The effect of BNC on the solvating power of dimethoxyethane (DME) was initially explored using DFT calculations. Various compositional models were generated, each containing one Li2S6 molecule as a representative of soluble polysulfide, alongside different combinations of DME and BNC molecules (Figures ) to (V)), namely, two DME, one DME, one DME and BNC, one BNC, two BNC molecules. Binding energies between the Li2S6 and the solvents/additives were used to assess the solvating power. To enable fair comparison across different number of solvents, binding energies have been scaled with number of solvents (see DFT Calculations in Supporting Information (SI)). Our DFT predictions revealed that Li2S6 in DME-rich scenarios (one DME and two DME) exhibit the strongest binding energies, predicted at -1.25 and -1.44 eV for one DME and two DMEs, respectively (Figure ). Substituting DME with BNC results in weaker binding energies: -1.06 eV for one DME and one BNC, -0.79 eV for one BNC, and -0.72 eV for two BNCs. This trend extended to other lithium polysulfides (Li2Sx, where x=8, 4, 2) as shown in Figures and Table in the SI, exhibiting much weaker binding energies as more BNC replacing DME molecules. The reduction in binding energy may result in decreased polysulfide solubility, which could help prevent the polysulfide shuttling effect. However, given the relatively low concentration of the additive in this study (0.01 and 0.11 M), we believe that while this benefit exists, its impact may be minor. The slightly stronger binding energy between Li2S6 and one DME compared to that between Li2S6 and two DMEs case may be attributed to the asymmetry of the cyclic sulfur structure in polysulfides, which decreases the repulsive effect with adjacent atoms in DME and consequently makes the binding energy stronger. These results demonstrate the relatively weaker solvating power of BNC when employed as an additive in the electrolyte, and thus it may change the coordination environment of lithium polysulfides. We next investigated the solvation structure of lithium polysulfides in electrolyte using AIMD simulations, focusing on the solvation structure of Li2S6 as a representative soluble polysulfide in DME and 1,3-dioxolane (DOL) (Figure and). Figure illustrates a distinct change in solvent molecular distribution around Li2S6 upon the introduction of BNC to the system. DME, known for its high Gutmann donor number and commonly used as an electrolyte solvent for Li-S batteries, is evenly distributed with DOL in the inner shell, defined as the region within 6 Å of the center of mass of the sulfur cluster (Figure ). This is attributed to DME's strong solvating power with Li, evident from its strong binding energy as described above. On the contrary, in the presence of BNC, both DME and DOL are pushed away from the inner shell towards the outer shell as shown in Figures and, resulting in a BNC coordinated inner shell with a weaker binding energy compared to that of DME. This alteration in the solvation structure of Li2S6 is believed to enhance polysulfide conversion, as polysulfides experience less constraint from DME, allowing greater interaction with anions (Sx 2-) during the SRR. This hypothesis is further supported by Li NMR experiments detailed in subsequent sections. Briefly, the addition of BNC resulted in a downfield shift with or without Li2S6. It is important to note that both DFT and AIMD simulations only provide qualitative representations of the electrolyte system, as low concentrations of BNC used in the simulations make rigorous quantitative analysis challenging. Therefore, DFT and AIMD serve as representative models rather than precise representations of the solvent concentrations. Given BNC's propensity to react with polysulfides, UV-vis was employed to investigate the significant influence of BNC concentration on the electrochemistry of Li-S batteries. The UV-vis instrument was initially calibrated using solution containing various concentrations of Li2S6 in DOL:DEM (1:1 volume ratio) (Figure ). Figure illustrates the UV-vis spectra of the Li2S6 solution upon the addition of 0.01 M BNC. The notable increase in the peak at 320 nm signifies the dissolution of powder BNC into the solution, contrasting with pure BNC samples (green dashed lines). Intriguingly, a new peak emerges at 400 nm, gradually intensifying over time, indicating moderate BNC interaction with Li2S6 and the formation of a new compound. This compound is dissolved in the electrolyte at this BNC concentration as indicated by the gradual increase in intensity. Visual confirmation in the inset further