Uncovering ZnS growth behavior and morphology control for high-performance aqueous Zn-S batteries

Aqueous Zn-S batteries provide competitive energy density for large-scale energy storage systems. However, the cathode active material exhibits poor electrical conductivity especially at the discharged state of ZnS. Its morphology generated in cells thus directly determines the cathode electrochemical activity. Here, we reveal the ZnS growth behavior and control its morphology by the anion donor number (DN) of zinc salts in electrolytes. The anion DN affects the salt dissociation degree and furthermore sulfide solubility in electrolytes, which finally determines ZnS growth preference on existing nuclei or carbon substrates. As a result, 3D ZnS is realized from the high DN ZnBr2 electrolyte, whereas a 2D passivation film is formed from low DN Zn(TFSI)2. Thanks to the facile electron paths and abundant reaction sites with 3D morphology, the sulfur cathode reaches a high capacity of 1662 mA h g-1 at 0.1 A g-1 and retains 872 mA h g-1 capacity after 400 cycles at 3 A g-1.