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Abstract
Lithium-sulfur (Li-S) batteries stand as promising candidates for next-generation energy storage systems, offering high specific capacity and cost-effectiveness. However, challenges persist due to the sluggish kinetics of polysulfides conversion and migration. Our study, employing operando X-ray absorption spectroscopy (XAS) and operando Raman spectroscopy, reveals that the 16-electron transfer reaction from S8 to Li2S during the sulfur reduction reaction (SRR) remains incomplete, contrary to the prevailing understanding. To address this issue, we introduce a novel bifunctional electrolyte additive, bis(4-nitrophenyl) carbonate (BNC), aimed at enhancing discharge kinetics, particularly for short-chain polysulfides conversion, while simultaneously immobilizing soluble polysulfides. Ab initio molecular dynamics (AIMD) simulations and nuclear magnetic resonance (NMR) spectroscopy confirm that BNC modifies the lithium-ion solvation structure, leading to stronger interactions with Sx2-. The BNC-containing electrolyte exhibits an average reduction of 40.6% in activation energy associated with polysulfide formation compared to the baseline. Additionally, X-ray fluorescence (XRF) mapping corroborated that the addition of BNC reduced sulfur deposition on the anode, thus mitigating the polysulfide shuttling effect. Moreover, via X-ray absorption near-edge structure (XANES) analysis, the cathode with the baseline electrolyte demonstrated a pre-edge peak at 2471.5 eV, indicative of sluggish SRR kinetics. Furthermore, this study explores the optimal concentration of BNC, recognizing that excessive concentrations may exacerbate sulfur depletion and accelerate capacity decay. The 0.01 M BNC-containing electrolyte enhances kinetics and suppresses polysulfide shuttling, standing favorable against literature results with an areal sulfur loading of 4 mg/cm2. These discoveries provide valuable insights into understanding the kinetics of SRR in Li-S batteries and offer significant guidance for developing advanced electrolyte systems.
Supplementary materials
Title
Mechanistic Understanding of a Bifunctional Electrolyte Additive as a Solvation-Property Modifier and Polysulfide Mediator for Enhanced Performance in Lithium-Sulfur Battery
Description
Materials details and cathode fabrication procedures, DFT calculation and AIMD simulation, UV-vis spectra of Li2S6 and 0.11 M BNC electrolyte, comparison of color change within different concentrations of BNC addition to the electrolyte contains different polysulfides, illustration of co-axial NMR tube and repeated 7Li NMR spectra, CV plots of three electrolytes, linear fitting of Randles-Sevcik plots for B1 and B2 peaks, voltage profile of in situ EIS, EIS and fitting results for each electrode at different DoD, Arrhenius plots and fitting results of baseline and 0.11 M BNC electrolyte, GITT plot of three electrolytes, illustration of operando Raman and operando XAS cell, Raman spectra of standard reference, normalized XAS spectra of standard reference, operando XAS spectra and MCR-ALS analysis results, XRF mapping and XANES comparison between washed and unwashed samples, XANES spectra on location #1, microscope images and XANES spectra of products from BNC with different polysulfides
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