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Comparison of Li-SPAN pouch cells with and without lithium treatment. The Li-SPAN pouch cell with the PVDF-HFP : DMF lithium treatment shows a LiF rich SEI. 

Lithium‐sulfur (Li‐S) batteries offer high specific capacities but their development is hindered by several issues, most notably polysulfide shuttle. Previously, a new form of titania nanomaterial, 1D lepidocrocite (1DL) nanofilaments was shown to serve as a sulfur (S) host for Li‐S batteries. In this work, porous mesostructured particles are introduced as a new morphology of the titania 1DL to improve its performance as a S host. Furthermore, employing a facile, aqueous, one‐step surface functionalization with dopamine enhances 1DL interactions with S, as confirmed by changes in infrared spectroscopy peaks and an increase in d‐spacing via X‐ray diffraction. This surface functionalization results in a reduction of 1DL band gap energy (E_g) from 3.62 to ≈2.29 eV, resulting in a 2.6‐fold increase in electrical conductivity. Additionally, the surface functionalization renders a more conformal coating of S on the 1DL, leading to increased S utilization and interaction with the 1DL. Electrochemical testing shows a 20% reduction in the polysulfide shuttle current in comparison to base 1DL and 560 mAh g⁻¹at 0.5 C at a S‐loading of 2 mg cm⁻². Postmortem X‐ray photoelectron spectroscopy analysis also reveals stronger thiosulfate signals in the dopamine‐functionalized 1DLs, further confirming improved S interactions compared to untreated 1DL. 

In Li–S batteries, the insulating nature of sulfur and Li 2 S causes enormous challenges, such as high polarization and low active material utilization. The nucleation of the solid discharge product, Li 2 S, during the discharge cycle, and the activation of Li 2 S in the subsequent charge cycle, cause a potential challenge that needs to be overcome. Moreover, the shuttling of soluble lithium polysulfide intermediate species results in active material loss and early capacity fade. In this study, we have used thiourea as an electrolyte additive and showed that it serves as both a redox mediator to overcome the Li 2 S activation energy barrier and a shuttle inhibitor to mitigate the notorious polysulfide shuttling via the investigation of thiourea redox activity, shuttle current measurements and study of Li 2 S activation. The steady-state shuttle current of the Li–S battery shows a 6-fold drop when 0.02 M thiourea is added to the standard electrolyte. Moreover, by adding thiourea, the charge plateau for the first cycle of the Li 2 S based cathodes shifts from 3.5 V (standard ether electrolyte) to 2.5 V (with 0.2 M thiourea). Using this additive, the capacity of the Li–S battery stabilizes at ∼839 mA h g −1 after 5 cycles and remains stable over 700 cycles with a low capacity decay rate of 0.025% per cycle, a tremendous improvement compared to the reference battery that retains only ∼350 mA h g −1 after 300 cycles. In the end, to demonstrate the practical and broad applicability of thiourea in overcoming sulfur-battery challenges and in eliminating the need for complex electrode design, we study two additional battery systems – lithium metal-free cells with a graphite anode and Li 2 S cathode, and Li–S cells with simple slurry-based cathodes fabricated via blending commercial carbon black/S and a binder. We believe that this study manifests the advantages of redox active electrolyte additives to overcome several bottlenecks in the Li–S battery field.