In Operando FTIR Study on the Effect of Sulfur Chain Length in Sulfur Copolymer-Based Li–S Batteries

Abstract

Synthesis of sulfur-rich copolymers using the inverse vulcanization reaction is a practical approach to modify the sulfur active material for enhanced stability in Li–S batteries. However, to effectively design such polymers, a thorough understanding of the underlying redox mechanisms is critical. Here, we study electrochemical behavior of sulfur-rich copolymers using in operando FTIR spectroscopy with attenuated total reflection. We used sulfur-diisopropenylbenzene copolymers [poly­(S-co-DIB)] as the active material in Li–S batteries and monitored the evolution of the C–S peak position and cyclic changes in the S–S bond stretching at different potentials during discharge and charge. Moreover, we synthesized various copolymers with sulfur wt % of 80 and 30 wt % and compared the electrochemical behavior and their corresponding IR response during cyclic voltammetry sweep. Our results indicated that the C–S bond in sulfur copolymers is not active in the voltage window of Li–S batteries. Moreover, we showed that the shift in the C–S peak position becomes smaller with increase in the monomer wt %. In addition, the S–S stretching peak at ∼500 cm–1 diminishes when the sulfur wt % is decreased from 80 to 30 wt %, highlighting a significant change in electrochemical behavior of the copolymers.

NEXAFS spectra of model sulfide chains: implications for sulfur networks obtained from inverse vulcanization

“…9 The electrochemical behaviour of S-DIB cells was investigated using operando Fourier transform-infrared spectroscopy with attenuated total reflection (FTIR-ATR). 10 This study provided further evidence for C-S bonds remaining intact during battery operation, as well as a different discharge mechanism occurring in cathodes composed of high and low S-content copolymers, with little to no formation of higher order Li-polysulfides in the latter. The significantly higher cycle stability found for the low S-content polymer was attributed to this, and it was proposed that the shuttle effect may be successfully mitigated by keeping the S-strand length below 4.…”

Switchable Photothermal Conversion Efficiency for Reprogrammable Actuation

“…As seen in the Fourier transform infrared spectra shown in Fig. 3c, a sharp peak at 1071 cm − 1 on behalf of the ν(S = O) band indicated the presence of sulfoxide (-S = O-) groups in the lms, 39 whereas only peaks related to the sulfur atom were found at 1255 cm − 1 and 694 cm − 1 , corresponding to Bi-S 40 or C-S 41 , respectively. That is, there were both sulfoxide (-S = O-) as well as a small amount of sulphone (-SO 2 -) bound to bismuth (III) ions in the original Bi-LCE lm.…”

Characterization of sulfur/carbon copolymer cathodes for Li-S batteries: a combined experimental and ab initio Raman spectroscopy study

“…In agreement with our theoretical prediction, the experimental measurements show that as the mass fraction of DIB increases (or similarly, as the average S chain length decreases), the Raman activity at around 473 cm −1 becomes less intensive. In a recent in operando FTIR study during discharge,36 it has also been observed that the characteristic S-S stretching vibration is absent in S/DIB copolymers containing short S n chains (n ≤ 4) throughout discharge. However, this peak evolves as a function of cell voltage in S/DIB copolymers with longer chains, clearly indicating the formation of different Li-polysulfides.In addition, in Fig.4we observe Raman activities at ∼165-200 cm −1 assigned to the sulfur chain deformation and S-S-S bending [see Fig.2(a) and (b)], which gradually disappear with increasing wt % of DIB (shorter sulfur chains).…”

“…Therefore, a stable cycling for 1500 cycles has been reported. 36 This clearly emphasizes the need for a synthesis strategy which facilitates the formation of S/DIB copolymers with short sulfur chains in a controllable way. The present study shows that Raman spectroscopy is a powerful tool to investigate structural properties of S/DIB copolymers and provides a way to probe the…”