High‐Performance High‐Loading Lithium–Sulfur Batteries by Low Temperature Atomic Layer Deposition of Aluminum Oxide on Nanophase S Cathodes

This study examines the effects of nanophase S and surface coatings via atomic layer deposition (ALD) on high‐loading sulfur cathodes for developing high‐performance and high‐energy lithium–sulfur (Li–S) batteries. It is first verified that ball milling is an effective and facile route for nanoengineering microsized S powders and the resultant nanoscale S particles exhibit better performance. Using these ball milled nanoscale S cathodes, it is found that ALD Al₂O₃ performed at 50 °C yields deposits that evolve with ALD cycles from dispersed nanoparticles, to porous, connected films, and finally to dense and continuous films. Moreover, this low temperature ALD process suppresses S loss by sublimation. The ALD Al₂O₃ greatly improves sulfur cathode sustainable capacity and Coulombic efficiency. This study postulates two different mechanisms underlying the effects of ALD Al₂O₃ surface coatings depending on their morphology. ALD Al₂O₃ nanoparticles dispersed on the sulfur surface mainly function to adsorb polysulfides, thereby inhibiting S shuttling and improving sustainable capacity and Coulombic efficiency. By contrast, ALD Al₂O₃ films behave as a physical barrier to prevent polysulfides from contacting the liquid electrolyte and dissolving. The dispersed Al₂O₃ nanoparticles improve both sustainable capacity and Coulombic efficiency while the closed Al₂O₃ films improve Coulombic efficiency while decreasing the capacity.