MOF-Derived CoS₂/N-Doped Carbon Composite to Induce Short-Chain Sulfur Molecule Generation for Enhanced Sodium–Sulfur Battery Performance

Abstract

Dissolution of intermediate sodium polysulfides (Na2S x ; 4≤x≤8) is a crucial obstacle for the development of room-temperature sodium-sulfur (Na–S) batteries. One promising strategy to avoid this issue is to load short-chain sulfur (S2–4), which could prohibit the generation of soluble polysulfides during the sodiation process. Herein, unlike in the previous reported cases where short-chain sulfur was stored by confinement within a small-pore-size (≤0.5 nm) carbon host, we report a new strategy to generate short-chain sulfur in larger pores (>0.5 nm) by the synergistic catalytic effect of CoS2 and appropriate pore size. Based on density functional theory calculations, we predict that CoS2 can serve as a catalyst to weaken the S–S bond in the S8 ring structure, facilitating the formation of short-chain sulfur molecules. By experimentally tuning the pore size of the CoS2-based hosts and comparing their performances as cathodes in Na–S and Li–S batteries, we conclude that such a catalytic effect depends on the proximity of sulfur to CoS2. This avoids the generation of soluble polysulfides and results in superior electrochemical properties of the composite materials introduced here for Na–S batteries. As a result, the optimized CoS2/N-doped carbon/S electrode showed excellent electrochemical performance with high reversible specific capacities of 488 mA h g–1 (962 mA h g(s) –1) after 100 cycles (0.1 A g–1) and 403 mA h g–1 after 1000 cycles (1 A g–1) with a superior rate performance (262 mA h g–1 at 5.0 A g–1).

Recent Advances of Catalytic Effects in Cathode Materials for Room‐Temperature Sodium‐Sulfur Batteries

“…[24] Subsequently, MOFderived CoS 2 /N-doped porous carbon cathode was reported by Rogach et al, exhibiting a considerable initial discharge capacity of 1861 mAh g À 1 at 0.1 A g À 1 (normalized by the S mass of 50.7 %). [25] From their points, CoS 2 shows high adsorption energy toward intermediate Na-polysulfides and facilitates the formation of short-chain S molecules, which is demonstrated by density functional theory calculations. In addition to cobalt sulfides, cobalt phosphides could also be used as electrocatalytic additives within S cathodes for RT-Na/S batteries.…”

