Nickel Hollow Spheres Concatenated by Nitrogen‐Doped Carbon Fibers for Enhancing Electrochemical Kinetics of Sodium–Sulfur Batteries

Abstract

The high energy density of room temperature (RT) sodium–sulfur batteries (Na‐S) usually rely on the efficient conversion of polysulfide to sodium sulfide during discharging and sulfur recovery during charging, which is the rate‐determining step in the electrochemical reaction process of Na‐S batteries. In this work, a 3D network (Ni‐NCFs) host composed by nitrogen‐doped carbon fibers (NCFs) and Ni hollow spheres is synthesized by electrospinning. In this novel design, each Ni hollow unit not only can buffer the volume fluctuation of S during cycling, but also can improve the conductivity of the cathode along the carbon fibers. Meanwhile, the result reveals that a small amount of Ni is polarized during the sulfur‐loading process forming a polar NiS bond. Furthermore, combining with the nitrogen‐doped carbon fibers, the Ni‐NCFs composite can effectively adsorb soluble polysulfide intermediate, which further facilitates the catalysis of the Ni unit for the redox of sodium polysulfide. In addition, the in situ Raman is employed to supervise the variation of polysulfide during the charging and discharging process. As expected, the freestanding S@Ni‐NCFs cathode exhibits outstanding rate capability and excellent cycle performance.

Transition metal sulfides meet electrospinning: versatile synthesis, distinct properties and prospective applications

“…For example, the SSB assembled with a self-supported S@Ni-NCFs electrode shows a large capacity of 738.7 mA h g -1 at 0.2 C and keep 249.8 mA h g -1 at 2.0 C, demonstrating a favorable electrochemical performance. 352 This result reveals that the electrochemical process is partially reversible. The initial capacity of S@Ni-NCFs cathode at 1.0 C is about 431 mA h g −1 and a capacity of 233 mAh g −1 is retained after 270 cycles.…”

Efficient Catalytic Conversion of Polysulfides by Biomimetic Design of “Branch-Leaf” Electrode for High-Energy Sodium–Sulfur Batteries

“…These results cooperatively manifest the high sulfur utilization and fast sulfur redox reaction via strong electrocatalytic Co in the “branch-leaf” CNF-L@Co/S electrode. To further validate the advantages of the CNF-L@Co/S cathode, we compared its structure and electrochemical activity with published studies about Co catalytic effect in RT Na–S batteries as shown in Table S2 [ 15 , 27 , 45 ]. It is worth mentioning that the CNFs contribute to the little capacity under the same conditions so it was negligible, as displayed in Fig.…”

“…Despite such promising results, the charge–discharge mechanism of cobalt as a catalyst in RT Na–S batteries is not clear and needs further investigation. In addition, traditional sulfur cathode, which is prepared based on slurry-casting technique, with large amounts of inactive materials (including conductive agent, polymer binder, and metal current collectors) would significantly decrease the energy density of batteries [ 27 ]. In contrast, self-supported binder-free cathode hosts, such as carbon nanofibers can avoid this disadvantage, thus have attracted much interest from researchers.…”

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).…”

“…In situ characterizations monitor real-time electrochemical reactions, which help probe the generation of intermediates and further conversion of metal polysulf ides. [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.…”