Microporous Sulfur–Carbon Materials with Extended Sodium Storage Window

Abstract Developing high‐performance carbonaceous anode materials for sodium‐ion batteries (SIBs) is still a grand quest for a more sustainable future of energy storage. Introducing sulfur within a carbon framework is one of the most promising attempts toward the development of highly efficient anode materials. Herein, a microporous sulfur‐rich carbon anode obtained from a liquid sulfur‐containing oligomer is introduced. The sodium storage mechanism shifts from surface‐controlled to diffusion‐controlled at higher synthesis temperatures. The different storage mechanisms and electrode performances are found to be independent of the bare electrode material's interplanar spacing. Therefore, these differences are attributed to an increased microporosity and a thiophene‐rich chemical environment. The combination of these properties enables extending the plateau region to higher potential and achieving reversible overpotential sodium storage. Moreover, in‐operando small‐angle X‐ray scattering (SAXS) reveals reversible electron density variations within the pore structure, in good agreement with the pore‐filling sodium storage mechanism occurring in hard carbons (HCs). Eventually, the depicted framework will enable the design of high‐performance anode materials for sodium‐ion batteries with competitive energy density.


DC-S
RT Na-S 26.9 500 516 - [5]   S-CS-600 RT Na-S 32.0 600 520 - [6]   SHC-500 RT Na-S 15.9 500 678 -           Table S3.The area ratio of the peaks obtained from XPS S2p and C1s regions using SC-800 as a reference.Supporting Note 6.The ICE of the disordered carbon anodes within the carbonate-based electrolytes is mainly reported as between 30 and 70%. [16]The ICE values reported here are well aligned with those previous reports on SIBs based on S-doped carbon anodes. [17]Recently, studies have shown that the ICE can be significantly improved by using some ether-based electrolytes, which are believed to increase the kinetics of the diffusion-controlled plateau region. [18]However, this can merely be possible by trying various combinations of salts and solvents, considering electrolyte compatibility is highly dependent on materials' physicochemical properties.Besides, different strategies can be used to enhance the ICE.For example, i) An increase in pyrolysis temperature induces a more ordered carbon texture with fewer defect sites often responsible for irreversible sodium ion adsorption. [19]ii) Pre-sodiation of the anode material. [20]i) Electrode surface engineering and design of artificial SEI layer. [21]iv) Electrolyte optimization. [22] (d) Randles circuit model for after-cycling reveals a second semi-circle associated with the growth of the passivation layer (RSEI). [27]ble S4.Internal, charge transfer, and SEI-related resistivity of the materials in Ohm cm -2 calculated from the Randles circuit model (electrode area, 1.13 cm 2 ).Supporting Note 11.In-operando SAXS measurements were conducted using a specialized half-cell, already proven by the following study, [29] with a Kapton film on the transmission window (Figure S23), comprising active material, separator, and a sodium metal counter/reference electrode, configured similarly to a two-electrode Swagelok-type cell.The cell was carefully sealed and precycled before the measurements to ensure stable performance during measurements.Sodiation and desodiation were carried out at a current density close to 30 mA g -1 .To mitigate the inhomogeneity issues caused by the amorphous nature of the carbon, the sample electrode was mapped at 16 distinct points to monitor consistency in the  The parameter   used in Eq. 4 in the manuscript has been calculated according to the previous works [11] by using the following relation:

Sample
where  ℎ is the structural density of graphite equal to 2.26 g cm -3 ,  002 and  002 ℎ the interlayer distance of the sample and of crystalline graphite, respectively, and  100 and  100 ℎ the in-plane distance of the sample and of crystalline graphite.The interlayer and in-plane distances of the samples have been calculated from the diffraction peak positions of the XRD patterns shown in Figure S9.

Supporting Note 2 .
From the TGA-MS profile (FigureS2), the stepwise thermal condensation of oligo-EDOT is observed.The intense signals from the masses (m/z) above 600C are assigned to the CxHy + , CO + , CO2 +/2+ , and OH + fragments.At 32 (m/z), the signals attributed to S + and O2 + are relatively intense and undergo a steady decrease even at temperatures over 800C, i.e., the sample still contains significant amounts of sulfur even at unusually high temperatures.No considerable mass losses over 50 (m/z) are observed to mirror the SOx + and CS2 + fragments.