“…Year/Ref Single metal electrocatalysts 80 wt % S@Co/C/rGO 10 wt % CB 10 wt % PVDF Co 37.5 % PFSA-Na in DMF and 1 M NaClO 4 in EC/DEC 0.5 C, 484.9-226 (1000) [18] Co@NPCNFs/S Co 38 w% 1 M NaClO 4 in EC/DEC 0.1 C, 905.6-843 (100) [19] CNF-L@Co/S Co 45 % 1 M NaClO 4 in EC/DEC 0.1 C, 1201-~700 (180) [20] S@Ni-NCFs Ni 36 % 1 M NaClO 4 in TEGDME 1 C, 431-233 (270) [21] 70 wt % CN/Au/S) 20 wt % super-P 10 wt % CMC Au 56.5 wt % 1 M NaClO 4 in PC/FEC 0.1 A g À 1 , 1967-701 (110) [22] Metal-based compound electrocatalysts 70 wt % NiS 2 @NPCTs/S 20 wt % CB 10 wt % CMC NiS 2 56 % 1 M NaClO 4 in EC/PC/FEC 1 A g À 1 , 960-401 (750) [23] 70 wt % CoNC@S 20 wt % TIMCAL 10 wt % CMC CoS -1 M NaFSI in DEC/BTFE 0.08 A g À 1 , 1095-500 (150) [24] 70 wt % CoS 2 /NC/S-3 15 wt % AB 15 wt % CMC CoS 2 50.7 wt % 1 M NaSO 3 CF 3 in DOL/DME 0.1 A g À 1 , 944-488 (100) [25] 70 wt % FeS 2 @NCMS/S 20 wt % CB 10 wt % CMC FeS 2 65.5 wt % 1 M NaClO 4 in PC/EC/FEC 0.1 A g À 1 , 1471-524 (300) [26] 80 wt % S/MoS 2 /NCS 10 wt % super-P 10 wt % CMC MoS 2 43.8 wt % S and Na 2 S 6 in DME 0.5 A g À 1 , 1397.4-590.6 (200) [27] 75 wt % MoO 3 @PCNT/S 15 wt % AB 10 wt % CMC MoO 3 50 wt % 1 M NaClO 4 in EC/PC 0.5 A g À 1 , 465-208 (1000) [28] 80 wt % rGO/VO 2 /S 10 wt % CB 10 wt % PVDF VO 2 40 wt % 1 M NaClO 4 in TEGDME 0.2 C, 876.4-400 (200) [29] 70 wt % S@CoP-Co/ NCNHC 20 wt % CB 10 wt % CMC CoP 53 wt % 1 M NaClO 4 in PC/EC/FEC 0.1 A g À 1 , 1101-592 (220) [30] VC-CNFs@S VC 42 wt % 1 M of NaPF 6 in DME/DOL 0.5 C, ~394-379 [31] S/TiN-TiO 2 @MCCFs TiN ~57 % 1 M NaClO 4 in EC/PC/FEC 0.1 A g À 1 , 1308.2-640.4 (100) [32] 85 wt % S@CB@AlOOH 15 wt % sodium-alginate AlOOH 44.3 wt % 1 M NaClO 4 and 0.2 M NaNO 3 in TEGDME 0.2 C, 668-554.4 (50) [33] Multifunctional hybrid electrocatalysts 80 wt % S@Ni/Co-C-12 10 wt % CB 10 wt % PVDF Ni and Co 41.4 % 1 M NaClO 4 in TEGDME 0.5 C, 1229.3-793.8 (200) [34] 80 wt % ZCS@S 10 wt % CB 10 wt % CMC ZnS and CoS 2 57 wt % 1 M NaClO 4 in DEC/EC/FEC 0.2 A g À 1 , ~1950-570 (1000) [35] 80 wt % Co 1 -ZnS/C@S 10 wt % CB 10 wt % CMC Co 1 and ZnS 65 wt % 1 M NaClO 4 in DEC/EC/FEC 0.1 A g À 1 , ~1650-640 (500) [36] 70 wt % FCNT@Co 3 C-Co/S 20 wt % AB 10 wt % CMC FCNT and Co 3 C-Co ~77 wt % 1 M NaClO 4 in EC/DEC 0.5 C, ~910-~800 (100) [37] [a] rGO: reduced graphene oxide, CB: carbon black, AB: acetylene black, PVDF: polyvinylidene fluoride, NPCNFs: N-doped porous carbon nanofibers, CNF-L: "branch-leaf"-structural carbon nanofiber, NCFs: N-doped carbon fibers, CN: N-doped…”

A hierarchically porous TiO2@C membrane with oxygen vacancies: a novel platform for enhancing the catalytic conversion of polysulfides

“…An obvious hysteresis loop appears at a relative pressure of about 0.5 with characteristic type-IV sorption, based on nitrogen (N 2 ) adsorption-desorption isotherms, indicating that all three kinds of membrane have a mesoporous structure. 20,21 BET analysis reveals a larger specific surface area of 126.5 m 2 g −1 for the TiO 2−x @C membrane in comparison with the TiO 2 @C membrane (109.2 m 2 g −1 ) and the C membrane (61.3 m 2 g −1 ) (Fig. 3a).…”

Exploration of the Unique Structural Chemistry of Sulfur Cathode for High‐Energy Rechargeable Beyond‐Li Batteries

“…CoS 2 /N-carbon/S [284] Dropwise technique and heat treatment CoP/Co-N-porous carbon nanotube hollow cages/S [139] Sequential carbonizationoxidation-phosphidation 1 M NaClO 4 in EC/PC with 3 wt% FEC A heterostructured "multi-region Janus-featured" cathode allowed optimization of sulfur conversion reactions. Besides, the conductive hollow cages of carbon scaffold endowed superior affinity toward longshort NaPS.…”