reveals that the 0.01 M BNC solution undergoes no discernible color change, whereas the 0.11 M BNC solution exhibits a distinct color shift, accompanied by precipitation at the bottom of the vial. Subsequently, we conducted UV-vis experiments at a higher BNC concentration of 0.11 M, as depicted in Figure . The reaction at this elevated concentration was exceptionally rapid, as indicated by the absorbance spectra immediately reaching the saturation limit of the instrument upon BNC addition, resulting in a discontinuous pattern with sharp noise. This phenomenon is further supported by the inset photographs in Figure . A more comprehensive comparison is provided in Figures and, illustrating different polysulfide-containing electrolyte mixtures with 0.01 and 0.11 M BNC. Our results show that adding an optimal concentration of BNC (0.01 M) results in the formation of a new soluble compound, while large quantities of BNC result in the formation of insoluble species, as shown by Goodenough et al. The solvation structure is further elucidated through Li NMR experiments. Employing a co-axial setup and LiCl in deuterium oxide (D2O) as the standard reference (Figures ), we initially conducted NMR experiments on the electrolyte with varying BNC concentrations in the absence of Li2S6. Notably, the 0.01 M BNC-containing electrolyte displays a downfield shift with a chemical shift of 0.035 ppm, indicative of de-shielded Li-ion (Figure ). The observed de-shielding phenomenon suggests enhanced interactions between Li cations and anions within the inner solvation shell due to a weakened interaction between Li ions and solvent molecules. However, with a further increase in BNC concentration up to 0.11 M, the Li peak shifts towards lower ppm values, exhibiting an upfield shift compared to the 0.01 M BNC-containing electrolyte. This phenomenon can be attributed to the formation of hydrogen bonding, with strength ranging from -0.11 to -0.17 eV between BNC molecules, from our DFT calculations (Figure and Table ). The excessive BNC molecules tend to aggregate and form clusters in the outer shell of the Li-ion solvation structure therefore weakening the interaction between Liion and anions. Despite this clustering, BNC still facilitates interaction between Li-ions and anions; however, this interaction is weaker compared to scenarios with lower concentrations. To ensure that the observed chemical shifts in NMR, particularly evident in the 0.11 M BNC case, are not artifacts resulting from individual experiments, we conducted multiple repetitions of all NMR experiments. This approach minimizes the possibility of any interference or artifacts, as illustrated in Figures and. The ionic conductivity obtained from the symmetric cell within the three electrolytes reinforces the findings from the Li NMR analysis (Figure ). Specifically, the baseline electrolyte displays the highest ionic conductivity at 11.78 mS/cm because the Li-ions are highly solvated with DME. Conversely, the 0.01 M BNC-containing electrolyte shows slightly lower conductivity, reduced to 10.85 mS/cm, owing to the stronger interaction between Li-ions and anions. Meanwhile, the 0.11 M BNC-containing electrolyte demonstrates a conductivity level almost identical to the baseline, indicating a weaker interaction between Li-ions and anions compared to 0.01 M case. Further Li NMR experiments were conducted on the solvents containing Li2S6, as depicted in Figure . In the 0.01 M BNC-containing electrolyte, a nearly identical downfield shift was observed compared to the case without Li2S6, indicating a strengthened interaction between Li-ions and anions, including S6 2-. This heightened affinity of Li-ions holds promise for the SRR, particularly in scenarios where multiple Sx 2-anions are present. Surprisingly, the 0.11 M BNC-containing electrolyte displayed a further downfield shift. However, this inconsistency underscores the intricate nature of the excessive reactions between BNC and polysulfides, rather than a mere alteration in the solvation structure of Li-ions. This shift is attributed to the intense reactivity between excessive BNC and Li2S6, resulting in a significant reduction in the concentration of both BNC and Li2S6. As a consequence, the solvation environment of Li-ions undergoes a drastic change, rendering this scenario incomparable to the case without Li2S6. The pronounced reaction between BNC and Li2S6, supported by UV-vis and NMR analyses, adds complexity to the electrolyte configuration, underscoring the need for concentration optimization of BNC to achieve the intended tailoring of the solvation structure.