Water-in-Salt (WiS) electrolytes could be a safer alternative to organic electrolytes for supercapacitors and battery applications. They show high lithium-ion mobility, crucial for use in batteries, but there is little understanding of the nanostructuring of the solutions and how this impacts the ionic movement. Two WiS systems were investigated in this study, published in ACS Nano, at varying salt concentrations and temperatures relevant to battery applications.
The researchers found that the system was made up of nanodomains of water inside the electrolyte. The shape of these domains depended on the concentration of the salt, but not temperature. As the nanodomains were confined by an anion-rich matrix, the shape and size of the anion is key to the morphology. This finding suggests that using bulky anions could lead to a significant improvement in the performance of future lithium based WiS electrolytes.
The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size, ACS Nano 2021, 15, 7, 11564–11572 DOI: 10.1021/acsnano.1c01737