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The development of practical lithium–sulfur (Li–S) batteries with prolonged cycle life and high Coulombic efficiency is limited by both parasitic reactions from dissolved polysulfides and mossy lithium deposition. To address these challenges, here lithium trithiocarbonate (Li₂CS₃)‐coated lithium sulfide (Li₂S) is employed as a dual‐function cathode material to improve the cycling performance of Li–S batteries. Interestingly, at the cathode, Li₂CS₃forms an oligomer‐structured layer on the surface to suppress polysulfide shuttle. The presence of Li₂CS₃alters the conventional sulfur reaction pathway, which is supported by material characterization and density functional theory calculation. At the anode, a stable in situ solid electrolyte interphase layer with a lower Li‐ion diffusion barrier is formed on the Li‐metal surface to engender enhanced lithium plating/stripping performance upon cycling. Consequently, the obtained anode‐free full cells with Li₂CS₃exhibit a superior capacity retention of 51% over 125 cycles, whereas conventional Li₂S cells retain only 26%. This study demonstrates that Li₂CS₃inclusion is an efficient strategy for designing high‐energy‐density Li–S batteries with extended cycle life.

 

The promise of secondary sulfur-based batteries as a sustainable and low-cost alternative to electrochemical energy storage has been long held back by the polysulfide shuttle problem. Herein, we demonstrate the utilization of electrolyte-soluble additives based on (oxo)thiomolybdate as a tool to mitigate the effect of the polysulfide shuttle in secondary sulfur-based batteries. Through a variety of techniques, it is shown that the Mo-containing anionic additives undergo spontaneous nucleophilic reactions with the highly soluble, long-chain polysulfides via a neutral S-atom transfer process, yielding higher S/Mo ratio complexes along with short-chain polysulfides. More importantly, it is shown how the O/S atomic substitution on the molybdenum center can induce enzymatic-level enhancement in the above reaction rate by lowering the homolytic S–S bond cleavage energy. Lastly, through anode-level inspections, it was realized that the dendritic electroplating of Li was suppressed considerably in the system with oxo/thiomolybdate, thereby reducing the cell impedance and overpotential, leading to significantly improved cycle-life. The positive influence of the increased polysulfide uptake reaction kinetics is evidenced by stable cycle-life and a low capacity-fade rate of 0.1% per cycle in Li–S cells with a high sulfur loading and lean electrolyte compositions. 

The electrochemical behavior of sulfur-based batteries is intrinsically governed by polysulfide species. Here, we compare the substitutions of selenium and tellurium into polysulfide chains and demonstrate their beneficial impact on the chemistry of lithium–sulfur batteries. While selenium-substituted polysulfides enhance cathode utilization by effectively catalyzing the sulfur/Li 2 S conversion reactions due to the preferential formation of radical intermediates, tellurium-substituted polysulfides improve lithium cycling efficiency by reducing into a passivating interfacial layer on the lithium surface with low Li + -ion diffusion barriers. This unconventional strategy based on “molecular engineering” of polysulfides and exploiting the intrinsic polysulfide shuttle effect is validated by a ten-fold improvement in the cycle life of lean-electrolyte “anode-free” pouch cells. Assembled with no free lithium metal at the anode, the anode-free configuration maximizes the energy density, mitigates the challenges of handling thin lithium foils, and eliminates self-discharge upon cell assembly. The insights generated into the differences between selenium and tellurium chemistries can be applied to benefit a broad range of metal–chalcogen batteries as well as chalcogenide solid electrolytes.