Water Vapor Induced Superionic Conductivity in ZnPS3

摘要

Next-generationbatteries based on sustainable multivalent workingions, such as Mg2+, Ca2+, or Zn2+, have the potential to improve the performance, safety, and capacityof current battery systems. Development of such multivalent ion batteriesis hindered by a lack of understanding of multivalent ionics in solids,which is crucial for many aspects of battery operation. For instance,multivalent ionic transport was assumed to be correlated with electronictransport; however, we have previously shown that Zn2+ canconduct in electronically insulating ZnPS3 with a low activationenergy of 350 meV, albeit with low ionic conductivity. Here, we showthat exposure of ZnPS3 to environments with water vaporat different relative humidities results in room-temperature conductivityincreases of several orders of magnitude, reaching as high as 1.44mS cm(-1) without decomposition or structural changes.We utilize impedance spectroscopy with ion selective electrodes, ionictransference number measurements, and deposition and stripping ofZn metal, to confirm that both Zn2+ and H+ actas mobile ions. The contribution from Zn2+ to the ionicconductivity in water vapor exposed ZnPS3 is high, representingsuperionic Zn2+ conduction. The present study demonstratesthat it is possible to enhance multivalent ion conduction of electronicallyinsulating solids as a result of water adsorption and highlights theimportance of ensuring that increased conductivity in water vaporexposed multivalent ion systems is in fact due to mobile multivalentions and not solely H+.