] In situ synchrotron XRD is a powerful technique to probe the crystallographic intermediates, which has been widely employed in the mechanistic studies of MSBs. [75,79,90,91,95,99,102] For instance, Dou et al conducted in situ XRD to track the conversions of intermediate polysulfides under different working stages, as shown in Figure 15a. [91] They showed that cobalt catalyzed Na 2 S 4 into elemental sulfur during the charge process, whereas irreversible Na 2 S 4 species were detected without the cobalt catalyst.…”