Figure S10 .
Figure S10.Raman spectra of materials showing D and G bands.Inset: Peak intensity ratios of D (Lorentzian) and G (BWF) bands.

Figure S14 .
Figure S14.EELS low-loss spectra, including plasmon peaks.Signals are normalized and shifted on the y-axis to highlight materials.

Figure S19 .
Figure S19.Nyquist plots and relative Randles circuit models of SC-800, SC-900, and SC-1000 (a) before cycling, (b) after cycling (60 cycles).(c) Randles circuit model for precycling, where R2 is the resistance associated with the electrolyte and electrode, whereas R1 is related to the charge transfer of the electrode.

Figure S21 .
Figure S21.(a) Electrolyte compatibility study for the NVP cathode.(b) Electrolyte compatibility of the SC-1000 anode.(c) Battery performance of NVP//SC-1000 full-cell.(negative electrode: SC-1000; positive electrode: NVP/C; electrolyte: 1M NaPF6 in EC/EMC (3:7 in vol.)).The current density and specific capacity are calculated based on the mass of active material of the positive electrode.(d) Cycling performance of the full-cell with 1M NaPF6 in EC/EMC (3:7 in vol.).
structural changes.Out of the 16 points considered, two were eliminated due to fluctuations in the scattering data, which can be attributed to the inhomogeneous nature of carbon.Overall, five spots are presented in this manuscript (namely, points A, B, C (shown in the main text), D, and E) to reveal the consistency of the data interpretation.Scattering data were collected at a time resolution of 4 seconds throughout the sodiation and desodiation processes.

Figure S23 .
Figure S23.Special design stainless steel cell with a transmission window.

Figure S24 .
Figure S24.The slopes in the double logarithmic plot of the small-angle signal among the five different measuring points.

Figure S25 .
Figure S25.Data and fits of two randomly selected points at the identical timestamps, revealing the accuracy of the fitting model.

Figure S26 .
Figure S26.Data and fits of two randomly selected points at the identical timestamps after constraining the slop to q -4 , supporting the fit presented in the main text.

Figure S27 .
Figure S27.The (002) peak of hard carbon is not distinct in the WAXS region throughout the in-operando SAXS/WAXS measurements.

Figure S28 .
Figure S28.The alteration in the Δ 0 (), Δ 1 (), and ∆ ̃ () during the sodiation and desodiation processes from a different point (Point A) to support reproducibility.The overpotential sodium deposition region is highlighted in the transparent purple area of the GCD curve.Uncertainties are accurately conveyed by propagating standard errors from the estimated best-fitting parameters and are visually represented with red vertical bars.

Figure S29 .
Figure S29.The alteration in the Δ 0 (), Δ 1 (), and ∆ ̃ () during the sodiation and desodiation processes from a different point (Point B) to support reproducibility.The overpotential sodium deposition region is highlighted in the transparent purple area of the GCD curve.Uncertainties are accurately conveyed by propagating standard errors from the estimated best-fitting parameters and are visually represented with red vertical bars.

Figure S30 .
Figure S30.The alteration in the Δ 0 (), Δ 1 (), and ∆ ̃ () during the sodiation and desodiation processes from a different point (Point D) to support reproducibility.The overpotential sodium deposition region is highlighted in the transparent purple area of the GCD curve.Uncertainties are accurately conveyed by propagating standard errors from the estimated best-fitting parameters and are visually represented with red vertical bars.

Figure S31 .
Figure S31.The alteration in the Δ 0 (), Δ 1 (), and ∆ ̃ () during the sodiation and desodiation processes from a different point (Point E) to support reproducibility.The overpotential sodium deposition region is highlighted in the transparent purple area of the GCD curve.Uncertainties are accurately conveyed by propagating standard errors from the estimated best-fitting parameters and are visually represented with red vertical bars.

Table S1 .
Comparison of recent studies regarding sulfur-carbon anode materials in Na-ion and RT Na-S batteries.

Table S2 .
Elemental compositions of the materials via EA and EDX.

Table S5 .
Calculated structural parameters from the first data frame for five different measuring spots.